Megohmmeters are mainly used for testing the breakdown strength of electrical insulation. They generate high voltage and low current signals for conducting the test. These meters have derived their name from the fact that the insulating resistance of a properly designed product is expressed in megohms (MO).

Salient Features

• Provided with remote controls that can be controlled by computers or other instruments.
• There is a built-in calibration that enables operator to calibrate test instruments without removing them from the test location.
• Comes with warning indicator lights, which indicate pass or fail conditions and mostly work in association with audible buzzers or alarms.
• Megohmmeter devices are often interfaced with programmable logic controllers in automated test environments.
• Supplied with a rapid cutoff circuitry for protecting electrical devices from excessively high levels of voltage or current.
• Have user-selectable output frequencies.
• These meters are also available with printer ports and scanner ports.
• These devices vary in terms of display and interface technologies.

Types

Megohmmeters vary in terms of display and interface technologies, and hence they are of the following types:

• Digital Megohmmeter
• : These electrical devices are used to test and measure the insulation resistance of cables, wires, transformers and electrical motors. The digital megohmmeter displays value with a numeric readout. The most common types of digital megohmmeter include liquid crystal display (LCD) and light emitting diode (LED) devices.
• Analog Megohmmeter
• : The analog meters are used for manual testing, which does not require high precision measurements. They are ideal for rugged, field portable, testing applications. These devices display values on a dial, usually with a needle or pointer.

Specifications

The vital specifications of these meters are:

• DC output voltage
• DC output current
• Current leakage rate
• Resistance range
• Test time

Applications

Some of the common applications are:

• Testing insulation resistance of wires, cables, transformers and electrical motors.
• Verifying specifications of aircraft fuel pumps.
• Testing insulation-resistance of cable reels, rectifiers, solid-state diodes, etc.
• Testing insulation resistance of various electrical components.