# Converting meters

Discussion in 'General Electronics Chat' started by Bobdotham1, Jun 1, 2005.

1. ### Bobdotham1 Thread Starter New Member

Jun 1, 2005
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I have a meter from I assume a Potter burglar alarm panel.
It is labeled POTTER and is 50 full scale.
How can I :
Tell if it is a mA or volt meter?
Convert it to a 50 volt DC meter?

Thanks
Bob

2. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Typically, if the meter was intended to measure current, the meter's input resistance will be extremely low. If it is intended for measuring voltage, the input resistance will be quite high. something on the order of several kilohms or higher.

If you have an ohmmeter, try measuring the input resistance. Just to be on the safe side set your ohmeter to the highest ohm scale initially. You should be less likely to damage the meter that way.

Provided it is configured as a voltage meter, you will need to know what the fullscale voltage is to design the resistor attenuator network needed to scale the meter for the desired range.

hgmjr

Jun 1, 2005
5
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4. ### Bobdotham1 Thread Starter New Member

Jun 1, 2005
5
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Thanks for the help.

I set the meter at 10Kohms and measured the resistance at 1,000 ohms. I then used a 1.5 v battery and the questionable meter pegged.
Bob

5. ### hgmjr Moderator

Jan 28, 2005
9,030
214
It appears to be safe to assume that the meter is configured for voltage measurement.

I suspect you have a meter that is going to register full scale with either 1 volt or 0.5 volts.

An interesting experiment would be to place a multi-turn potentiometer in series with a known voltage and feed it into the meter. Start with the potentiometer set to its maximum voltage and slowly decrease the resistance until the meter registers full scale. Then measure the voltage across the meter and that will give you the value of the full scale voltage.

Once you have the full scale voltage level then you can compute the series resistance you will need to set it up to register 50 volts at full scale.

Good Luck,
hgmjr

Jun 1, 2005
5
0

7. ### Bobdotham1 Thread Starter New Member

Jun 1, 2005
5
0
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Thanks, I really appreciate the help.
Bob