Construction of an IR tester

When installing new electrical machinery or electronic equipment in your office, testing insulation resistance with an IR tester is important. IR testing is performed as a quality control measure as well as to provide a baseline reading which is then used as a reference for future testing. You would also need an IR tester as a periodic preventative tool to check whether your electrical insulation has started to deteriorate with age or due to any external factor like temperature, humidity or environmental conditions.

What are the construction features and the components found in an IR tester? Let’s find out.

Components found in an IR tester

  • Deflecting coil and control coil
  • Two permanent magnets
  • Pointer
  • Scale
  • DC generator for manually operated/Battery connection for automatic
  • Two pressure coils and one current coil

Construction of an IR tester

Deflecting coil and control coil: The deflecting coil and control coil are positioned at right angles to each other and placed parallel to the DC generator. The polarities are such that the torque produced by them is in the opposite direction.

Permanent magnets: Two permanent magnets that produce a magnetic field between their poles that deflects the pointer.

Pointer: One end of the pointer is connected to the deflecting and control coils while the other endpoints towards a scale which provides the value of resistance ranging from zero to infinity.

Scale: A scale showing resistance readings from zero to infinity is an important feature of an IR tester. The units on the scale are in Ohms. The pointer is set at infinity when at rest. The pointer moves from infinity position to zero position on the resistance scale when the IR tester experiences a torque.

Let’s find out what happens when an electrical circuit with an unknown resistance is tested by an IR tester. If the pointer deflects and points towards infinity then there is no shorting on the insulation and the resistance is high. In contrast, if the pointer moves towards zero, the resistance of the in-test electrical circuit is low and there may be a short circuit. In short, the deflection of the pointer is directly proportional to the voltage applied to the external circuit.

DC generator or battery connection: For a manually operated IR tester, the testing voltage comes from a hand-operated DC generator that comes with a crank handle and a centrifugal clutch. On the other hand, a battery or electronic voltage charger is used to provide the power for an automatic IR tester.

Pressure coil resistance and current coil resistance: The pressure and current coils protect the IR tester from any damage, should any unstable external electrical resistance occur while performing an IR test. Periodic use of an IR tester will help you keep your electrical circuits in your power system run smoothly and ensure personnel safety as well.

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