The signal conditioning module or the isolation transmitter is a device that uses photoelectric, magnetoelectric and other isolation technologies to realize the isolation and conversion of input and output signals. Because of its strong anti-interference ability and high transmission accuracy, it is widely used in instrumentation, oil field, petrochemical processing, equipment manufacturing and other fields, and is an important part of industrial control systems.
First, what is the signal conditioning module?
The signal conditioning module is essentially an isolation amplifier. Its main function is to amplify the signal and protect the front-end circuit. Because of its high isolation voltage, it greatly improves the use of the measuring device under the harsh conditions without being broken down. performance. In the field of industrial automation, it mainly carries out various signals such as voltage and current, AC, 4-20 mA, 0-5 V, mV millivolt, PWM pulse, Hz frequency, Pt100 thermal resistance, sine wave, square wave, potentiometer, and rotational speed. Integrated circuits for transmission, conversion, isolation, amplification, and remote transmission can be used with various industrial sensors to meet the needs of users to monitor remote data collection locally, while improving system fitness and environmental reliability. Little squatting.
Figure 1 signal conditioning module
Second, the three isolation concept of the signal conditioning module
The three isolations of signal conditioning refer to: isolation between the input and output of the signal; isolation between the input and output of the power supply; isolation between the signal path and the power supply channel. as shown in picture 2.
Figure 2 Three isolation concepts for signal conditioning
For the three isolation products, there is a high blocking between the power supply and the signal transmission, which reduces the mutual influence. The isolation of the signal allows the ground loop and the interaction between the front and rear stages to be blocked as much as possible.
Third, signal conditioning isolation transmission application
As shown in Figure 3, the MCU processes the signals of the digital temperature and humidity sensors. After the processing is completed, it is isolated by the signal conditioning module and then transmitted out to connect with the current input of the field or the voltage input type power meter, and has the function of isolation. To prevent the interference signal from the front end of the sensor from being connected to the power meter, PLC, DCS, etc. at the site.
Figure 3 Signal Conditioning Isolated Transmission Application
Generally, the temperature and humidity signals processed by the MCU will be converted to voltage analog quantities by DA, while the field instruments, DCS, etc. may require current input signals or voltage input signals. For this, the corresponding signal conditioning module can be used to achieve Different output interfaces. The recommended models are as follows:
Second, the application of the sensor front end
In some power system temperature and humidity acquisition applications, the temperature/humidity sensor with analog output is used. The MCU is far away from the sensor. When the temperature and humidity sensor signals are transmitted to the MCU, the signal of the sensor is small and the line is long. Additional interference is introduced and useful signals may be overwhelmed by interfering signals.
At this time, as shown in FIG. 4, between the sensor and the MCU, a current output type ZCM module is used, and the voltage signal of the sensor is isolated and converted into a current signal, which is sent to the MCU for processing, and the signal is amplified and isolated. It can greatly enhance the transmission distance of the signal and reduce the distortion of the signal.
Figure 4 Application of sensor front end
After the MCU processes the temperature and humidity signals on the site, it may need to form a network with the nodes collected by other sensors, and finally pass to the central control room, or be processed centrally by an MCU. The industrial site network generally adopts RS-485 or CAN bus. At this time, RSM485 module and CTM isolation CAN transceiver can be used to form a stable and reliable on-site communication network. Related product information is as follows:
(The manuscript is provided by ZLG Zhiyuan Electronics )
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