Ammeter

http://people.ee.duke.edu/~cec/final/node22.html

Ammeter

An ideal ammeter has zero resistance so that the the circuit in which it has been placed is not disturbed. An ideal ammeter is a short circuit. However, as with the voltmeter, no ammeter can ever be ideal, and therefore all ammeters have some ( hopefully) small internal resistance. To determine the resistance of the ammeter, we will use the circuit in Figure . According to Ohm's Law, the current in this circuit will be  where . So the current can be found using the equation:
 
By using the known quantities  and R, we can solve for the unknown quantity .
In the procedure that follows it is extremely important that you take precise and accurate measurements. Record each measurement as precisely as the instrument will allow.

1. Select a 100  resistor. Measure and record its actual value.
2. Assemble the circuit in Figure . Set the multimeter to the ammeter mode for dc current measurement. Recall this means two things: Place the test leads in the correct banana jacks and press the proper sequence of softkeys.
3. Use the oscilloscope to measure the voltage across the DC power supply.
4. Measure the value of the current using the ammeter.
5. Determine the value of  from Equation .