Constructing Ammeters and Voltmers

[mark1989]

We just did a lab on constructing ammeters and voltmers using a galvanometer. We had to figure out the meter constants for V, I, and R. Our teacher told us that we could not just use an ohmmeter to measure the internal resistance of the galvanometer and we had to calculate Rg. Why can't we just use an ohmmeter, I don't get it?

 

[AlephZero]

An ohmmeter works by applying a voltage (usualy from a battery inside the meter) across the two measring probes, and measuring the current that flows through the resistance you want to measure.

A galvanometer usually only needs a few millivolts applied to it to give its full scale reading. An ohmmeter would apply several volts to it (in other words, about 1000 times more voltage that it was designed for) and that would probably damage or destroy it.

 

[mark1989]

Thanks for clearing that up for me. Glad I didn't do it