The accurate measurement of Surge pulses for equipment calibration purposes requires that a Surge generator output be measured in both Differential and Common modes. Common mode measurements are relatively straightforward as the measurement is of a single output referenced to earth potential. Differential measurements however require that both the high and common of a Surge generator output are measured. This requires use of two high voltage probes and a dual channel oscilloscope capable of arithmetic functions.

High voltage probes are notoriously sensitive to measurement position (vertical, horizontal), proximity of metal sheets, etc. In addition annual calibration of high voltage probes is NOT sufficient to ensure an accurate IMPULSE measurement can be made. So before each measurement, the probe(s) must be adjusted to the test equipment and measurement position. This is time consuming and requires additional test equipment or know-how not always readily available. To reduce the difficulties of Differential measurements from Surge generators, HAEFELY  have developed an active probe specially for IMPULSE measurements on floating outputs.

Applications: