The two-wire current and four-wire current only have two signal wires, the difference: the two signal wires of the two-wire current not only need to supply power to the sensor or transmitter, but also provide the current signal; and the two-wire current The signal line only provides current signals.
Therefore, sensors or transmitters that provide two-wire current signals are usually passive; sensors or transmitters that provide four-wire current signals are active.
Therefore, when the plc template input channel is set to connect to the four-wire sensor, the plc only collects analog signals from the template channel terminals, and when the plc template input channel is set to connect to the two-wire sensor, the plc analog input A DC 24v power supply is also output on the channel of the template to drive the two-wire sensor to work.
Sensor model:
- Two-wire system (it needs to supply 24vDC power itself, the output signal is 4-20MA, current) that is + connected to 24vdc, negative output 4-20mA current.
- Four-wire system (with its own power supply, generally 220vac, the signal line output + is 4-20ma positive and-is 4-20ma negative.
Plc:
- (Take 2 plus and minus 3 as an example) When two-wire system is used, positive electrode 2 outputs 24VDC voltage and 3 receives current), so when encountering two-wire sensor, one connection method is 2 to the sensor positive and 3 to the sensor negative ; The jumper is a two-wire current signal. Two connection methods are 2 floating, 3 negative of the sensor, and the sensor is about to connect to 24vdc in the cabinet; the jumper is a two-wire current signal.
- (Take 2 positive and 3 negative for example) In the four-wire system, the positive electrode 2 is the receiving current and 3 is the negative electrode. (The advantage of the four-wire system is that when the negative signal of the sensor and the M in the cabinet are at different levels, the accuracy will not be greatly affected, because it is the current loop of the sensor itself.) When encountering the four-wire sensor, one method is to connect the sensor to 2 and 3 Connect the sensor negative, plc jumper is 4-wire current.
- (Take 2 positive and 3 negative for example) Four-wire sensor and plc two-wire jumper connection method: the negative signal line is connected to the M line in the cabinet. Connect the sensor to PLC 3, 2 is floating, and the jumper is a two-wire current.
- (Take 2 positive and 3 negative as examples) Voltage signal: 2 connects the sensor positive, 3 connects the sensor negative, plc jumper is the voltage signal.
PLC ONE 