Views: 5 Author: Site Editor Publish Time: 2022-04-08 Origin: Site
Common sensors connected to PLC include proximity switch, travel switch, photoelectric sensor, temperature sensor, position sensor (electronic ruler), encoder, pressure sensor, etc. Sensor signals mainly include digital signals (that is, on and off) and analog signals (voltage signal 0~10V, -10~+10v, current signal 0~20ma, etc.). The digital signal can be directly connected with the input terminal of the PLC, and the analog signal needs to be input through the AD module
The problem of connecting the sensor to the PLC has nothing to do with the sensor itself. All the signals to be transmitted to the PLC are the signals output by the sensor, so we focus on analyzing the signal forms output by the sensor. And analyze how the signal should be connected.
The most common is the transistor output, (PNP, NPN and push-pull push-pull output). If it is PNP or NPN, then the input signal port of the PLC must be the corresponding PNP or NPN model (if it is not correct, the time Can not be connected for use), when wiring: PNP is a pull-down load, connected to the PLC and connected to the signal line and the power supply minus two lines; NPN is a pull-up load, so it is connected to the PLC and the signal line and the power supply plus two lines . Push-pull push-pull output can be used for both PNP and NPN, so if you want to use it as a PNP, then connect the output and power negative wires as well; if you want to use it as an NPN, then connect the signal and the power supply is two wires.
The output of analog voltage or current is a bit complicated, because the PLC itself does not have the function of collecting analog quantities, so an external extended analog module must be connected. The connection method is to connect the sensor to the analog module first, and then the analog module is connected to the PLC. (Connect the analog output line and 0V line of the sensor to the positive and negative electrodes of the analog module respectively) as shown below:
Relay output; this kind of output is relatively simple to connect to the PLC, the relay is to control the on-off of the loop, and the two wires of the relay can be directly connected in series in the loop.
NAMUR output, this output is generally used in explosion-proof environment. At this time, in order to ensure that the safety output signal cannot be directly connected to the PLC, the NAMUR signal must be connected to the safety gate first, and then the safety gate is transferred to the PLC.
IO-LINK output, this is currently relatively popular. This kind of sensor must be connected to the following IO-LINK module first, and then this module communicates with the PLC through the bus.
Analog signal: voltage signal or current signal! Used to provide analog input signals to PLC and other equipment.
For example: pressure transmission signal, liquid level transmission signal, temperature transmission signal, differential pressure transmission signal, valve opening feedback signal, etc. are all analog signals.
Supplement: The standard voltage signal is generally: 1v-5v, and the standard current signal is generally: 4mA-20mA. Of course there are other voltage and current signals.
Digital signal sensor type: valve open signal, valve close signal, proximity switch on-off signal, infrared induction signal, etc.
Digital signals are generally two states, 0 and 1, on or off, which are used to provide on-off signals to PLC and other equipment.
Analog input port: accept analog signals from sensors and other devices.
Digital input port: accept digital signals from sensors and other devices.
Analog output port: used to control analog output, etc. For example: control valve opening.
Digital output port: used to control the on-off of the circuit, etc.
The analog sensor is connected to the PLC analog input port, and the corresponding output port can be analog and digital.
The digital sensor is connected to the PLC digital input port, and the corresponding output port is generally a digital signal.
The sensor signal type needs to be the same as the PLC input port type.
There are many types of PLCs. Generally, PLCs have digital input ports that can directly connect digital signals.
If the PLC does not have an analog input port, it needs to be equipped with an analog expansion module of the same type. Generally, PLC will be equipped with 1-2 sets of analog ports.
Pay attention to the power supply and signal during the use of the sensor, do not reverse it, otherwise the PLC may be damaged.
There are many types of sensors, such as two-wire system, three-wire system, four-wire system, etc. It must be distinguished when wiring, and signal isolators need to be installed when necessary.
Pay attention to the input and output terminals during the use of PLC, and use it safely.