[ozzie34231]

I have a DC voltmeter 0-100 volts.
I want to use it 0-300 volts.
I remember from high school, over 50 years ago, that I measure the resistance of the meter, but,
then what???
What size resistor do I put where???

Ozzie

[Al_The_Man]

A couple of ways.
The meter has an internal series resistor, the resistance of the meter is very low compared to the series resistor, You could either measure the current at a given voltage to calculate the current required for the meter, or a simpler way is to ignore the low resistance of the meter and just measure the total resistance and multiply by 2 and add this resistance in series with the meter to get a full range of 300v.
To ensure precision, you would need the resistance of the meter movement and the full scale current of the meter.
This is then ohms law to calculate the total resistance of the meter and series resitor in order to pass the full scale current at the selected scale voltage.
Al.

[ozzie34231]

Thanks AL !
Ozzie