favorite temp sensors

[David Lesher]

So we're looking to sense temps in the ~~0-40C range, and
wondered what to use. In the past I've used LM35's and would
again, but all the cool kids seem to using this digital stuph,
so I was wondering what's a roughly parallel sensor that has
some ilk of digital output?

They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[John Larkin]

On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:

>So we're looking to sense temps in the ~~0-40C range, and
>wondered what to use. In the past I've used LM35's and would
>again, but all the cool kids seem to using this digital stuph,
>so I was wondering what's a roughly parallel sensor that has
>some ilk of digital output?
>
>They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

LM71, 3 wire SPI.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

[Bill Sloman]

On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
> So we're looking to sense temps in the ~~0-40C range, and
> wondered what to use. In the past I've used LM35's and would
> again, but all the cool kids seem to using this digital stuph,
> so I was wondering what's a roughly parallel sensor that has
> some ilk of digital output?
>
> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

Depends whether you want an accurate sensor.

At the moment interchangeable glass-encapsulated thermistors leave everything else for dead at +/-0.2C (or better, if you are prepared to pay more).

You've got to put together a bridge and an A/D to turn the resistance into a digital number, which is going to be a non-linear function of temperature

http://en.wikipedia.org/wiki/Thermistor

but sorting out the Steinhart-Hart relationship won't overload a 32-bit CPU\.

--
Bill Sloman, Sydney

[Jim Thompson]

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

[Jim Thompson]

On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
<bill....@ieee.org> wrote:

There are simpler ways, methods of which I have posted multiple times
on this newsgroup.

Slowman, You're a has-been... if you ever WERE in the first place. Go
away.

[David Lesher]

Bill Sloman <bill....@ieee.org> writes:

>On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>> So we're looking to sense temps in the ~~0-40C range, and
>> wondered what to use. In the past I've used LM35's and would
>> again, but all the cool kids seem to using this digital stuph,
>> so I was wondering what's a roughly parallel sensor that has
>> some ilk of digital output?
>>
>> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

>Depends whether you want an accurate sensor.

A few degrees won't matter....

[mrob...@att.net]

David Lesher <wb8...@panix.com> wrote:
> So we're looking to sense temps in the ~~0-40C range, and wondered
> what to use. In the past I've used LM35's and would again, but all the
> cool kids seem to using this digital stuph, so I was wondering what's
> a roughly parallel sensor that has some ilk of digital output?

The hobby 8-bit microcontroller people seem to like the Dallas DS18B20/
DS18S20 and similar parts. They speak Dallas' "1-Wire" protocol, so
you can string several of them on one I/O pin. The TO-92 case seems
to be popular but you can also get them as SOIC. They claim +/- 0.5 C
accuracy, and somewhere between 0.1 to 0.75 seconds per reading
depending on how many (configurable) bits of resolution you want.

I think those parts are popular in that area because they are always
short of I/O port pins, and because there are ready-made software
libraries that will handle bit-banging the protocol for you.

These seem to be reasonably available 1 or 2 at a time (Digi-Key has
them in minimum quantity 1), but they now come from Maxim. For other
kinds of parts, I have heard varying things about Maxim's willingness
to sell parts in small quantities, where "small" is defined as "less
than 100,000 at a time".

When PC motherboards started sprouting temperature sensors, a lot of
them seemed to be National (now TI) LM75 or similar. The LM75 speaks
I2C, claims +/- 2 C and comes in a couple of surface-mount packages.
There are similar parts all the way from LM63 to LM94; some of the
options are SPI, different resolutions, programmable alarm points,
lower power consumption, etc. You need more than one I/O pin to make
these work.

These also seem to be reasonably available 1 or 2 at a time (Digi-Key).
I haven't heard anything bad about TI's small-quantity availability.

Standard disclaimers apply; I don't get money or other consideration
from any companies mentioned.

Matt Roberds

[David Lesher]

Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:


>There are simpler ways, methods of which I have posted multiple times
>on this newsgroup.

I'm all ears. TO92 case is nice, fanatical accuracy is not required,
Price is part of the decision....we can always use just LM35's.....

[Jim Thompson]

On Fri, 12 Apr 2013 05:09:48 +0000 (UTC), David Lesher
<wb8...@panix.com> wrote:

>Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>
>
>>There are simpler ways, methods of which I have posted multiple times
>>on this newsgroup.
>
>I'm all ears. TO92 case is nice, fanatical accuracy is not required,
>Price is part of the decision....we can always use just LM35's.....

In the morning. It's quite trivial... and fundamental.

[Bill Sloman]

On Friday, 12 April 2013 14:10:50 UTC+10, Jim Thompson wrote:
> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
>
> <bill....@ieee.org> wrote:
>
> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
> >> So we're looking to sense temps in the ~~0-40C range, and
> >> wondered what to use. In the past I've used LM35's and would
> >> again, but all the cool kids seem to using this digital stuph,
> >> so I was wondering what's a roughly parallel sensor that has
> >> some ilk of digital output?
> >>
> >> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
> >
> >Depends whether you want an accurate sensor.
> >
> >At the moment interchangeable glass-encapsulated thermistors leave everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
> >
> >You've got to put together a bridge and an A/D to turn the resistance into a digital number, which is going to be a non-linear function of temperature
> >
> >http://en.wikipedia.org/wiki/Thermistor
> >
> >but sorting out the Steinhart-Hart relationship won't overload a 32-bit

> >CPU.

>
> There are simpler ways, methods of which I have posted multiple times
> on this newsgroup.

Sure. Make the thermistor the frequency determining element in an astable, but then you have to cope with the temperature dependence of the reactive element.

I was recommending an accurate solution, rather than a simple one.

> Slowman, You're a has-been... if you ever WERE in the first place. Go
> away.

I may be a has-been, but I provided real - and potentially useful - information. You've just claimed to know a "better" way (probably incorrectly), without giving any indication of what it might be, and followed it up with gratuitous personal abuse. Definitely an exhibition of psychopathology, though you've skipped the criminal aspect on this particular occasion.

--
Bill Sloman, Sydney

[Bill Sloman]

On Friday, 12 April 2013 14:50:45 UTC+10, David Lesher wrote:
> Bill Sloman <bill....@ieee.org> writes:
>
> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>
> >Depends whether you want an accurate sensor.
>
> A few degrees won't matter....

So why bother measuring it at all?

--
Bill Sloman, Sydney

[Jan Panteltje]

On a sunny day (Fri, 12 Apr 2013 02:41:04 +0000 (UTC)) it happened David
Lesher <wb8...@panix.com> wrote in <kk7s80$no9$1...@reader1.panix.com>:

>So we're looking to sense temps in the ~~0-40C range, and
>wondered what to use. In the past I've used LM35's and would
>again, but all the cool kids seem to using this digital stuph,
>so I was wondering what's a roughly parallel sensor that has
>some ilk of digital output?
>
>They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

I think some of those LM things also come with iic interface?

[Phil Hobbs]

On 4/12/2013 12:10 AM, Jim Thompson wrote:
> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> <bill....@ieee.org> wrote:
>
>> On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>>> So we're looking to sense temps in the ~~0-40C range, and
>>> wondered what to use. In the past I've used LM35's and would
>>> again, but all the cool kids seem to using this digital stuph,
>>> so I was wondering what's a roughly parallel sensor that has
>>> some ilk of digital output?
>>>
>>> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>>
>> Depends whether you want an accurate sensor.
>>
>> At the moment interchangeable glass-encapsulated thermistors leave everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
>>
>> You've got to put together a bridge and an A/D to turn the resistance into a digital number, which is going to be a non-linear function of temperature
>>
>> http://en.wikipedia.org/wiki/Thermistor
>>
>> but sorting out the Steinhart-Hart relationship won't overload a 32-bit CPU\.
>
> There are simpler ways, methods of which I have posted multiple times
> on this newsgroup.
>

There are lots of simpler ways, they're just less accurate. Bill's
right about thermistors, especially if you're interested in working near
a single temperature. Junctions aren't in the same class, because
parameters like doping density and beta aren't as well controlled. IC
temperature sensors have crappy thermal time constants, their
temperatures are dominated by conduction through the leads (which is
sometimes what you want, but often not), and for accurate temperature
control, they're strictly in the "just keep banging the rocks together,
guys" class. (*)

Mixed technology wins again. ;)

For slightly wider ranges, platinum RTDs are all the go, especially if
you pulse the excitation so you can use a higher voltage without
horrible self-heating.

But AFAIK nobody makes thermistors with built-in I2C or one-wire or
whatever the OP is looking for. So ICs are probably useful for
something after all. ;)

Cheers

Phil Hobbs


(*) "So a big hello to all intelligent life-forms everywhere, and to
anybody else, the secret is just keep banging the rocks together, guys."
-- Douglas Adams, "The Hitchhiker's Guide to the Galaxy"

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

[Bill Sloman]

On Friday, 12 April 2013 22:45:57 UTC+10, Phil Hobbs wrote:
> On 4/12/2013 12:10 AM, Jim Thompson wrote:
> > On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> > <bill....@ieee.org> wrote:
> >> On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>
> >>> So we're looking to sense temps in the ~~0-40C range, and
> >>> wondered what to use. In the past I've used LM35's and would
> >>> again, but all the cool kids seem to using this digital stuph,
> >>> so I was wondering what's a roughly parallel sensor that has
> >>> some ilk of digital output?
> >>>
> >>> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
> >>
> >> Depends whether you want an accurate sensor.
> >>
> >> At the moment interchangeable glass-encapsulated thermistors leave
> >> everything else for dead at +/-0.2C (or better, if you are prepared to pay > >> more).
> >>
> >> You've got to put together a bridge and an A/D to turn the resistance into > >>a digital number, which is going to be a non-linear function of temperature
> >>
> >> http://en.wikipedia.org/wiki/Thermistor
> >>
> >> but sorting out the Steinhart-Hart relationship won't overload a 32-bit

> >> CPU.

> >
> > There are simpler ways, methods of which I have posted multiple times
> > on this newsgroup.
> >
> There are lots of simpler ways, they're just less accurate. Bill's
> right about thermistors, especially if you're interested in working near
> a single temperature. Junctions aren't in the same class, because
> parameters like doping density and beta aren't as well controlled. IC
> temperature sensors have crappy thermal time constants, their
> temperatures are dominated by conduction through the leads (which is
> sometimes what you want, but often not), and for accurate temperature
> control, they're strictly in the "just keep banging the rocks together,
> guys" class. (*)
>
> Mixed technology wins again. ;)
>
> For slightly wider ranges, platinum RTDs are all the go, especially if
> you pulse the excitation so you can use a higher voltage without
> horrible self-heating.

As I pointed out back in 1978

Sloman, A.W. "On microdegree thermostats", Journal of Physics E: Scientific Instruments, 11, 967-968 (1978).

platinum resistance thermometers have a lower thermal resistance to ambient than thermistors, which does compensate - to some extent - for the lower sensitivity. Any place I'd have wanted to sue them I'd have had to use AC excitation to get the sensitivity I wanted. Reversing DC will do - but a bifilar wound Blumlein transformer bridge is a very neat way of setting up a very stable bridge, and that usually takes a couple of kHz if you want to use a nice compact ferrite cored transformer.

> But AFAIK nobody makes thermistors with built-in I2C or one-wire or
> whatever the OP is looking for. So ICs are probably useful for
> something after all. ;)

Too true.

--
Bill Sloman, Sydney

[George Herold]

On Apr 11, 11:25 pm, John Larkin

<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
> >So we're looking to sense temps in the ~~0-40C range, and
> >wondered what to use. In the past I've used LM35's and would
> >again, but all the cool kids seem to using this digital stuph,
> >so I was wondering what's a roughly parallel sensor that has
> >some ilk of digital output?
>
> >They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>
> LM71, 3 wire SPI.

