Thermal relay calibration is the most common application of high current testers. Many electrical maintenance engineers have to do this job every year, but those who are not familiar with the operational details often have to explore on site for a long time. Organize the complete process and follow it without any problems.

Step 1: Wiring

Disconnect the external connection of the thermal relay and connect the high current output terminal (dedicated output line with a cross-sectional area ≥ 70mm ²) of HZ-109S to the current input terminal of the thermal relay to form a complete current circuit.

Connect the action contact (normally open or normally closed, choose according to the instructions) of the thermal relay to the stopwatch input terminal on the instrument panel, and turn the stopwatch contact/potential switch to the "contact" position.

The grounding wire must be connected before all other wiring to ensure reliable grounding of the instrument.

Step 2: Set parameters

After turning on, confirm that the stopwatch mode is "dual" (default) and reset the stopwatch to zero. Based on the rated current of the tested thermal relay, estimate the required test current (usually 1.05 times, 1.2 times, 1.5 times, 7.2 times the set value, and other test points).

Step 3: Upflow

First confirm that the voltage regulating knob is in the zero position, press the "output" button (red light on), slowly rotate the regulating knob clockwise, and the I1 reading on the LCD screen gradually increases, raising the current to the target test value.

Do not increase the current speed too fast - especially when testing the 1.2x action characteristics (inverse time zone), it is necessary to first stabilize at the target value, wait for the thermal relay to naturally operate, and record the action time. Excessive flow can cause a rapid increase in the internal temperature of the instrument, shortening the duration of a single continuous operation.

Step 4: Wait for action and reading

After the current stabilizes, the stopwatch on the screen starts counting from 0. After the thermal relay is activated (contact closed), the stopwatch automatically stops and reads the action time. At the same time, the screen displays the measured current I1 (to confirm whether it is accurately maintained at the target value).

Step 5: Stop outputting

After reading, first turn the pressure regulating knob counterclockwise back to zero, then press the "Output" button to stop the output, and finally press "Reset" to reset the stopwatch, ready for the next test.

The output cannot be stopped by turning off the power supply directly, so that the voltage regulator may not be at zero after the next startup, and current impact will occur when re output.

Cooling interval

If the last output time is long, the instrument must be cooled for more than 10 minutes before proceeding to the next test.