Simple MAF Sensor I made today..

[Jamie]

Today for a test, I made the most practical but yet
last minut silly device..



10V+
|
.-.
| |
| | R1
'-'
+
|
|
+-----------------+ ADC/PLC ADC input
|
|
+
.-.
| |
| | R2
'-'
|
|
===
GND

R1 and R2 are a single piece of steel piano wire ~0.005" in size
and center tapped. For now, we'll ID it as 2 R's

R2 is placed in proximity of the area behind a wall while R1 is just
above R2 in the path of the stream.
I used standard 3 conductor 18 AWG shielded data wire to connect to
this structure and fed it back to a PLC input for the time being as
test. It works flawlessly, I only need to tweak the program to look for
an increase above 5 volts.

That is just about as simple as it gets.

Btw, this is leading up to a more serious application later on. :)

Jamie

[brent]

On Feb 7, 7:28 pm, Jamie

Nice,

Speaking of Mass Airflow Sensors... I was having some intermittent
performance probs with my daughter's car (my car actually) and finally
changed the MAF and it has been running smooth ever since (about 3
months without probs) but the prob was intermittent especially bad in
wet cold weather. [Knock on wood]

[Jim Thompson]

The only MAF problem I ever had was on a '77 280Z... literally had a
swinging flap driving a pot :-(

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | 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.

[George Herold]

On Feb 7, 7:28 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:

Neat, Steel may not be the best choice... all that rust. But all
metals are 'pretty much' equal in dR/dT. You might try an alloy.
Phosphur bronze is nice, and availible in thin gages.

George H.

[Jamie]

I was thinking of using some heat shrink fep type of tubing around it to
protect it. The wire temperature only seems to get up around 300F.

We were using music wire today which seems to be an alloyed of some
sort instead of high carbon steel .


Jamie

[miso]

You can clean some of them. I drove through a socal fire and managed to
get the MAF coated with fine particulates. It was under warranty so that
was the easier solution.

One of the reasons I'm not keen on hybrid cars is you get every headache
of a gas engine (flaky sensors), plus whatever problem you get with an
electric transport system. And electric car can be quite simple. No
transmission required (unless you want Telsa speed) and even no
differential if you use two motors. Of course the auto PC will be still
be some overpriced computer.

I haven't looked into that Chevy Volt to see if they allow simpler
emission rules for the standby engine.

[mike]

Simple in concept, but I'd be interested in how you solved the practical
issues.

Smallest piano wire I have is .025". It measures 0.2 ohms/foot.
If .005 wire has 25x the resistance, that's 5 ohms/foot.
A foot of wire is gonna cost you 2 amps = 20Watts.
And the shielded part of the wire is gonna get pretty hot.
The tempco is not all that large. How much change in voltage
do you experience at the tap?

You're gonna want a kelvin connection to the sensor. Voltage drop in
connecting wires can be a substantial source of error if the power
goes thru the sense wires.

Shielding one of the resistors from the airflow temperature
compensates the system ONLY if the temperature of the air
is the same as the temperature of the wall. That doesn't
work well for sensing flow in a heating/cooling duct.

You can achieve the same device using two light bulbs in series.
Bust the glass off one of them and stick them both in the
air flow. You can get some measure of protection from physical
damage by screening the sensor. But that doesn't do much
for dust build up on the filament. Maybe if you keep it hot,
the dust will burn off. Straight filament probably works
better than a coiled one in this respect. I like #382 lamps
because they're small and I have a lot of 'em.
They have a filament coil that's tight compared to the size
of dust particles.
You can run them relatively hot without using a lot of power
or burning down the house. The resistance is high enough
that you might get by with the 4-wires you have to work with.

I think the classical solution uses a physically large and a relatively
smaller thermistor. Servo the currents to make the temperatures equal.
The differential power required to balance the bridge is proportional to
the air flow. I haven't tried to figure out the math, but I think it has to
do with the surface area being proportional to the square of the dimension
and the volume being proportional to the cube.

