Tutorial 3a

BEKG 1233

PRINCIPLES OF INSTRUMENTATION & MEASUREMENT

CHAPTER 3

ALTERNATING CURRENT (AC) METER

(TUTORIAL)

1. What do AC meters show, is it the RMS or peak voltage?

2. List 5 AC meter principle meter movements & includes one application for the principle.

3. A d'Arsonval meter movement with a full-scale deflection current rating of 200 uA and an internal resistance of 500 12 is to be used in an AC voltmeter using full-wave rectification. Calculate the value of the multiplier resistor for a 50-V peak-to-peak sine-wave range.

4. Calculate the ac and dc sensitivity and the value of the multiplier resistor required to limit current to the full-scale deflection current in the circuit shown.

5. Calculate the ac and dc sensitivity and the value of the multiplier resistor required to limit current to the full-scale deflection current in the circuit shown . All diodes have a forward resistance of 300 12 and an infinite reverse resistance.

6. Using a PMMC with Ra-2502 and Is-1mA, design two AC voltmeters. The diodes have a forward resistance of 50?.

a) One with half wave rectifier for Vm-30 V.

b) The second one is with full wave rectifier for Vr-30V.

c) Find the DC and AC sensitivity for each meter.

d) If a shunt resistor of 250 ? is connected in parallel with the PMMC, find the new multiplier resistor for both cases.

ANSWER

1. AC voltmeters and ammeters show the RMS value of the voltage or current

2. a) Electrodynamometer - Standard meter

b) Iron-vane - Indicator applications

c) Electrostatic - High voltage

d) Thermocouple - Radio frequency measurement

e) D'Arsonval (PMMC) - Currents

3. R= 79.05kohm

4. Sac =19.5, Sdc= 2.7

5. Sac=15.3, Sdc=12.5

6.