Why does Analog Multimeter need AAA Batery
Newbie
Just got this little hobbyist's pocket analog multimeter, and it has a slot
for 1 AAA battery, currently empty. The manual only mentions it and doesn't
say why is the battery needed. When I connect the probes to test the power,
the needle deflects, correctly indicating voltage/resistance, once again -
without the battery present. So what is the battery for then?
Marilyn & Bob
news:z1TTd.31699$uO.9...@news20.bellglobal.com...
--
Peace,
BobJ
G. Morgan
Newsgroup: alt.home.repair
=> Newbie <= wrote:
It would be needed to measure resistance. How on Earth are you measuring
resistance without a voltage source? Tell the truth... Did you REALLY measure
a resistor?
--
-Graham
Remove the snails to email
jimmy
on the resistance scale and touch the probe tips together, the meter
should deflect to the zero ohms end if the battery is installed.
Terry
should require a battery for is continuity/resistance tests.
You are correct; an analog meter will measure external sources of electrical
voltage and/or current without the battery.
However when you desire to measure an inanimate or other wise unpowered
circuit or item the source of electricity for that measurement is the small
battery inside the meter.
By the way don't try to measure any external voltage or current with the
meter set to "Ohms" or "Resistance" ranges!
For an example; holding a bulb/lamp in your hand you connect the test leads
(set to ohms/continuity etc.) to a lamp/bulb in attempt to find out if it's
'blown' or OK?
You will not get any reading at all unless that battery is in place!
That makes sense of course because current will not flow without a source of
voltage.
BTW is this a troll?
If not suggest that a quick self paced course on basic Ohm's Law will assist
advantageous use of the meter and perhaps minimize the chances of "Blowing
the sh**" out of it! Which we have all done at one time or another.
Also read the little book that should come with the meter. There are some
applications where such a small analog meter can do better job than a more
sophisticated more sensitive one!
HvacTech2
Hi Newbie, hope you are having a nice day
On 25-Feb-05 At About 13:38:17, Newbie wrote to All
Subject: Why does Analog Multimeter need AAA Batery
N> From: "Newbie" <sfl...@hotmail.com>
N> I'll embarrass myself with this one, but so what...
N> Just got this little hobbyist's pocket analog multimeter, and it has
N> a slot for 1 AAA battery, currently empty. The manual only mentions
N> it and doesn't say why is the battery needed. When I connect the
N> probes to test the power, the needle deflects, correctly indicating
N> voltage/resistance, once again -without the battery present.
N> So what is the battery for then?
It is needed for the resistance ( Ohm) readings.
-=> HvacTech2 <=-
.. **FLASH** Eveready Bunny arrested, charged with battery.
___ TagDude 0.92á+[DM]
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
spam protection measure, Please remove the 33 to send e-mail
nicks...@ece.villanova.edu
> Just got this little hobbyist's pocket analog multimeter, and
> it has a slot for 1 AAA battery... what is the battery for then?
It's an annoyance. Take the meter out of a drawer, and the battery's dead.
You might add a diode and series 47K ohm resistor to the switch contact used
to measure 120 VAC and leave the meter leads plugged into a wall socket to
monitor house voltage and keep the battery charged.
Nick
Newbie
obvious that resistance measurement requires some kind of power source...
Thanks again everyone....
"Terry" <tsan...@nf.sympatico.ca> wrote in message
news:iTUTd.56865$Am3.1...@news20.bellglobal.com...
tra...@optonline.net
dead.
You might add a diode and series 47K ohm resistor to the switch contact
used
to measure 120 VAC and leave the meter leads plugged into a wall socket
to
monitor house voltage and keep the battery charged. "
Another example of practical advice from pointed head academia.
David Martel
I don't follow this. When the meter is set to measure 120 VAC the battery
is not in the circuit and can not be charged, I think. Also can you safely
charge non rechargeable batteries? This sounds like very bad advice,
especially for a newbie.
Dave M.
Travis Jordan
> It's an annoyance. Take the meter out of a drawer, and the battery's
> dead. You might add a diode and series 47K ohm resistor to the switch
> contact used to measure 120 VAC and leave the meter leads plugged
> into a wall socket to monitor house voltage and keep the battery
> charged.
Bad advice, and technically incorrect.
Ross Mac
<nicks...@ece.villanova.edu> wrote in message
news:cvpqlm$6...@acadia.ece.villanova.edu...
