Ee11a Electrical Measurements

EE11A – ELECTRICAL MEASUREMENTS

Problem Sets

PROBLEM SET 3

Q1 Determine the resistor value required to convert a 0-1 mA, 125W meter into a 0-1V meter.

Q2 What value of shunt resistor is required if a 50mA meter movement with internal resistance 500W is to be used to measure 0-500mA?

Q3 What series resistance must be used to extend the 0-200 V range of a 20kW/V meter to 0-2000V? What must the power rating of this resistor be?

Q4 Figure Q4 represents a series type ohmmeter designed to operate with a 6V battery.

Figure Q4

The ammeter is a 100mA, 2000W PMMC movement. The value of R1 is 49kW.

(a) Assuming that the battery voltage has fallen to 5.9V, calculate the value of Rz required to zero the meter.

(b) Under the conditions of part (a), an unknown resistor is connected to the meter causing a 60% meter deflection. Calculate the value of the unknown resistance.

Q5 Figure Q5 represents a half-wave rectifier AC voltmeter. The meter movement is a 1mA, 250W PMMC. The diodes have a forward resistance of 50W and infinite reverse resistance. Calculate

(a) The series resistance required for full-scale meter deflection when 25V rms is applied to the meter terminals; and

(b) The sensitivity of the meter.

Figure Q5

Q6 After measuring the voltage across R2 in Figure Q6 with a 100W/V meter on the 50V, 150V and 300V ranges, the meter read 4.65V on the lowest range. What is the value of R2?

Figure Q6

Q7 Figure Q7 shows the circuit for a full-wave rectifier AC voltmeter using a 4-diode arrangement called a bridge rectifier. For the positive half cycle of the AC waveform, diodes D1 and D3 conduct. For the negative half cycle of the AC waveform, diodes D2 and D4 conduct. The ammeter responds to the average of the full-wave rectified sine wave. Repeat problem Q5 for this circuit.

Figure Q7