In partial discharge detection, the unit of "apparent discharge capacity" is picoku (pC), but the instrument initially measures the amplitude of the pulse voltage, not the amount of charge. To convert voltage readings into accurate picoku values, a specialized calibration must be performed using a calibration pulse generator before the experiment. This step cannot be omitted, nor can it be performed after applying high voltage.

Why is calibration necessary

The partial discharge detection circuit consists of a test sample, coupling capacitor, input unit, cable, and detector. The signal attenuates during transmission, and different test sample capacitors, wiring methods, and cable lengths can affect the actual signal amplitude reaching the instrument. The sensitivity of the instrument (how many millivolts correspond to how many pC) varies with different circuit parameters and cannot be directly read based on factory calibration values.

The principle of correction

The JZF type calibration pulse generator can inject a standard pulse with a known precise charge amount (such as 50pC) into the test sample end. After receiving this standard pulse, the instrument adjusts the internal gain through the automatic calibration function to make the screen display exactly 50pC. Afterwards, the gain and charge conversion relationship of the entire testing circuit is determined, and the pC value read after applying high voltage is the actual apparent discharge amount.

Key operational points

The red terminal of the calibration pulse generator should be connected to the high voltage end of the test sample, and the black terminal should be connected to the low voltage end. The wire should be as short as possible to reduce the influence of parasitic parameters.

Operation steps for HZJF-9041D: Select the frequency band (fL and fH), press "coarse adjustment" to select "automatic" mode, and then press the "calibration" button. The instrument will automatically complete calibration and display the same amount as the injection.

After calibration, it must be disconnected

After calibration is completed, be sure to disconnect the connection wire between the calibration pulse generator and the test sample before applying high voltage. Direct cause: Once the high voltage of tens of kilovolts is applied along the connecting line to the calibration pulse generator, the equipment is immediately damaged. This step cannot be forgotten.