In industrial control, some input (such as pressure, temperature, flow rate, rotational speed, etc.) is a continuous change of analog, some actuators (e.g., servo motor, regulating valve, recorder, etc.) for PLC output analog signal, and the PLC CPU can only deal with digital quantity. Analog was first sensor and transmitter is converted into A standard current or voltage, such as 4 ~ 20 ma, 1 ~ 5 v, 0 ~ 10 v, PLC with A/D converter convert them to digital quantity. The digital quantity can be binary, may also be A decimal, plus or minus current or voltage after A/D conversion generally use two's complement representation.
D/A converter converts PLC digital output to analog voltage or current, then to control the actuator. Analog I/O module's main task is to complete A/D conversion (analog input) and D/A conversion (analog output).
(Ⅰ) PLC analog input module
Analog input module, also known as A/D module, the field generated by the sensors and the continuous analog signal is converted into the PLC CPU can receive digital quantity, for 12 bit binary number more commonly, digital quantity the more digits module, the higher resolution.
(Ⅱ) PLC analog output module
Analog output module is also known as D/A module, the PLC CPU to the analog output module convert the digital quantity of external equipment can receive analog (voltage or current). Analog output module receives the digital signal of 12 bit binary number more commonly, digital quantity the more digits module, the higher resolution.