Why Do Some Voltmeters Not Show 10V at Full Scale on a Potentiometer?

[a3sportback54]

The attached graph shows an experiment I performed where I had a potentiometer connected to a DC 10V supply, the voltage across the pot was measured with 5 different voltmeters of varying internal resistance. I guess the one with the highest internal resistance, to the order of 10megohm, is the straight line, v2, am I right in thinking this?

Can anyone tell me why some of the voltmeters didnt read 10V at 100% rotation?

 

[berkeman]

The attached graph shows an experiment I performed where I had a potentiometer connected to a DC 10V supply, the voltage across the pot was measured with 5 different voltmeters of varying internal resistance. I guess the one with the highest internal resistance, to the order of 10megohm, is the straight line, v2, am I right in thinking this?

Can anyone tell me why some of the voltmeters didnt read 10V at 100% rotation?

Did you measure the resistance between the wiper and the CW contact? If it's not zero Ohms (probably isn't), then your lower-input-impedance voltmeters may still cause a voltage drop at full CW...

 

[oswaler]

I would first like to commend you on conducting an experiment and analyzing the results. It is important to understand the behavior of equipment and how it may impact the accuracy of your measurements.

Based on the information provided, it is likely that the voltmeters with higher internal resistance (such as v2) would have a more accurate reading at 100% rotation. This is because the higher internal resistance would minimize the loading effect on the potentiometer. In other words, the voltmeter with higher internal resistance would draw less current from the potentiometer, resulting in a more accurate measurement of the voltage across the potentiometer.

As for why some of the voltmeters did not read 10V at 100% rotation, there could be a few reasons. One possibility is that the voltmeters themselves may have some inherent error or variation in their readings. Another possibility is that the potentiometer may have some nonlinearity or drift, which can affect the accuracy of the voltmeter readings. It is also important to consider the precision and accuracy of the voltmeters used in the experiment.

In conclusion, the voltmeter with the highest internal resistance is likely to have the most accurate reading at 100% rotation. However, it is important to consider other factors such as inherent error and nonlinearity of the equipment when analyzing the results of an experiment.