I'd be interested in more details of your setup.
I want a simple method to balance air flow in a Heat Recovery Ventilator.
mike

[George Herold]

On Feb 7, 8:38 pm, Jamie

>    Jamie- Hide quoted text -
>
> - Show quoted text -

Well try some other metals. If you don't like copper there are nickel
alloys too.

George H.

[Tim Williams]

"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:LhkYq.3523$Tu....@newsfe05.iad...

> We were using music wire today which seems to be an alloyed of some sort
> instead of high carbon steel .

Nope, actually it's hard drawn carbon steel -- amazingly, the drawing
process strengthens the wire so much, it has the strength of a high quality
alloy steel, particularly in the thinner wires!

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

[ehsjr]

You can try phosphor bronze guitar strings.

Ed

[Dennis]

"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
news:LhkYq.3523$Tu....@newsfe05.iad...

Would coating the wire with h/shrink insulate the wire & defeat its purpose
as a MAF?

[Jasen Betts]

On 2012-02-08, George Herold <ghe...@teachspin.com> wrote:
> On Feb 7, 7:28 pm, Jamie
><jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
>> Today for a test, I made the most practical but yet

>

> Neat, Steel may not be the best choice... all that rust. But all
> metals are 'pretty much' equal in dR/dT. You might try an alloy.
> Phosphur bronze is nice, and availible in thin gages.
>
> George H.

stainless steel is pretty good for thermistors, ordinary steel not
so much, and nichrome has a tc very close to zero.

--
⚂⚃ 100% natural

--- Posted via news://freenews.netfront.net/ - Complaints to ne...@netfront.net ---

[George Herold]

On Feb 8, 7:04 am, Jasen Betts <ja...@xnet.co.nz> wrote:

> On 2012-02-08, George Herold <gher...@teachspin.com> wrote:
>
> > On Feb 7, 7:28 pm, Jamie
> ><jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> >> Today for a test, I made the most practical but yet
>
> > Neat, Steel may not be the best choice... all that rust.  But all
> > metals are 'pretty much' equal in dR/dT.  You might try an alloy.
> > Phosphur bronze is nice, and availible in thin gages.
>
> > George H.
>
> stainless steel is pretty good for thermistors, ordinary steel not
> so much, and nichrome has a tc very close to zero.

I started this Wiedemann-Franz law project last year....(temporarily
on hold.)
I only then came to realize that the tempco of resistors is pretty
amazing. Given that most metals go as 1/T (with T in Kelvin.)

George H.

(Soldering to stainless is also a bit of a pain.... nasty fluxes)
>
> --
> ⚂⚃ 100% natural
>
> --- Posted via news://freenews.netfront.net/ - Complaints to n...@netfront.net ---

[Jamie]

Not totally, we tried it today, it only slows the effect a bit, but it
still works. The FEP tubing is very thin.. Good think too, it isn't the
cheapest stuff around however, we just happen to manufacture that stuff
at our location, not shrink tubing per say but we do extrude FEP and I
had some steel wire pulled through a head and drawn down to about 5 mils
wall thickness. :)

I suppose if you need instant response it would be an issue in which
case, you could use platinum wire or something that is less corrosive.

Jamie

[Jamie]

but copper does not have a TC like steel does.. so I don't think that is
going to work..:)

Jamie

[Jamie]

Today we connected it to a front end of a basic op-amp. Put a VD pot on
the (-) input and the steel wire divider on (+) input. The same source
as the VDivider Pot drives both.

The interesting part of this is, because both dividers are using the
same source, which is current limited via a R. When current increases
in the steel wire divider, it will of course drop the voltage at this
source. The (-) input of the op-amp now gets dropped a little which
gives you more increase of gain over all. I guess you could call this
a cheap form of a bridge ;)



For basic room test, we get a dt of 50mv moving a 1 foot wire at ~ 20
FPM speed. We are using a 5 mil or close to that, wire. a 12 inch piece
of wire is giving me ~ 2 ohms. and using 2 volts giving me 1 amp of
current at room temp. I don't think 2 watts is much to worry about.