The way I see it you are suggesting a 1.5 volt battery be charged at a rate
of 25 ma at 60 volts pulsating DC? Or did you mean 1.5V zener diode? If you
were to use a *standard diode* you would be limited to about a half a volt
and the battery would never charge. I think you also failed to mention the
battery would have to be across only the diode. In any event it would still
be a poor charger........Ross
Dick
You don't want to fool with a rechargeable battery in an analog VOM.
For that matter, you don't want one in a digital voltmeter either.
Alkaline batteries have a shelf life of several years. As others have
already pointed out, the only thing the battery is for is in measuring
resistance. This reading depends upon measuring the current flow
through resistors in the meter. If there is no battery, there will be
no current flow. The meter would work fine for all other measurements
because they generate their own source of power to operate the meter.
Dick
Terry
bit!
Probably not worth while because even the simplest kind of primary cell is
so cheap (25 to 50 cents?) and available and last so long. Prob. not worth
doing it to a simple $6 to $15 'pocket style multimeter'?
Rechargeable for a 'digital' display meter might be OK; especially if I tend
to leave ours with its LCD display switched on after use!!!!!
In a simple analog meter, the battery, which powers only the
resistance/continuity scales, is so little used that it will last its shelf
life and then some. And since meters tend to be stored in reasonable
environment; unless it's in my vehicle glove box and the battery freezes,
the battery will normally die of old age rather than use?
In a typical analog meter, the battery supplies, and only momentarily,
something of the order of one half milliamp (that's one 2000th of one amp
for only the few seconds of testing!).
So if it does not leak or rust away the battery will have potential for
years!
I've seen one or two cells that were 20 years old and still had enough
potential to fully deflect the meter. After all the batteries in our smoke
detectors last a year and they 'are' providing a 'constant' small drain.
Keeping a spare pack of the cheapest batteries available a good idea. Also,
in effect an analog meter tests its own battery; every time you check FSD
for zero ohms; right?
BTW on the subject of small cell batteries, including those 9v 'Transistor'
style, one of the most useful and productive 'gadgets' is one of those
R.Shack battery testers. Sometimes on sale for half price at around $5 to
$8.
Being congenitally unable to 'not tinker' with anything! Have started to
modify our little battery tester, hopefully to enable one hand testing of
the continuity of say fuses and/or lamps! Despite that we have several
multi-meters; but justify that a combined battery/fuse/lamp tester would
result in one less thing (multimeter) to carry around? :-)
Suggestions: When you chuck out an old shaver save the zipped and slightly
soft padded container, often just right size for a multimeter! By then the
cardboard box the meter came in from Taiwan, China or Mexico will have
crumbled. And; those soft padded/insulated fabric school lunch 'boxes' are
an excellent container for a test instrument, test leads, low wattage AC
bulb for checking mains supply, short extension cord, neon tester etc. and a
couple of small hand tools. All in one package; so when your favourite Aunt
Ida phones and says her lights are blinking, again, and she also needs a new
bulb in her flashlight, just grab it and go.
Have fun out there!
Ross Mac
"Dick" <LeadWinger> wrote in message
news:7ab1219sg8hl2igv6...@4ax.com...
Why wouldn't you use a rechargeable battery in a meter? I've had one in my
$400 Fluke DMM, sent out for repair and calibration and it came back with
the rechargeable still in place. Apparently they didn't have a problem with
it nor have I for at least 15+ years. Just curious Dick....take care, Ross
Dick
Maybe it was just a "fluke?" :-)
My Fluke Model 87 uses a standard 9-volt alkaline battery, The first
one lasted 9-years. The second one is going on 5-years. Are you sure
we are still talking about hand-held, portable instruments? How do
you recharge it? I never heard of a portable DVM with rechargeable
batteries. I can't imagine being out in the field without AC power
and having the meter go dead.
Dick
Ross Mac
"Dick" <LeadWinger> wrote in message
I too have Model 87 and a Model 8060A along with two Tek Scopes a couple of
True RMS clamps and all of them use rechargeables. Now I must admit that I
do keep a spare rechargeable in every case and I used these instruments
*alot* ( now retired ). My batteries would require a recharge about once a
year and I could even recharge them with my inverter in my truck (fodder for
another discussion). I can't say I ever got the life out of a 9V that you
did (Duracell) and I always shut the meter off when I wasn't using it and
have always been surprised the switch didn't wear out...So now you got the
rest of the story....but hey...we all have different use patterns and
experiences.......take care Dick, Ross
Rich
"Dick" <LeadWinger> wrote in message
I have an old led display Fluke (Model 8030A) that uses 4 NiCads. You leave
it plugged in when in when possible.
http://www.tucker.com/java/jsp/doorway_partnoFLU8030A_invid9533.htm
Dick
I can only surmise that you put the rechargeable in? My Fluke 87
manual clearly does not call for rechargeable. When I got it back
from Fluke after calibration, it didn't have one in then either. It
had a new battery, as Fluke always puts a new one in. I have only had
it recalibrated once as I am a very light and non-critical user. I am
still curious as to how you charge the battery in your 87 as there is
no provision for doing that. Surely, you don't take the meter apart
each time.
