I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!

On Sunday, 16 July 2017 14:33:04 UTC+1, Chris wrote:
I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!

Are they calibrated?


NT

On Sunday, July 16, 2017 at 9:33:04 AM UTC-4, Chris wrote:
I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!



Do your DMMs and analogues agree with each other when using fixed resistors out of circuit?

On Sun, 16 Jul 2017 07:01:34 -0700, John-Del wrote:

Do your DMMs and analogues agree with each other when using fixed
resistors out of circuit?

Yes they do. Sorry, should have mentioned that in the OP.

In article , says...

I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!

If you are measuring in circuit resistance of solid state circuits, then
you often will.

The analog meter has enough voltage/current to turn on the junctions of
diodes and transistors. The DMM will not have enough to turn them on.

If you have a diode out of the circut and use an analog meter you will
often see a small resistance in one direction and if you reverse the
leads a high resistance. The DMM will usually show a high resistance in
both directions unless you use the diode setting if the dmm has one.

In article , says...

On Sun, 16 Jul 2017 07:01:34 -0700, John-Del wrote:

Do your DMMs and analogues agree with each other when using fixed
resistors out of circuit?

Yes they do. Sorry, should have mentioned that in the OP.

Yes, and have reversed the leads as Ralph suggests...

Mike.

On Sun, 16 Jul 2017 10:41:02 -0400, Ralph Mowery wrote:

The analog meter has enough voltage/current to turn on the junctions of
diodes and transistors. The DMM will not have enough to turn them on.

If you have a diode out of the circut and use an analog meter you will
often see a small resistance in one direction and if you reverse the
leads a high resistance. The DMM will usually show a high resistance in
both directions unless you use the diode setting if the dmm has one.

Damnit, Ralph! You beat me to it. I was going to say that. ;-)
I have a couple of analogue meters too. They test for resistance at 15V
which is more than enough to turn on those semiconductors, but also more
than enough to destroy a lot of chips that can't tolerate much more than
5V. Horses for courses/different strokes and all that.

On 16/07/2017 14:29, Chris wrote:
I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!


Try with different probe leads and resistors with different termination
metals, maybe small dissimilar metals producing voltages that are
interpreted differently by the different metering systems

On Sun, 16 Jul 2017 16:36:56 +0100, N_Cook wrote:

Try with different probe leads and resistors with different termination
metals, maybe small dissimilar metals producing voltages that are
interpreted differently by the different metering systems

It's okay now I believe Ralph has nailed the problem entirely in his
post. (thanks, Ralph).

On Sun, 16 Jul 2017 13:29:07 -0000 (UTC), Chris
wrote:

I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

If you're doing in circuit resistance measurements, you're probably
measuring the resistance of a non-linear device such as a transistor
or diode. These will show different resistances at different applied
voltages. Umm... this assumes that you've unplugged the circuit that
you're testing and have discharged any BFC's (big fat caps).

Disconnect whatever you're measuring. Take one of the DVM's that has
the highest input resistance, set it to VOLTS, and measure the VOLTAGE
across the leads of the other meters. You'll find quite a bit of
variation. My guess(tm) is that the meter with the highest voltage,
will read the lowest resistance.

If you have an ESR (equivalent series resistance) meter, you can do in
circuit low resistance measurements without worrying much about the
effects of semiconductors. That's because the voltages involved are
so small, that the semiconductor doesn't even being to conduct, and is
therefore essentially out of the circuit.

There's really no way to "fix" the problem of measuring in circuit
resistances. If I want to accurately measure a resistor that's in a
circuit, I usually have lift one lead, and measure only that resistor.
I've got four DMMs and two analogs. The DMMs agree with the other
DMMs
and the analogs agree with each other. But the different types don't
agree with each other!

The analog meters (VOM) require more current in order to obtain a
resistance reading. More current means more applied voltage across
the leads, which means that the semiconductors in your test circuit
are well into conduction. Try measuring a resistor and diode in
parallel and you'll see the problem in action.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 16 Jul 2017 15:05:34 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 16 Jul 2017 10:41:02 -0400, Ralph Mowery wrote:

The analog meter has enough voltage/current to turn on the junctions of
diodes and transistors. The DMM will not have enough to turn them on.