For a bit more money I saw a project that had a whole bunch of
DS18B20's that did a temperature profile of metal plate. (Maxim
though...)

George H.
>
> --
>
> John Larkin                  Highland Technology Incwww.highlandtechnology.com  jlarkin at highlandtechnology dot com

[k...@attt.bizz]

On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher
<wb8...@panix.com> wrote:

>So we're looking to sense temps in the ~~0-40C range, and
>wondered what to use. In the past I've used LM35's and would
>again, but all the cool kids seem to using this digital stuph,
>so I was wondering what's a roughly parallel sensor that has
>some ilk of digital output?
>
>They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

I've been using the AD7414. With appropriate wiring and board
stuffind, I can get eight on an I2C interface (used for thermal
testing only).

[Nico Coesel]

David Lesher <wb8...@panix.com> wrote:

>So we're looking to sense temps in the ~~0-40C range, and
>wondered what to use. In the past I've used LM35's and would
>again, but all the cool kids seem to using this digital stuph,
>so I was wondering what's a roughly parallel sensor that has
>some ilk of digital output?
>
>They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...

Microchip has some pretty cheap ones. Like everything from Microchip
they are a bit crappy but if accuracy isn't the prime goal...

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

[John Larkin]

There is an LM35 in a TO220 package. We use them to measure heatsink
temperatures, part of running a realtime dynamic model of mosfet junction temps
for a "smart" overload shutdown.

--

John Larkin Highland Technology Inc

www.highlandtechnology.com jlarkin at highlandtechnology dot com

[George Herold]

On Apr 12, 8:45 am, Phil Hobbs

> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>
> - Show quoted text -

Not a digital solution, But I've been using diode connected
transistors (in TO-220 packs) as temp sensors. I like that it comes
with a mounting hole :^)
I did a calibration run (versus a spendy lakeshore diode) and then a
single point calibration after that. (all transistors with the same
date code.) I've got to do another calibration in the near future,
and it will be interesting to see how different the next batch is.
How important are all the process variations for a diode connected
transistor?

George H.

[Phil Hobbs]

That's turning a bug into a feature, for sure. George has mentioned
using TO220 transistor junctions for the same sort of job.

Cheers

Phil Hobbs

[Jim Thompson]

On Thu, 11 Apr 2013 23:21:25 -0700, Jim Thompson
<To-Email-Use-Th...@On-My-Web-Site.com> wrote:

>On Fri, 12 Apr 2013 05:09:48 +0000 (UTC), David Lesher
><wb8...@panix.com> wrote:
>
>>Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>>
>>
>>>There are simpler ways, methods of which I have posted multiple times
>>>on this newsgroup.
>>
>>I'm all ears. TO92 case is nice, fanatical accuracy is not required,
>>Price is part of the decision....we can always use just LM35's.....
>
>In the morning. It's quite trivial... and fundamental.
>
> ...Jim Thompson

(1) Connect a transistor as a diode (B-C short)

(2) Operate it at low enough current that bulk resistive effects and
dissipation are nil

(3) Observe basic equation: vBE = kT/q * ln(Ie/Is)

(4) Pulse transistor with squarewave of current, Imax = 10*Imin

(5) Observe voltage squarewave at B-C of value kT/q * ln(10) (P-P)

(6) Gain this up (AC-coupled) to desired amplitude

(7) Maybe do DC restore if you like ;-)

(8) Pretty much device independent, though large/power devices make it
easier to observe condition (2)

[Jim Thompson]

On Fri, 12 Apr 2013 00:01:14 -0700 (PDT), Bill Sloman

<bill....@ieee.org> wrote:

>On Friday, 12 April 2013 14:10:50 UTC+10, Jim Thompson wrote:
>> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
>>
>> <bill....@ieee.org> wrote:
>>
>> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>> >> So we're looking to sense temps in the ~~0-40C range, and
>> >> wondered what to use. In the past I've used LM35's and would
>> >> again, but all the cool kids seem to using this digital stuph,
>> >> so I was wondering what's a roughly parallel sensor that has
>> >> some ilk of digital output?
>> >>
>> >> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>> >
>> >Depends whether you want an accurate sensor.
>> >
>> >At the moment interchangeable glass-encapsulated thermistors leave everything else for dead at +/-0.2C (or better, if you are prepared to pay more).
>> >
>> >You've got to put together a bridge and an A/D to turn the resistance into a digital number, which is going to be a non-linear function of temperature
>> >
>> >http://en.wikipedia.org/wiki/Thermistor
>> >
>> >but sorting out the Steinhart-Hart relationship won't overload a 32-bit
>> >CPU.
>>
>> There are simpler ways, methods of which I have posted multiple times
>> on this newsgroup.
>
>Sure. Make the thermistor the frequency determining element in an astable, but then you have to cope with the temperature dependence of the reactive element.
>
>I was recommending an accurate solution, rather than a simple one.
>
>> Slowman, You're a has-been... if you ever WERE in the first place. Go
>> away.
>
>I may be a has-been, but I provided real - and potentially useful - information. You've just claimed to know a "better" way (probably incorrectly),

Better way posted. Your way is asinine.

> without giving any indication of what it might be, and followed it up with gratuitous personal abuse. Definitely an exhibition of psychopathology, >though you've skipped the criminal aspect on this particular occasion.

[k...@attt.bizz]

On Fri, 12 Apr 2013 13:59:23 GMT, ni...@puntnl.niks (Nico Coesel)
wrote:

>David Lesher <wb8...@panix.com> wrote:
>
>>So we're looking to sense temps in the ~~0-40C range, and
>>wondered what to use. In the past I've used LM35's and would
>>again, but all the cool kids seem to using this digital stuph,
>>so I was wondering what's a roughly parallel sensor that has
>>some ilk of digital output?
>>
>>They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>
>Microchip has some pretty cheap ones. Like everything from Microchip
>they are a bit crappy but if accuracy isn't the prime goal...

Seiko has some cheap ones, too.

[John Devereux]

Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:

> On Thu, 11 Apr 2013 23:21:25 -0700, Jim Thompson
> <To-Email-Use-Th...@On-My-Web-Site.com> wrote:
>
>>On Fri, 12 Apr 2013 05:09:48 +0000 (UTC), David Lesher
>><wb8...@panix.com> wrote:
>>
>>>Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>>>
>>>
>>>>There are simpler ways, methods of which I have posted multiple times
>>>>on this newsgroup.
>>>
>>>I'm all ears. TO92 case is nice, fanatical accuracy is not required,
>>>Price is part of the decision....we can always use just LM35's.....
>>
>>In the morning. It's quite trivial... and fundamental.
>>
>> ...Jim Thompson
>
> (1) Connect a transistor as a diode (B-C short)
>
> (2) Operate it at low enough current that bulk resistive effects and
> dissipation are nil
>
> (3) Observe basic equation: vBE = kT/q * ln(Ie/Is)
>
> (4) Pulse transistor with squarewave of current, Imax = 10*Imin
>
> (5) Observe voltage squarewave at B-C of value kT/q * ln(10) (P-P)
>
> (6) Gain this up (AC-coupled) to desired amplitude
>
> (7) Maybe do DC restore if you like ;-)
>
> (8) Pretty much device independent, though large/power devices make it
> easier to observe condition (2)

Is this accurate to +/- 0.2'C (without calibration)?

--

John Devereux

[George Herold]

On Apr 12, 12:09 pm, John Devereux <j...@devereux.me.uk> wrote:

> Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-Web-Site.com> writes:
> > On Thu, 11 Apr 2013 23:21:25 -0700, Jim Thompson
> > <To-Email-Use-The-Envelope-I...@On-My-Web-Site.com> wrote:
>
> >>On Fri, 12 Apr 2013 05:09:48 +0000 (UTC), David Lesher
> >><wb8...@panix.com> wrote:
>

> >>>Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-Web-Site.com> writes:
>
> >>>>There are simpler ways, methods of which I have posted multiple times
> >>>>on this newsgroup.
>
> >>>I'm all ears. TO92 case is nice, fanatical accuracy is not required,
> >>>Price is part of the decision....we can always use just LM35's.....
>
> >>In the morning.  It's quite trivial... and fundamental.
>
> >>                                        ...Jim Thompson
>
> > (1) Connect a transistor as a diode (B-C short)
>
> > (2) Operate it at low enough current that bulk resistive effects and
> > dissipation are nil
>
> > (3) Observe basic equation:  vBE = kT/q * ln(Ie/Is)
>
> > (4) Pulse transistor with squarewave of current, Imax = 10*Imin
>
> > (5) Observe voltage squarewave at B-C of value kT/q * ln(10) (P-P)
>
> > (6) Gain this up (AC-coupled) to desired amplitude
>
> > (7) Maybe do DC restore if you like ;-)
>
> > (8) Pretty much device independent, though large/power devices make it
> > easier to observe condition (2)
>
> Is this accurate to +/- 0.2'C (without calibration)?

Not in my experience. (but my experience is fiarly limited... a few
transitors tested.)

I always got a number that was a bit off ~0.3%, so about 1 degree at
room temp. I always assumed the error was due to the transistor
beta... Since the current is Ic and Ib. (I think I got a temperature
that was always a bit high, but I'd have to check my notebook.) You
could add some beta 'fudge factor'.... but then beta changes with
temperature too.

It also depended a bit on the collector current. (1 uA to 10uA were
'nice' currents)

George H.
>
> --
>
> John Devereux- Hide quoted text -

[David Lesher]

So midst the noise I've seen the following mentioned:

LM71
DS18B20
LM75
AD7414

Of those, only a few seem to come in non-surface mount packages
and I'm not sure how we'd couple surface mount devices to the
copper cooling lines.

Given that we just want to measure the coolent temperature on
both sides of the liquid-cooled heatsink, and not reinvent
anything [1]; it looks like the DS18B20 may do the trick.

It's 2-4X the price of LM35's but still affordable.


Thanks for the suggestions.

1] Or rather "we are inventing enough on the product; we don't
need to do so on the test instrumentation too..."

[Jim Thompson]

On Fri, 12 Apr 2013 05:09:48 +0000 (UTC), David Lesher
<wb8...@panix.com> wrote:

>Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>
>
>>There are simpler ways, methods of which I have posted multiple times
>>on this newsgroup.
>
>I'm all ears. TO92 case is nice, fanatical accuracy is not required,
>Price is part of the decision....we can always use just LM35's.....

Here it is done at the device-level on one of my chips...

http://www.analog-innovations.com/SED/TempMeasureViaCurrentRatio.pdf

Of course you can do it with off-the-shelf OpAmps and analog switches,
which is what the devices are all about.

[Jim Thompson]

If you use a large device it should be. For those of you in the
discrete world keeping the current ratio firmly at 10:1 (or whatever
ratio you choose) will be your biggest problem.

I think Jim Williams wrote this up a long time ago except he used
resistors instead of current mirrors. I have two of his books, but
didn't find it. Maybe an EDN article? Or maybe it was Bob Pease??

[whit3rd]

On Friday, April 12, 2013 9:09:27 AM UTC-7, John Devereux wrote:
> Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:

[about thermometry]

> > (1) Connect a transistor as a diode (B-C short)
>
> > (2) Operate it at low enough current that bulk resistive effects and
> > dissipation are nil
>
> > (3) Observe basic equation: vBE = kT/q * ln(Ie/Is)
>
> > (4) Pulse transistor with squarewave of current, Imax = 10*Imin

> Is this accurate to +/- 0.2'C (without calibration)?

It's an absolute-temperature measurement, so +/- 0.2 C implies better
than a part-per-thousand error band. Voltage references and resistor
values for the current pulse would have to be better than 0.1%, so probably
the answer is NO. The only way to get components with that accuracy
is with trimming, and that means ALL qualified sensors are dependent
on calibration or trimming. You can choose which, but you
must pay, either way.

Calibration after soldering is better than trimming before soldering.