Dick
Dick
>
>"Dick" <LeadWinger> wrote in message
>> My Fluke Model 87 uses a standard 9-volt alkaline battery, The first
>> one lasted 9-years. The second one is going on 5-years. Are you sure
>> we are still talking about hand-held, portable instruments? How do
>> you recharge it? I never heard of a portable DVM with rechargeable
>> batteries. I can't imagine being out in the field without AC power
>> and having the meter go dead.
>>
>> Dick
>
>I have an old led display Fluke (Model 8030A) that uses 4 NiCads. You leave
>it plugged in when in when possible.
>
>http://www.tucker.com/java/jsp/doorway_partnoFLU8030A_invid9533.htm
>
Yes, but you are talking about a bench instrument, not a portable,
hand-held like the OP was asking about.
Dick
Ross Mac
"Dick" <LeadWinger> wrote in message
often....I have never had to send the 87 in for repair and cal but the 8060A
has been in several times and they have not changed the battery out....,my
.02.....Ross
Dick
<this.is...@example.invalid> wrote:
>Why wouldn't you use a rechargeable battery in a meter? I've had one in my
>$400 Fluke DMM, sent out for repair and calibration and it came back with
>the rechargeable still in place. Apparently they didn't have a problem with
>it nor have I for at least 15+ years. Just curious Dick....take care, Ross
>
I just checked on the Fluke website, and the very latest version of
the 87, the V series, still uses the same old 9-volt alkaline as used
by my 14 year old 87. If yours has a rechargeable, I am certain that
someone added it after it was shipped from Fluke.
Dick
Ross Mac
"Dick" <LeadWinger> wrote in message
Actually I think the OP probably had a cheap instrument and never gave us a
make/model....so hard to say how it would react to rechargeables but if the
meter was cheap....it shouldn't make much difference since accuracy would
not be an issue with such an instrument.... :>) Ross
Ross Mac
"Dick" <LeadWinger> wrote in message
Very possible...I will check the site myself....might be one of those
situations where we are both correct by situation....not particularly
important as long as our fine meters get the job done...and fine they
are...take care Dick, Ross
Rich
"Dick" <LeadWinger> wrote in message
It is portable. It came with a carrying case and all. Just that when on
the bench you can keep it plugged in to keep the batteries charged. But
those LED displays draw a lot of current.
Ross Mac
"Rich" <nos...@att.net> wrote in message
news:5r7Ud.81296$Th1....@bgtnsc04-news.ops.worldnet.att.net...
rechargeables with no problems and that was on meters I used to calibrate to
.001 volts....I'm with you...they work just fine...Ross
Dick
<this.is...@example.invalid> wrote:
>
>"Dick" <LeadWinger> wrote in message
>news:cfu121djbb84bp156...@4ax.com...
>> On Sat, 26 Feb 2005 22:26:27 GMT, "Rich" <nos...@att.net> wrote:
>>
>>>
>>>"Dick" <LeadWinger> wrote in message
>>
>>>> My Fluke Model 87 uses a standard 9-volt alkaline battery, The first
>>>> one lasted 9-years. The second one is going on 5-years. Are you sure
>>>> we are still talking about hand-held, portable instruments? How do
>>>> you recharge it? I never heard of a portable DVM with rechargeable
>>>> batteries. I can't imagine being out in the field without AC power
>>>> and having the meter go dead.
>>>>
>>>> Dick
>>>
>>>I have an old led display Fluke (Model 8030A) that uses 4 NiCads. You
>>>leave
>>>it plugged in when in when possible.
>>>
>>>http://www.tucker.com/java/jsp/doorway_partnoFLU8030A_invid9533.htm
>>>
>> Yes, but you are talking about a bench instrument, not a portable,
>> hand-held like the OP was asking about.
>>
>> Dick
>
>Actually I think the OP probably had a cheap instrument and never gave us a
>make/model....so hard to say how it would react to rechargeables but if the
>meter was cheap....it shouldn't make much difference since accuracy would
>not be an issue with such an instrument.... :>) Ross
>
You're right. It would just be an unnecessary expense.