If you have a diode out of the circut and use an analog meter you will
often see a small resistance in one direction and if you reverse the
leads a high resistance. The DMM will usually show a high resistance in
both directions unless you use the diode setting if the dmm has one.

Damnit, Ralph! You beat me to it. I was going to say that. ;-)
I have a couple of analogue meters too. They test for resistance at 15V
which is more than enough to turn on those semiconductors, but also more
than enough to destroy a lot of chips that can't tolerate much more than
5V. Horses for courses/different strokes and all that.

I have heard this several times about analog meters destroying chips,
because the chips cant tolerate over 5v. At the same time, I have never
seen any analog meter using more than two batteries. That's 3 volts.
I have several analog meters and they all use two AA batteries. Except
for the one mini meter which only has only one AA battery.

So we have this theory about these analog meters ruining chips for
exceeding 5v, but none of the meters can provide more than 3volts. This
makes me think that this theory is based on advertisers trying to sell
digital meters, or just an old wives tale with no backing. (Unless there
are some analog meters which use 4 batteries [6volts], or use a 9v
battery). If meters do exist, which are powered by more than 3v, I have
never seen them.

On Sun, 16 Jul 2017 13:20:54 -0700, Jeff Liebermann
wrote:

On Sun, 16 Jul 2017 14:48:48 -0400, wrote:

...I have never
seen any analog meter using more than two batteries. That's 3 volts.
I have several analog meters and they all use two AA batteries. Except
for the one mini meter which only has only one AA battery.

The Simpson 260 VOM used a single D cells and a 15V battery (Eveready
417) for the Rx10K range. Later models switched to a 9V battery and
then to 4ea AA batteries. The Triplett 630 used a single D cell and a
30V (Eveready 413).

Ok, I guess you have meters that I've never seen. I have to wonder why
they need such high voltage to measure resistance. However, I would not
use those meters on modern circuits if I owned them.

My analog meters are all older Radio Shack meters, which I have owned
for many years. All (except the mini), have two AA batteries.

I also have a few VTVM's. I am not sure what they output, so I dont use
them on any solid state devices. But they are well suited for tube gear,
and can handle the high voltages in tube gear, which a lot of the
battery operated portable VOM's cant handle.

On Sun, 16 Jul 2017 14:48:48 -0400, wrote:

...I have never
seen any analog meter using more than two batteries. That's 3 volts.
I have several analog meters and they all use two AA batteries. Except
for the one mini meter which only has only one AA battery.

The Simpson 260 VOM used a single D cells and a 15V battery (Eveready
417) for the Rx10K range. Later models switched to a 9V battery and
then to 4ea AA batteries. The Triplett 630 used a single D cell and a
30V (Eveready 413).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sun, 16 Jul 2017 15:46:36 -0400, oldschool wrote:

Ok, I guess you have meters that I've never seen.

You've never seen any AVO/Megger meters?? Like this for example:

http://www.ebay.co.uk/itm/Bakelite-A...ter-Excellent-
Condition-100-Tested-/152599935777?hash=item2387aa3b21:g:1csAAOSw241YZTX 1

They've been exported all over the world for decades!

They typically use one 15V battery (about the size of a AA cell) and a
single 1.5V D cell.

On Sunday, July 16, 2017 at 4:50:45 PM UTC-4, wrote:
But they are well suited for tube gear,
and can handle the high voltages in tube gear, which a lot of the
battery operated portable VOM's cant handle.

Maybe the Harbor Freight free-with-any-purchase DMM can't handle higher voltage, but I've never seen any DMM that can't handle tube gear voltages. If you're talking about the old plate voltages of the horiz output or HV rectifier tube in televisions, no meter without an accessory HV probe will read those without some damage.

Unless you're doing peak and null, you shouldn't be using your analogue meters in my opinion.

In article ,
says...


I have heard this several times about analog meters destroying chips,
because the chips cant tolerate over 5v. At the same time, I have never
seen any analog meter using more than two batteries. That's 3 volts.
I have several analog meters and they all use two AA batteries. Except
for the one mini meter which only has only one AA battery.

