As the dependence of the microcomputer is increasing, the massive use of equipment, complexity of our electromagnetic environment, so external interference such as impulse noise, radiation electromagnetic fields, static electricity, lightning, voltage variations, etc., triggered by the malfunction produced by the machine or even the destruction of the situation, such as radio communications, radar, big brother, TV, musical instruments, etc., often interfere with the TV, and even cause the use of medical equipment in the use of malfunction affecting the safety of flight. The new technology is designed to provide a high level of performance and reliability, and is designed to meet the demands of the market.
Internationally, for electronic, electrical, industrial equipment products, immunity testing has become increasingly important, and tends to integrate the IEC (InternationalElectrotechnicalCommission) international specifications for the test standard, the European **** the same body to take the lead in the development of EMC prevention and control regulations in 1996, the full implementation of immunity testing. Three-phase into the power supply in the NFB (no fuse circuit breaker) and transformer installed between the noise filter (NoiseFilter), the filter's input line the shorter the better.
Power and high-current wires are routed close to the bottom of the electrical box and along the corners.
Switching power supplies are equipped with isolation shields to prevent radiated emissions. Filter selectors use π-type or T-type filters to suppress wide-band noise, and ceramic ferromagnets (Ferrite) are used to suppress radio frequency noise.
The two ends of the power supply line are isolated and grounded to prevent the GroundLoop from forming a common impedance coupling (CommonImpedanceCoupling) that couples noise to the signal line.
The power and signal lines are isolated or wired separately as much as possible.
Power transformer should be isolated (Shielding), the shell must be well grounded.
Single-phase AC control wires are recommended to be stranded.
Stranded wire is recommended for wiring DC leads.
Avoid connecting power and signal wires to the same connector. Signal input and output wires should be avoided to line up together to cause interference.
The remaining CABLE wires should be grounded at one end to avoid an inductive loop.
Consider twisting the signal wires close to the power supply.
The signal lines of different categories should not be mixed in one connector, and should be categorized by category and isolated by ground.
Input signal lines and output lines try to avoid the same in a connector, such as can not be avoided when the input and output signals should be staggered.
Higher sensitivity of the low signal line, in addition to the use of stranded wire can be added to isolate the mask. High frequency analog signal and pulse signal line is recommended to use isolation line.
High-frequency analog signal line using coaxial isolation line, low-frequency analog signal line using stranded wire, if necessary, can be added to the isolation mask, never use coaxial isolation line.
Connector mounting position must be cleaned, connectors and metal surface contact resistance must be less than 2.5m ohms.
The analog circuit interference to the waveform distortion-based, suppression methods are mainly in the filter selected characteristics, such as; bandwidth, frequency response value.
The analog signal line and the digital line must be perpendicular to each other. Avoid the use of unisolated shielded wires to transmit digital signals, it is advisable to use multi-stranded stranded wires plus isolation wires.
Digital circuit interference with external magnetic interference, should be added isolation measures.
Digital circuits are susceptible to high-energy electric field interference, and must be isolated by using an isolation line to prevent high-energy electric field interference of 200V/m in the 1?10MHz band as the best isolation option.
Digital circuits are designed to suppress the pulses and spikes of neighboring circuits.
Digital circuits are designed to avoid the use of long, un-isolated wires. Interference circuits, such as clock pulses, actuators, switching power supply ON and OFF, and oscillator-type control signals, should be isolated and shielded.
The PCB circuit design of the various types of low-noise components as far as possible, and must take into account the relationship between noise changes and ambient temperature changes.
The Ferritecore is suitable for high-frequency filtering, but attention should be paid to the load power loss through this coil.
The regulator must consider the suppression of inter-line **** pass impedance coupling (CommonImpedanceCoupling) EMI problems.
The oscillator itself, the smaller the better, such as the need for a larger output, it is appropriate to be amplified by the amplifier.
Power amplification should be isolated to prevent radiated emissions.
Electrolytic capacitors are suitable for removing high ripple and transient voltage variations.
Power line disturbances include low voltage (or instantaneous power failure) overvoltage and surges, which usually come from the operation of power switches, the instant of switching on and off of heavy loads, the operation of power semiconductors, the blowing of fuses, and lightning inductance...etc. These disturbances are often caused by the operation of power switches, the instant of turning heavy loads on and off, the operation of power semiconductors, the blowing of fuses, and lightning inductance.
The following items should be considered for suppression:
Use of power filters.
Appropriate power distribution.
Conversion of the interfering device to another circuit.
Packaging electronic parts and filters appropriately.
Use an isolation transformer.
Device a varistor.
AC solenoid contactor coils and solenoid valves must be connected to a spark arrestor.
The output side of the thermoelectric stage of the solenoid switch must be connected to a three-phase spark arrestor.
The DC relay coil should be connected with diode for reverse voltage protection.
The closer the spark arrestor is to the load side, the better.
Installing a surge absorber between circuit switches and noise filters, between wires, and between wires and ground will effectively absorb surges.