Dick
Dick
<this.is...@example.invalid> wrote:
>
>"Dick" <LeadWinger> wrote in message
>news:cuu1215momk2kf7er...@4ax.com...
>> On Sat, 26 Feb 2005 13:48:48 -0500, "Ross Mac"
>> <this.is...@example.invalid> wrote:
>>
>>
>>>Why wouldn't you use a rechargeable battery in a meter? I've had one in my
>>>$400 Fluke DMM, sent out for repair and calibration and it came back with
>>>the rechargeable still in place. Apparently they didn't have a problem
>>>with
>>>it nor have I for at least 15+ years. Just curious Dick....take care, Ross
>>>
>>
>> I just checked on the Fluke website, and the very latest version of
>> the 87, the V series, still uses the same old 9-volt alkaline as used
>> by my 14 year old 87. If yours has a rechargeable, I am certain that
>> someone added it after it was shipped from Fluke.
>>
>> Dick
>
>Very possible...I will check the site myself....might be one of those
>situations where we are both correct by situation....not particularly
>important as long as our fine meters get the job done...and fine they
>are...take care Dick, Ross
>
Agreed. The Fluke 87 is one of the best investments in test gear that
I ever made.
Dick
meirman
<this.is...@example.invalid> posted:
>
>Actually I think the OP probably had a cheap instrument and never gave us a
>make/model....so hard to say how it would react to rechargeables but if the
>meter was cheap....it shouldn't make much difference since accuracy would
>not be an issue with such an instrument.... :>) Ross
I believe accuracy should be independent of whether the battery is
fully charged or not. They set it up so the measurement is in
proportion to a known resistance, so it should read correctly at any
battery voltage. (although eventually the battery is too weak to move
the needle or power the lcd's.)
BTW, everyone mentions alkaline batteries, but one of my digital
meters requires a 9-volt carbon zinc battery. An alkaline battery
won't fit in the space provided. (Unlike C, D, AA, and AAA batteries,
9 volt batteries are different in size between carbon-zinc and
alkaline.)
Meirman
--
If emailing, please let me know whether
or not you are posting the same letter.
Change domain to erols.com, if necessary.
nicks...@ece.villanova.edu
>> You might add a diode and series 47K ohm resistor to the switch contact
>> used to measure 120 VAC and leave the meter leads plugged into a wall
>> socket to monitor house voltage and keep the battery charged.
>What's wrong with a spare rechargable battery and a cheap charger.
Well, that way you need two batteries and a charger, and rechargable batteries
are more expensive than plain carbon zinc, and the meter may not work well on
1.2 vs 1.5 V, and this arrangement won't monitor house voltage, and it takes
more human attention, and it's less fun.
>The way I see it you are suggesting a 1.5 volt battery be charged at a rate
>of 25 ma at 60 volts pulsating DC?
More like 1 mA, altho that's too much for an Eveready 1212 AAA with a 540 mAh
capacity that loses 10% of its energy over a year. That only needs 0.10x540
= 54 mAh over a year, or about 6 microamps on a continuous basis, if the meter
is never used for anything else, but the movement might require another 100
microamps. And why waste power in that resistor, vs a charge pump like this,
viewed in a fixed font?
- C
| \ | | | 1.5 V
------------------| |--------------->|-------------------->
. | | | | |
120V . --- ---
. ^ -
------------ | |
| | |
| / | | |
- --- --- ---
- _ -
Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01 microfarads.
The battery would be a fine smoother and voltage regulator. Harbor Freight
stores sell $2.99 digital multimeters. Maybe they need less than 100 uA.
My flashlight plugs into the wall. Very convenient, because I know where to
find it and don't have to change batteries. My CO and barn heat detectors
work that way too, by design, with audible and remote X10 alarms and "non-
rechargable" batteries that rarely need changing. I hate changing batteries.
I lose my cheap Casio watches with 7 year Li batteries before they go dead.
Nick
Ross Mac
<nicks...@ece.villanova.edu> wrote in message
news:cvsdk0$7...@acadia.ece.villanova.edu...
> Ross Mac <this.is...@example.invalid> wrote:
>
>>> You might add a diode and series 47K ohm resistor to the switch contact
>>> used to measure 120 VAC and leave the meter leads plugged into a wall
>>> socket to monitor house voltage and keep the battery charged.
>
>>What's wrong with a spare rechargable battery and a cheap charger.
