For two wire pressure sensors, two wires are used to connect the power supply. How does the PLC collect its analog signals from the 4-20mA?
One line of the two-wire pressure sensor is 24V, the other is the analog signal of 4-20mA, the analog module of PLC, 24V (power +) - sensor + + sensor ---- PLC+ ---- PLC----- 24V (power supply). Other procedures to achieve, if the analog signal is converted to digital, and then enter the PLC, which in the middle to analog and digital signal conversion.
For example, capacitive pressure sensors are passed through the capacitor - current linear conversion into the PLC, and the transformation part of the circuit power consumption is very small, negligible, so that you can save a line!
Two wire sensor is current output, a series of resistors in the loop, measuring the voltage changes on the resistance can be.