Of course, these calculations are under a load. I didn't measure the
wire R with no current.

I should clarify that a bit, the 1 foot of wire had 6 inches of it
covered, so only the other 6 was getting the actual cooling while we
moved it that slow. And, the 50mv I was getting is at the input, not the
output. The output was, well, full rail at very small air currents.

P.S.
It seems that our stock of piano wire is inconsistent in quality but
for what it was designed for, i guess it's fine.

Jamie

[Jim Yanik]

Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> wrote
in news:39h3j7tg6374l17vs...@4ax.com:

> On Tue, 7 Feb 2012 16:32:40 -0800 (PST), brent
><bule...@columbus.rr.com> wrote:

>>Speaking of Mass Airflow Sensors... I was having some intermittent
>>performance probs with my daughter's car (my car actually) and finally
>>changed the MAF and it has been running smooth ever since (about 3
>>months without probs) but the prob was intermittent especially bad in
>>wet cold weather. [Knock on wood]
>
> The only MAF problem I ever had was on a '77 280Z... literally had a
> swinging flap driving a pot :-(
>
> ...Jim Thompson

I took apart the failed MAF from my Nissan Sentra Spec V.
it has a metal thin film sensor,and a hybrid ceramic circuit with a large
bare-die IC gold wire bonded to it,with the usual thick-film resistors and
chip caps.
the ceramic PCB was covered in clear silicone rubber,it was still kinda
sticky.the thin film sensor was wire bonded to the ceramic substrate,lots
of gold wires. a microscope revealed a complex pattern etched on the thin
film sensor.

nice thing was,I was able to find a replacement MAF sensor online for $78
without having to buy the whole duct/housing too($400)or mess with core
exchange.


--
Jim Yanik
jyanik
at
localnet
dot com

[Robert Baer]

Does the ADC go into a fairly "intelligent" program that can
determine if music can be detected and speech ignored?

[Jamie]

That sounds like a derogatory remark?

If any one is interested, today I lengthen the wire "0.005"mil and was
able to detect some one blowing air through their lips 10 feet away.

Actually, I had problems calibrating it at first due to the air
currents in the lab that were virtually unnoticeable. I had to bring it
in a closet area to calibrate it. I thought at first I was getting some
RF demodulated at the input but scope readings revealed that was not the
case.

The use of a JFET front end op-amp gave me this additional
sensitivity instead of using a monolith front end, old stand by.


I really don't have a need for this range of sensitivity. Tomorrow we'll
be receiving some phosphor bronze wire to experiment with, as suggested
by some one here.

Jamie

[mike]

Wonder if it helps to coil it up to increase the surface area?

>
> Actually, I had problems calibrating it at first due to the air currents
> in the lab that were virtually unnoticeable. I had to bring it in a
> closet area to calibrate it. I thought at first I was getting some RF
> demodulated at the input but scope readings revealed that was not the case.
>
> The use of a JFET front end op-amp gave me this additional sensitivity
> instead of using a monolith front end, old stand by.

Your source impedance is essentially zero. How did the JFET-ness help?

[Jamie]

It helped in two ways, first, I am able to use a H-Z ref for the (-) in
and second, with the way it is being used as a bridge I am getting
better linear response on the output. I wouldn't say it's perfect but it
is better.

The op-amp I used is a Bi-fet and TC seems to be much better with this
one. Also I have a much better gain response in the linear region.

Although CMRR does not seem to play a part in this, simply due to the
fact that the total voltage dt is no more than a 150mv, I have ruled out
any aggravating effects from that.

Voltage gain is actually less with the Bi-fet than what I was using
however, when I plotted the response curve I was able to get a much
better looking output.

The other issues are, it is very possible I was getting some
demodulated RF with the monolithic front end, but that still remains
up in the air with that. I'd prefer the use monolithic due to it being
safer to handle but I could add ESD protection if needed.


