Current sensor and PLC wiring

The sensor's action distribution mode is mainly divided into 2-wire and 4-wire, and the output analog signals are also different, but the common 0-20 ma, 4-20 ma current signal and 0-75 mv, 0 -5 v, 1-5 v voltage signal. PLC common input devices include buttons, proximity switches, diverters, dialers, various sensors, etc. The output devices include relays, contactors, solenoid valves, and so on. Here we mainly introduce the wiring method of the current sensor and PLC. The correct connection of the input and output circuits is the prerequisite for ensuring the safe and reliable operation of the PLC.

In order to introduce the analog signal of the current sensor into the PLC/DCS/FCS/MCU/FA/PC system, match the function and technical characteristics of the sensor and data collection system to select the matching option, and also need to consider the data collection system of the industrial field sensor and PLC. Differences in power supply and the impact of various EMC interferences.

The general analog sensors are divided into 2-wire and 4-wire. The 2-wire type is passive, eliminating the need to supply additional operating power to the sensor and requiring simultaneous supply of power and current and voltage signals. The 4-wire type 2 signal lines supply only current signals, and the 4-wire type current sensors need to be supplied with operating power. Therefore, in the case where the template input channel of the data collection system such as PLC is set toconnect the 4-wire sensor, the PLC collects the analog signal only from the terminal of the template channel, and the template input channel of the data collection system such as PLC is set to the connection 2 Line sensor.

Current sensors commonly used in the industry include a DC current sensor and an AC current sensor. The AC current sensor is a device that can convert the measured AC current into a linear ratio and output DC voltage or DC current. The AC current sensor is connected to the PLC to separate the measured AC current with a linear scale and output the output DC standard current DC4- 20 ma or DC voltage. Directly sent to the corresponding indicator meter or DCS MCU DSP PLC system to achieve AC current measurement and control. Products are widely used in electric power, postal, petroleum, coal, metallurgy, railway, municipal and other departments of electrical equipment, automatic control and scheduling systems. Even if the DC current sensor input is a DC input, it is a DC current or voltage.

Twowire type refers to the field transmitter. In order to connect with the control room meter, only two wires are used. These two wires are both power lines and signal lines. 2-wire and 3-wire (1 positive power line, 2 signal lines, 1 of which is common ground), 4-wire type (2 positive and negative power lines, 2 signal lines, one of which is ground) ).