The instrument ZEH 634 is used for testing Thyristors.

The trigger characteristics of the gate, the latching current and the holding current in the anode circuit are measured:

1. Gate Trigger test

Two methods are available, to determine the lowest gate current:

a. Approximation method (similar to successive approximation): The gate trigger current is converged gradually towards the necessarily lowest gate trigger current. The duration of the gate pulse is 400 µs at a time, the pulses are repeated every millisecond.

b. Gate current ramp function: The gate current is increased at constant speed until the ignition takes place.

2. Latching current test

The standard procedure according to DIN IEC 747 intends a repetition of ignitions with a rising anode current until the latching current is reached. Similar to the ignition test, the ZEH 634 optimizes the measurement duration using an approximate procedure.

3. Holding current test

During the holding current test, the anode current is lowered continuously until the current breaks. The result depends in most cases on the rate of change of the anode current.