05-12-2012, 01:31 PM
Introduction to Electronic and Digital Measurement
[attachment=42596]
LOADING EFFECT OF A VOLTMETER
If a meter (represented by R3) with a resistance of 10 ohms is connected in parallel with R2, as in Figure (B), the combined resistance of R2 and R3 (Rn) is equal to 5 ohms. The voltage across R2 and R3 is now 6.25 volts, and that is what the meter will indicate. Notice that the voltage across R1 and the circuit current have both increased. The addition of the meter (R3) has loaded the circuit.
Notice that the voltage across R, and the circuit current in Figure © are much closer to the values in Figure (A). The current (IR4) through the meter (R4) in Figure © is also very small compared to the current (IR2) through R2.
[attachment=42596]
LOADING EFFECT OF A VOLTMETER
If a meter (represented by R3) with a resistance of 10 ohms is connected in parallel with R2, as in Figure (B), the combined resistance of R2 and R3 (Rn) is equal to 5 ohms. The voltage across R2 and R3 is now 6.25 volts, and that is what the meter will indicate. Notice that the voltage across R1 and the circuit current have both increased. The addition of the meter (R3) has loaded the circuit.
Notice that the voltage across R, and the circuit current in Figure © are much closer to the values in Figure (A). The current (IR4) through the meter (R4) in Figure © is also very small compared to the current (IR2) through R2.