Anti-jamming measures for analog sensors - Solutions - Huaqiang

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1. Anti-interference design of power supply system The most serious hazard to the normal operation of sensors and instruments is the power grid spike interference. The power equipment that produces spike interference is: electric welder, large motor, controllable machine, relay contactor, belt Inflatable lights for ballasts, even electric irons. Spike interference can be suppressed by a combination of hardware and software.
(1) There are three main methods for suppressing the influence of spike interference by hardware lines:
1 Intervene the interference controller designed according to the principle of spectrum equalization at the input end of the AC power supply of the instrument, and distribute the energy concentrated by the peak voltage to different frequency bands, thereby reducing its destructiveness;
2 Add a super isolation transformer at the input end of the AC power supply of the instrument to suppress the spikes by the principle of ferromagnetic resonance;
3 Parallel varistor at the input of the AC power supply of the instrument. When the spike is applied, the resistance value is reduced to reduce the voltage of the instrument from the power supply, thus weakening the influence of interference.
(2) Using software method to suppress spike interference For periodic interference, time filtering can be performed by programming, that is, the program can be used to control the thyristor conduction without instantaneous sampling, thereby effectively eliminating interference.
(3) Using a hard and software-linked watchdog technique to suppress the effects of spikes. Software: Before the timer expires, the CPU accesses the timer once, letting the timer restart, and the normal program runs. There will be no overflow pulses and the watchdog will not work. Once the "flying program" occurs in the spike interference, the CPU will not access the timer before the timing is reached, and the timing signal will appear, causing a system reset interrupt to ensure that the smart instrument returns to the normal program.
(4) Implement power supply grouping, for example, separate the driving power of the executing motor from the control power supply to prevent interference between devices.
(5) The noise filter can also effectively suppress the interference of the AC servo drive to other devices. This measure can effectively suppress the above several interference phenomena.
(6) The use of an isolation transformer takes into account the high-frequency noise. The transformer is mainly not based on the mutual inductance coupling of the primary and secondary coils, but is coupled by the primary and secondary parasitic capacitances. Therefore, the shielding between the primary and secondary of the isolation transformer is shielded. Layer isolation reduces its distributed capacitance to improve resistance to common mode interference.
(7) Power supplies with high anti-interference performance, such as high anti-interference power supplies designed by spectrum equalization method. This kind of power supply is very effective against random interference. It can convert the high-peak disturbance voltage pulse into a low-voltage peak (voltage peak is less than TTL level), but the energy of the interference pulse is constant, which can improve the sensor and instrumentation. Anti-interference ability.
2. Anti-interference design of signal transmission channel (1) Optocoupler isolation measure In the long-distance transmission process, the optocoupler can be used to cut off the input and output channels of the control system and the input channel, output channel and servo driver. Contact. If opto-isolation is not used in the circuit, external spikes will enter the system or go directly into the servo drive, creating the first type of interference.
The main advantage of optoelectronic coupling is that it can effectively suppress spikes and various noise interferences, and greatly improve the signal-to-noise ratio of the signal transmission process. Although the interference noise has a large voltage amplitude, the energy is very small, and only a weak current can be formed, and the light-emitting diode of the input part of the optocoupler operates in a current state, and the general on-current is 10 mA to 15 mA, so even if there is Very large interference, which can also be suppressed by not providing enough current.
(2) The long-distance transmission signal of the twisted-pair shielded wire is affected by the interference factors such as electric field, magnetic field and ground impedance during transmission. The grounding shielded wire can reduce the interference of the electric field. Compared with the coaxial cable, the twisted pair has a high frequency band, but has high wave impedance and strong anti-common mode noise, which can cancel the electromagnetic induction interference of each small link. In addition, in the long-distance transmission process, differential signal transmission is generally adopted, which can improve anti-interference performance. Long-distance transmission with twisted-pair shielded wires can effectively suppress the generation of (2), (3), and (4) interferences in the interference phenomenon mentioned above.
3. Elimination of local error. In low-level measurement, strict attention must be paid to the material used in the signal path. The solder, wires, and terminals encountered in a simple circuit may be Produce the actual thermoelectric potential. Since they often appear in pairs, it is very effective to keep these pairs of thermocouples at the same temperature. For this reason, heat shields, heat sinks are arranged along the isotherms or high power circuits and low power are used. Circuit separation, etc., the purpose is to minimize the thermal gradient. The junction of two standard manufacturers (such as nickel-chromium-constantan) can produce a temperature drift of 0.2mV/°C, which is equivalent to high-precision and low-drift. The temperature drift of the op amp (OP·27CP) is twice the temperature drift of the chopper amplifier (7650CPA). Although the use of socket switches, connectors, relays, etc. can make it easier to replace electrical components or components, the disadvantage is that contact resistance, thermoelectric potential, or both may occur, at the expense of increasing the resolution of the low level. Stability, that is to say it is worse than the direct connection system, low precision, increased noise, and reduced reliability. Therefore, it is an important measure to reduce the number of faults and improve the accuracy by using switches and connectors as much as possible in low-level amplification.