So we have this theory about these analog meters ruining chips for
exceeding 5v, but none of the meters can provide more than 3volts. This
makes me think that this theory is based on advertisers trying to sell
digital meters, or just an old wives tale with no backing. (Unless there
are some analog meters which use 4 batteries [6volts], or use a 9v
battery). If meters do exist, which are powered by more than 3v, I have
never seen them.


The Simpson 260 series used a 1.5 V D cell and several voltages for the
highest resistance range. Very old ones used a 15 volt battery I think,
some used several AA batteries and the two I have use a standard 9 volt
battery. Tripplit made a similar VOM. I have not looked inside one of
those, but would bet it had 2 batteries similar to the Simpson.

The caution before ICs came out was not to use the lowest current range
for solid state devices. That 1.5 volt battery could supply enough
current to destroy some simiconductors. Not voltage, but current.

The caution was way before the DMMs and ICs came out.

In article ,
says...


The Simpson 260 VOM used a single D cells and a 15V battery (Eveready
417) for the Rx10K range. Later models switched to a 9V battery and
then to 4ea AA batteries. The Triplett 630 used a single D cell and a
30V (Eveready 413).

Ok, I guess you have meters that I've never seen. I have to wonder why
they need such high voltage to measure resistance. However, I would not
use those meters on modern circuits if I owned them.

My analog meters are all older Radio Shack meters, which I have owned
for many years. All (except the mini), have two AA batteries.

I also have a few VTVM's. I am not sure what they output, so I dont use
them on any solid state devices. But they are well suited for tube gear,
and can handle the high voltages in tube gear, which a lot of the
battery operated portable VOM's cant handle.


Radio Shack tells all. Anyone that says old school should have heard of
and maybe used the Simpson or Tripplit meter. Don't recall the number
of the Triplett as I only used one in school over 40 years ago.

The RS meters may have a meter of around 30 uA and the others have 50 uA
meters. It takes more voltage to operate them in the higher resistance
ranges. I don't know what the RS meters have for full scale of the
resistance ranges, but it may not be as much.

Even the Free HF meter I have says it will do 1000 VDC and 700 VAC. Not
too much common tube equipment has voltages over that, unless much
higher and special HV probes are needed. I think my old Heathkit VTVM
may do 1500 Volts. Have not had it out in years except to give it a
check a year or two ago to see if it still works.

On Sun, 16 Jul 2017 15:46:36 -0400, wrote:

Ok, I guess you have meters that I've never seen.

You haven't seen any of these?
http://www.simpson260.com
https://www.google.com/search?tbm=isch&q=simpson+260
These were probably the most common VOM's available. At one time, I
had about 5 of them. They've been replaced by more modern meters, but
I still keep one of them on the shelf, just in case.

I have to wonder why
they need such high voltage to measure resistance. However, I would not
use those meters on modern circuits if I owned them.

Most (not all) VOM's did NOT have amplifiers with gain. Therefore,
resistance measurements needed to be using the basic meter
sensitivity. The meter sensitivity and battery voltage put a limit on
the highest resistor value that could be accurately measured.

The meter face usually had the meter sensitivity. In this example:
https://cdn6.bigcommerce.com/s-a1x7hg2jgk/images/stencil/500x659/products/42383/204330/50126_2__62784.1490313691.jpg?c=2
It says "20,000 ohms per volt" (on DC scales) which is the same as:
1 / 20K ohms/volt = 50 µA full scale
You could probably read 1/10th of full scale accurately. So, what's
the largest resistance that you could read at 1/10th of full scale,
using a 9V battery?
R = E / I = 9V / 5*10-6A = 45M
Good enough to measure common resistors of the 1960's. However, if
you tried it with a 1.5V battery, you would get:
R = E / I = 1.5 / 5*10-6A = 7.5M
That's too low, because there were plenty of resistors up to 22M in
older tube sets, that such a meter could not measure.

My analog meters are all older Radio Shack meters, which I have owned
for many years. All (except the mini), have two AA batteries.