>
> Well, that way you need two batteries and a charger, and rechargable
> batteries
> are more expensive than plain carbon zinc, and the meter may not work well
> on
> 1.2 vs 1.5 V, and this arrangement won't monitor house voltage, and it
> takes
> more human attention, and it's less fun.
>
Absolutely incorrect. That is not how a meter works.
And anyhow....a spare battery and a charger???....That is not expensive....
Not trying to fire ya up here but those are the facts.
>>The way I see it you are suggesting a 1.5 volt battery be charged at a
>>rate
>>of 25 ma at 60 volts pulsating DC?
>
My math error...E=IR 60PVDC/47Kohms = 1.2ma or so....The incorrect charging
rate for a rechargeable.
> that's too much for an Eveready 1212 AAA with a 540 mAh
> capacity that loses 10% of its energy over a year. That only needs
> 0.10x540
Those batteries are normally referred to as "Puny Duty" and typically never
make it to 10 recharges...
I don't think this is a good recomendation to the NG....
> = 54 mAh over a year, or about 6 microamps on a continuous basis, if the
> meter
> is never used for anything else, but the movement might require another
> 100
> microamps. And why waste power in that resistor, vs a charge pump like
> this,
> viewed in a fixed font?
>
> - C
> | \ | | | 1.5 V
> ------------------| |--------------->|-------------------->
> . | | | | |
> 120V . --- ---
> . ^ -
> ------------ | |
> | | |
> | / | | |
> - --- --- ---
> - _ -
>
> Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01
> microfarads.
> The battery would be a fine smoother and voltage regulator. Harbor Freight
> stores sell $2.99 digital multimeters. Maybe they need less than 100 uA.
>
I cannot make heads nor tales out of your schematic, fixed font or not, but
it appears we now have a capacitor in the circuit...what happened to the
"diode and resistor" and you still need a regulator since you still have 60
volts across a 1.5 volt battery.
And please no, no....not that doorstop 3 buck meter...a good set of leads
will cost you more than that thing. That meter is more likely to get you
into more trouble than it ever gets you out of. That "THING" would only be
good for very crude troubleshooting.
This post is beginning to smell of TROLL.....well maybe not....but the bait
and switch characteristics are there!
> My flashlight plugs into the wall. Very convenient, because I know where
> to
> find it and don't have to change batteries. My CO and barn heat detectors
> work that way too, by design, with audible and remote X10 alarms and "non-
> rechargable" batteries that rarely need changing. I hate changing
> batteries.
> I lose my cheap Casio watches with 7 year Li batteries before they go
> dead.
>
> Nick
As for connectiong the active and passive circuits in the meter....I want to
be there when you try to measure the 240vac coming into the house and you
put 120pvdc across that battery with a camera to catch the absolute look of
surprise......Ross
nicks...@ece.villanova.edu
> - C
> | \ | | | 1.5 V
>------------------| |--------------->|-------------------->
> . | | | | |
> 120V . --- ---
> . ^ -
>------------ | |
> | | |
> | / | | |
> - --- --- ---
> - _ -
>
>Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01 microfarads.
Oops. Q = 340C makes C = 0.0047, or two 0.01s in series in case one shorts.
Or a 20 mW LimeLight, with less power. What does it take to power a 648A PIC?
Nick
nicks...@ece.villanova.edu
>>>> You might add a diode and series 47K ohm resistor to the switch contact
>>>> used to measure 120 VAC and leave the meter leads plugged into a wall
>>>> socket to monitor house voltage and keep the battery charged.
>>
>>>What's wrong with a spare rechargable battery and a cheap charger.
>>
>> Well, that way you need two batteries and a charger, and rechargable
>> batteries are more expensive than plain carbon zinc, and the meter
>> may not work well on 1.2 vs 1.5 V, and this arrangement won't monitor
>> house voltage, and it takes more human attention, and it's less fun.
>Absolutely incorrect. That is not how a meter works.
Huh?
>My math error...E=IR 60PVDC/47Kohms = 1.2ma or so....The incorrect charging
>rate for a rechargeable.
Incorrect, eh? :-)
>>that's too much for an Eveready 1212 AAA with a 540 mAh capacity that
>loses 10% of its energy over a year. That only needs 0.10x540, ie 6 uA...
>Those batteries are normally referred to as "Puny Duty" and typically never
>make it to 10 recharges...
Who's talking about recharging?
>I don't think this is a good recomendation to the NG....
Pity.
>> ...And why waste power in that resistor, vs a charge pump like
>> this, viewed in a fixed font?