[whit3rd]

On Friday, April 12, 2013 9:27:51 AM UTC-7, David Lesher wrote:
[about temperature measurement, with mention of 0.2C accuracy]

> Given that we just want to measure the coolent temperature on

> both sides of the liquid-cooled heatsink...

If you want the difference to be accurately measured, that's
actually an ideal place to put in a thermocouple, or several
thermocouples in series. If you use a single batch
of thermocouple wire, it'll have a good zero-temp-difference
characteristic guaranteed by design. Input pipe is hot
junction, output pipe is cold junction, and an autozero op amp
can condition the signal easily.

[k...@attt.bizz]

On Fri, 12 Apr 2013 16:27:51 +0000 (UTC), David Lesher
<wb8...@panix.com> wrote:

>
>So midst the noise I've seen the following mentioned:
>
>LM71
>DS18B20
>LM75
>AD7414
>
>Of those, only a few seem to come in non-surface mount packages
>and I'm not sure how we'd couple surface mount devices to the
>copper cooling lines.

Which section of your specification was that in? ;-)

[Jon Kirwan]

On Fri, 12 Apr 2013 08:03:52 -0700, Jim Thompson
<To-Email-Use-Th...@On-My-Web-Site.com> wrote:

><snip>

>
>(1) Connect a transistor as a diode (B-C short)
>
>(2) Operate it at low enough current that bulk resistive effects and
>dissipation are nil
>
>(3) Observe basic equation: vBE = kT/q * ln(Ie/Is)
>
>(4) Pulse transistor with squarewave of current, Imax = 10*Imin
>
>(5) Observe voltage squarewave at B-C of value kT/q * ln(10) (P-P)
>
>(6) Gain this up (AC-coupled) to desired amplitude
>
>(7) Maybe do DC restore if you like ;-)
>
>(8) Pretty much device independent, though large/power devices make it
>easier to observe condition (2)

A published source on this is found here:
http://cds.linear.com/docs/en/application-note/an45f.pdf

Starting on top of page 7.

...

I take George's recent experiences using these seriously,
though. I'll add a short note to his writing on the topic.

Jon

[Jim Thompson]

Thanks! So I did remember correctly that it was a Jim Williams'
scheme! And stored it mentally, then redid it with current mirrors
instead of analog switches and resistors...

in a custom chip...

http://www.analog-innovations.com/SED/TempMeasureViaCurrentRatio.pdf

[John Larkin]

On Fri, 12 Apr 2013 06:50:22 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:

>On Apr 11, 11:25�pm, John Larkin
><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
>> >So we're looking to sense temps in the ~~0-40C range, and
>> >wondered what to use. In the past I've used LM35's and would
>> >again, but all the cool kids seem to using this digital stuph,
>> >so I was wondering what's a roughly parallel sensor that has
>> >some ilk of digital output?
>>
>> >They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>>
>> LM71, 3 wire SPI.
>
>For a bit more money I saw a project that had a whole bunch of
>DS18B20's that did a temperature profile of metal plate. (Maxim
>though...)

Cool, if you can't afford a FLIR.


--

John Larkin Highland Technology, Inc

jlarkin at highlandtechnology dot com

http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators

Custom laser drivers and controllers

Photonics and fiberoptic TTL data links

VME thermocouple, LVDT, synchro acquisition and simulation

[Jon Kirwan]

On Fri, 12 Apr 2013 09:26:40 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:

>On Apr 12, 12:09�pm, John Devereux <j...@devereux.me.uk> wrote:

>> <snip of pulsed current through diode-connected BJT idea>

>> Is this accurate to +/- 0.2'C (without calibration)?

>Not in my experience. (but my experience is fiarly limited... a few
>transitors tested.)
>
>I always got a number that was a bit off ~0.3%, so about 1 degree at
>room temp. I always assumed the error was due to the transistor
>beta... Since the current is Ic and Ib. (I think I got a temperature
>that was always a bit high, but I'd have to check my notebook.) You
>could add some beta 'fudge factor'.... but then beta changes with
>temperature too.
>
>It also depended a bit on the collector current. (1 uA to 10uA were
>'nice' currents)

Hi, George. I posted up a link to Linear's AN45 elsewhere
under this topic. See page 7 there. But I take your
experiences here seriously and wanted to think about this,
not at the 'charged gas' theory level but at the higher (and
more usual for an EE) device modeling level.

The two-current pulse method, using say 1X and 10X currents,
depends upon the following:

dV = (k/q) * ln( 1+Ic/Is ) dT

Although k and q are known, the entire factor that includes
the ln( 1+Ic/Is ) part isn't knowable in advance. But if one
assumes that the +1 term is negligible then the two pulsed
currents results in:

dV1/dT = (k/q) * ln( Ic1 ) - (k/q) * ln( Is )
dV2/dT = (k/q) * ln( Ic2 ) - (k/q) * ln( Is )

Subtracting dV1/dT from dV2/dT yields:

dV1 - dV1 = (k/q) * ln( Ic2/Ic1 ) ) dT

And if the ratio of Ic2/Ic1 is known a priori then the entire
factor, (k/q) * ln( Ic2/Ic1 ) ), is also known. And as a
consequence could be used to measure temperature without
having to calibrate the system. Or so it seems at first
blush.

But it's also the case that the value of the saturation
current, Is, is itself a rather complex function of T:

Is(T) = Is(Tn) * (T/Tn)^3 * e^( -(q*Eg/k) * (1/T-1/Tn) )

Where Tn is some chosen T(nominal).

In fact, this particular component is what overwhelms the
first equation (which is positive vs temperature) and yields
the usually quoted -2mV/K figure (very approximately.) So, in
fact, Is(T) is the dominant factor in Vbe change over T and
in no possible way is it a simple function of T!

(Even the above Is(T) equation itself is a simplification.
The power ((T/Tn)^3) for example is an approximation and not
strictly true in practice. Same with Eg, which itself is also
taken as a single approximation value.)

Just as a guess, the idea of ln( Is ) being cancelled
entirely out of the equation by ratiometry, even assuming
that the die is at thermal equilibrium, would make me worry a
little. (I accept that pulsing the 1X/10X current change fast
enough or that using low enough currents, like the 1uA and
10uA you mention, would yield a near-equilibrium state.) I'm
just not sure that at this level of modeling, that _Is_
remains dead stable as a modeling parameter when facing a 10X
current change. There is a lot of linearity over orders of
magnitude change, as a broad statement. But exactly how
linear is it when provided a two point ratio a decade apart,
vs device variation?

I wonder that some temperature error is swept under this
Is(T) rug and hidden from the analysis, so to speak. Even
assuming thermal equilibrium. Because it may really be that
Is(V,T), not Is(T), as both the power (^3) and Eg are taken
as simple constants for simplification when they aren't, in
fact, invariant at this level of modeling.

You mention base currents as a possible error. I've ignored
that so far. The equation:

dV = (k/q) * ln( 1+Ic/Is ) dT

in the diode connected case refers to Ic. The currents
through it, on whole, are (beta+1)/beta times as much. If you
cobble up precision current sources at exactly 1X and 10X,
the ratio of Ic2/Ic2 would still be 10, even though you are
driving Ie, I think. However, beta itself changes vs Ic. So
there is that to account for, if you were only using a beta
level model. But the:

dV1 - dV1 = (k/q) * ln( Ic2/Ic1 ) ) dT

method doesn't use or rely upon beta. So I'm not imagining a
problem there because (1) the ratio is still 10X and (2) beta
isn't used in the analysis method.

Interesting problem getting past a certain level of accuracy,
though. There must be several papers that go beyond the AN45
app note I'd posted up earlier. I haven't seen one, yet.

Jon

[John S]

On 4/12/2013 3:00 PM, John Larkin wrote:
> On Fri, 12 Apr 2013 06:50:22 -0700 (PDT), George Herold
> <ghe...@teachspin.com> wrote:
>
>> On Apr 11, 11:25 pm, John Larkin
>> <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
>>>> So we're looking to sense temps in the ~~0-40C range, and
>>>> wondered what to use. In the past I've used LM35's and would
>>>> again, but all the cool kids seem to using this digital stuph,
>>>> so I was wondering what's a roughly parallel sensor that has
>>>> some ilk of digital output?
>>>
>>>> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>>>
>>> LM71, 3 wire SPI.
>>
>> For a bit more money I saw a project that had a whole bunch of
>> DS18B20's that did a temperature profile of metal plate. (Maxim
>> though...)
>
> Cool, if you can't afford a FLIR.
>
>

Did you see my post that I bought the one you pointed out? It is due
here this afternoon sometime.

John S

[Bill Sloman]

But accurate, and precise. Your idea of "better" needs work.

--
Bill Sloman, Sydney

[Jim Thompson]

On Fri, 12 Apr 2013 13:56:13 -0700 (PDT), Bill Sloman

Whenever is a thermistor "precise" ??

[Bill Sloman]

On Saturday, 13 April 2013 02:27:51 UTC+10, David Lesher wrote:
> So midst the noise I've seen the following mentioned:
>
> LM71
> DS18B20
> LM75
> AD7414
>
> Of those, only a few seem to come in non-surface mount packages
> and I'm not sure how we'd couple surface mount devices to the
> copper cooling lines.

Thermally conductive adhesive? The AD7414 data sheet mentions this on part 14.

http://www.analog.com/static/imported-files/data_sheets/AD7414_7415.pdf

> Given that we just want to measure the coolant temperature on

> both sides of the liquid-cooled heatsink, and not reinvent
> anything [1]; it looks like the DS18B20 may do the trick.
>
> It's 2-4X the price of LM35's but still affordable.

If the copper inlet and outlet pipes run close together - or can be made to run close together, you might mount two AD7414 parts on a flexible printed circuit, and glue the back of one to the inlet pipe and the back of teh other to the outlet pipe. You'd separate the two AD7414 parts on the flexy by more than the worst-case separation of the two bits of pipe to which you were going to glue each one (with thermally conductive epoxy) so a to leave a bow in the flexy to accommodate any movement between the two points.

And you'd have to do a zero-point calibration when the heat-sink wasn't dissipating any power. The temperature error data on page 15 of the data sheet is a bit depressing. Interchangable thermistors can be quite a bit more accurate - put two (one on each pipe) in a bridge, and AC-drive with a bifilar wound centre-tapped transformer to set up a Blumlein bridge.

http://www.diybanter.com/metalworking/275783-precision-electronic-levels-blumlein-bridge.html

--
Bill Sloman, Sydney

[John Larkin]

On Fri, 12 Apr 2013 16:27:51 +0000 (UTC), David Lesher
<wb8...@panix.com> wrote:

>
>So midst the noise I've seen the following mentioned:
>
>LM71
>DS18B20
>LM75
>AD7414
>
>Of those, only a few seem to come in non-surface mount packages
>and I'm not sure how we'd couple surface mount devices to the
>copper cooling lines.

Both LM35 (analog) and LM71 (digital) types could have problems at the
ends of long cables. LM35s love to oscillate if they see much load
capacitance, and any induced noise can make them do weird things. SPI
would of cource have to be handled carefully at the end of a cable.

RTDs and thermocouples are better for field temperature measurements.

[Spehro Pefhany]

On Fri, 12 Apr 2013 13:00:22 -0700, the renowned John Larkin
<jla...@highlandtechnology.com> wrote:

>On Fri, 12 Apr 2013 06:50:22 -0700 (PDT), George Herold
><ghe...@teachspin.com> wrote:
>
>>On Apr 11, 11:25�pm, John Larkin
>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
>>> >So we're looking to sense temps in the ~~0-40C range, and
>>> >wondered what to use. In the past I've used LM35's and would
>>> >again, but all the cool kids seem to using this digital stuph,
>>> >so I was wondering what's a roughly parallel sensor that has
>>> >some ilk of digital output?
>>>
>>> >They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>>>
>>> LM71, 3 wire SPI.
>>
>>For a bit more money I saw a project that had a whole bunch of
>>DS18B20's that did a temperature profile of metal plate. (Maxim
>>though...)
>
>Cool, if you can't afford a FLIR.

