Calibration Method of Electrostatic Discharge Simulator_Century Wisdom (Suzhou) Testing Technology Co., Ltd

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Calibration Method of Electrostatic Discharge Simulator

Release time:

2023-03-13 15:12

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　　Calibration Method of Electrostatic Discharge Simulator

　　1. Preface

This article mainly introduces the use, structure, measurement characteristics, calibration conditions, calibration items and calibration methods of electrostatic discharge simulator. It is written with reference to GB/T 17626.2-2018/IEC61000-4-2:2008 and can be used during verification or calibration by measurement institutions during electrostatic discharge simulator in EMC laboratory.

　　2. Overview of Electrostatic Discharge Simulator

　　2.1 Uses

It is mainly used to simulate the electrostatic discharge of the human body or object to adjacent electrical and electronic equipment to evaluate the performance of electrical and electronic equipment when subjected to electrostatic discharge.

　　2.2 structure

The main parts include:

----- Charging resistor Rc ----- Discharge switch

----- Energy storage capacitor Cs ----- Replaceable discharge electrode head

----- distributed capacitance Cd ----- discharge loop cable

----- Discharge resistor Rd ----- Charge switch

----- Voltage indicator ----- Power supply unit

Fig.1 Diagram of electrostatic discharge simulator

　　2.3 real figure

The electrostatic discharge simulator used in the laboratory of our company (Century Huize) is the Swiss EMTEST brand NX30. The contact discharge and air discharge voltages can reach 30kV, and it is equipped with four modules to meet the testing requirements of civilian products and automotive electronics.

Fig. 2 Electrostatic Discharge Simulator (NX30)

　　3. Measurement characteristics

　　3.1 output voltage

Output voltage: 1kV ~ 15kV, allowable output voltage value ± 5%, output voltage polarity can be positive or negative polarity.

　　3.2 contact discharge current

The waveform of contact discharge current is consistent with fig. 3. the parameters of only single module 150pF/330Ω are shown in table 1 for civil product testing. the parameters of four modules required for automotive electronic testing can refer to the standard GB/T 19951-2019/ISO 10605:2008.

Fig.3 Contact discharge current waveform

Table 1 Waveform parameters

　　4. Calibration conditions

　　4.1 environmental conditions

4.1.1 Temperature: 15 ℃ ~ 35 ℃

4.1.2 Relative humidity: 30% ~ 60%

4.1.3 No electromagnetic interference and mechanical vibration affecting the normal calibration work around

　　4. 2 Equipment for calibration

4.2.1 High-voltage meter or single instrument or combination of multiple instruments with similar functions and indicators, such as the combination of high-voltage attenuator and oscilloscope or DC voltmeter, electrostatic voltmeter can also be used. (See Fig. 4 for high pressure table)

Range: ≥ 15kV;

Input impedance: ≥ 1GΩ.

Fig. 4 High Pressure Meter

4.2.2 High-speed oscilloscope or a single instrument or a combination of multiple instruments with similar functions and indicators. (See Fig. 5 for 2GHz oscilloscope)

Analog bandwidth: ≥ 2GHz

Figure 5 Tektronix 2GHz Oscilloscope MSO54

4.2.3 Electrostatic discharge target (see Fig. 6)

Electrostatic discharge targets shall comply with the requirements of IEC 61000-4-2:2008 Appendix. The electrostatic discharge target shall be fitted with an appropriate attenuator and cable for connection to the oscilloscope. The low frequency transfer impedance of the ESD target-attenuator-cable link shall be calibrated. Bandwidth of electrostatic discharge target-attenuator-cable link: ≥ 4GHz.

The change in the insertion loss of the ESD target-attenuator-cable link shall not exceed:

　　±0.5dB,<1GHz ;

　　±1.2dB,1GHz~4GHz。

Figure 6 Electrostatic Discharge Target (CTR2)

　　4.2.4 The size of the front panel used to install the electrostatic discharge target shall be at least 1.2m × 1.2m, and the edge from the center of the target to the plane of the front panel shall be at least 0.6m (see Figure 7). After the oscilloscope is placed on the front panel, ensure that the calibration system has sufficient interference immunity.