I also have a few VTVM's. I am not sure what they output, so I dont use
them on any solid state devices. But they are well suited for tube gear,
and can handle the high voltages in tube gear, which a lot of the
battery operated portable VOM's cant handle.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sunday, 16 July 2017 21:50:45 UTC+1, wrote:
On Sun, 16 Jul 2017 13:20:54 -0700, Jeff Liebermann
wrote:

On Sun, 16 Jul 2017 14:48:48 -0400, wrote:

...I have never
seen any analog meter using more than two batteries. That's 3 volts.
I have several analog meters and they all use two AA batteries. Except
for the one mini meter which only has only one AA battery.

The Simpson 260 VOM used a single D cells and a 15V battery (Eveready
417) for the Rx10K range. Later models switched to a 9V battery and
then to 4ea AA batteries. The Triplett 630 used a single D cell and a
30V (Eveready 413).

Many old meters used 9v or 15v batteries as well as a 1.5v.

Ok, I guess you have meters that I've never seen. I have to wonder why
they need such high voltage to measure resistance.

To enable the highest R range to work

However, I would not
use those meters on modern circuits if I owned them.

they're fine, just don't use the top R range on anyhing delicate.

My analog meters are all older Radio Shack meters, which I have owned
for many years. All (except the mini), have two AA batteries.

I also have a few VTVM's. I am not sure what they output, so I dont use
them on any solid state devices. But they are well suited for tube gear,
and can handle the high voltages in tube gear, which a lot of the
battery operated portable VOM's cant handle.

voltmeters don't output anything. They should be fine measuring solid state.


NT

In article ,
says...


Most (not all) VOM's did NOT have amplifiers with gain. Therefore,
resistance measurements needed to be using the basic meter
sensitivity. The meter sensitivity and battery voltage put a limit on
the highest resistor value that could be accurately measured.

The meter face usually had the meter sensitivity. In this example:
https://cdn6.bigcommerce.com/s-a1x7hg2jgk/images/stencil/500x659/products/42383/204330/50126_2__62784.1490313691.jpg?c=2
It says "20,000 ohms per volt" (on DC scales) which is the same as:
1 / 20K ohms/volt = 50 µA full scale
You could probably read 1/10th of full scale accurately. So, what's
the largest resistance that you could read at 1/10th of full scale,
using a 9V battery?
R = E / I = 9V / 5*10-6A = 45M
Good enough to measure common resistors of the 1960's. However, if
you tried it with a 1.5V battery, you would get:
R = E / I = 1.5 / 5*10-6A = 7.5M
That's too low, because there were plenty of resistors up to 22M in
older tube sets, that such a meter could not measure.


The Simpson did have a 20 meg mark on the scale. It is almost worthless
at that resistance. About all that can be told is that the reistor is
not totally open. Around 2 to 5 meg ohms is abut the best anyone can
tell close to the resistance. The resistance scale is similar to a log
scale so as the resistance value goes up and below about 1/4 scale the
values start getting very close together.

I have not looked into the 260 working in many years. I know of the 20
K per volt and how it works on the DC ranges, but not sure where it
comes into play on the ohms scale for this meter.

The meter movement is just under 50 uA and has a pot that I think goes
across it so the first step in calibrating one is to set it for 50 uA
full scale.

On Sun, 16 Jul 2017 16:34:56 -0700, tabbypurr wrote:

voltmeters don't output anything. They should be fine measuring solid
state.

DMMs and VOMs give different readings in certain circumstances (see
Ralph's post). In GB (at least) for a long time the service manuals for
decent gear would provide expected voltage readings for 20k OpV analogue
meters, the AV0 model 8 specifically IIRC, which saved the technician the
extra bother of scratching his head when checking hi-z parts of a circuit.

Chris wrote:

--------------


I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?


** The fact you are totally clueless ?

Semiconductors are not resistors and there is no right value to measure.

DMMs are designed NOT to cause didoes or BJT junctions to conduct when using the ohms ranges.

Also, DMMs ohm ranges are very sensitive to any residual DC or AC voltage on a component while analogue meters are much less so.

Interesting fact: you can measure the resistance of a loudspeaker voice coil with either type, but not if the room is full of loud bass noise.

Think about it.


....... Phil

In article , says...


DMMs and VOMs give different readings in certain circumstances (see
Ralph's post). In GB (at least) for a long time the service manuals for
decent gear would provide expected voltage readings for 20k OpV analogue
meters, the AV0 model 8 specifically IIRC, which saved the technician the
extra bother of scratching his head when checking hi-z parts of a circuit.