Can your FLIR output an array of the temperatures for further
analysis?


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[John Larkin]

On Fri, 12 Apr 2013 18:40:14 -0400, Spehro Pefhany
<spef...@interlogDOTyou.knowwhat> wrote:

>On Fri, 12 Apr 2013 13:00:22 -0700, the renowned John Larkin
><jla...@highlandtechnology.com> wrote:
>
>>On Fri, 12 Apr 2013 06:50:22 -0700 (PDT), George Herold
>><ghe...@teachspin.com> wrote:
>>
>>>On Apr 11, 11:25�pm, John Larkin
>>><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
>>>> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
>>>> >So we're looking to sense temps in the ~~0-40C range, and
>>>> >wondered what to use. In the past I've used LM35's and would
>>>> >again, but all the cool kids seem to using this digital stuph,
>>>> >so I was wondering what's a roughly parallel sensor that has
>>>> >some ilk of digital output?
>>>>
>>>> >They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>>>>
>>>> LM71, 3 wire SPI.
>>>
>>>For a bit more money I saw a project that had a whole bunch of
>>>DS18B20's that did a temperature profile of metal plate. (Maxim
>>>though...)
>>
>>Cool, if you can't afford a FLIR.
>
>Can your FLIR output an array of the temperatures for further
>analysis?
>
>

It can save images, and you can measure every pixel on a PC.

[Bill Sloman]

> >> >astable,but then you have to cope with the temperature dependence of the

> >> >reactive element.
> >> >
> >> >I was recommending an accurate solution, rather than a simple one.
> >> >
> >> >> Slowman, You're a has-been... if you ever WERE in the first place. Go
> >> >> away.
> >> >
> >> >I may be a has-been, but I provided real - and potentially useful -
> >> >information. You've just claimed to know a "better" way (probably
> >> >incorrectly),
> >>
> >> Better way posted. Your way is asinine.
> >
> >But accurate, and precise. Your idea of "better" needs work.
>
> Whenever is a thermistor "precise" ??

Whenever you pay for a "interchangeable glass-encapsulated thermistor", as I recommended earlier in this thread. I don't know when Yellow Springs Instruments first introduced them, but I got told about their parts in 1974, and other people jumped an that particular band-waggon early on. I've bought Betatherm parts from Farnell which are just as tightly specified.

You probably don't know about that kind of stuff - thermistors don't seem to be susceptible to integration onto silicon.

--
Bill Sloman, Sydney

[Jim Thompson]

On Fri, 12 Apr 2013 16:04:53 -0700 (PDT), Bill Sloman

What do you have to pay for 0.1% thermistor interchangeability?

BTW... my chopper-stabilized thermistor apparatus made with Germanium
devices... 51 years ago...

http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf

[Phil Hobbs]

IC temperature sensors are all crap. Every single one, AFAICT--none
that I know of claims accuracy better than 1 degree C, even the trimmed
ones. Why would that be, if it's so fundamental?

[George Herold]

> Jon- Hide quoted text -

>
> - Show quoted text -

Jon, I'm going to have to reread some of that.
But I've got some data for a TIP31C. (Shipped out a month ago.)
The transistor is at the end of a ~12" cable and 18" SS probe.
The to220 tab is stuck to a hunk of copper at the bottom of the
probe.
Here's the forward voltage vs current.
I list the temperature as 297.75K
There's a FET opamp with a DC offset of -0.30mV


I(uA) V(mV) delta
0.01 243.365 63.42
0.1 306.785 60.82
1.0 367.606 59.91
10 427.519 59.50
100 487.020 59.57
1k 546.590 61.40
10k 607.986

The delta's are that current minus the one below.
The measurement were just taken in room air.. no control,
and the temperature drifted up (voltage down about 20uV) during the
measurment.

I get a T of 299.6K at the lowest voltage difference.

Oh.. it's a 1/2 kelvin connection... there's just one ground lead and
two leads for current and voltage to the emitter.

I think I did better with a 2N3904.. except it had more resistance.

George H.

[George Herold]

On Apr 12, 4:00 pm, John Larkin <jlar...@highlandtechnology.com>
wrote:

> On Fri, 12 Apr 2013 06:50:22 -0700 (PDT), George Herold
>
>
>
>
>
> <gher...@teachspin.com> wrote:
> >On Apr 11, 11:25 pm, John Larkin
> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
> >> On Fri, 12 Apr 2013 02:41:04 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:
> >> >So we're looking to sense temps in the ~~0-40C range, and
> >> >wondered what to use. In the past I've used LM35's and would
> >> >again, but all the cool kids seem to using this digital stuph,
> >> >so I was wondering what's a roughly parallel sensor that has
> >> >some ilk of digital output?
>
> >> >They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
>
> >> LM71, 3 wire SPI.
>
> >For a bit more money I saw a project that had a whole bunch of
> >DS18B20's that did a temperature profile of metal plate.  (Maxim
> >though...)
>
> Cool, if you can't afford a FLIR.
>
> --
>
> John Larkin         Highland Technology, Inc
>

> jlarkin at highlandtechnology dot comhttp://www.highlandtechnology.com

>
> Precision electronic instrumentation
> Picosecond-resolution Digital Delay and Pulse generators
> Custom laser drivers and controllers
> Photonics and fiberoptic TTL data links

> VME thermocouple, LVDT, synchro   acquisition and simulation- Hide quoted text -

>
> - Show quoted text -

How much is an FLIR?

George H.

[George Herold]

On Apr 12, 7:18 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-

I think we buy 0.2 degree C thermistors from YSI for a few bucks
each....
(no more than $5)

George H.

>
> BTW... my chopper-stabilized thermistor apparatus made with Germanium
> devices... 51 years ago...
>
> http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf
>
>                                         ...Jim Thompson
> --
> | James E.Thompson                                 |    mens     |
> | Analog Innovations                               |     et      |
> | Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
> | Phoenix, Arizona  85048    Skype: Contacts Only  |             |
> | Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |

> | E-mail Icon athttp://www.analog-innovations.com|    1962     |
>
> I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -

[George Herold]

On Apr 12, 7:30 pm, Phil Hobbs

> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -

>
> - Show quoted text -

Still, A sensor that's got 'built in' calibration to ~1% is kinda
nice.
(and it costs a dime or two.)

I've got data for 77K.. I think I had a ~+2 degree error there too.

(I guess it can't be a beta error, cause that would be in the other
direction.(?) It's the dreaded 'non-ideality factor', which last time
we checked had something to do with recombination in the base..
IIRC)

George H.

[Jim Thompson]

0.2�C accurate at one temperature, or over the whole span?

>
>George H.
>>
>> BTW... my chopper-stabilized thermistor apparatus made with Germanium
>> devices... 51 years ago...
>>
>> http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf
>>
>> � � � � � � � � � � � � � � � � � � � � ...Jim Thompson

[snip]

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |

| E-mail Icon at http://www.analog-innovations.com | 1962 |

[Jim Thompson]

I don't know of a single commercial unit that uses the ratiometric
current method, they're all PTAT's, some trimmed, some not.

>>
>> Cheers
>>
>> Phil Hobbs
>>
>> --
>> Dr Philip C D Hobbs
>> Principal Consultant
>> ElectroOptical Innovations LLC
>> Optics, Electro-optics, Photonics, Analog Electronics
>>
>> 160 North State Road #203
>> Briarcliff Manor NY 10510 USA
>> +1 845 480 2058
>>
>> hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted text -
>>
>> - Show quoted text -
>
>Still, A sensor that's got 'built in' calibration to ~1% is kinda
>nice.
>(and it costs a dime or two.)
>
>I've got data for 77K.. I think I had a ~+2 degree error there too.
>
>(I guess it can't be a beta error, cause that would be in the other
>direction.(?) It's the dreaded 'non-ideality factor', which last time
>we checked had something to do with recombination in the base..
>IIRC)
>
> George H.

[George Herold]

On Apr 12, 8:44 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-

> | E-mail Icon athttp://www.analog-innovations.com|    1962     |
>
> I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -
>
> - Show quoted text -

Over some span around room temp. Maybe 0 to 60C.. you can pay more
and get better specs.

It's totally worth it for us. I use them for diode laser thermal
control, diodes are measured in my setup, but will then 'work' in
everyone else's.

(I measure wavelength at one temperature.)

George H.

[George Herold]

On Apr 12, 8:46 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-

Jim, I'm confused (or just ignorant again).. I thought PTAT's used the
current ratio trick.

George H.

>
>
> >> Cheers
>
> >> Phil Hobbs
>
> >> --
> >> Dr Philip C D Hobbs
> >> Principal Consultant
> >> ElectroOptical Innovations LLC
> >> Optics, Electro-optics, Photonics, Analog Electronics
>
> >> 160 North State Road #203
> >> Briarcliff Manor NY 10510 USA
> >> +1 845 480 2058
>

> >> hobbs at electrooptical dot nethttp://electrooptical.net-Hide quoted text -

>
> >> - Show quoted text -
>
> >Still, A sensor that's got 'built in' calibration to ~1% is kinda
> >nice.
> >(and it costs a dime or two.)
>
> >I've got data for 77K.. I think I had a ~+2 degree error there too.
>
> >(I guess it can't be a beta error, cause that would be in the other
> >direction.(?)  It's the dreaded 'non-ideality factor', which last time
> >we checked had something to do with recombination in the base..
> >IIRC)
>
> > George H.
>
>                                         ...Jim Thompson
> --
> | James E.Thompson                                 |    mens     |
> | Analog Innovations                               |     et      |
> | Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
> | Phoenix, Arizona  85048    Skype: Contacts Only  |             |
> | Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |

> | E-mail Icon athttp://www.analog-innovations.com|    1962     |
>
> I love to cook with wine.     Sometimes I even put it in the food.- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -

[George Herold]

> George H.- Hide quoted text -

>
> - Show quoted text -

PS
Sorry, just thinking about how important voltage references are to the
whole signal chain.

Geo

[Spehro Pefhany]

On Fri, 12 Apr 2013 16:04:53 -0700 (PDT), the renowned Bill Sloman

Both YSI and Betatherm were acquired by Measurement Specialties about
seven years ago.

[Jim Thompson]

Different ratio. PTAT's generate a voltage that indeed is ratio'd by
using two devices of differing areas, thus different current
_densities_.

The Jim Williams' technique, using resistors and adapted by me to use
current sources, uses the same device, "measured" at two carefully
ratio'd currents.

The PTAT effect depends on lots of other variables as well.

I'll dredge thru my files and find one I can show.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |

| E-mail Icon at http://www.analog-innovations.com | 1962 |

[Bill Sloman]

On Saturday, 13 April 2013 09:18:22 UTC+10, Jim Thompson wrote:
> On Fri, 12 Apr 2013 16:04:53 -0700 (PDT), Bill Sloman
> <bill....@ieee.org> wrote:
> >On Saturday, 13 April 2013 07:09:04 UTC+10, Jim Thompson wrote:
> >> On Fri, 12 Apr 2013 13:56:13 -0700 (PDT), Bill Sloman
> >> <bill....@ieee.org> wrote:
> >> >On Saturday, 13 April 2013 01:06:07 UTC+10, Jim Thompson wrote:
> >> >> On Fri, 12 Apr 2013 00:01:14 -0700 (PDT), Bill Sloman
> >> >> <bill....@ieee.org> wrote:
> >> >> >On Friday, 12 April 2013 14:10:50 UTC+10, Jim Thompson wrote:
> >> >> >> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:

<snip>

> >> Whenever is a thermistor "precise" ??
> >
> >Whenever you pay for a "interchangeable glass-encapsulated thermistor", as I recommended earlier in this thread. I don't know when Yellow Springs Instruments first introduced them, but I got told about their parts in 1974, and other people jumped an that particular band-waggon early on. I've bought Betatherm parts from Farnell which are just as tightly specified.
> >
> >You probably don't know about that kind of stuff - thermistors don't seem to be susceptible to integration onto silicon.
>
> What do you have to pay for 0.1% thermistor interchangeability?

Newark sells a +/0.2C part for $9.57, 1-off Newark Part Number: 10M5351,
Fenwall (Honeywel) Part No: 192-303QET-A01

The Betatherm part, also +/0.2C costs $4.79 1-off Newark Part Number: 93K1990
Betatherm part no.:1K2A1B

Thermometrics do a +/-0.1C part for $8.18 Newark Part Number: 65J5900
but it's on special today for $5.43 (1-9)

> BTW... my chopper-stabilized thermistor apparatus made with Germanium
> devices... 51 years ago...
>
> http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf

Terrible circuit diagram, not that American schematics from that period were ever much better. I'd have to redraw if before I could make any sense of it.

--
Bill Sloman, Sydney

[Spehro Pefhany]

On Fri, 12 Apr 2013 19:30:38 -0400, the renowned Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>
>
>IC temperature sensors are all crap. Every single one, AFAICT--none
>that I know of claims accuracy better than 1 degree C, even the trimmed
>ones. Why would that be, if it's so fundamental?
>
>Cheers
>
>Phil Hobbs

That was true a few years ago, but the ADT7320 has quite impressive
specs- +/-0.2�C from -10 to 85�C with a 3V supply and +/-0.25�C from
-20 to 105�C with supply +/- 10%.

Nasty package for field use, of course, and it's going to measure it's
own temperature rise, and not particularly cheap (>$5 in q100), but it
does include its own ADC. I'd worry about the solder fatiguing if it
saw a lot of cycling.

I've recently designed in a similar TI part with specs about twice as
bad, but still quite good (+-/ 0.5�C, IIRC)and I didn't care very much
about the absolute temperature- it was for compensation, so trimming
was built into the process).

[George Herold]

On Apr 12, 9:31 pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-

Web-Site.com> wrote:
> On Fri, 12 Apr 2013 18:02:52 -0700 (PDT), George Herold
>
>
>
>
>

> >> >> hobbs at electrooptical dot nethttp://electrooptical.net-Hidequoted text -

Ahh, got it thanks. I must have read the Jim Williams app note.. I
remember the baby bottles.

George H.

[John Larkin]

Not Jim Williams.

http://en.wikipedia.org/wiki/Brokaw_bandgap_reference

and

http://en.wikipedia.org/wiki/Bandgap_voltage_reference



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators

Custom timing and laser controllers

Photonics and fiberoptic TTL data links

VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

[David Lesher]

Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:

>Here it is done at the device-level on one of my chips...

>http://www.analog-innovations.com/SED/TempMeasureViaCurrentRatio.pdf

>Of course you can do it with off-the-shelf OpAmps and analog switches,
>which is what the devices are all about.

I'm sorry if I gave anyone the wrong idea. We don't want to
invent new temp monitoring schemes; just choose a chip to use.

Trying to hang surface mount chips onto coolant lines has
little appeal to us...





--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[David Lesher]

whit3rd <whi...@gmail.com> writes:


>> Given that we just want to measure the coolent temperature on
>> both sides of the liquid-cooled heatsink...

>If you want the difference to be accurately measured, that's
>actually an ideal place to put in a thermocouple, or several
>thermocouples in series.

No, I dealt with TC's in my youth, but I've been in recovery
for decades.

[John Larkin]

On Sat, 13 Apr 2013 02:00:31 +0000 (UTC), David Lesher <wb8...@panix.com> wrote:

>Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>
>>Here it is done at the device-level on one of my chips...
>
>>http://www.analog-innovations.com/SED/TempMeasureViaCurrentRatio.pdf
>
>>Of course you can do it with off-the-shelf OpAmps and analog switches,
>>which is what the devices are all about.
>
>I'm sorry if I gave anyone the wrong idea. We don't want to
>invent new temp monitoring schemes; just choose a chip to use.
>
>Trying to hang surface mount chips onto coolant lines has
>little appeal to us...

Thinfilm RTDs are cheap. Here's one that I epoxied into a soda straw for outdoor
temp measurement.

https://dl.dropboxusercontent.com/u/53724080/Truckee/Automation/RTD_outside.jpg

[David Lesher]

John Larkin <jla...@highlandtechnology.com> writes:


>Both LM35 (analog) and LM71 (digital) types could have problems at the
>ends of long cables. LM35s love to oscillate if they see much load
>capacitance, and any induced noise can make them do weird things. SPI
>would of cource have to be handled carefully at the end of a cable.

>RTDs and thermocouples are better for field temperature measurements.

I used LM35's on far longer cables than this in years past. It's
only a foot or less from the motor controller CPU to the JFET
heatsink. There's not that much room under a Miata hood.

[Phil Hobbs]

On 04/12/2013 09:39 PM, Spehro Pefhany wrote:
> On Fri, 12 Apr 2013 19:30:38 -0400, the renowned Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>>
>>
>> IC temperature sensors are all crap. Every single one, AFAICT--none
>> that I know of claims accuracy better than 1 degree C, even the trimmed
>> ones. Why would that be, if it's so fundamental?
>>
>> Cheers
>>
>> Phil Hobbs
>
>
> That was true a few years ago, but the ADT7320 has quite impressive
> specs- +/-0.2�C from -10 to 85�C with a 3V supply and +/-0.25�C from
> -20 to 105�C with supply +/- 10%.
>
> Nasty package for field use, of course, and it's going to measure it's
> own temperature rise, and not particularly cheap (>$5 in q100), but it
> does include its own ADC. I'd worry about the solder fatiguing if it
> saw a lot of cycling.
>
> I've recently designed in a similar TI part with specs about twice as
> bad, but still quite good (+-/ 0.5�C, IIRC)and I didn't care very much
> about the absolute temperature- it was for compensation, so trimming
> was built into the process).
>
>
>
> Best regards,
> Spehro Pefhany
>

Good news, thanks. Now all we need is the same thing in a package that
isn't such a good thermal insulator. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

[Jim Thompson]

We've all been thru that. I was "blessed" by the MIT ability to sleep
in bursts, so I always drew bottle detail in the middle of the night.
I could put the baby between us, prop up the bottle, and never roll
over on the baby (X4 :-)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |

| E-mail Icon at http://www.analog-innovations.com | 1962 |

[Jim Thompson]

On Fri, 12 Apr 2013 18:34:24 -0700 (PDT), Bill Sloman

You're behaving like the brat.

[Bill Sloman]

On Saturday, 13 April 2013 14:12:45 UTC+10, Jim Thompson wrote:
> On Fri, 12 Apr 2013 18:34:24 -0700 (PDT), Bill Sloman
> <bill....@ieee.org> wrote:
> >On Saturday, 13 April 2013 09:18:22 UTC+10, Jim Thompson wrote:
> >> On Fri, 12 Apr 2013 16:04:53 -0700 (PDT), Bill Sloman
> >> <bill....@ieee.org> wrote:
> >> >On Saturday, 13 April 2013 07:09:04 UTC+10, Jim Thompson wrote:
> >> >> On Fri, 12 Apr 2013 13:56:13 -0700 (PDT), Bill Sloman
> >> >> <bill....@ieee.org> wrote:
> >> >> >On Saturday, 13 April 2013 01:06:07 UTC+10, Jim Thompson wrote:
> >> >> >> On Fri, 12 Apr 2013 00:01:14 -0700 (PDT), Bill Sloman
> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >On Friday, 12 April 2013 14:10:50 UTC+10, Jim Thompson wrote:
> >> >> >> >> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> >> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
> >
> ><snip>
> >
> >> >> Whenever is a thermistor "precise" ??
> >> >
> >> >Whenever you pay for a "interchangeable glass-encapsulated thermistor", as I recommended earlier in this thread. I don't know when Yellow Springs Instruments first introduced them, but I got told about their parts in 1974, and other people jumped an that particular band-waggon early on. I've bought Betatherm parts from Farnell which are just as tightly specified. >
> >> >
> >> >You probably don't know about that kind of stuff - thermistors don't seem to be susceptible to integration onto silicon.
> >>
> >> What do you have to pay for 0.1% thermistor interchangeability?
> >
> >Newark sells a +/0.2C part for $9.57, 1-off Newark Part Number: 10M5351,
> >Fenwall (Honeywel) Part No: 192-303QET-A01
> >

> >The Betatherm part, also +/0.2C costs $4.79 1-off Newark Part No: 93K1990

> >Betatherm part no.:1K2A1B
> >
> >Thermometrics do a +/-0.1C part for $8.18 Newark Part Number: 65J5900
> >but it's on special today for $5.43 (1-9)
> >
> >> BTW... my chopper-stabilized thermistor apparatus made with Germanium
> >> devices... 51 years ago...
> >>
> >> http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf
> >
> >Terrible circuit diagram, not that American schematics from that period were > >ever much better. I'd have to redraw if before I could make any sense of it.
>
> You're behaving like the brat.

Scarcely. Un-intelligible schematics are very nearly useless - too much risk that a crucial detail will be misinterpreted.

--
Bill Sloman, Sydney

[John Devereux]

whit3rd <whi...@gmail.com> writes:

> On Friday, April 12, 2013 9:09:27 AM UTC-7, John Devereux wrote:
>> Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:

> [about thermometry]
>> > (1) Connect a transistor as a diode (B-C short)
>>
>> > (2) Operate it at low enough current that bulk resistive effects and
>> > dissipation are nil
>>
>> > (3) Observe basic equation: vBE = kT/q * ln(Ie/Is)
>>
>> > (4) Pulse transistor with squarewave of current, Imax = 10*Imin

>
>> Is this accurate to +/- 0.2'C (without calibration)?
>

> It's an absolute-temperature measurement, so +/- 0.2 C implies better
> than a part-per-thousand error band. Voltage references and resistor
> values for the current pulse would have to be better than 0.1%, so probably
> the answer is NO. The only way to get components with that accuracy
> is with trimming, and that means ALL qualified sensors are dependent
> on calibration or trimming. You can choose which, but you
> must pay, either way.

Yes this is true. It is not clear that Jims way is simpler. As others
have said, manufacturers have gone to a lot of trouble to get IC sensors
that still do not achieve this. A 0.1% ratio reference resistor is
cheap. If you don't want Bills bridge+adc, you can do something like this:

<http://ee.devereux.me.uk/ratio-coded-adc.png>

(opamp choice just for simulation)

> Calibration after soldering is better than trimming before soldering.

--

John Devereux

[Bill Sloman]

On Saturday, 13 April 2013 12:06:21 UTC+10, Phil Hobbs wrote:
> On 04/12/2013 09:39 PM, Spehro Pefhany wrote:
> > On Fri, 12 Apr 2013 19:30:38 -0400, the renowned Phil Hobbs
> > <pcdhSpamM...@electrooptical.net> wrote:

> >> IC temperature sensors are all crap. Every single one, AFAICT--none
> >> that I know of claims accuracy better than 1 degree C, even the trimmed
> >> ones. Why would that be, if it's so fundamental?
> >

> > That was true a few years ago, but the ADT7320 has quite impressive

> > specs- +/-0.2C from -10 to 85C with a 3V supply and +/-0.25C from
> > -20 to 105C with supply +/- 10%.

> >
> > Nasty package for field use, of course, and it's going to measure it's
> > own temperature rise, and not particularly cheap (>$5 in q100), but it
> > does include its own ADC. I'd worry about the solder fatiguing if it
> > saw a lot of cycling.

Power dissipation is 0.7mW and thermal resistance to ambient air is 37C/W, which is 0.026C of self-heating, which isn't too shabby.

http://www.analog.com/static/imported-files/data_sheets/ADT7320.pdf?ref=ASC-PR-479

I like it.

