Calibrating the open circuit output voltage of a surge generator using the P6015A probe

The surge generator is an important instrument used in electromagnetic compatibility and anti-interference tests. It consists of a DC voltage generator, a discharge switch, and a waveform network. It is mainly used to simulate the impact of surges propagating along the power grid on electronic instruments and equipment, and to examine the ability of the tested electronic instruments and equipment to resist surges. The calibration of the surge generator is based on the provisions of GB/T 17626.5-1999, mainly calibrating the two parameters of the surge generator open-circuit output voltage and short-circuit output current. This article mainly discusses the use of the P6015A probe to calibrate the open-circuit output voltage of the surge generator.

1 Technical parameters of open circuit output voltage of surge generator

When calibrating the open-circuit output voltage of the surge generator, the open-circuit output voltage pulse wavefront time T1 and the open-circuit output voltage pulse half-slope time T2 can be calibrated at the same time. The typical 1.2/50μs open-circuit voltage waveform technical parameters are as follows:

Open circuit output voltage: (0.5～4.0)kV±10％; open circuit output voltage pulse wavefront time: 1.2μs±30％; open circuit output voltage pulse half slope time: 50μs±20％; polarity: positive polarity, negative polarity; equivalent output impedance: 2Ω.

The 1.2/50 μs open circuit voltage waveform is shown in Figure 1.

2 Calibration method

According to the requirements of GB/T 17626.5-1999, the open-circuit load of the surge generator must be greater than or equal to 10 kΩ. Therefore, TEK's P6015A probe and DPO4104 digital oscilloscope are selected to calibrate the open-circuit output voltage of the surge generator.

P6015A is a high-voltage probe with an attenuation ratio of 1 000:1. It consists of a high-voltage probe and a compensation box. The probe, compensation box and connecting wires use equipotential shielding technology, which has the characteristics of good linearity, strong anti-interference ability and stable performance. It can be used with an oscilloscope (impedance must be set to 1 MΩ, P6015A circuit design requirements) to measure AC and DC voltages and pulse peak voltages. Main technical indicators: input impedance is 100 MΩ, impedance accuracy is ±2%, input capacitance is less than or equal to 3 pF, DC voltage measurement is up to 20 kV, pulse voltage measurement is up to 40 kV, bandwidth is 75 MHz, rise time is no more than 4.67 ns, and as a standard instrument, it can meet the calibration technical requirements.

The open circuit voltage connection diagram of the P6015A calibrated surge generator is shown in Figure 2.

Steps:

(1) Set the impedance of the DPO4104 digital oscilloscope to 1 MΩ and connect it to the output of the P6015A high-voltage probe. Then connect the "high end" of the generator output to the "high end" of the P6015A high-voltage probe input, and connect the "low end" of the generator output to the "low end" of the P6015A high-voltage probe input.

(2) Set the generator voltage polarity and calibration points (e.g., ±160 V, ±500 V, ±1 000 V, ±2 000 V, ±3 000 V, ±4 000 V). The vertical sensitivity of the oscilloscope varies with the calibration points. Adjust the time slot and trigger mode so that the waveform occupies about 80% of the screen. Record the measurement data and save the waveform graphs at different points to complete all calibration points.

(3) When measuring the pulse wavefront time T1 of the open-circuit output voltage of the generator, the connection is as shown in Figure 2. It can be calibrated together with the open-circuit voltage peak value. Set the oscilloscope scanning time to an appropriate gear and use the cursor to measure the pulse wavefront time (30% to 90%) T. Use the formula: T1=1.67×T (as specified in GB/T17626.5-1999) to calculate the T1 value corresponding to each voltage point.

(4) When measuring the half-slope time T2 of the generator open-circuit output voltage pulse, connect as shown in Figure 2. It can be calibrated together with the open-circuit voltage peak value. Set the oscilloscope scanning time to an appropriate gear and use the cursor to measure the T2 value corresponding to each voltage point.

3 Uncertainty analysis

The open-circuit output voltage of the UCS500M4 simulator surge generator was measured using a P6015A high-voltage probe and a DPO4104 digital oscilloscope. Taking the 1 000 V voltage point as an example, the measurement was repeated 10 times. The measurement results are shown in Table 2.

Uncertainty evaluation of the open-circuit output voltage of the generator. The measurement uncertainty consists of Class A and Class B:

4. Notes on calibration

The following issues should be noted during calibration:

(1) The P6015A probe compensation box cannot be adjusted at will to ensure that the parameters of the probe remain unchanged;

(2) When using P6015A, the ground wire must be connected properly to ensure the safety of the instrument and personnel;

(3) P6015A use time: When used for a long time (≥30 min) at a temperature of 0 to 35°C, the upper limit of the measurement voltage is 14 kV; when used for a short time (<30 min), the upper limit of the measurement voltage is 20 kV. Otherwise, the output attenuation ratio may change significantly due to the increase in temperature, and even have an adverse effect on the insulation performance of the high-voltage probe.

5 Conclusion

The open-circuit output voltage, pulse wavefront time and half-slope time of the open-circuit output voltage pulse of the surge generator are calibrated using the TEK company's P6015A high-voltage probe and digital oscilloscope DPO4104, ensuring the accuracy and reliability of the performance parameters of the surge generator. It can be widely used in measurement work.