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Fault Simulation - What is it and why should you be doing it?

When carrying out end of line safety testing it is imperative to know that the test equipment is operating within specification to ensure that any faults within the equipment under test are identified. Routine calibration of test equipment in line with manufacturer’s recommendations will ensure that the equipment is measuring accurately and without fault at the time of calibration, but what about during the interim period?

Consider this scenario -A piece of test equipment that has not been checked since its last calibration is returned to the manufacturer for calibration. It is found that the performance is out of specification, such that it could potentially fail to identify a safety issue within the equipment under test. What could the impact of this be? A manufacturer would find themselves with the following questions to ask:

  • At what point between calibration intervals did the fault occur?
  • How many potentially unsafe products could have been deemed safe and sent to customers?
  • Should a recall be issued on all products produced since the last test equipment calibration date?

This could result in an extremely costly and damaging exercise, but thankfully one that can be easily avoided by performing simple, regular performance checks on the test equipment.

A fault simulator is a simple performance checking device that is tested like a dummy product. Its function is to present the test equipment with a known test failure condition in order to confirm the “trip” circuits operate correctly. A typical fault simulator would incorporate a failure condition for earth continuity, insulation resistance and dielectric strength testing.

As an example, during dielectric testing the fault simulator may be designed to produce a fault current greater than 5mA to protective earth once a given voltage level is applied. The test would involve applying this voltage whilst the fail level of the test equipment is set to 5mA, and observing that the test equipment does indeed indicate a failed condition. Whilst it may sound contradictory, in this instance a failure means the test equipment has passed the test!

So how often should fault simulation be performed? This may depend on a number of factors, but as a general guide, fault simulation at least once a day is recommended, and it is common practise to carry out checks at the start of every shift, if daily shift patterns are employed.

A typical fault simulation check will take no longer than a minute to perform, and could save both time and money in the long run.

Seaward produce a number of fault simulation equipment to aid the fast and simple checking of electrical safety test equipment. You can view the full range at /faultsimulators.

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