> > I've recently designed in a similar TI part with specs about twice as

> > bad, but still quite good (+-/ 0.5C, IIRC)and I didn't care very much

> > about the absolute temperature- it was for compensation, so trimming
> > was built into the process).
>

> Good news, thanks. Now all we need is the same thing in a package that
> isn't such a good thermal insulator. ;)

There's an "exposed pad" under the device, which you could solder to a copper ground pad, or couple - without electrical connection - with thermal conductive adhesive. What kind of package did you have in mind - one of the options that National Semiconductor offered for the LM12?

http://www.ti.com/lit/ds/snosby8d/snosby8d.pdf

They did have an order of magnitude less thermal resistance to ambient ...

--
Bill Sloman, Syndey

[Spehro Pefhany]

On Sat, 13 Apr 2013 00:30:20 -0700 (PDT), the renowned Bill Sloman
<bill....@ieee.org> wrote:

>On Saturday, 13 April 2013 12:06:21 UTC+10, Phil Hobbs wrote:
>> On 04/12/2013 09:39 PM, Spehro Pefhany wrote:
>> > On Fri, 12 Apr 2013 19:30:38 -0400, the renowned Phil Hobbs
>> > <pcdhSpamM...@electrooptical.net> wrote:
>
>> >> IC temperature sensors are all crap. Every single one, AFAICT--none
>> >> that I know of claims accuracy better than 1 degree C, even the trimmed
>> >> ones. Why would that be, if it's so fundamental?
>> >
>> > That was true a few years ago, but the ADT7320 has quite impressive
>> > specs- +/-0.2C from -10 to 85C with a 3V supply and +/-0.25C from
>> > -20 to 105C with supply +/- 10%.
>> >
>> > Nasty package for field use, of course, and it's going to measure it's
>> > own temperature rise, and not particularly cheap (>$5 in q100), but it
>> > does include its own ADC. I'd worry about the solder fatiguing if it
>> > saw a lot of cycling.
>
>Power dissipation is 0.7mW and thermal resistance to ambient air is 37C/W, which is 0.026C of self-heating, which isn't too shabby.

Ummm.. Bill, I _really_ question the general validity of that 37�C/W
number in the datasheet .. I bet that's measured on a good-size chunk
of FR4*.. think about putting a watt(!) into something that tiny. They
don't state the coupon size in the datasheet. Fine, if you're
measuring PCB temperature, maybe not fine otherwise.

A Pt100 at 0.2mA is 4uW, even a Pt1000 at the same current is still
only 40uW- with similar surface area and a much nicer form factor.

*Okay, EIA/JESD 51-X (if that's what they're using) calls for
something like a 3 x 4" chunk of 4-layer FR-4 with 1-oz ground and
power planes!! A TO-220 (with maybe an order of magnitude more
surface area) has typical Theta-JA of 60�C/W (and that would include
heat flow down the leads). WAG for the Theta-JA on a thin bit of flex?
Maybe 500-1000�C/W?

Often the thermal impedance and response times of temperature sensors
are 'optimistically' rated in air blasting at 3m/s or stirred oil.

BTW, note too that there is a temperature dependency in the power
dissipation, especially in continous mode. At 1sps & 3V, power goes
down to a fairly constant 150uW, which is more reasonable.

Can't complain too much though, it's the sort of thing that keeps food
on the table and the wine fridge fairly well-stocked.

[Bill Sloman]

On Saturday, 13 April 2013 21:02:50 UTC+10, Spehro Pefhany wrote:
> On Sat, 13 Apr 2013 00:30:20 -0700 (PDT), the renowned Bill Sloman
> <bill....@ieee.org> wrote:
> >On Saturday, 13 April 2013 12:06:21 UTC+10, Phil Hobbs wrote:
> >> On 04/12/2013 09:39 PM, Spehro Pefhany wrote:
> >> > On Fri, 12 Apr 2013 19:30:38 -0400, the renowned Phil Hobbs
> >> > <pcdhSpamM...@electrooptical.net> wrote:

<snip>

> >> > That was true a few years ago, but the ADT7320 has quite impressive
> >> > specs- +/-0.2C from -10 to 85C with a 3V supply and +/-0.25C from
> >> > -20 to 105C with supply +/- 10%.
> >> >
> >> > Nasty package for field use, of course, and it's going to measure it's
> >> > own temperature rise, and not particularly cheap (>$5 in q100), but it
> >> > does include its own ADC. I'd worry about the solder fatiguing if it
> >> > saw a lot of cycling.
> >
> >Power dissipation is 0.7mW and thermal resistance to ambient air is 37C/W, which is 0.026C of self-heating, which isn't too shabby.
>
> Ummm.. Bill, I _really_ question the general validity of that 37°C/W
> number in the datasheet .. I bet that's measured on a good-size chunk
> of FR4*.. think about putting a watt(!) into something that tiny. They
> don't state the coupon size in the datasheet. Fine, if you're
> measuring PCB temperature, maybe not fine otherwise.

The exposed pad on the under-side of the package is for thermally coupling it to the board you mount it on. If you thermally couple that board to the object whose temperature you are measuring - in David Lesher's case, a copper pipe - I can't see that there's going to be much of a problem.

The tiny packages haven't got much surface area, but they are thin,and there's not a lot of plastic packaging to slow down the heat flow. You may well be right, but it's not guaranteed.

> A Pt100 at 0.2mA is 4uW, even a Pt1000 at the same current is still
> only 40uW- with similar surface area and a much nicer form factor.

It depends on the Pt100. If it's a thin film sensor on an alumina substrate, thermal resistance can be quite low. I got enthusiastic about that in print back in 1978

Sloman, A.W. "On microdegree thermostats", Journal of Physics E: Scientific Instruments, 11, 967-968 (1978).

> *Okay, EIA/JESD 51-X (if that's what they're using) calls for
> something like a 3 x 4" chunk of 4-layer FR-4 with 1-oz ground and
> power planes!! A TO-220 (with maybe an order of magnitude more
> surface area) has typical Theta-JA of 60°C/W (and that would include
> heat flow down the leads). WAG for the Theta-JA on a thin bit of flex?
>
> Maybe 500-1000°C/W?

Probably not. Your TO-220 thermal resistance of 60°C/W is from junction to air. The thermal resistance from junction to case is about 1.5°C/W, and it's a much fatter package than that of the ADT7320.

> Often the thermal impedance and response times of temperature sensors
> are 'optimistically' rated in air blasting at 3m/s or stirred oil.

The ADT7320 quotes the junction-to-ambient at 37°C/W in still air, the junction-to-case as 33°C/W. Thermistors are often quoted "in a stirred oil bath", but semiconductor manufacturers have a pretty well-defined set of rules.

> BTW, note too that there is a temperature dependency in the power

> dissipation, especially in continuous mode. At 1sps & 3V, power goes

> down to a fairly constant 150uW, which is more reasonable.

150uW is better than 700uW, but it's not spectacularly less.

> Can't complain too much though, it's the sort of thing that keeps food
> on the table and the wine fridge fairly well-stocked.

People not thinking about self-heating can also be good for an extra citation ...

Sloman A. W. “Comment on ‘A versatile thermoelectric temperature controller with 10 mK reproducibility and 100 mK absolute accuracy’ [Rev. Sci. Instrum. 80, 126107 (2009)] “, Review of Scientific Instruments 82, 27101 - 027101-2 (2011).

There were claiming 100mK absolute accuracy while generating 200mK of self-heating in their thermistor. Clown car stuff.

--
Bill Sloman, Sydney

[Jim Thompson]

On Fri, 12 Apr 2013 21:38:27 -0700 (PDT), Bill Sloman

Maybe you need your reading glass prescription upped to a double lens
stack?

[Jim Thompson]

On Sat, 13 Apr 2013 07:22:10 +0100, John Devereux
<jo...@devereux.me.uk> wrote:

>whit3rd <whi...@gmail.com> writes:
>
>> On Friday, April 12, 2013 9:09:27 AM UTC-7, John Devereux wrote:
>>> Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> writes:
>> [about thermometry]
>>> > (1) Connect a transistor as a diode (B-C short)
>>>
>>> > (2) Operate it at low enough current that bulk resistive effects and
>>> > dissipation are nil
>>>
>>> > (3) Observe basic equation: vBE = kT/q * ln(Ie/Is)
>>>
>>> > (4) Pulse transistor with squarewave of current, Imax = 10*Imin
>>
>>> Is this accurate to +/- 0.2'C (without calibration)?
>>
>> It's an absolute-temperature measurement, so +/- 0.2 C implies better
>> than a part-per-thousand error band. Voltage references and resistor
>> values for the current pulse would have to be better than 0.1%, so probably
>> the answer is NO. The only way to get components with that accuracy
>> is with trimming, and that means ALL qualified sensors are dependent
>> on calibration or trimming. You can choose which, but you
>> must pay, either way.
>
>Yes this is true. It is not clear that Jims way is simpler.

In my case it was. No calibration needed, and it handles an added-on
external device to also measure temperatures away from the chip.

Some systems don't need +/- 0.2�C... particularly most of my stuff,
which is commercial or even consumer level.

>As others
>have said, manufacturers have gone to a lot of trouble to get IC sensors
>that still do not achieve this. A 0.1% ratio reference resistor is
>cheap. If you don't want Bills bridge+adc, you can do something like this:
>
><http://ee.devereux.me.uk/ratio-coded-adc.png>
>
>(opamp choice just for simulation)
>
>> Calibration after soldering is better than trimming before soldering.

[Jim Thompson]

On Fri, 12 Apr 2013 18:31:19 -0700, Jim Thompson

<To-Email-Use-Th...@On-My-Web-Site.com> wrote:

>On Fri, 12 Apr 2013 18:02:52 -0700 (PDT), George Herold
><ghe...@teachspin.com> wrote:
>
>>On Apr 12, 8:46�pm, Jim Thompson <To-Email-Use-The-Envelope-I...@On-My-
>>Web-Site.com> wrote:
>>> On Fri, 12 Apr 2013 17:43:33 -0700 (PDT), George Herold
>>>

[snip]

>>>
>>> >> IC temperature sensors are all crap. Every single one, AFAICT--none
>>> >> that I know of claims accuracy better than 1 degree C, even the trimmed
>>> >> ones. Why would that be, if it's so fundamental?
>>>
>>> I don't know of a single commercial unit that uses the ratiometric
>>> current method, they're all PTAT's, some trimmed, some not.
>>
>>Jim, I'm confused (or just ignorant again).. I thought PTAT's used the
>>current ratio trick.
>>
>>George H.
>>

[snip]

>
>Different ratio. PTAT's generate a voltage that indeed is ratio'd by
>using two devices of differing areas, thus different current
>_densities_.
>
>The Jim Williams' technique, using resistors and adapted by me to use
>current sources, uses the same device, "measured" at two carefully
>ratio'd currents.
>
>The PTAT effect depends on lots of other variables as well.
>
>I'll dredge thru my files and find one I can show.
>
> ...Jim Thompson

A very old one I designed for Fairchild...

http://www.analog-innovations.com/SED/PTAT_Demo_SED.pdf

Explanation to follow... I'm off to the 5-year-old grandson's ice
hockey practice... he made the team >:-}

[Joe Gwinn]

In article <51680205...@electrooptical.net>, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

> On 4/12/2013 12:10 AM, Jim Thompson wrote:
> > On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> > <bill....@ieee.org> wrote:
> >
> >> On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:

> >>> So we're looking to sense temps in the ~~0-40C range, and
> >>> wondered what to use. In the past I've used LM35's and would
> >>> again, but all the cool kids seem to using this digital stuph,
> >>> so I was wondering what's a roughly parallel sensor that has
> >>> some ilk of digital output?
> >>>
> >>> They'll feed a 32bit CPU so I'm sure we can scare up so IO lines...
> >>
> >> Depends whether you want an accurate sensor.
> >>
> >> At the moment interchangeable glass-encapsulated thermistors leave
> >> everything else for dead at +/-0.2C (or better, if you are prepared to pay
> >> more).
> >>
> >> You've got to put together a bridge and an A/D to turn the resistance into
> >> a digital number, which is going to be a non-linear function of
> >> temperature
> >>
> >> http://en.wikipedia.org/wiki/Thermistor
> >>
> >> but sorting out the Steinhart-Hart relationship won't overload a 32-bit

> >> CPU\.

