How to set up an Elcometer Continuous DC High Voltage Holiday Detector
When it comes to testing the porosity of protective coatings on pipelines, ballast tanks, or bridges for example - or testing for flaws in coatings on concrete - typically the high voltage or holiday detection method is used.
The high voltage method comes in two versions – Continuous DC and Pulsed DC. In this video, we’ll be introducing you to the Continuous DC method, which is used to test non-conductive coatings up to 7.5mm (300mils) thick on conductive substrates.
Put simply, a high voltage of between 0.5-30kV is applied to a probe. The probe is then passed over the coated surface. The voltage to the probe is constant, hence the name Continuous DC. The voltage used should be high enough so that in areas where the coating is electrically weaker due to a flaw or discontinuity, there is sufficient voltage to break down the gap between the probe and the substrate.
When this break down occurs the current flows from the probe, through the substrate, and back into the holiday detector, via grounding cable which is clipped to an uncoated section of the substrate being tested, completing a circuit. This instantly triggers an alarm to signal a flaw has been detected.
As the high voltage method can locate any area where the coating is weaker than specified, this allows you to detect flaws that don’t go all the way down to the substrate, as well as voids within the coating.
Elcometer has two continuous DC detectors: the Elcometer 236, where the high voltage supply is generated within the instrument and sent to the probe handle via a high voltage cable; and the Elcometer 266, where the high voltage supply is generated within the handle, and connected to the instrument via a low voltage cable, resulting in a safer way to test for flaws.