Some DMM and AMM questions

[120520125]

Why is it desirable for a current meter to have a low internal resistance and a voltage meter to have a high internal resistance? Based on your experimental data, discuss the accuracy in making electrical measurements using DMM and AMM.


State the advantages and disadvantages of using DMM and AMM. Under what situation do you prefer an AMM to a DMM?

 

[Audioguru]

A current meter needs a very low resistance so that it does not cause a large voltage drop.
A voltmeter needs a very high resistance so that it does not "load down the voltage" if the source has a high resistance which causes a voltage drop.

A high quality DMM has both and is accurate. A cheapo DMM might not and is not accurate.

 

[kam1787]

Why is it desirable for a current meter to have a low internal resistance and a voltage meter to have a high internal resistance? Based on your experimental data, discuss the accuracy in making electrical measurements using DMM and AMM.


State the advantages and disadvantages of using DMM and AMM. Under what situation do you prefer an AMM to a DMM?

where is the experimental data?

 

[chuckey]

A circuit has a 1.5V battery feeding a 3 A bulb. The resistance of the bulb must be 1.5/3 = .5 ohms. If your current meter has a resistance of .5 ohm then the total resistance will be .5 + .5 = 1 ohm, the new current will be 1.5/1 = 1.5 A, so your meter will read 1.5 A. If the meter is a more conventional one, used on its 10 A range it would drop .1 V at 10 A, so its resistance would be .1/10 = .01 ohm. The total circuit resistance in the bulb circuit would be .5 + .01 = .51 ohms, the current that would flow would be 1.5/.51 = 2.94 A which is a lot closer to the real value (3A).
Frank