High current injection test method_Century Wisdom (Suzhou) Testing Technology Co., Ltd

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High current injection test method

Release time:

2022-07-29 00:00

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　　1 Introduction

　　In recent years, with the development of automobiles in the direction of electrification, intelligence and networking, more and more electronic devices are integrated in the limited space of automobiles, and these electronic devices also bring more and more electromagnetic compatibility problems. In order to deal with electromagnetic compatibility problems, electronic components must be tested for electromagnetic compatibility before they are installed on the vehicle. Among them, the Bulk Current Injection (BCI) method only needs to be carried out in a shielded room, and the cost is much lower than that of the radiation immunity that must be carried out in an anechoic chamber. At the same time, it does not invade the device under test, so it has become the first choice for electronic component verification. Required method. The large current injection (BCI) method is a method of using a current injection probe to directly couple the disturbance signal to the wiring harness for immunity testing. The injection probe is a current transformer through which the wiring harness of the equipment under test (EUT) is passed. The immunity test is carried out by changing the severity level of the test and the frequency of the induced disturbance.

　　2. High current injection test method

　　The test method for immunity test using the large current injection method is generally divided into substitution method and closed-loop method.

　　The substitution method means that after using the current injection clamp calibration device to obtain the signal source level corresponding to the corresponding test level, the signal source level is directly output during the test. It is required to place injection clamps at three positions 150mm, 450mm and 750mm away from the EUT for testing. As shown in Figure 1.

Figure 1 BCI trial layout - alternative method

　　The closed-loop method refers to: after using the current injection clamp calibration device to obtain the signal source level corresponding to the corresponding test level (record the net power at this time as the calibration power), use the current probe to monitor the actual injected current during the test. The power is 4 times greater than the calibration power, and the measured injection current still does not reach the current specified in the standard, so stop increasing the injection power. It is required that the injection clamp be placed at a distance of 900mm from the EUT, and the current probe at a distance of 50mm. As shown in Figure 2.

Figure 2 BCI test layout - closed loop method

　　The substitution method and the closed-loop method have the following differences:

　　A, the length of the test harness for the alternative method is 1700mm, and the length of the test harness for the closed-loop method is 1000mm;

　　B, The current injection position of the substitution method is 150mm, 450mm, 750mm, while the current injection position of the closed-loop method is 900mm;

　　C, the closed-loop method must use a current monitoring probe, the probe is located at 50mm, and the current monitoring probe is generally not used in the substitution method test;

　　D, The substitution method is an open-loop test based on a given injection power, while the closed-loop method is a closed-loop test that is monitored in real time by a current monitoring probe.

　　3 Test device

　　The test needs to be carried out in a shielded room, and the main test equipment required are: signal source (with modulation function), power amplifier, power meter, artificial power network, current injection probe, current injection probe calibration fixture, current monitoring probe, etc. Figure 3 is a block diagram of the test system connection.

Figure 3 BCI test system connection block diagram

　　4 Test arrangement

　　In the layout of the test platform, the equipment under test and the wiring harness are placed 50mm above the ground plane. The ground plane should be made of copper, brass or galvanized steel with a thickness of at least 0.5mm. The minimum width is 1000mm, the minimum length is 2000mm, or 200mm larger than the sides of the entire device, whichever is larger. The height of the grounding plane (test bench) should be located at (900±100) mm above the ground, the grounding plane is electrically lapped with the shielding shell, the distance between the grounding copper strips is 300mm, and the DC resistance shall not exceed 2.5mΩ. The material with a thickness of 50mm and a relative dielectric constant (≤ 1.4) is used as a support between the wiring harness and the copper plate. The power supply supplies power to the device under test through two artificial source networks, one of which is connected to the positive pole of the power supply and the other is connected to the negative pole of the power supply. Figure 4 and Figure 5 are the layout of the test.

Figure 4 Test arrangement - side view

Figure 5 Test Layout - Top View

　　5 Test process

　　5.1 Alternative method test process

　　An alternative method uses forward power as a reference for calibration and testing, using an unmodulated sine wave for calibration.

　　5.1.1 Calibration

　　Calibrate according to the specified test level (current), and record the forward power required to produce the specified current on the 50Ω calibration fixture at each test frequency. One end of the calibration fixture is connected to a 50Ω load (high power), the other end is connected to a 50Ω RF power meter, and a 50Ω attenuator of corresponding power is connected in series to protect the power meter. Apply a test signal level to the fixture and record the corresponding forward power. This method calibrates the relationship between the predetermined power and current of the large current injection system before the test. As shown in Figure 6.

Figure 6 Alternative Method Calibration Arrangement

　　5.1.2 Testing

　　When testing the EUT after the wiring harness is connected, a predetermined power is applied to the injection probe. It should be noted that the monitored power for injection into the probe is a predetermined power. The test setup is shown in Figure 1.

　　5.2 Closed-loop test process

　　The closed-loop method uses forward power as a reference for calibration and testing, and uses an unmodulated sine wave for calibration.

　　5.2.1 Calibration

　　Used to determine the power limit for EUT testing. Calibrate before the test according to the specified test level (current), and determine the forward power required to generate the specified current on the 50Ω calibration fixture for each test frequency. One end of the calibration fixture is connected to a 50Ω load (high power), the other end is connected to a 50Ω RF power meter, and a 50Ω attenuator of corresponding power is connected in series to protect the power meter. Apply a test signal level to the fixture and record the corresponding forward power. This method calibrates the relationship between the predetermined power and current of the large current injection system before the test. As shown in Figure 6.

　　5.2.2 Testing

　　During the test, use a current probe to monitor the actual injected current. If the injected power is 4 times greater than the calibrated power and the measured injected current still does not reach the current specified in the standard, stop increasing the injected power. The test layout is shown in Figure 2.

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