RC filter
When the signal source is the sensor whose signal changes slowly, such as thermocouple and strain gauge, the use of small size and low cost passive Rc filter will have a better suppression effect on serial-mode interference. However, it should be mentioned that Rc filters reduce serial-mode interference at the expense of system response speed.
Ac power filter
The power supply network absorbs a variety of high and low frequency noise, for which Lc filters are commonly used to suppress the noise mixed with the power supply.
Dc power filter
The DC power supply is often shared by several circuits, in order to avoid interference between several circuits through the internal resistance of the power supply, Rc or Lc decoupling filter should be added to the DC power supply of each circuit to filter out low-frequency noise.
Photocoupling technique
Photoelectric coupler is a kind of electric-optical coupler, it is composed of light-emitting diode and phototriode package, its input and output are electrically insulated, so this device in addition to photoelectric control, is now more and more used to improve the system's resistance to common mode interference capability. When a driving current flows through the light-emitting diode in the photocoupler, the phototriode is saturated with light. Its emitter output high level, so as to achieve the purpose of signal transmission. So even if there is interference in the input loop. As long as it is within the threshold, it will not affect the output.
Noise suppression in pulse circuits
If there is interference noise in the pulse circuit. The input pulse can be differentiated and then integrated, and then set a threshold voltage of a certain amplitude, so that the signal less than the threshold voltage is filtered out. Analog signals can be converted using A/D first. The noise is then filtered out in this way.
The use of these anti-interference technologies should be selected according to the actual situation. It must not be used blindly, otherwise it will not only fail to achieve the purpose of anti-interference, but also may have other adverse effects.
