Analog inputs are widely used in process control, such as temperature, pressure, flow rate, displacement, and other industrial measurements that correspond to the magnitude of voltage and current. Analog signals are converted into standard signals by sensors or transmitters, and input modules use A/D converters to convert them into digital signals for processing by the CPU. Therefore, the analog input module is also known as the A/D conversion input module.
The output module of analog quantity converts the binary digital signal processed by the CPU into analog voltage or current, and then controls the actuator. Therefore, the analog output module is also known as the D/A conversion output module.
Small programmable controllers often do not have analog I/O modules, or only 8-bit A/D and D/A modules with limited channel numbers. Large and medium-sized programmable controllers can be configured with hundreds or thousands of analog channels, and their A/D and D/A converters are 12 bit.
The input and output signals of analog I/O modules can be voltage or current, which can be unipolar such as 0-5V, 0-10V, 1-5V, 4-20mA, or bipolar such as ± 5V, ± 10V, and ± 20mA. The module can generally input multiple ranges of current or voltage.
Extended Information
One major advantage of PLC is its strong anti-interference ability. At the input end of the PLC, all input signals are optically coupled and filtered by an RC circuit before being sent to the internal amplifier of the PLC.
After adopting photoelectric coupling and RC filtering measures, interference caused by stray electromagnetic waves in the environment can be effectively eliminated. In addition, the input/output of the optocoupler has high insulation resistance and can withstand high voltage above 1500V without breakdown. Therefore, this anti-interference method of PLC has been adopted by other circuits.
The PLC provides DC power supply internally. When the input switch is turned on, the photoelectric coupling is turned on, and the light emitting diode (LED) installed on the PLC panel displays that a certain input port has a signal input.
