Nidhi > Em > Task_6

6. INFLUENCE OF THE WAVEFORM OF MEASURED VOLTAGE ON THE METER READING 6.1. Tasks of the measurement 6.1.1. Measure the voltage across a load. The power is controlled by triac-based circuit for switching phase α approximately 0°, 45° and 90° by means of digital voltmeters V1 to V4. 6.1.2. Observe the voltage waveform on the oscilloscope (connect the oscilloscope to the output of the resistive divider). 6.1.3. Find which multimeters measure the true RMS and evaluate the relative measurement error for the remaining devices. 6.1.4. Find the rectified mean value of the measured voltage waveforms from reading of remaining multimeters. 6.1.5. For switching phase α = 90° calculate the rectified mean (RM) and RMS values using their definitions. Compare the calculated and measured values. In case of discrepancies, analyze their possible reasons.

6.2. Schematic diagram A

Regulating circuit B1

~ 48 V, 50 Hz

R1 V1

B2 R2

Fig. 6.1 Measuring circuit connection

Fig. 6.2 Measured voltage waveforms

V4

OSC

6.3. List of the used equipment A - iron-vane ammeter; accuracy class ..., range ...; Z - model of the load with two bulbs B1, B2 and resistive divider R1, R2; V1 - laboratory multimeter, type ...; V2 - laboratory multimeter, type ...; V3 - handheld multimeter, type ...; V4 - handheld multimeter, type ...; V5 - electronic voltmeter, type ... Regulating circuit - device for current waveform control

Theoretical background See the textbook: M. Sedláček, J. Holub, D. Hejtmanová: Laboratory Excercises in Electrical Measurements, CTU Publishing House, Prague, 2005