We used what we had at the bench that was easy to test with. We still
have lots of dip IC's to work with and they make good test jig models.

I was going to use a comparator for the application but since I want
to limit BW to reduce the chance of parasitic noise or oscillations, I
thought a Op_amp would work just fine with their inherent miller in
them. I don't need to worry about phase error in this app :)

Jamie

[josephkk]

On Tue, 7 Feb 2012 22:26:19 -0600, "Tim Williams" <tmor...@gmail.com>
wrote:

>"Jamie" <jamie_ka1lpa_not_v...@charter.net> wrote in message
>news:LhkYq.3523$Tu....@newsfe05.iad...
>> We were using music wire today which seems to be an alloyed of some sort
>> instead of high carbon steel .
>
>Nope, actually it's hard drawn carbon steel -- amazingly, the drawing
>process strengthens the wire so much, it has the strength of a high quality
>alloy steel, particularly in the thinner wires!
>
>Tim

Grain alignment does wonders for metal strength.

?-)

[josephkk]

On Wed, 8 Feb 2012 06:36:05 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>On Feb 8, 7:04 am, Jasen Betts <ja...@xnet.co.nz> wrote:
>> On 2012-02-08, George Herold <gher...@teachspin.com> wrote:
>>
>> > On Feb 7, 7:28 pm, Jamie
>> ><jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
>> >> Today for a test, I made the most practical but yet
>>
>> > Neat, Steel may not be the best choice... all that rust.  But all
>> > metals are 'pretty much' equal in dR/dT.  You might try an alloy.
>> > Phosphur bronze is nice, and availible in thin gages.
>>
>> > George H.
>>
>> stainless steel is pretty good for thermistors, ordinary steel not
>> so much, and nichrome has a tc very close to zero.
>
>I started this Wiedemann-Franz law project last year....(temporarily
>on hold.)
>I only then came to realize that the tempco of resistors is pretty
>amazing. Given that most metals go as 1/T (with T in Kelvin.)
>
>George H.
>
>(Soldering to stainless is also a bit of a pain.... nasty fluxes)
>>

Each to their own, i would braze a contact point on then solder to that.
Just easier for me. Works best with an Oxy-MAPP or hotter torch.

?-)

[mike]

spot welder?

[Jamie]

I tried out some Phosphor bronze (0.005") and also, I tried 0.012
" which we use in house for production on some products that has
a bronze braid, expensive stuff.


Both worked well, the 0.012 more demanding then need be but is ok
in cases where you have enough space to coil that much for lowering
the current.

This sensor will be in a ozone rich environment so we'll see how long
it'll last :)

The other items on the list is how conductive is ozone? I may need to
consider some thinking on the mechanical end that houses the sensing wire.


Jamie

[George Herold]

On Feb 13, 6:33 pm, Jamie

<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> mike wrote:
> > On 2/12/2012 6:16 PM, josephkk wrote:
>
> >> On Wed, 8 Feb 2012 06:36:05 -0800 (PST), George Herold

> >> <gher...@teachspin.com>  wrote:

> Jamie- Hide quoted text -
>
> - Show quoted text -

There are other alloys too. I like phosphur bronze becasue it's non-
magnetic.

I might worry about the oxidation caused by ozone, maybe some alloy of
stainless would work better?

George H.

[Tim Williams]

"George Herold" <ghe...@teachspin.com> wrote in message
news:d02304e8-d216-4df0...@15g2000vbq.googlegroups.com...

> (Soldering to stainless is also a bit of a pain.... nasty fluxes)

Not really -- maybe with a torch, there's lots of interesting chemistry
going on in a flame.

I've done it numerous times, in open air, inductive heated -- it probably
helps that heating is relatively quick, but the flux was regular Handy Flux
and the filler regular silver solder.

Works wonders on copper pipe, too (which we use a lot of, since, how else do
you carry kiloamperes cheaply..), though a lot slower because the copper
reflects magnetic fields so nicely.