Note: If it can be proved by measurement that the direct coupling path to the measurement system does not affect the calibration results, then the oscilloscope may not need to be shielded. If the oscilloscope is not triggered in the following situations, then the calibration system can be considered to have sufficient immunity to interference, without the need for a shielded room or Faraday cage.

Figure 7 Electrostatic Discharge Target Mounting Plate

The electrostatic discharge target mounting plate designed by our company (Century Huize) can meet the calibration requirements and can replace Faraday cage when transported with light weight.

　　5. Calibration Items and Calibration Methods

　　5.1 output voltage calibration

Output voltage calibration is shown in Figure 8. The electrostatic discharge simulator operates in contact discharge mode or air discharge mode. Connect the discharge electrode of the electrostatic discharge simulator to the input of the high voltage meter. Measure the open circuit output voltage at different set voltages.

Figure 8 Output voltage calibration

　　5.2 Contact Discharge Current Calibration

5.2.1 Contact discharge current calibration arrangement is shown in Fig. 9

Fig. 9 Contact Discharge Current Calibration Layout

The electrostatic discharge target must be installed in the center of a vertical alignment plane that meets the requirements of Figure 7. At least 0.6m from the center of the target to the edge of the plane. The ground wire of the electrostatic discharge simulator should be connected to the terminal at the bottom center of the target plane 0.5m below the target. It should be pulled back from the middle of the ground wire to form an isosceles triangle. During the calibration process, it is not allowed to place the ground wire on the floor.

During calibration, the electrostatic discharge simulator is mounted on a tripod or equivalent non-metallic low-loss support.

When performing contact discharge, the discharge electrode of the electrostatic discharge simulator should be perpendicular to the electrostatic discharge target plane.

5.2.2 Electrostatic Discharge Simulator and Oscilloscope Setup

The electrostatic discharge simulator operates in contact discharge mode. Set the voltage to ± 2kV,± 4kV,± 6kV and ± 8kV respectively, set the oscilloscope impedance to 50Ω, set the oscilloscope to an appropriate range and trigger mode that can observe the complete waveform of the electrostatic discharge current (set the oscilloscope according to the technical specifications of the electrostatic discharge target), and set the horizontal time axis of the oscilloscope to 10ns/div. At each voltage level, perform 5 contact discharges on the electrostatic discharge target, and record the discharge current waveform with an oscilloscope as described in 5.2.3 to 5.2.6.

The electrostatic target used by our company (Century Huize) is CTR2 (see Figure 6), and the technical indicators are shown in Table 2.

Table 2 Technical specifications of electrostatic discharge target CTR2

Case analysis:

For example, when calibrating the 2kV contact discharge current, set the impedance of the oscilloscope to 50Ω, estimate the waveform display value of the oscilloscope, and set the vertical amplitude mV/div of each frame of the oscilloscope:

Estimated oscilloscope display voltage value Vm = 2kV peak current nominal value 7.5A * electrostatic target transfer impedance 0.2Ω = 1.5V, because the oscilloscope vertical amplitude display range is 8 cells, so the vertical amplitude is set to 200 mV/div per cell.

Apply a 2kV voltage to the electrostatic target, read the actual voltage value Vm displayed by the oscilloscope, and calculate the peak current I:

Peak current I = actual display voltage value Vm÷ electrostatic target transfer impedance Zsys

5.2.3 First peak current measurement

According to the current waveform collected by the oscilloscope, the value of the first peak voltage is recorded, and the current value is obtained by dividing the voltage value by the transfer impedance of the electrostatic target.

5.2.4 30ns and 60ns current measurement

According to the current waveform collected by the oscilloscope, the voltage values after 30ns and 60ns are recorded respectively at the point when the first peak value is 10% as the time starting point, and the current value is obtained by dividing the voltage value by the transfer impedance of the electrostatic target.

5.2.5 Current rise time measurement

According to the current waveform collected by the oscilloscope, the interval time from 10% to 90% of the first peak value is recorded as the rise time.

5.2.6 Discharge current waveform

Can save the oscilloscope collected current waveform.

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