What is a pinhole detector?
A pinhole detector is a non-destructive instrument for detecting discontinuities in a coating system including pinholes, cracks and thin spots. Other names include porosity detector, continuity tester, sponge tester and holiday detector.
Low voltage detectors, like the PosiTest LPD, are typically used on coating systems less than 500 µm (20 mils) thick.
What is measured?
A low-voltage pinhole test is performed by moving a moistened, electrified sponge over a non-conductive coating applied to a conductive substrate. The instrument is ‘grounded’ or ‘earthed’ to the conductive substrate, typically by clamping onto an uncoated area.
When the coating is continuous and no defects are present, electricity is unable to pass from the sponge to the substrate through the non-conductive coating. But when the electrified sponge encounters a flaw in the coating, electricity is able to flow into the substrate and travel back to the instrument through the ground wire, completing the circuit and setting off the audible and visible alarms.