The following is a detailed introduction to the input and output signal types of PLC Control Cabinet:
1. Digital input signal
Digital input signals play a key role in triggering and status detection in PLC Control Cabinet. Among them, dry contact signals are a common type of digital input. For example, signals from various mechanical limit switches. When the mechanical parts move to a specific position, the limit switch acts and generates a dry contact signal input to the PLC Control Cabinet. This signal is simple and reliable, and only represents two states, namely open and closed.
In addition, source and drain input signals are also widely used in digital input. In source input, current flows from the input point into the PLC, which is common in the output signals of some sensors. For example, when a photoelectric sensor detects an object, it outputs a high-level source signal to the PLC. The drain input is the opposite, and the current flows out of the PLC from the input point. In practical applications, it is necessary to select the appropriate input method according to different sensor types and the input characteristics of the PLC.
Digital input signals can also be provided by devices such as digital encoders. Digital encoders can convert rotary motion or linear motion into digital pulse signals and input them into PLC, thus achieving precise position detection and control.
2. Analog input signals
Analog input signals can continuously reflect changes in physical quantities. Common voltage signals such as 0-10V and 0-5V are widely used in the output of various sensors. For example, a pressure sensor can convert the detected pressure value into a corresponding analog voltage signal and input it into a PLC. Through the analog input module of the PLC, these voltage signals can be converted into digital signals for processing.
Current signals such as 4-20mA are also important analog input types. This signal has good anti-interference ability when transmitted over long distances and is suitable for some occasions with high signal accuracy requirements. For example, a temperature transmitter can convert the temperature value into a 4-20mA current signal and input it into a PLC for temperature monitoring and control.
Thermistor signals (RTDs) reflect temperature changes by measuring changes in resistance values. Common thermal resistors include Pt100 and Cu50. These thermal resistors are connected to the analog input module of the PLC through a specific wiring method, and after signal conversion and processing, accurate temperature measurement is achieved.
Thermocouple signals (TC) use the thermoelectric effect of two different metals to measure temperature. Different types of thermocouples have different temperature measurement ranges and accuracies, and are suitable for temperature measurement in various high-temperature or special environments.
3. Digital output signals
Digital output signals are mainly used to control the switching state of various actuators. Relay output is a common digital output method. It can control high-power loads such as motors, solenoid valves, etc. Relay output controls the on and off of external devices by closing or opening the contacts of the relay. This output method has a high load capacity, but the response speed is relatively slow.
Transistor output is divided into NPN type and PNP type, which are usually used to control low-power loads such as indicator lights, small relays, etc. Transistor output is fast and has a long life, but the load capacity is relatively weak. In some occasions where high response speed is required, transistor output has obvious advantages.
In addition, digital output signals can also be output controlled by devices such as solid-state relays. Solid-state relays have the advantages of no contact, long life, and strong anti-interference ability, and are suitable for some occasions with high reliability requirements.
4. Analog output signal
Analog output signals are used to control equipment that requires continuous adjustment. Voltage outputs such as 0-10V and 0-5V can be used to control the output frequency of the inverter, thereby realizing the speed control of the motor. Through the analog output module of the PLC, the digital signal can be converted into the corresponding analog voltage signal output.
Current output such as 4-20mA is also commonly used for analog output. In some occasions where long-distance signal transmission is required or high signal accuracy is required, 4-20mA current output has better stability and anti-interference ability. For example, when controlling the opening of the regulating valve, the analog output signal can be used to accurately control the position of the valve.
In short, the input and output signal types of PLC Control Cabinet are rich and varied, which can meet the needs of different industrial automation control. In practical applications, it is necessary to select the appropriate input and output signal type according to the specific control tasks and equipment requirements to ensure the stable and reliable operation of the control system.
