Immunity to interference of the isolator

 Anti-interference design of power supply system The most serious harm to the normal operation of sensors and instruments is the power grid peak pulse interference, and the electrical equipment that produces peak interference includes: electric welding machine, large motor, controllable machine, relay contactor, inflatable lighting with ballast, etc. Spike interference can be suppressed by a combination of hardware and software.

Interference controller
(1) Use hardware lines to suppress the effects of spike interference. There are three main methods: (1) the interference controller designed according to the principle of spectrum equalization is connected to the AC power input of the instrument, and the energy concentrated by the peak voltage is distributed to different frequency bands, thereby reducing its destructiveness; (2) Add a super isolation transformer to the AC power input of the instrument, and use the ferromagnetic resonance principle to suppress the spike pulse; (3) Connect varistors in parallel at the input end of the AC power supply of the instrument, and reduce the resistance value when the spike pulse arrives to reduce the voltage distributed by the instrument from the power supply, thereby weakening the influence of interference.

(2) Use software methods to suppress spike interference. For periodic interference, time filtering can be programmed for time filtering, that is, the program is used to control the thyristor to turn on instantaneously without sampling, thereby effectively eliminating interference.

(3) The watchdog technology combined with hardware and software is used to suppress the influence of spikes. Software: Before the timer is timed, the CPU accesses the timer once, let the timer restart the timekeeping, the normal program runs, the timer does not generate overflow pulses, and the watchdog will not work. Once the spike interference appears "flying program", the CPU will not access the timer before the timing is reached, so the timing signal will appear, causing the system reset to interrupt and ensure that the smart instrument returns to the normal program.

(4) Implement power group power supply, for example: separate the drive power supply of the actuator motor from the control power supply to prevent interference between equipment.

(5) The use of noise filters can also effectively suppress the interference of AC servo drives to other equipment. This measure can effectively suppress the above interference phenomena.

(6) Isolation transformer is adopted. Considering that the high-frequency noise through the transformer is not mainly coupled by the mutual inductance of the primary and secondary coils, but by the primary and secondary parasitic capacitance, the primary and secondary of the isolation transformer are isolated with a shielding layer to reduce their distributed capacitance to improve the resistance to common-mode interference.

(7) Power supplies with high anti-interference performance, such as high anti-interference power supplies designed by spectrum equalization. This power supply is very effective against random interference, it can convert the high spike disturbance voltage pulse into a low voltage peak (voltage peak is less than TTL level) voltage, but the energy of the interference pulse remains unchanged, which can improve the anti-interference ability of sensors and instruments.