>>
>> - C
>> | \ | | | 1.5 V
>> ------------------| |--------------->|-------------------->
>> . | | | | |
>> 120V . --- ---
>> . ^ -
>> ------------ | |
>> | | |
>> | / | | |
>> - --- --- ---
>> - _ -
>>
>> Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01
>> microfarads. The battery would be a fine smoother and voltage regulator.
>> Harbor Freight stores sell $2.99 digital multimeters. Maybe they need
>> less than 100 uA.
I just measured a Craftsman digital VOM... 9 V at 1.54 mA.
>I cannot make heads nor tales out of your schematic...
Pity. That's "tails," BTW.
Nick
Ross Mac
<nicks...@ece.villanova.edu> wrote in message
news:cvt2sn$7...@acadia.ece.villanova.edu...
Kind of the response I expected....no answers just juvenile
quips......PLONK......
nospam.c...@sny.der.on.ca
<this.is...@example.invalid> wrote:
>
><nicks...@ece.villanova.edu> wrote in message
>news:cvsdk0$7...@acadia.ece.villanova.edu...
>> Ross Mac <this.is...@example.invalid> wrote:
>>
>>>> You might add a diode and series 47K ohm resistor to the switch contact
>>>> used to measure 120 VAC and leave the meter leads plugged into a wall
>>>> socket to monitor house voltage and keep the battery charged.
The majority of analog multimeters only need the battery to use it as
an ohm meter. If only reading voltage, unless it is a transistorized
(extremely high impedence) unit the battery is not required.
nicks...@ece.villanova.edu
> | \ | | | 3 V
>------------------| |--------------->|-------------------->
> . | | | | |
> 120V . --- ---
> . ^ -
>------------ | |
> | | |
> | / | | |
> - --- --- ---
> - _ -
>What does it take to power a 648A PIC?
That might be an Insteon/X10 interface PIC...
The data sheet says it uses about 100 nanoamps at 3 V in sleep mode and
12 microamps at 32 kHz. If it's awake 1% of the time, say 1 second out of 100,
when it talks to a central controller, it would need 0.99x0.1+0.01x12 = 0.22
microamps. Q = 340C coulombs and I = 60Q = 0.22x10^-6 amps makes C = 10 pF,
theoretically-speaking :-)
If we needed more power and worried about overcharging the 2 AAAs, we might
use the PIC to measure the voltage and only enable the charge pump as needed.
Nick
Lawrence Wasserman
Newbies <sfl...@hotmail.com> wrote:
>I'll embarrass myself with this one, but so what...
>
>Just got this little hobbyist's pocket analog multimeter, and it has a slot
>say why is the battery needed. When I connect the probes to test the power,
>the needle deflects, correctly indicating voltage/resistance, once again -
>without the battery present. So what is the battery for then?
>
>
Measuring resistance.
--
Larry Wasserman Baltimore, Maryland
lwas...@charm.net
m II
> The majority of analog multimeters only need the battery to use it as
> an ohm meter. If only reading voltage, unless it is a transistorized
> (extremely high impedence) unit the battery is not required.
Very true. The really cheap meters will say something like 2 Kohm / volt or 3 K
ohm / volt on the face. A better quality one will say something like 20K ohm /
volt. These ratings are usually based on 1 milliamp giving full scale deflection
of the needle. The batteries for resistance readings only.
It was a pain trying to measure voltages across very high resistances. The meter
would be in parallel with the resistance and completely mess up the real values.
Getting my first Field Effect Transistor powered meter was a reall blessing. It
had something like 2 MEG ohms / volt sensitivity. Most of the digital stuff now
probably has 10 or 20 Meg ohms / volt. In some cases that's no good. With
almost no loading on a circuit/wire you can get voltages seemingly appearing out
of nowhere, giving rise to much head scratching.
mike
GregL
twil...@cybermesa.net
On 2005-03-01 ub5521dqbs678bc1m...@4ax.com said:
>Newsgroups: alt.home.repair,alt.energy.homepower
>nospam.c...@sny.der.on.ca wrote:
[snip]
> ... The really cheap meters will say something like 2 Kohm /
>volt or 3 K ohm / volt on the face. A better quality one will say
>something like 20K ohm / volt. These ratings are usually based on 1
>milliamp giving full scale deflection of the needle.
No, not 1 mA.
2 Kohm/volt = .5 mA
3 Kohm/volt = .33 mA
20 Kohm/volt = 50 microAmps
[snip]
>Getting my first Field Effect Transistor powered meter was a reall
>blessing. It had something like 2 MEG ohms / volt sensitivity. Most
>of the digital stuff now probably has 10 or 20 Meg ohms / volt.