> >
> > There are simpler ways, methods of which I have posted multiple times
> > on this newsgroup.
> >
>

> There are lots of simpler ways, they're just less accurate. Bill's
> right about thermistors, especially if you're interested in working near
> a single temperature. Junctions aren't in the same class, because
> parameters like doping density and beta aren't as well controlled. IC
> temperature sensors have crappy thermal time constants, their
> temperatures are dominated by conduction through the leads (which is
> sometimes what you want, but often not), and for accurate temperature
> control, they're strictly in the "just keep banging the rocks together,
> guys" class. (*)
>
> Mixed technology wins again. ;)
>
> For slightly wider ranges, platinum RTDs are all the go, especially if
> you pulse the excitation so you can use a higher voltage without
> horrible self-heating.
>
> But AFAIK nobody makes thermistors with built-in I2C or one-wire or
> whatever the OP is looking for. So ICs are probably useful for
> something after all. ;)

I recently designed a system to measure the temperature of the metal
structure holding parts of a radar antenna up. The resolution was 0.1
C, and the accuracy was nominally 1.0 C, the purpose being to be able
to calibrate over a range of temperatures with a reasonable number of
temperature sensors. The cable between cabinet and measurement point
was up to 10 meters long.

First tried thermocouples. The problem was getting the signal through
standard mil-spec connectors - the junction from chromel-alumel to
brass to copper was not temperature controlled, and things rapidly got
complex.

Then tried thermistors. The beads were good enough, and the resistance
was high enough to render cable resistance immaterial. But the ICs
available to put on the circuit board had too few ADC bits, yielding
too coarse a resolution.

Settled on platinum RTDs in a full Kelvin (4-wire) configuration, after
finding a suitable IC from Maxim (or LT?). This chip is ratiometric,
so we used a low-tempco metal-film resistor as the comparison. If
people are interested, I'll look up the chip number.

Joe Gwinn

[John Larkin]

I used 1K platinum RTDs, 2-wire, and RG174 coax for my cabin automation temp
sensing. The longest run is about 75 feet. I took out the coax resistance by
calculation and got better than 1 deg C. I got compulsive (cabin fever?) and did
an ice-point cal to final trim things up.

I did a simple mux thing with 0.1% resistors, ratiometric, all the math in
PowerBasic.

There are some 24 bit SPI delta-sigma ADCs with two differential channels. Hang
an RTD and a good resistor in series, across the ADC reference supply, and
measure the two voltage drops, and do the math. That will measure RTD resistance
to within a few PPM of the reference resistor. For the cabin, I wasn't *that*
compulsive.

[Michael A. Terrell]

Jim Thompson wrote:

>
> Bill Sloman wrote:
> >
> >Scarcely. Un-intelligible schematics are very nearly useless - too much risk that a crucial detail will be misinterpreted.
>
> Maybe you need your reading glass prescription upped to a double lens
> stack?

He must be brain dead, if he can't read that. Maybe Farnell has a
copy of the book: "Schematic Reading For The Rankest Of Amateurs" in
stock for him.

[Phil Hobbs]

I was very impressed by your improvement (Figure 6) of the infamous
four-wire-junction by a full 25%. ;)

[John Larkin]

I think I've done eight, once.

[Joe Gwinn]

In article <es8jm8luo0gh5kle5...@4ax.com>, John Larkin

That would work. If I recall, my chip can be configured to do that.

Now I will need to look the chip up. I don't recall the number of
bits, but it may have been 24. It wasn't fast. I used 100 ohm RTDs
and Kelvin configuration because we were making about 100 units, I
wanted zero cable sensitivity, and I didn't want anything to be fussy.

Joe Gwinn

[Jim Thompson]

On Sat, 13 Apr 2013 15:38:15 -0400, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

I have no clue as to what you are talking about. What is it with
which that you are taking issue?

[Jamie]

I was pricing some 16 bit SPI DAC's and I thought 55 bucks for an 8 pin
chip was a little steep. So I can imagine what a 24 bit ADC cost...

Jamie

[Jim Thompson]

On Sat, 13 Apr 2013 09:40:38 -0700, Jim Thompson

http://www.analog-innovations.com/SED/Killian_Thompson_Age_5.mp4

[Bill Sloman]

On Sunday, 14 April 2013 01:08:27 UTC+10, Jim Thompson wrote:
> On Fri, 12 Apr 2013 21:38:27 -0700 (PDT), Bill Sloman
> <bill....@ieee.org> wrote:
> >On Saturday, 13 April 2013 14:12:45 UTC+10, Jim Thompson wrote:
> >> On Fri, 12 Apr 2013 18:34:24 -0700 (PDT), Bill Sloman
> >> <bill....@ieee.org> wrote:
> >> >On Saturday, 13 April 2013 09:18:22 UTC+10, Jim Thompson wrote:
> >> >> On Fri, 12 Apr 2013 16:04:53 -0700 (PDT), Bill Sloman
> >> >> <bill....@ieee.org> wrote:
> >> >> >On Saturday, 13 April 2013 07:09:04 UTC+10, Jim Thompson wrote:
> >> >> >> On Fri, 12 Apr 2013 13:56:13 -0700 (PDT), Bill Sloman
> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >On Saturday, 13 April 2013 01:06:07 UTC+10, Jim Thompson wrote:
> >> >> >> >> On Fri, 12 Apr 2013 00:01:14 -0700 (PDT), Bill Sloman
> >> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >> >On Friday, 12 April 2013 14:10:50 UTC+10, Jim Thompson wrote:
> >> >> >> >> >> On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> >> >> >> >> >> <bill....@ieee.org> wrote:
> >> >> >> >> >> >On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:
>
> >> ><snip>
>

> >> >> BTW... my chopper-stabilized thermistor apparatus made with Germanium
> >> >> devices... 51 years ago...
> >> >>
> >> >> http://www.analog-innovations.com/BS_Thesis_JE_Thompson_1962.pdf
> >> >
> >> >Terrible circuit diagram, not that American schematics from that period
> >> >were ever much better. I'd have to redraw if before I could make any
> >> >sense of it.
> >>
> >> You're behaving like the brat.
> >
> >Scarcely. Un-intelligible schematics are very nearly useless - too much risk > >that a crucial detail will be misinterpreted.
>
> Maybe you need your reading glass prescription upped to a double lens
> stack?

I've got Zeiss varifocal lenses, and they work fine, and I can take them off for close work - the short-sighted eye focusses perfectly on stuff that's between four and ten inches away

The problem isn't seeing the symbols, but the way they are organised - or not organised in this particular case - on the schematic.

There's an art to making a schematic easily readable, and you hadn't mastered it back then. Your recent stuff is much better, if still a bit wee\sk on grouping stuff by function.

--
Bill Sloman, Sydney

[Bill Sloman]

On Sunday, 14 April 2013 10:35:22 UTC+10, Jamie wrote:
> John Larkin wrote:
> > On Sat, 13 Apr 2013 12:53:44 -0400, Joe Gwinn <joeg...@comcast.net> wrote:
> >>In article <51680205...@electrooptical.net>, Phil Hobbs
> >><pcdhSpamM...@electrooptical.net> wrote:
> >>>On 4/12/2013 12:10 AM, Jim Thompson wrote:
> >>>>On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> >>>><bill....@ieee.org> wrote:
> >>>>>On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher wrote:

<snip>

> > There are some 24 bit SPI delta-sigma ADCs with two differential channels.
> > Hang an RTD and a good resistor in series, across the ADC reference

> > supply,and measure the two voltage drops, and do the math. That will

> > measure RTD resistance to within a few PPM of the reference resistor.
> > For the cabin, I wasn't *that* compulsive.
> >
> I was pricing some 16 bit SPI DAC's and I thought 55 bucks for an 8 pin
> chip was a little steep. So I can imagine what a 24 bit ADC cost...

You seem to have imagined wrong

http://parametric.linear.com/Analog-to-Digital_Converters_%28ADC%29#!cols_1049,1030,2201,1097,1059,1058,1054,1367,10002!s_1049,1!gtd_!1049_24:24!1030_2

Newark lists the LTC2402 at $11 one-off, and the LTC2412 at $9.52, though they've got a promotion going on so today's price is only $7.41.

TI has similar parts that are cheaper. The ADS1226 seems to be $7.65 (1 to 9)
from Mouser.

--
Bill Sloman, Sydney

[John Larkin]

AD7191 is under $4 at 1K. Delta-sigmas are cheap.

Octal 16 bit DACs are cheap nowadays, too, well under $1 per channel.

[Spehro Pefhany]

On Sat, 13 Apr 2013 17:30:08 -0700, the renowned Jim Thompson

So, can we count on you incorporating hockey metaphors into your
posts? Say "deke" and "stick-handle", for starters?

[Jim Thompson]

I know not any of ice hockey "lingo". But Killian has certainly taken
to it.

[George Herold]

On Apr 12, 4:24 pm, Jon Kirwan <j...@infinitefactors.org> wrote:
> On Fri, 12 Apr 2013 09:26:40 -0700 (PDT), George Herold
>
>
>
>
>
> <gher...@teachspin.com> wrote:
> >On Apr 12, 12:09 pm, John Devereux <j...@devereux.me.uk> wrote:
> >> <snip of pulsed current through diode-connected BJT idea>

> >> Is this accurate to +/- 0.2'C (without calibration)?