Yes, I have seen some schematics specify the voltage was measured with a
certain ohms/volt meter. It does take some guess work or head
scratching out of the servicing. Makes a big difference when measuring
the screen votltage that is fed with a high value resistor and you use a
vtvm or a 20 k ohms/volt or a 5 k ohms /volt meter.

I don't think I have done any trouble shooting on a tube circuit in 20
or 30 years. Last thing I recall even looking at with tubes was my
Heathkit sb101 that was many years ago. Only other thing I have with
tubes are a couple of RF amplifiers and they use voltages that I don't
work on with any power on them.

On Sun, 16 Jul 2017 23:12:42 -0500, Jon Elson
wrote:

Chris wrote:

I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!
I have some older DMMs. I get odd resistance readings the first time I set
it to Ohms scale. By wiggling the plugs on the probes at the meter end, and
occasionally working the range selector dial around a few times, I get a
stable Ohms reading of about 0.4 Ohms with the probes shorted. Then, I get
more sensible readings on circuits. So, these meters get poor contact on
the range selector switch and the bannana jacks. So, that is one thing to
check for.

Second, most DMMs use very low voltage to meke Ohms measurements. Analog
meters often used 9 or even 22 V batteries for the Ohms range, to push
enough current to move the needle on high resistance circuits.

If there are any seminconductors in your circuit, a DMM likely will not give
enough voltage to forward bias any junctions, while an analog meter will.

Jon

Sounds to me like you need to spray some contact cleaner in your test
meter switches, and clean the plug contacts too.

On Sun, 16 Jul 2017 16:30:03 -0700, Jeff Liebermann
wrote:

On Sun, 16 Jul 2017 15:46:36 -0400, wrote:

Ok, I guess you have meters that I've never seen.

You haven't seen any of these?
http://www.simpson260.com
https://www.google.com/search?tbm=isch&q=simpson+260
These were probably the most common VOM's available. At one time, I
had about 5 of them. They've been replaced by more modern meters, but
I still keep one of them on the shelf, just in case.

Yep, I've seen several of them models. I just never owned any of them. I
generally used one of my VTVMs (Heathkit or Eico) for most in circuit
testing on tube gear. I have always been pretty satisfied with my older
Radio Shack VOMs. I blew up a few of them many years ago, but I learned
what NOT to do, and to pay attention and make sure I dont have the meter
on the ohms scale when I measure voltages.

I also have a GB Instruments model GMT-19A VOM sitting right next to me,
that I use for darn near everything, and it's held up well for many
years.

I am not real fond of digital meters. I find them confusing, since they
tend to pick up stray voltages and they also take awhile to "settle" on
a reading. I have some of them, and I use them for some things, but my
analog meter are usually the first ones I grab.

Seeing those Simpson meters makes me want to look for one to buy though.
Just seems there should be one on my bench.......

Chris wrote:

I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?

I've got four DMMs and two analogs. The DMMs agree with the other DMMs
and the analogs agree with each other. But the different types don't
agree with each other!
I have some older DMMs. I get odd resistance readings the first time I set
it to Ohms scale. By wiggling the plugs on the probes at the meter end, and
occasionally working the range selector dial around a few times, I get a
stable Ohms reading of about 0.4 Ohms with the probes shorted. Then, I get
more sensible readings on circuits. So, these meters get poor contact on
the range selector switch and the bannana jacks. So, that is one thing to
check for.

Second, most DMMs use very low voltage to meke Ohms measurements. Analog
meters often used 9 or even 22 V batteries for the Ohms range, to push
enough current to move the needle on high resistance circuits.

If there are any seminconductors in your circuit, a DMM likely will not give
enough voltage to forward bias any junctions, while an analog meter will.

Jon

Jon Elson wrote:

-----------------

I have some older DMMs. I get odd resistance readings the first time I set
it to Ohms scale. By wiggling the plugs on the probes at the meter end, and
occasionally working the range selector dial around a few times, I get a
stable Ohms reading of about 0.4 Ohms with the probes shorted. Then, I get
more sensible readings on circuits. So, these meters get poor contact on
the range selector switch and the bannana jacks. So, that is one thing to
check for.


** A little WD40 or similar will fix that in seconds.

A short squirt under the edge of the switch followed by a few complete rotations is all you do. Clean up any excess.

Wet a cloth to do the 4mm plugs and a cotton bud to do the sockets.


...... Phil

In article , says...

On Sun, 16 Jul 2017 16:34:56 -0700, tabbypurr wrote:

voltmeters don't output anything. They should be fine measuring solid
state.

DMMs and VOMs give different readings in certain circumstances (see
Ralph's post). In GB (at least) for a long time the service manuals for
decent gear would provide expected voltage readings for 20k OpV analogue
meters, the AV0 model 8 specifically IIRC, which saved the technician the
extra bother of scratching his head when checking hi-z parts of a circuit.

For amusement I fetched the Avo Model 7 that I inherited from my father
(goodness knows when he got it!). The plate on the back specifies 1.5V
cell for 1M, 2x4.5 for 1M, and external voltage sources for 10m and
40M ranges.

It also weighs 5lb (2+kg). I guess in those days servicemen were MEN!

Mike.

On Mon, 17 Jul 2017 09:08:01 +0100, Mike Coon wrote:

It also weighs 5lb (2+kg). I guess in those days servicemen were MEN!

Yes, and built like a tank! I have a Model 7, too, IIRC it was made in
1943 and is still going strong. I'll wager when it was first produced,
techs of the day marvelled at how light and portable it was.

On Sun, 16 Jul 2017 21:24:23 -0000 (UTC), Cursitor Doom
wrote:

On Sun, 16 Jul 2017 15:46:36 -0400, oldschool wrote:

Ok, I guess you have meters that I've never seen.

You've never seen any AVO/Megger meters?? Like this for example:

http://www.ebay.co.uk/itm/Bakelite-A...ter-Excellent-
Condition-100-Tested-/152599935777?hash=item2387aa3b21:g:1csAAOSw241YZTX 1

They've been exported all over the world for decades!

They typically use one 15V battery (about the size of a AA cell) and a
single 1.5V D cell.

This is one I've never seen. I have seen Simpson and Triplett vom's but
not this one.

I dont think I'd want any of these that need these special batteries. I
have looked at some of the specs for the older Simpson 260 meters and
some of the early models had oddball batteries too. The series 5 has D
and AA batteries, and the series 6 an above have D and 9V.

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?

My Radio Shack and GB meters only have 2 AA cells, and work fine.

On Monday, 17 July 2017 09:31:17 UTC+1, Cursitor Doom wrote:
On Mon, 17 Jul 2017 09:08:01 +0100, Mike Coon wrote:

It also weighs 5lb (2+kg). I guess in those days servicemen were MEN!

Yes, and built like a tank! I have a Model 7, too, IIRC it was made in
1943 and is still going strong. I'll wager when it was first produced,
techs of the day marvelled at how light and portable it was.

My 1920s v/i meter weighs a small fraction of that. Avos were high impedance accurate bench meters.


NT

On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.

"High impedance" back then, yeah.

On Mon, 17 Jul 2017 05:00:55 -0400, oldschool wrote:

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?


Dunno. I'm sure someone here will, though.
Fortunately, although 15V batteries are largely unobtainium these days,
10x1.5V AAA cells will get you there and the battery compartment is
capacious enough (AVOs are anyway) to house them all comfortably.

On Monday, 17 July 2017 11:21:54 UTC+1, Cursitor Doom wrote:
On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.

"High impedance" back then, yeah.

They were, you could always get lower resistance meters for a lot less. Why it took so long for analogue meters to get FETs I don't know. My 1920s meter is moving iron, so the resistance is dreadful & it's nonlinear. But its worst shortcoming is that the case is the -ve electrode, you hold it in your hand and it's bare metal. AND it's low resistance, so measuring radio/TV HT was always a fun experience. Maybe they figured if they killed their customers there wouldn't be any requests for refund.


NT

On Monday, 17 July 2017 11:05:20 UTC+1, wrote:

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?

A 1.5v cell is high capacity, high current & cheap. 15v batteries are low capacity, low current & never cheap.


