Page 365 - Mechanic Diesel - TT

MECHANIC DIESEL - CITS

5 Resolution: Consider the resolution of the ohmmeter. Higher resolution allows for more detailed readings.

6 Range Selection: Select a range on the ohmmeter that covers the resistance you intend to measure, without
exceeding its maximum range.
Methodology

A and B Conjunction When the value is zero, maximum electric current flows through the circuit. In this method
the oscillator indicator of the zero adjustment resistor is adjusted to the zero position of the scale. ‘Zero’ on the
scale is on the right. When connections A and B are kept apart from each other, the indicator shows zero electric
current and infinite resistance on the scale.
When an unknown resistance is connected between connectors A and B, the indicator of the instrument directly
shows the resistance in ‘Ohm’ on the scale. The scale of this instrument is not proportional.
Features
1 Through this instrument, the value of unknown resistance can be read directly in ‘Ohm’ and there is no need
to do any kind of calculation.
2 Many measuring ranges can be made in this instrument by connecting additional resistors and batteries. For
each scale there is a ‘multiplier’ which is marked on the switch positions of the instrument; Like – R = 1, R =
1
1
1000 etc.
Advantages of using megger-residual magnetism-residual voltage and current
Using a megger (insulation resistance tester) with a residual voltage test feature offers several advantages:

1 Enhanced Safety: It ensures safety by confirming that the insulation is safe to test, as residual voltage could
pose a risk during testing if not properly discharged.

2 Accurate Results: The residual voltage test helps in obtaining more accurate insulation resistance
measurements by ensuring that any residual voltage is dissipated before conducting the test.
3 Prevents Damage: It helps prevent damage to the insulation or the tester itself by discharging any residual
voltage, thus extending the lifespan of both.
4 Compliance: Some regulations or standards may require residual voltage testing to ensure compliance with
safety guidelines.

5 Diagnostic Capability: It can provide diagnostic insights into the condition of the insulation by detecting any
residual voltage, which could indicate underlying issues such as leakage or degradation.
Overall, incorporating a residual voltage test into megger testing procedures improves safety, accuracy, and
reliability of insulation resistance measurements.

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CITS : Automotive - Mechanic Diesel - Lesson 126 - 128