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2021/10/13

What interference does the outside world have on the sensor's transmission signal?

In the field of sensors, everyone must be very familiar with analog sensors and switch sensors. After all, in the control system, whether it is signal input or output, a parameter is either an analog quantity or a switch quantity.

The switch signal is a discontinuous signal, and only has two states, such as the on and off of the switch, the on and off of the relay, the on and off of the solenoid valve, etc. Because the signal transmission is single and does not need to be continuously uploaded, so external factors The interference to the signal transmission of the switch sensor is small. The analog signal transmission is more complicated and more susceptible to external influences, so the following will focus on the interference of the external world to the analog sensor transmission signal.

The analog sensor is different from the switch sensor. The signal transmitted by the analog sensor is a continuous signal (the independent variable has a defined signal in the entire continuous time range is a time continuous signal or a continuous time signal, referred to as continuous signal), through voltage, Current, resistance, etc. indicate the size of the parameter. It should be noted that the continuous signal refers to time continuous, that is, the signal transmission of the analog sensor can be discontinuous, but the recording time must be continuous.

External interference that affects the analog sensor

According to the different application scenarios of the sensor equipment, there are various interferences during on-site operation. We need to deal with specific situations and take different measures for different interferences.

However, this flexible processing method is obviously in contradiction with the universality of the sensor. The current solution is to adopt a modular method. In addition to the basic components, the equipment can be equipped with different options for different operating situations to effectively resist interference. , Improve reliability.



Types of external interference affecting analog sensors:
 
1. Electrostatic induction
Electrostatic induction is due to the parasitic capacitance between two branch circuits or components, so that the charge on one branch is transferred to the other branch through the parasitic capacitance. Sometimes it is also called capacitive coupling.

2. Electromagnetic induction
When there is mutual inductance between two circuits, the change of current in one circuit will be coupled to the other circuit through the magnetic field. This phenomenon is called electromagnetic induction. This situation is often encountered when the sensor is in use and requires special attention.

3. Leakage current sensing
Due to the poor insulation of the component brackets, terminals, printed circuit boards, capacitors internal media or housings, especially the increase in the application environment humidity of the sensor, the insulation resistance of the insulator will decrease, and the leakage current will increase at this time. Cause interference. Especially when the leakage current flows into the input stage of the measuring circuit, its influence is particularly serious.

4. Radio frequency interference
It is mainly the interference generated when large-scale power equipment starts and stops operation, as well as high-order harmonic interference.

5. Other interference
It mainly refers to the poor working environment of the system, which is easily affected by environmental factors such as mechanical interference, thermal interference and chemical interference.

Through the above five types of external interference, we understand that there are two main sources of interference for sensors: one is interference generated by circuit induction, such as electrostatic induction interference, electromagnetic induction interference, leakage current induction interference, etc.; the other is large-scale circuit equipment And the induction of communication lines introduces interference, such as radio frequency interference.

In summary, if we want to clarify why our sensors are interfered, we should first determine what the transmission type of our sensors is. After knowing the transmission type, we should specifically analyze the source of interference in the environment and the sensitivity of the signal transmission line. Check whether grounding treatment and sensor signal line shielding measures are in place, and whether large power equipment is installed nearby. Determine the actual situation and take measures, and must not blindly handle it to prevent more serious consequences.