The purpose of this test is to verify the resistance to electrostatic discharge (ESD) caused by the approach or contact of objects or people or devices. Or people’s interior can accumulate electrostatic charges higher than 15kv voltage. Experience shows that many unexplained failures and damages are probably caused by ESD. Through discharging from the ESD simulator to the surface of EUT and near EUT, the test instrument (EUT) can obtain the ESD activity. The severity level of discharge is clearly defined in the product standard and EMC test plan prepared by the manufacturer. EUT checks for functional failure or interference in all its operating modes. Pass/fail criteria must be defined in the EMC test plan and determined by the manufacturer of the product.
PCB transient conductivity resistance
The purpose of this test is to verify EUT’s resistance to transient short-duration impact with fast rise time, which may be caused by inductive load or contactor. The rapid rise time and repetitive nature of the test pulse lead to these spikes easily penetrating the circuit of EUT and possibly interfering with the operation of EUT. Instantaneous permittivity directly acting on the total power supply and signal line. In other PCB immunity tests, EUT should be monitored according to the pass/fail standard using the configuration of general operation.
Anti-electromagnetic radiation of PCB
The purpose of this test is to verify the PCB anti-interference ability of the products to radios, radio transceivers, mobile GSM/AMPS phones, and various electromagnetic fields generated by industrial electromagnetic sources. If the system is not shielded, the electromagnetic radiation can be coupled on the interface cable and enter the circuit through the conductive path; Or it can be directly coupled to the wiring of the printed circuit. When the amplitude of RF electromagnetic field is large enough, the induced voltage and demodulation carrier can affect the normal operation of the device.
PCB radiation resistance test run? This test is usually the longest and most difficult to run, requiring very expensive instruments and considerable experience.Compared with other PCB immunity tests, the success / failure criteria defined by the manufacturer and the written test plan must be sent to the test room.When the EUT is sent into the radiation field, it must be set in the normal operation and the most sensitive mode.
When EUT is exposed to graded interference field with frequency exceeding the required frequency range of 80MHz to 1GHz, normal operation must be established in the test room.Some PCB anti-interference standards start at 27MHz.Severity level: this standard usually requires 1V / m, 3V / m or 10V / m for PCB immunity level.However, equipment specifications may have their own requirements for a specific “problem (interference) frequency.”.What is the appropriate level of interest for PCB manufacturers.
The new PCB immunity standard en50082-1:1997 refers to IEC / en61000-4-3.IEC / en61000-4-3 requires a unified test environment based on test samples.The test environment is implemented in an anechoic room with tiles arranged by ferrite absorbers, which are used to block reflection and resonance in order to establish a unified test site in the room.This overcomes the sudden and frequent unrepeatable test errors caused by reflections and field gradients in traditional unlined rooms.(semi anechoic room is also an ideal environment to measure the radiation emission of abnormal indoor environment.
For semi anechoic rooms, RF absorbers shall be arranged on the walls and ceiling of semi anechoic rooms.The mechanical and RF design specifications should be adapted to the heavy ferrite bricks arranged on the roof of the room.The ferrite brick is located on the dielectric material and attached to the top of the room.In the unlined room, the reflection of metal surface will lead to resonance and standing wave, which will produce wave crest and trough on the strength of test space.In a typical unlined room, the field gradient can reach 20 to 40 dB, and this will lead to sudden failure of the test sample in a very low field.Resonance in the room results in low test repeatability and a high probability of “over testing.”.The new PCB anti-interference standard iec1000-4-3, which has the same requirements on site, makes up for these serious defects.
The hardware and software of the test site require that a high-power broadband RF amplifier be used to drive a broadband transmitting antenna with a frequency range of more than 26MHz to 2GHz, which is 3 meters away from the tested equipment. Under the control of the software, the full-automatic testing and calibration can achieve the best operation, which provides greater flexibility for testing and full control of all key parameters, such as scanning rate, frequency pause time, modulation and field strength. Software hooks allow synchronization of monitoring and stimulation of EUT functionality. In the actual test, interactive functions are needed to realize the real-time change of EMC test software and EUT parameters. This user access feature allows all data to be recorded quickly, so as to effectively evaluate and evaluate the EMC performance of EUT.
Pyramid absorber The traditional pyramid (cone) absorber is effective, but the huge size of the pyramid makes it unable to be used for testing the small available space in the room. For the lower frequency of 80MHz, the length of pyramid absorber should be 100cm, while for the lower frequency of 26MHz, the length of pyramid absorber should exceed 2m. Pyramid absorbers also have disadvantages. They are fragile, easily damaged by collision, and flammable. It is also impractical to use these absorbers on the floor of a room. Because of the heat generated by the pyramid absorber, the field strength greater than 200V/m will cause a high risk of fire after it lasts for more than a period of time.
Ferrite tile absorber
Ferrite tiles are space-efficient, however, they add significant weight to the roof, walls and doors of the room, so the mechanical structure of the room becomes very important. They can work effectively at low frequencies, but when the frequency is higher than 1GHz, their work becomes relatively inefficient. The ferrite tile is very dense (100mm×100mm×6mm thick) and can withstand the field strength of over 1000V/m without the danger of fire.
Difficulties in PCB radiation resistance test Because the auxiliary equipment used to operate EUT provides stimulus signals to monitor its own performance, it must be anti-interference to the sensitive field, which is an inherent difficulty in running radiation sensitivity test. This often brings a lot of difficulties, especially when the auxiliary equipment is complicated, and many cables and interfaces connected to EUT that are perforated and run through the shielded test room are needed. All cables passing through the test room must be shielded, and/or filtered to shield them from the test field, so as to avoid lowering the shielding performance of the test room. The compromise of the shielding performance of the test room will result in the unintentional leakage of the test field to the surrounding environment, which may cause interference to spectrum users. RF filters using data or signal lines are not always feasible, such as when there is a lot of data or a high-speed data link is used.
