Page 364 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

LESSON 126 - 128 : Read and interpret the name plate

details-selecting ohmmeter for proper
range-advantages of using megger-

residual magnetism-residual voltage

and current

Objectives

At the end of this lesson you shall be able to
• select ohm meter for proper range and Use of ohmmeter
• use megger.

Read and interpret the name plate details-selecting ohmmeter for proper range
Ohmmeter

Ohmmeter is a direct reading device for calculating resistance. The precision of this instrument is less, although
less precision does not affect the efficiency of the instrument. This instrument is used to find the approximate
value of resistance.
Structure
Ohmmeter mainly consists of a micro-ammeter, battery current regulator, resistor, zero adjusting resistor
(potentiometer) and ‘probes’. These instruments are of two types: 1. Series type 2. Shunt type. In series type
instrument, the unknown resistor is connected in series with the battery and micro-ammeter. It is used to measure
medium and high resistance values. In a shunt type instrument, an unknown resistor is connected in parallel with
a micro-ammeter. It is used to measure low and medium resistance values.

1 Check Resistance Range: Look for the resistance range specified on the equipment. It might be given in
ohms (Ω) or kilohms (ΚΩ).
2 Maximum Value: Identify the maximum resistance value the ohmmeter can accurately measure. This is
crucial to avoid damaging the equipment.
3 Minimum Value: Note the minimum resistance value the ohmmeter can measure accurately. This ensures
accurate readings for low-resistance components.

4 Accuracy: Determine the accuracy of the ohmmeter within its specified range. This ensures precise
measurements.

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