[Energy Conservation Academy] Application of Ankerui signal isolator in boiler control system

summary

Boilers are common power equipment in industry, and the reliability of their control systems directly affects the safety and economic operation of boilers. In actual work, the PLC control system of the boiler sometimes has interference problems, causing the boiler to shut down for no reason, abnormal display, and data fluctuations. Connecting a signal isolator can reasonably reduce external interference and improve the reliability of the system.

Overview

Boilers are common power equipment in power plants and other industrial enterprises. Their function is to convert the energy stored in the fuel into heat through combustion and transmit it to various equipment in the form of steam or hot water. The industrial boiler system is complex. In order to achieve the ideal control effect, boiler PLC control systems are gradually widely used. With the rapid development of science and technology, the application of boiler PLC control systems has gradually developed from the initial boiler data monitoring to water level control, pressure control, combustion control and flow metering, etc. Its reliability directly affects the safety and economic operation of the boiler. At present, most boiler control systems are in a harsh electromagnetic environment formed by high-voltage circuits and high-voltage equipment. Installing a signal isolator between the two devices is one of the reasonable ways to solve interference.

Boiler PLC control system control process and principle

The overall structure of the boiler PLC control system is shown in Figure 1. The system uses PLC as the controller, thermal resistor temperature sensor, and differential pressure sensor to collect data information. The signal is converted into a standard signal through the temperature transmitter and pressure transmitter, and then isolated and converted through the signal isolator. The isolated output signal is then transmitted to the PLC processor. The PLC given output signal is then transmitted to the actuator through the signal isolator, and the entire combustion process is controlled by controlling the opening of the solenoid valve and the speed of the motor.

Figure 1 Boiler PLC control system

Application of signal isolator in boiler control system

Interference in Boiler PLC Control System

The main interference sources of boiler PLC control system are space radiation interference, ground interference and conducted interference including power supply interference and signal lead interference. Among them, conducted interference is more common and more serious in industrial sites.

Space radiation interference mainly refers to the interference generated by power grid, transient process of electrical equipment, lightning, radio, high-frequency induction heating equipment, etc. The schematic diagram is as follows. Its distribution is complex, and if the PLC system is in the radio frequency field, it will be affected by interference.

Figure 2 Space radiation interference

Ground interference is mainly shown in Figure 3, which refers to the uneven distribution of potential at different grounding points. There is a ground potential difference at different grounding points, which causes ground loop current and affects the normal operation of the logic circuit and analog circuit in the PLC.

Figure 3 Ground interference

The interference introduced by the signal line is shown in Figure 4, which is mainly the grid interference introduced by the transmitter power supply and the external interference on the signal line. This is a relatively serious problem. The interference introduced by the signal line will cause abnormal signal operation, reduce measurement accuracy, and cause component damage in severe cases. For the boiler PLC system, these interferences will cause it to transmit wrong commands, which may cause abnormal parameters such as water flow and temperature, causing boiler failure and shutdown, or even worse, the control system crashes, reducing work efficiency and causing safety problems.

Figure 4 Signal line introduces interference

The role of signal isolator in boiler PLC system

In actual work, in order to improve its reliability, installing an appropriate signal isolator between the signal connections of the two devices is one of the reasonable ways to solve the interference of the boiler PLC control system.

As shown in Figure 5 below, the feedback signal from the valve positioner is input to the signal isolator, and then the isolated output signal is transmitted to the DCS and PLC control room. This method has high isolation strength, strong load capacity, simple installation and wiring, stable operation, safety and reliability, and solves the problems of electromagnetic interference and high-frequency signal penetration.

Figure 5

As shown in Figure 6, using a signal isolator in a process loop can disconnect the direct circuit in the process loop without affecting the normal transmission of the process signal, and can reasonably solve ground interference. It can also solve problems such as signal conversion and signal distribution while having high flexibility.

Figure 6

The interference introduced by the signal line can also be reasonably handled by installing a signal isolator. There are many sensors in the boiler control system, and serious interference introduced by the signal line will cause mutual interference. The signal isolator can isolate the power supply, input, and output from each other. Connect a signal isolator between the sensor and the PLC system, as shown in Figure 7. By using its characteristics, the power supplies can be relatively independent and the safety of the power supply can be improved.

Figure 7

Ankerui BM100 signal isolator

BM100 series signal isolators are used in industrial production to increase instrument load capacity and ensure that instruments connected to the same signal do not interfere with each other, thereby improving electrical safety performance. BM100 signal isolators support three input modes, are compatible with three sensor wiring methods, isolate input signals for output, and safely transmit them to secondary instruments or PLC/DCS for use.

BM100 signal isolator wiring diagram

Appearance of BM100 series signal isolator

Technical Parameters

Conclusion

Installing a signal isolator in the boiler PLC control system can reasonably solve the interference problem in the control system, and provide a guarantee for improving the accuracy of the PLC/DCS control system's measurement signal and the safe, stable and reliable operation of the system.