[Jamie]

Ok, I'll need to look up the TC of Stainless.

Jamie

[George Herold]

On Feb 13, 9:47 pm, Jamie

The same about 0.3% at 300K.

Opps forget that! Stainless (304, 310) looks pretty flat from room
temp to 20 K.

I'm going to have to go back and re-read my solid state books.
(There's never enough practical stuff in the physics ones.)

The pure elements all look pretty good... But not a whole lot too
choose from.

The highest room temperature resistivity that I see is,
(In units of 10^-8 ohm-meters)

Ti 42.7
Pb 21
Nb 14.4
Fe 9.7

Cu 1.68 (for comparison)

Have you looked how others are making MAF's... Steal whatever they
use.

George H.

[George Herold]

On Feb 13, 7:59 pm, "Tim Williams" <tmoran...@gmail.com> wrote:
> "George Herold" <gher...@teachspin.com> wrote in message

>
> news:d02304e8-d216-4df0...@15g2000vbq.googlegroups.com...
>
> > (Soldering to stainless is also a bit of a pain.... nasty fluxes)
>
> Not really -- maybe with a torch, there's lots of interesting chemistry
> going on in a flame.

I built several low temperature (liquid helium) probes in my 'mis-
spent' youth.
Lots of thin walled SS. We'd 'hard' solder (silver solder, with oxy-
acetelyne) the permenant joints. But we'd want some to be removable.
For those we used 'soft' solder, heated with normal blow torch. But
the flux would 'splatter' all over when heated and if a little drop
got on a piece of thin walled stainless... then maybe in a few months
a little pin-hole leak might grow.

So 'nasty' in that you really have to clean everything.

George H.

[Jamie]

We had a 100 ft of 0.005" steel wire past through a FEP extrusion
today, which put 0.0015 mill wall on it. Yes, that is thin but it past
the hi-pot test. And then we subjected it to a environmental chamber for
a while today, at maximum effect for 6 hours.

I only had an hour to test it afterwards but it looks good and
responds very well.

The phosphor bronze also works out well but has a much lower R/1M so
not so good for small area sensors but works great for door or window
ways as a candle test. Then again, I didn't have the smallest gauge
available of the phosphor bronze to start with.

Jamie

[George Herold]

On Feb 14, 7:35 pm, Jamie

Yeah, sorry about that. It looks most alloys have a 'zero temperature
resistance' and that puts a limit on the 1/T behavior. But there may
be 'alloys' that have a bigger temperature dependence. Thermistors
for instance. Could you put a couple of thermistors on heat sinks
coupled to the air flow?

George H.

so
> not so good for small area sensors but works great for door or window
> ways as a candle test. Then again, I didn't have the smallest gauge
> available of the phosphor bronze to start with.
>

[gregz]

Jim Thompson <To-Email-Use-Th...@On-My-Web-Site.com> wrote:
> On Tue, 7 Feb 2012 16:32:40 -0800 (PST), brent

> <bule...@columbus.rr.com> wrote:
>
>> On Feb 7, 7:28 pm, Jamie
>> <jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
>>> Today for a test, I made the most practical but yet

>>> last minut silly device..
>>>
>>> 10V+
>>> |
>>> .-.
>>> | |
>>> | | R1
>>> '-'
>>> +
>>> |
>>> |
>>> +-----------------+ ADC/PLC ADC input
>>> |
>>> |
>>> +
>>> .-.
>>> | |
>>> | | R2
>>> '-'
>>> |
>>> |
>>> ===
>>> GND
>>>
>>> R1 and R2 are a single piece of steel piano wire ~0.005" in size
>>> and center tapped. For now, we'll ID it as 2 R's
>>>
>>> R2 is placed in proximity of the area behind a wall while R1 is just
>>> above R2 in the path of the stream.
>>> I used standard 3 conductor 18 AWG shielded data wire to connect to
>>> this structure and fed it back to a PLC input for the time being as
>>> test. It works flawlessly, I only need to tweak the program to look for
>>> an increase above 5 volts.
>>>
>>> That is just about as simple as it gets.
>>>
>>> Btw, this is leading up to a more serious application later on. :)
>>>
>>> Jamie
>>

