High Voltage Technique: The high voltage, or porosity technique, can be used to test coatings up to 25mm (1”) thick and is ideal for inspecting pipelines and other protective coatings. Coatings on concrete can also be tested using this method.
A power supply generates a high voltage pulsed DC to a probe. As the probe passes over a flaw, a spark at the contact point sets off the alarm.
The pulsed DC holiday detector is designed to ensure that the energy is contained within very short pulses, each pulse having more energy than an equivalent continuous DC system. This means that a holiday detector can be used to test for holidays over slightly conductive coatings, dirty or damp surfaces.
For more information, see the Elcometer Guide to Pinhole & Porosity.