NT

On Mon, 17 Jul 2017 05:00:55 -0400, wrote:

I do have to ask, why these meters used BOTH the D cells and other
batteries as well. (In other words, more than one kind of battery). Why
didn't they just use one battery or one set of batteries for the whole
device?

The Rx10K scale needs high voltage and low current to measure large
resistors. The Rx1 scale needs low voltage and high current to
measure the small resistors. One could use the high voltage 15v
battery for measuring low resistances, but you would be replacing 15v
batteries at an a alarming rate. Be thankful that the ancient
designers of the VOM did not include a different battery for each
resistance scale.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Mon, 17 Jul 2017 10:17:54 -0000 (UTC), Cursitor Doom
wrote:

On Mon, 17 Jul 2017 02:50:34 -0700, tabbypurr wrote:

My 1920s v/i meter weighs a small fraction of that. Avos were high
impedance accurate bench meters.

"High impedance" back then, yeah.

Not high enough. If you want to measure really high resistances, such
as insulation leakage, you need a Megger (which is actually the name
of the company that makes them but has become somewhat of a generic
term for high voltage resistance testers):
https://www.google.com/search?q=megger+meter&tbm=isch
If you want to see if you really have water in the coax cables, you
need one of these insulation testers.

I have an old and ugly meter, which has a hand crank generator. It
produces enough voltage to have given me a rather nasty shock. It's
fairly difficult to electrocute oneself while operating the crank, but
I managed. Some modern Megger models still have such hand cranks
generators:
http://www.tequipment.net/Megger212160.html
http://us.megger.com/extended-range-insulation-resistance-testers-210170-and-210600-
These small testers will deliver 1000V in order to measure up to 2000
Mohms. Now, does anyone still want to complain about 15v batteries?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sunday, July 16, 2017 at 8:36:16 PM UTC-4, Phil Allison wrote:
Chris wrote:

--------------


I'm finding I get different results (vastly different in some cases) when
measuring the total resistance of a circuit with a) a DMM and b) an old
analog meter with a physical needle. And this doesn't only happen at high
impedance points, either. What could account for this?


** The fact you are totally clueless ?

Semiconductors are not resistors and there is no right value to measure.

DMMs are designed NOT to cause didoes or BJT junctions to conduct when using the ohms ranges.

Also, DMMs ohm ranges are very sensitive to any residual DC or AC voltage on a component while analogue meters are much less so.

Interesting fact: you can measure the resistance of a loudspeaker voice coil with either type, but not if the room is full of loud bass noise.

Think about it.


...... Phil

Come on Phil, lighten up. The guy didn't know and asked the question. We aren't all born full of knowledge; it's acquired by experience and asking questions.

Remember when you asked your mother why you have no friends, and she told you that you're obnoxious, pig headed and your feet smell like a fetid swamp? Same thing..

On Mon, 17 Jul 2017 07:59:41 -0700, Jeff Liebermann wrote:

Not high enough. If you want to measure really high resistances, such
as insulation leakage, you need a Megger (which is actually the name of
the company that makes them but has become somewhat of a generic term
for high voltage resistance testers):
https://www.google.com/search?q=megger+meter&tbm=isch
If you want to see if you really have water in the coax cables, you need
one of these insulation testers.

Yeah, I have one. They can still be used perfectly servicably if they're
within spec. The people at Megger tell me that every so often, an old
hand-crank version from the 50s or 60s will come in for re-calibration!
The one I have is the 250V model which is relatively unusual here in the
UK as almost all of them here are 500V. We would typically use the 500V
version for testing our 240V domestic wiring. I guess the 250V model was
intended for export to countries which use 110/120V.

The current range of Meggers are quite expensive, IRO $1200 but at least
you don't have to crank them any more.

On Mon, 17 Jul 2017 09:47:17 -0700, John-Del wrote:

Come on Phil, lighten up. The guy didn't know and asked the question.
We aren't all born full of knowledge; it's acquired by experience and
asking questions.

It's no problem. I plonked Phil some time ago on the advice of other
posters here so I rarely get to see any of his unfortunate, socially-
embarrassing outbursts. ;-)

Remember when you asked your mother why you have no friends, and she
told you that you're obnoxious, pig headed and your feet smell like a
fetid swamp? Same thing..

LOL!!! Most amusing. :*D