A voltage withstand inspection tests a product by passing a current, determining the item as failing when a current above a certain threshold flows, and passing when a current below this threshold flows. Therefore, even if the voltage withstand tester is producing the specified voltage, a broken wire or poor contact can mean that the specified voltage is not applied to the measurement terminals, so that a current below the threshold flows and the product is incorrectly passed. The 3931 monitors the voltage on the measurement terminals, and eliminates faulty test results due to broken wires or poor contacts. It also detects a reduction in the voltage from the voltage withstand tester due to fluctuations in the power supply voltage, adding extra reliability to voltage withstand testing.

The 3931 connects directly to the HIOKI voltage withstand tester series, without any special settings. It does not support insulation resistance testing, and thus cannot be used with the 3153 and 3159 continuous testing functions (withstand voltage + insulation testing), or the 3153 programmed testing function. Since it is a dedicated unit for AC withstand voltage testing, it cannot be used in a DC voltage withstand test.

Combining the result from the 3931 with the result of the voltage withstand test provides a complete analysis of the measurement object. Since the check for broken wires and poor contacts is carried out at the same time as the voltage withstand test, the reliability of the voltage withstand test can be increased, without adding to the production cycle time.