Mike Howell
EASA Technical Support Specialist

Most service centers perform some form of surge comparison testing, though terminology and methodology may vary. In simple terms, two winding responses or waveforms from a fast rise-time surge are compared and if there is an excessive difference, the unit under test may have a defect. The waveform that is produced by the pulse is unique to the unit under test, which for example, could be a stator winding. The waveform will be a function of the resistance, capacitance and inductance of the test circuit and quite a few variables can affect those characteristics.

One difficulty or challenge with surge comparison testing has been its subjectivity. That is, it is not always easy for operators to reach the same conclusion when comparing two waveforms. Within the last few decades, several equipment manufacturers have begun to utilize analytical methods to evaluate the surge comparison test results. The goal is to remove as much subjectivity as possible so that disposition of the unit under test is a simple decision for the operator. The analytical method that has become most popular, in various forms, is use of the Error Area Ratio (EAR).

Do you have to have EAR capabilities in order to perform surge comparison testing satisfactorily? No, but if you have the capability, a basic understanding of the data reported by the equipment can help you make an informed decision.

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