> >Not in my experience.  (but my experience is fiarly limited... a few
> >transitors tested.)
>
> >I always got a number that was a bit off ~0.3%, so about 1 degree at
> >room temp.  I always assumed the error was due to the transistor
> >beta... Since the current is Ic and Ib.  (I think I got a temperature
> >that was always a bit high, but I'd have to check my notebook.)  You
> >could add some beta 'fudge factor'.... but then beta changes with
> >temperature too.
>
> >It also depended a bit on the collector current.  (1 uA to 10uA were
> >'nice' currents)
>
> Hi, George. I posted up a link to Linear's AN45 elsewhere
> under this topic. See page 7 there. But I take your
> experiences here seriously and wanted to think about this,
> not at the 'charged gas' theory level but at the higher (and
> more usual for an EE) device modeling level.
>
> The two-current pulse method, using say 1X and 10X currents,
> depends upon the following:
>
>         dV = (k/q) * ln( 1+Ic/Is ) dT
>
> Although k and q are known, the entire factor that includes
> the ln( 1+Ic/Is ) part isn't knowable in advance. But if one
> assumes that the +1 term is negligible then the two pulsed
> currents results in:
>
>         dV1/dT = (k/q) * ln( Ic1 ) - (k/q) * ln( Is )
>         dV2/dT = (k/q) * ln( Ic2 ) - (k/q) * ln( Is )
>
> Subtracting dV1/dT from dV2/dT yields:
>
>         dV1 - dV1 = (k/q) * ln( Ic2/Ic1 ) ) dT
>
> And if the ratio of Ic2/Ic1 is known a priori then the entire
> factor, (k/q) * ln( Ic2/Ic1 ) ), is also known. And as a
> consequence could be used to measure temperature without
> having to calibrate the system. Or so it seems at first
> blush.
>
> But it's also the case that the value of the saturation
> current, Is, is itself a rather complex function of T:
>
>   Is(T) = Is(Tn) * (T/Tn)^3 * e^( -(q*Eg/k) * (1/T-1/Tn) )
>
> Where Tn is some chosen T(nominal).
>
> In fact, this particular component is what overwhelms the
> first equation (which is positive vs temperature) and yields
> the usually quoted -2mV/K figure (very approximately.) So, in
> fact, Is(T) is the dominant factor in Vbe change over T and
> in no possible way is it a simple function of T!
>
> (Even the above Is(T) equation itself is a simplification.
> The power ((T/Tn)^3) for example is an approximation and not
> strictly true in practice. Same with Eg, which itself is also
> taken as a single approximation value.)
>
> Just as a guess, the idea of ln( Is ) being cancelled
> entirely out of the equation by ratiometry, even assuming
> that the die is at thermal equilibrium, would make me worry a
> little. (I accept that pulsing the 1X/10X current change fast
> enough or that using low enough currents, like the 1uA and
> 10uA you mention, would yield a near-equilibrium state.) I'm
> just not sure that at this level of modeling, that _Is_
> remains dead stable as a modeling parameter when facing a 10X
> current change. There is a lot of linearity over orders of
> magnitude change, as a broad statement. But exactly how
> linear is it when provided a two point ratio a decade apart,
> vs device variation?
>
> I wonder that some temperature error is swept under this
> Is(T) rug and hidden from the analysis, so to speak. Even
> assuming thermal equilibrium. Because it may really be that
> Is(V,T), not Is(T), as both the power (^3) and Eg are taken
> as simple constants for simplification when they aren't, in
> fact, invariant at this level of modeling.
>
> You mention base currents as a possible error. I've ignored
> that so far. The equation:
>
>         dV = (k/q) * ln( 1+Ic/Is ) dT
>
> in the diode connected case refers to Ic. The currents
> through it, on whole, are (beta+1)/beta times as much. If you
> cobble up precision current sources at exactly 1X and 10X,
> the ratio of Ic2/Ic2 would still be 10, even though you are
> driving Ie, I think. However, beta itself changes vs Ic. So
> there is that to account for, if you were only using a beta
> level model. But the:
>
>         dV1 - dV1 = (k/q) * ln( Ic2/Ic1 ) ) dT
>
> method doesn't use or rely upon beta. So I'm not imagining a
> problem there because (1) the ratio is still 10X and (2) beta
> isn't used in the analysis method.
>
> Interesting problem getting past a certain level of accuracy,
> though. There must be several papers that go beyond the AN45
> app note I'd posted up earlier. I haven't seen one, yet.
>
> Jon- Hide quoted text -

>
> - Show quoted text -

Hey Jon, I was thinking about this, and it seems like the error is
due to the non-ideality factor (NIF) in the equation. Now I've only
read about the NIF in the context of pn junctions, but wouldn't there
be something similar in a diode connected transistor?
Now according to Streetman the NIF arises because of carrier
recombination in the transition region. I know when I looked at the
temperature dependence of some pn diodes (maybe 1n4148's?) that the
NIF was much closer to 2.
So then what transitors would have NIF's close to 1?
I wonder if they list NIF's in the spice models?

George H.

[George Herold]

On Apr 13, 12:53 pm, Joe Gwinn <joegw...@comcast.net> wrote:
> In article <51680205.2090...@electrooptical.net>, Phil Hobbs

> Joe Gwinn- Hide quoted text -

>
> - Show quoted text -

Hi Joe that's neat, I'm a bit confused as to why platinum RTD's were
easier thant thermistors?
I've never used a platinum RTD.

George H.

[George Herold]

On Apr 13, 11:17 pm, Spehro Pefhany

"Keep your stick on the ice!"

George H.

>
> Best regards,
> Spehro Pefhany
> --
> "it's the network..."                          "The Journey is the reward"
> sp...@interlog.com             Info for manufacturers:http://www.trexon.com

> Embedded software/hardware/analog  Info for designers:  http://www.speff.com- Hide quoted text -

[Jim Thompson]

[snip]

Yep. A fundamental rule.

[Bill Sloman]

On Sunday, 14 April 2013 13:38:49 UTC+10, George Herold wrote:
> On Apr 13, 12:53 pm, Joe Gwinn <joegw...@comcast.net> wrote:
> > In article <51680205.2090...@electrooptical.net>, Phil Hobbs
> > <pcdhSpamMeSensel...@electrooptical.net> wrote:
> > > On 4/12/2013 12:10 AM, Jim Thompson wrote:
> > > > On Thu, 11 Apr 2013 21:00:09 -0700 (PDT), Bill Sloman
> > > > <bill.slo...@ieee.org> wrote:
> > > >> On Friday, 12 April 2013 12:41:04 UTC+10, David Lesher  wrote:

<snip>

> > I recently designed a system to measure the temperature of the metal
> > structure holding parts of a radar antenna up.  The resolution was 0.1
> > C, and the accuracy was nominally 1.0 C, the purpose being to be able
> > to calibrate over a range of temperatures with a reasonable number of
> > temperature sensors.  The cable between cabinet and measurement point
> > was up to 10 meters long.
> >
> > First tried thermocouples.  The problem was getting the signal through
> > standard mil-spec connectors - the junction from chromel-alumel to
> > brass to copper was not temperature controlled, and things rapidly got
> > complex.
> >
> > Then tried thermistors.  The beads were good enough, and the resistance
> > was high enough to render cable resistance immaterial.  But the ICs
> > available to put on the circuit board had too few ADC bits, yielding
> > too coarse a resolution.
> >
> > Settled on platinum RTDs in a full Kelvin (4-wire) configuration, after
> > finding a suitable IC from Maxim (or LT?).  This chip is ratiometric,
> > so we used a low-tempco metal-film resistor as the comparison.  If
> > people are interested, I'll look up the chip number.
>

> Hi Joe that's neat, I'm a bit confused as to why platinum RTD's were

> easier than thermistors?

>
> I've never used a platinum RTD.

They aren't. I think that what Joe Gwinn was saying that he didn't discover 24-bit sigma delta A/D converters (mostly they aren't better than 20-bit, but they all produce three eight-bit bytes of output data)until after he'd decided to try the Platinum RTDs.

Pt RTDs give about +0.4% resistance change per degree Kelvin, thermistors about -4%, so they aren't easier to use. Their self-heating isn't usually as bad, and they don't go nuts if you put too much current through them, but it takes even a sophisticated user a while to get conscious of this kind of problem.

--
Bill Sloman, Sydney

[Jon Kirwan]

On Sat, 13 Apr 2013 20:35:32 -0700 (PDT), George Herold
<ghe...@teachspin.com> wrote:
><snip>

>Hey Jon, I was thinking about this, and it seems like the error is
>due to the non-ideality factor (NIF) in the equation. Now I've only
>read about the NIF in the context of pn junctions, but wouldn't there
>be something similar in a diode connected transistor?

The BJT models are rife with "emission coefficients," which
is what I think you are talking about. In BJTs, my meager
practical experience (small signal BJTs at low frequency and
DC) is they really are very close to 1. Yes, an emission
coefficient, if different than 1, would affect things. But
only the step size. At least, given the simple models I was
discussing earlier.

>Now according to Streetman the NIF arises because of carrier
>recombination in the transition region. I know when I looked at the
>temperature dependence of some pn diodes (maybe 1n4148's?) that the
>NIF was much closer to 2.

Diodes quite commonly have emission coefficients > 1. Some as
high as 4 or more, I think. LTspice (I just checked) shows
their single (I'm sure there should be more than one model as
it is a widely sourced part) model having an emission
coefficient of 1.752. Which is, as you say, much closer to 2
than to 1.

>So then what transitors would have NIF's close to 1?
>I wonder if they list NIF's in the spice models?

Yeah, they do. Forward, reverse, high current, low current,
upside down, ... Go into LTspice, then access the Help.
Search on Q. The just look down the list for emission
coefficients. 5 of them pop up right away. If there is a
modeled diode anywhere, backwards or forwards, there is a
separate emission coefficient for it, I think. ;) Almost
gives Rube Goldberg a run for his money.

If you see step size variations from part to part, but
consistent within a given part, I'd tend to lump that one
onto the simple emission coefficient. It's a quick fix. But
step size variations over T on the same part? There is
something else involved... or the single emission coefficient
isn't enough... which is about the same problem.

It all comes down to teasing out what you can assign to a
priori physics and remove from the modeling by applying a
better physical model and what you are stuck gluing onto an
existing model, which uses some mathematical behavior as a
tool but where there is no real physics underneath it. It can
get pretty hairy.

Assuming there is any additional fruit to be had using these
as temperature sensors, better than the simple models
provide, I think means delving into the deeper nature of the
parts and not getting hung up tinkering on the high level
modeling side. It's like the scenario where you are using a
simple, small-angle pendulum model to understand the behavior
of pendulums made by children. You can argue all day about
tinkering with pasted on parameters to make the model match
experience, but unless you delve deeper into how the kids are
building them and see they are using different sized holes
(and different diameter rods rocking in them) and develop a
better more physically based model, those parameters will
never get you that far. You'll be mired in limited degrees of
freedom pasted to the wrong math models for the physics
involved and never extracate yourself (with any remaining
sanity.)

It would be fun to horse around trying to make really good T
sensors from BJTs, if no one else had already scraped that
bowl clean. But I suspect there have been a number of Ph.D.s
already squandered without achieving a great deal more
utility than we already see.

Did you do a single-point calibratation on your probe, by the
way? Or how did you establish where on the absolute scale
things were at?

Jon

[Joe Gwinn]

In article
<5a898470-df09-46e6...@l5g2000yqe.googlegroups.com>,

I forgot to mention a big practical problem with thermistors - they are
not much used in industrial temperature sensing where the "point" (the
location being measured) is outside of the equipment shelter, so one
cannot buy suitable *robust* industrial cables and probes. By
contrast, thermocouples and RTDs are widely used for such things, and
so are widely supported by multiple vendors.

<http://www.omega.com/temperature/tsc.html>

The other problem was the unavailability of suitable ICs to convert
thermocouple electrical signals into computer-readable data.

Joe Gwinn

[Jim Thompson]

That's why BJT's make better "diodes" than diodes do. M (or N,
depending on whose equation) rarely varies from "1" in conventional
BJT's... as long as you stay away from HV devices.

Beware: You _will_ occasionally see Spice models with M =/= 1. This
is because the modelers don't know how to fit equations to data.

[John Larkin]

On Sat, 13 Apr 2013 20:38:49 -0700 (PDT), George Herold <ghe...@teachspin.com>
wrote:

RTDs are very accurate and stable and are usable over a wide temp range, things
that termistors aren't. Thinfilm platinum RTDs are fairly cheap, too, much
cheaper than a thermistor of similar accuracy.

RTDs are easy to linearize, too, in hardware or software. I have somewhere
around here a dual-opamp circuit that does 3-wire RTD conditioning with
linearization. In software, a bit of second-order correction is usually all you
need... just a few lines even in assembly.

Thermistors can be good over a narrow temp range where you want a lot of signal,
like a crystal oven or some such.

[Jim Thompson]

On Sat, 13 Apr 2013 18:08:44 -0700 (PDT), Bill Sloman

You, Slowman, are just a wee bit "weak" (*) at following schematics.
My drawings are hierarchical by function, AND by matching
requirements. So it is a rarity that a component in one hierarchical
block has to match something in another hierarchical.

(*) Maybe because you aren't capable of recognizing functions at the
device-level ?>:-}

And your oscillator claims are down-right farcical.

[k...@attt.bizz]

On Sat, 13 Apr 2013 20:35:22 -0400, Jamie
<jamie_ka1lpa_not_v...@charter.net> wrote:

We're paying around a buck for eight channel, 24-bit, differential
DACs and about a buck-fifty for four channel ADCs with input
diagnostics. Delta-sigma audio stuff is really cheap.