No, not "per volt". That's the input resistance for DC measurements.
My Beckman 3020 DMM is 22 megohms input resistance.
Fluke 27 and 73 read 11 megs on the Beckman
Fluke 36 DMM and clamp-on AC/DC ammeter reads 2 megs.
Tom Willmon
near Mountainair, (mid) New Mexico, USA
Net-Tamer V 1.12.0 - Registered
moder...@worldnet.att.net
> <nicks...@ece.villanova.edu> wrote in message
> news:cvsdk0$7...@acadia.ece.villanova.edu...
> > <SNIP> And why waste power in that resistor, vs a charge pump like
> > this, viewed in a fixed font? <SNIP>
> > Q = 170C coulombs and I = 60Q = 106 x 10^-6 amps makes C = 0.01
> > microfarads.
> > The battery would be a fine smoother and voltage regulator. Harbor
Freight
> > stores sell $2.99 digital multimeters. Maybe they need less than
100 uA.
> I cannot make heads nor tales out of your schematic, fixed font or
not, but
> it appears we now have a capacitor in the circuit...what happened to
the
> "diode and resistor" and you still need a regulator since you still
have 60
> volts across a 1.5 volt battery.
The "diode and resistor" have been replaced by a "charge pump" (you can
google this) for the reason of "why waste power in that resistor." This
is not a bait and switch, it is merely an improvement on an earlier
proposal.
If you remove the battery from Nick's charge pump circuit proposal, you
have what's commonly called a "voltage doubler" (you can google this)
and the open-circuit output voltage will peak at twice the AC input
amplitude, which would be 340V for "normal" 120VAC-RMS input. Limiting
the size of the capacitor limits the current output capability. Placing
a battery across the output limits the output voltage by shunting the
current flowing through the capacitor. Also remember the
current=C*dV/dt, and dV/dt peaks at 170volts/sec. So to reiterate,
current and voltage have been limited: as long as the battery is there
and can accept the current, you do not have 60V, 120V, 340V or
whatever, you have 1.5V regulated by the battery and no additional
regulator is necessary.
I would modify this design by replacing the diode whose anode connects
to ground with a zener rated for 2.5 to 5 volts. That way, if the
battery should open-circuit, the downstream components won't see the
370V spike, it having been shunted by the zener. Similar
"transformerless stepdown" circuits are used to supply regulated 12VDC
to motion detectors.
I think Nick was off in his original math because he may not have
considered that the output diode (the one with the cathode connected to
the battery) begins conducting roughly as the AC input wave rises from
its -170V minimum, and continues to conduct roughly till the input
reaches its 170V maximum (we're ignoring .6V and 1.5V voltage drops
across diodes and batteries as insignificant compared to 170V).
Therefore the total charge moved per cycle is Q=C*340volts over the
full voltage swing of -170 to +170. (I now see and agree with his math
ammended in a subsequent post.) Current in amps (coulombs per second)
is Q*60 because there are 60 cycles per second. Substituting the
suggested value of .0047 uF for C, and current comes out to be 96
microamps. This is not meant to recharge a battery that has been run
flat, but rather to compensate for the self-discharge of the battery
such that it does not discharge during storage.
The question of whether the negative terminal of the battery is
connected to an identifiable "common" node in the VOM's internal
circuit is left for further consideration.
%mod%
nicks...@ece.villanova.edu
>If you remove the battery from Nick's charge pump circuit proposal, you
>have what's commonly called a "voltage doubler"... as long as the battery
>is there and can accept the current... you have 1.5V regulated by the
>battery and no additional regulator is necessary.
>
>I would modify this design by replacing the diode whose anode connects
>to ground with a zener rated for 2.5 to 5 volts... if the battery should
>open-circuit, the downstream components won't see the 370V spike...
Good idea. Two caps in series might also help with single point failures.
>Similar "transformerless stepdown" circuits are used to supply regulated
>12VDC to motion detectors.
UL-approved, in plastic boxes. I've heard California is banning
the transformer ilk because of the standby power.
>The question of whether the negative terminal of the battery is
>connected to an identifiable "common" node in the VOM's internal
>circuit is left for further consideration.
That's only a problem for alt.home.repair nitwits, IMO :-)
Nick
m II
> > ... The really cheap meters will say something like 2 Kohm /
> >volt or 3 K ohm / volt on the face. A better quality one will say
> >something like 20K ohm / volt. These ratings are usually based on 1
> >milliamp giving full scale deflection of the needle.
