There are essentially two high voltage direct current (or DC) technologies used for testing a coating’s porosity – Continuous DC and Pulsed DC.

Continuous DC is where you set the voltage to a constant value, usually determined by the specified coating thickness, and a signal return cable is clipped directly to an uncoated section of the substrate under test. During the test, the voltage is constantly sent to the probe, and the current at the probe is low. But, when a flaw is located a spike in the current is created, which is then detected by the unit as a break down in the coating. This in turn triggers the unit's alarm.

Continuous DC, or DC units as they are commonly called, are typically used to test insulation coatings on conductive substrates up to 7.5mm (300mils) thick.

Whilst typically you still set a Pulsed DC unit to a voltage determined by the specified coating thickness, unlike the Continuous DC method, the voltage on Pulsed DC units is actually rapidly switching between 0 and the voltage you’ve set, typically at speeds of 30 pulses per second (30 Hz).

This pulsing voltage not only allows you to test non-conductive coatings up to 25mm (1”) thick on conductive substrates, but as the pulsing energy stops the probe from building up a charge on the surface, Pulsed DC units allow you to safely test for flaws on damp, dirty, or slightly conductive coatings, making it the ideal method for testing structures in-situ.

Additionally, as you are effectively applying a pulsing voltage between 0 and the applied voltage, Pulsed DC units such as the Elcometer 280 can be used with a trailing earth cable which doesn’t have to be connected to the substrate, making it perfect for quickly testing large surfaces and pipelines, without constantly having to clip and unclip the return lead every time the length runs out.

The Elcometer 280 makes working out your test voltage easier than ever before, with its in-built voltage calculator. Simply choose your test standard, enter the specified coating thickness, and gauge will automatically calculate and set the correct voltage.

Furthermore, the Elcometer 280 has an internal jeep tester, ensuring your chosen voltage matches your actual test voltage.

To ensure safe testing, voltage isn’t sent to the probe until the two-stage safety switch is activated, which avoids accidental switch-on, and automatically cuts power to the probe should you lose grip of the handle.