Page 121 - CITS - Electrician - Trade Practical

ELECTRICIAN - CITS

EXERCISE 51 : To determine the errors in PMMC and MI

meters

Objectives
At the end of this exercise you shall be able to:
• identify the different types of PMMC and MI meters
• read, compare and differentiate the scale of PMMC and MI meters
• connect and measure the electrical quantities by PMMC and MI meters
• calibrate & determine the errors in PMMC and MI meters with standard meters.

Requirements

Tools/Equipments/Instruments
• Combination Plier 165mm, • AC Voltmeter (Old) MI, 0-300 V -1 No.
insulated -1 No. • AC Ammeter (Standard/New)
• Screw Driver 150mm, MI, 10 A -1 No.
insulated stem -1 No. • AC Ammeter (Od) MI, 10 A -1 No.
• Neon Tester 75mm, 500 V -1 No. • Lamp load 5 KW, 230 V -1 No.
• Electrician knife insulated -1 No. • 1 Ph. Auto transformer 0-270 V -1 No.
• DC Voltmeter (Standard/New) • ICDP switch 16 A -1 No.
PMMC, 0-300 V -1 No. • Digital Multi meter 3 digit -1 No.
1/2
• DC Voltmeter (Old) • Rheostat 750 Ω, 1.5 A -1 No.
PMMC, 0-300 V -1 No. Materials/Components
• DC Ammeter (Standard/New)
PMMC, 10 A -1 No. • PVC copper wire 2.5 sq.mm - 5 meter
• DC Ammeter (Od) PMMC, 10 A -1 No. • Test lamp 100 W, 230V -1 No.
• AC Voltmeter (Standard/New) • Cotton waste -as reqd.
MI, 0-300 V -1 No.
Procedure

Calibration of Electrical meters:

The Electrical meters are classified as PPMC (DC) meters and MI (AC) meters which measures the electrical
quantities like voltage, current and power in electrical circuits. The electrical meters are manufactured with
accuracy which varies from + 0.05 % to + 5 %
The accuracy of Electrical meter will be reduced after long usage due to electrical & mechanical errors, aging etc.
Therefore electrical meters are to be calibrated periodically to ascertain their standard values.
The electrical meters are calibrated by comparing the true value of voltage OR current in the circuit with a
standard meters.
TASK 1: Iedntify the PMMC & MC instruments
1 Draw the circuit diagram of calibration of voltmeter & ammeter.
2 Check and identify different types of PMMC and MI electrical meters.

3 Check the scale, terminals and range of PMMC and MI meters
4 Connect and measure the voltage & current values by PMMC and MI meters.

TASK 2: Test and calibrate the PPMC & MI Voltmeter and Ammeter with standard meter
1 Make the connections for calibration of PMMC Voltmeter as per circuit diagram.
2 Check the connections and set the rheostat to cut-in position.
3 Switch ON the DC supply, slowly vary the resistance in rheostat step by step.

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