On what principle does the low voltage wet sponge unit operate?
A1. The low voltage instrument employs a cellulose sponge as an inspection electrode. When moistened with water, the electrode is moved over the coated surface under inspection; when the electrode passes a void or bare spot, moisture from the wet sponge (electrode) penetrates the coating making contact with the conductive substrate, resulting in a drop in electrical resistance. As a result, a small current flow activates an audible alarm enabling identification of the defect location.