>> Nice,

>>
>> Speaking of Mass Airflow Sensors... I was having some intermittent
>> performance probs with my daughter's car (my car actually) and finally
>> changed the MAF and it has been running smooth ever since (about 3
>> months without probs) but the prob was intermittent especially bad in
>> wet cold weather. [Knock on wood]
>
> The only MAF problem I ever had was on a '77 280Z... literally had a
> swinging flap driving a pot :-(
>
> ...Jim Thompson

What problem did you have. Mine gave me problems until I learned how to
adjust it. I sold mine in great condition 3 years ago.

Oh, one day I was driving along a ca freeway near La. Started to give out
all kinds of black smoke. Found foam filter I put on got sucked in keeping
the flap open!!!

Wasn't that thing designed by Bosch.

Greg

[josephkk]

Don't have one. Though i am thinking of buying a used dental spot welder.
Just the right size for the things i want to do.

?-)

[josephkk]

On Mon, 13 Feb 2012 16:50:01 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>
>>   I tried out some Phosphor bronze (0.005") and also, I tried 0.012
>> " which we use in house for production on some products that has
>>   a bronze braid, expensive stuff.
>>
>>    Both worked well, the 0.012 more demanding then need be but is ok
>> in cases where you have enough space to coil that much for lowering
>> the current.
>>
>>    This sensor will be in a ozone rich environment so we'll see how long
>> it'll last :)
>>
>>    The other items on the list is how conductive is ozone? I may need to
>> consider some thinking on the mechanical end that houses the sensing wire.
>>
>> Jamie- Hide quoted text -
>>
>> - Show quoted text -
>
>There are other alloys too. I like phosphur bronze becasue it's non-
>magnetic.
>
>I might worry about the oxidation caused by ozone, maybe some alloy of
>stainless would work better?

Maybe, i would worry about the ozone leaching the carbon out of the SS.

[josephkk]

On Mon, 13 Feb 2012 16:50:01 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>
>>   I tried out some Phosphor bronze (0.005") and also, I tried 0.012
>> " which we use in house for production on some products that has
>>   a bronze braid, expensive stuff.
>>
>>    Both worked well, the 0.012 more demanding then need be but is ok
>> in cases where you have enough space to coil that much for lowering
>> the current.
>>
>>    This sensor will be in a ozone rich environment so we'll see how long
>> it'll last :)
>>
>>    The other items on the list is how conductive is ozone? I may need to
>> consider some thinking on the mechanical end that houses the sensing wire.
>>
>> Jamie- Hide quoted text -
>>
>> - Show quoted text -
>
>There are other alloys too. I like phosphur bronze becasue it's non-
>magnetic.
>
>I might worry about the oxidation caused by ozone, maybe some alloy of
>stainless would work better?
>
>George H.

Got slightly interested, googled once, found this:

http://www.nibco.com/assets/ChemGuide.pdf

Seems pretty good, the company is reputable.

?-)

[mike]

There are lots of plans on the web about how to use a microwave oven
transformer.
I built one and used a PAL to implement a cycle counter that controls
a solid-state relay in the primary. So, I can select
how many full cycles of AC it puts into the work.
If you don't do that, you can get some significant variabilities due
to the previous state of the core...saturation.

Worked great except that a low-voltage system like this depends
greatly on the contact resistance. Open-circuit was only a couple of volts.
I used it to weld battery tabs,
but had repeatability issues.

A commercial CD welder was MUCH more repeatable because the much higher
voltage makes the current much less a function of contact resistance.
I can get 7V across a milliohm.

Don't know what technique they use in a dental welder. CD is much
more repeatable than straight transformer/resistive.

If you're building one, a split-bolt connector or any kind of wire connector
that uses a screw for compression might work just fine.