The effect of the industrial control system is gre

  • Detail

The effect of industrial control system is greatly reduced due to too much interference. How to save it

the designed industrial control system is about to be successful. However, when it is powered on, it is found that the system interference is too large, resulting in a great difference from the ideal effect, or even worse. I have sorted out this knowledge and give it to more friends

the basic principle of anti-interference measures is to suppress the interference source, cut off the interference propagation path, and improve the anti-interference performance of sensitive devices

suppress interference source

suppress interference source is to reduce du/dt and di/dt of interference source as much as possible. This is the highest priority and the most important principle in anti-interference design, and it often achieves twice the result with half the effort. Reducing du/dt of interference source is mainly realized by paralleling capacitors at both ends of interference source. Reducing di/dt of interference source is realized by connecting inductance or resistance in series and adding freewheeling diode in the circuit of interference source

common measures to suppress interference sources are as follows:

1 A freewheeling diode is added to the relay coil to eliminate the back EMF interference when the coil is disconnected. Only adding freewheeling diode will delay the breaking time of the relay. After adding zener diode, the relay can act more times in unit time

2. Spark suppression circuit is connected at both ends of relay contact in parallel (generally RC series circuit, with resistance of several K to tens of K and capacitance of 0.01uF)

3. Add a filter circuit to the motor, and pay attention to the capacitor and inductance leads to be as short as possible

4. Each IC on the circuit board shall be connected in parallel with a 0.01 μ F——0.1 μ F high frequency capacitor to reduce the influence of IC on power supply. Pay attention to the wiring of high-frequency capacitor. The wiring should be close to the power end and as short as possible. Otherwise, it will increase the equivalent series resistance of the capacitor and affect the filtering effect

5. Avoid 90 degree broken line during wiring to reduce high-frequency noise emission

6. RC suppression circuit is connected at both ends of the thyristor in parallel to reduce the noise generated by the thyristor (when the noise is serious, the thyristor may be broken down)

cut off the propagation path

the common measures to cut off the interference propagation path are as follows:

1 Fully consider the influence of power supply on single chip microcomputer. If the power supply is well done, more than half of the anti-interference of the whole circuit will be solved. Many single chip computers are very sensitive to the power supply noise. It is necessary to add a filter circuit or a voltage regulator to the single chip computer power supply to reduce the interference of the power supply noise to the single chip computer. For example, magnetic beads and capacitors can be used to form a π shaped filter circuit. Of course, 100 Ω resistance can also be used to replace magnetic beads when conditions are not high

2. If the i/o port of the single chip microcomputer is used to control noise devices such as motors, isolation shall be added between the i/o port and the noise source (π shaped filter circuit shall be added). For controlling noise devices such as motor, isolation shall be added between i/o port and noise source (π shaped filter circuit shall be added)

3. Pay attention to the crystal oscillator wiring. The crystal oscillator shall be close to the pin of the single chip microcomputer as far as possible, and the clock area shall be isolated by the ground wire. The shell of the crystal oscillator shall be grounded and fixed. This measure can solve many difficult problems

4. The circuit board shall be reasonably partitioned, such as strong and weak signals, digital and analog signals. Try to keep the interference source (such as motor and relay) away from sensitive components (such as single chip microcomputer)

the tank fermentation cycle is shortened from 40 days to 10 days

5 The digital area shall be isolated from the analog area by the ground wire. The digital area and the analog area shall be separated, and finally connected to the power ground at one point. The wiring of a/d and d/a chips is also based on this principle. The manufacturer has considered this requirement when allocating the pin arrangement of a/d and d/a chips

6. The ground wires of single-chip microcomputer and high-power devices should be grounded separately to reduce mutual interference. High power devices shall be placed on the edge of the circuit board as far as possible

7 the anti-interference performance of the circuit can be significantly improved by using anti-interference components such as magnetic beads, magnetic rings, power filters and shielding covers in key places such as the i/o port of the single chip microcomputer, the power line and the connecting line of the circuit board

improving anti-interference performance

improving interference performance mainly refers to improving the anti-interference performance of sensitive devices in the system. To improve the anti-interference performance of sensitive devices means to reduce the pick-up of interference noise as far as possible from the sensitive devices and recover from abnormal state as soon as possible

common measures to improve the anti-interference performance of sensitive devices are as follows:

1 When wiring, try to reduce the area of the loop to reduce the induced noise

2. When wiring, the power line and ground wire shall be as thick as possible. In addition to reducing the voltage drop, it is more important to reduce the coupling noise

3. For the idle i/o port of the single chip microcomputer, do not hang it in the air, but connect it to the ground or power supply. The idle time of other ICs shall be utilized in China for R & D and industrialization. The terminals shall be grounded or connected to the power supply without changing the system logic

4. The anti-interference performance of the whole circuit can be greatly improved by using power monitoring and watchdog circuits for single chip microcomputer, such as imp809, imp706, imp813, X25043, X25045, etc

5. On the premise that the speed can meet the requirements and adhere to the government guidance, industry coordination, enterprise main body, market operation and think tank support, try to reduce the crystal vibration of single chip microcomputer and select low-speed digital circuit

6ic devices shall be directly welded on the circuit board as far as possible, and IC seats shall be used less

check software

1 I am used to clearing the unused code space into "0", because it is equivalent to NOP and can be returned when the program runs

2. Add several NOPs before the jump instruction for the same purpose as 1

3. When there is no hardware watchdog, the software can be used to simulate the watchdog to monitor the operation of the program

4. When dealing with the parameter adjustment or setting of external devices, in order to prevent the external devices from making errors due to interference, the parameters can be sent again regularly, so that the external devices can be recovered as soon as possible

5. For anti-interference in communication, data check bit can be added, and the strategy of 2 out of 3 or 3 out of 5 can be adopted

6. When there are communication lines, such as i^2c, three wire system, etc., in practice, we find that setting the data line, CLK line, INH line as high as normal is better than setting it as low

check the hardware

1 The part of ground wire and power line must be important

2. Decoupling of lines

3. Separation of digital and analog earth

4. Each digital element shall have 104 capacitors between the ground and the power supply

5. In relay applications, especially in case of large current, to prevent the interference of relay contact spark to the circuit, a 104 and diode can be connected between the relay coil, and an indirect 472 capacitor can be connected between the contact and the constant start. The effect is good

6. To prevent the crosstalk of i/o ports, i/o ports can be isolated by diode isolation, gate circuit isolation, optical couple isolation, electromagnetic isolation, etc

7. Of course, the anti-interference of multi-layer board is certainly better than that of single panel, but the cost is several times higher

8 contact information show contact Choosing a device with strong anti-interference ability is more effective than any other method. I think this should be the most important. It is difficult to make up for the inherent shortcomings of devices with external methods, but those with strong anti-interference ability are more expensive. It mainly depends on your application occasions

Copyright © 2011 JIN SHI