1. Pulse + direction
When discussing control systems, I/O point is the term most often heard. It refers to the input/output point, I stands for INPUT, which refers to input, and O stands for OUTPUT, which refers to output.
Input/output are all for the control system. Input refers to the measured parameter entered from the instrument into the control system, and output refers to the parameter output from the control system to the actuator. A parameter is called a point. The scale of a control system is sometimes determined according to the maximum number of I/O points it can control.
Analog quantity and switch quantity
In the control system, a common term is analog quantity and switch quantity. Regardless of input or output, a parameter is either an analog or a switch.
The analog quantity refers to the size of the control system quantity is a continuous value that changes within a certain range, such as temperature from 0 to 100 degrees, pressure from 0 to 10 MPA, liquid level from 1 to 5 meters, and electric valve opening from 0 to 100 %, etc. These quantities are all analog quantities.
Analog quantity is a continuously changing physical quantity, such as voltage, temperature, pressure and speed. The PLC cannot directly process the analog quantity. It needs the A/D converter in the analog input module to convert the analog quantity into a digital quantity proportional to the input signal for use by external actuators (such as electric control valves or inverters).
The switch value includes binary input and binary output. It is a digital signal and only has two states of "0" and "1".
The binary input comes from a contact outside the protection device for use by the protection device. The opening amount is the contact provided by the protection device to the outside, which is supplied to the external equipment, such as the on/off state of the switch, the closing/opening of the relay, the on/off of the solenoid valve, and so on. PLC can directly input and output switch signals.
Usually for the control of analog quantities, a controller determines an output quantity according to an input quantity and according to certain rules and algorithms. In this way, the input and output form a control loop.
The control loop has the difference between open loop and closed loop.
Open-loop control loop means that the output is based on a reference quantity, and there is no direct relationship between input and output.
The closed loop loop feeds back the output of the control loop as the loop input, and compares it with the set value or the expected output value of the quantity. Closed loop control, also called feedback control, is the most common control method in control systems.