> No, not 1 mA.
> 2 Kohm/volt = .5 mA
> 3 Kohm/volt = .33 mA
> 20 Kohm/volt = 50 microAmps
You forget that there are different scales on the meter face. Full scale
deflection on one scale may be reading 250 volts and 10 volts on another. The
meter movement HAS to see the same amperage in order to get fullscale
deflection. The amount of resistance you have to add will, of course, vary with
each scale, but at no time can the current EXCEED the 1 ma (or whatever) at full
scale.
> [snip]
> >Getting my first Field Effect Transistor powered meter was a reall
> >blessing. It had something like 2 MEG ohms / volt sensitivity. Most
> >of the digital stuff now probably has 10 or 20 Meg ohms / volt.
> No, not "per volt". That's the input resistance for DC measurements.
You are right. I had ohms per volt on the brain from the previous paragraph. I
was just trying to show how much less circuit loading there was with a vtvm (or
FET) type of meter.
please, shoot me now...
mike
twil...@cybermesa.net
On 2005-03-02 d02mgt$hj8$1...@reader2.nmix.net said:
>Newsgroups: alt.home.repair,alt.energy.homepower
>twil...@cybermesa.net wrote:
>> > ... The really cheap meters will say something like 2 Kohm /
>> >volt or 3 K ohm / volt on the face. A better quality one will
>>say >something like 20K ohm / volt. These ratings are usually
>>based on 1 >milliamp giving full scale deflection of the
>needle.
>> No, not 1 mA.
>> 2 Kohm/volt = .5 mA
>> 3 Kohm/volt = .33 mA
>> 20 Kohm/volt = 50 microAmps
>You forget that there are different scales on the meter face.
No I didn't. Unless my simple, ohm's law calculations were wrong, meter
movement sensitivity is 1 / ohms per volt. To set measuring range of
meter you select a multiplier resistor which supplies full scale meter
current at your desired full scale voltage.
A 1Kohms/volt meter would use 10K to read 10V full scale.
A 20Kohms/volt would need 200K for the same range.
Full
>scale deflection on one scale may be reading 250 volts and 10 volts
>on another. The meter movement HAS to see the same amperage in
>order to get fullscale deflection. The amount of resistance you
>have to add will, of course, vary with each scale,
Yup.
>but at no time
>can the current EXCEED the 1 ma (or whatever) at full
>scale.
Huh? Sorry, not clear to me what your point is here.
[snip]
>please, shoot me now...
>mike
Naw - you're doing OK now.
Cheers.
m II
> >> > ... The really cheap meters will say something like 2 Kohm /
> >> >volt or 3 K ohm / volt on the face. A better quality one will
> >>say >something like 20K ohm / volt. These ratings are usually
> >>based on 1 >milliamp giving full scale deflection of the
> >needle.
> >> No, not 1 mA.
> >> 2 Kohm/volt = .5 mA
> >> 3 Kohm/volt = .33 mA
> >> 20 Kohm/volt = 50 microAmps
> >You forget that there are different scales on the meter face.
> No I didn't. Unless my simple, ohm's law calculations were wrong, meter
> movement sensitivity is 1 / ohms per volt. To set measuring range of
> meter you select a multiplier resistor which supplies full scale meter
> current at your desired full scale voltage.
I thought I had said something similar to that, in my own, obviously unclear
manner. We're stuck with the designed current rating of the meter, however, so
we can't vary the current for full deflection, Your formula is therefore better
stated as R = V/1ma, that is supposing a 1ma movement, as before. R is the
resistance needed to allow the needle to move all the way over on that
particular V scale.
> A 1Kohms/volt meter would use 10K to read 10V full scale.
> A 20Kohms/volt would need 200K for the same range.
Yes...and 10K and 200K ohms on the 100V scale.
Ah well..sorry for any misunderstanding I may have
caused/engendered/espoused/advocated or just plain originated.
mike
meirman
<tsan...@nf.sympatico.ca> posted:
>There are some
>applications where such a small analog meter can do better job than a more
>sophisticated more sensitive one!
One thing is allowing you to watch a capacitor charge. Eventually the
needle reaches the resistance of the circuit, not counting the
capacitance.
Jeff Wisnia
>
>
> .. **FLASH** Eveready Bunny arrested, charged with battery.
***** Sentenced to 2-4 years in a dry cell.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
"As long as there are final exams, there will be prayer in public
schools"