Analog meters: Why do they need a 9V battery?

Joerg

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Mar 14, 2017, 4:34:36 PM3/14/17

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My trusty old Russky meter died and I can't be sans analog meter for
long. Must be cheap and simple because they get dropped, crushed,
snatched, whatever. Has anyone used the HM-102S while in the service?

https://www.amazon.com/SOLTEC-HM-102S-Analog-Multimeter-VOLTS/dp/B01M1ETSF9

Why do these need a 9V battery? At 20k/V input impedance that just
doesn't make sense.

--
Regards, Joerg

http://www.analogconsultants.com/

alan.yea...@gmail.com

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Mar 14, 2017, 4:54:27 PM3/14/17

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Perhaps for reading high (Meg) Ohms.

Joerg

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Mar 14, 2017, 4:57:42 PM3/14/17

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On 2017-03-14 13:51, Ray Otwell wrote:
> That meter also measures resistance. It needs the battery so it can
> source current to measure the resistance. V/A measurements shouldn't
> need the battery to operate on their own.
>

Yes, but it also needs two AA cells (most meters only need one) and that
ought to be enough. This meter requires a whopping three batteries, two
AA and one 9V.

If for some reason they use 9V for the highest ohms range that would be
ok because it's no big deal when that doesn't work for long.

> Ray Otwell

Joerg

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Mar 14, 2017, 4:58:39 PM3/14/17

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Possible but still strange because the two AAs should be plenty for a
meter with such a sensitive coil in it.

Reinhard Zwirner

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Mar 14, 2017, 5:36:30 PM3/14/17

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Joerg schrieb:

> On 2017-03-14 13:54, alan.yea...@gmail.com wrote:

[...]

>> Perhaps for reading high (Meg) Ohms.

> Possible but still strange because the two AAs should be plenty for a
> meter with such a sensitive coil in it.

The meter has an Ohm x 10k range; the highest resistance mark on the
Ohms scale is 20k: that corresponds to 200 MOhm. With a 9 V battery,
the current through a 200 MOhm resistor will be 45 nA ...

HTH

Reinhard

Joerg

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Mar 14, 2017, 5:53:06 PM3/14/17

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Some of my previous meters were able to do this but if the 9V battery is
only used for the highest resistance range that would be fine. I just
want to be sure since I do not want any electronics in the way for DC
measurements. I had a analog transistor voltmeter before and in the
presence of pulsed RF it was about as fickle as DVMs are. It was so bad
that I scrapped the thing.

Peter Heitzer

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Mar 15, 2017, 10:00:20 AM3/15/17

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Ray Otwell <ray(no space here)otwell(at)gmail(dot)com> wrote:
>That meter also measures resistance. It needs the battery so it can
>source current to measure the resistance. V/A measurements shouldn't
>need the battery to operate on their own.

If I don't need to measure resistors >100 k, 1.5V is sufficient.
Diode test can have a need of higher voltages if one wants to test LEDs
also.

--
Dipl.-Inform(FH) Peter Heitzer, peter....@rz.uni-regensburg.de

k...@notreal.com

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Mar 15, 2017, 1:49:18 PM3/15/17

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On 15 Mar 2017 14:00:15 GMT, "Peter Heitzer"

<peter....@rz.uni-regensburg.de> wrote:

>Ray Otwell <ray(no space here)otwell(at)gmail(dot)com> wrote:
>>That meter also measures resistance. It needs the battery so it can
>>source current to measure the resistance. V/A measurements shouldn't
>>need the battery to operate on their own.
>
>If I don't need to measure resistors >100 k, 1.5V is sufficient.
>Diode test can have a need of higher voltages if one wants to test LEDs
>also.

100K is pretty low.

Phil Allison

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Mar 15, 2017, 8:56:45 PM3/15/17

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Joerg wrote:

>>
> https://www.amazon.com/SOLTEC-HM-102S-Analog-Multimeter-VOLTS/dp/B01M1ETSF9
>
> Why do these need a 9V battery? At 20k/V input impedance that just
> doesn't make sense.
>

** Course it does - when the meter has an " Ohms x 10K" range.

At centre scale, the reading is 200kohms needing about 25uA to get - so
requires at least 5v supply.

The meter has no "ohms x 100" range, which could be a problem.

.... Phil