About what exactly is the purpose of PLC variable it - - programmable logic

As an electrical engineer, PLC programming that is often contact, so for the programming software, to understand and master the basic knowledge of it is very important, it also related to the work after the fluency and accuracy. For variable we should be clear, it is really our programming language and a connection between the real device, the mechanical action of a point or simulation of a numerical transformation to our PLC controller language, able to identify the variables that is variable.

we common variables is roughly divided into the following:

DI: switch input and DO: switch output AI: analog input AO: analog output communication point above these levels, make us the most commonly used in programming points, all of the points, finally are assigned to these forms, then our detailed look at these points.

switch quantity, just as its name implies is our common switch, button, etc. , only the data in the form of open and close. When open to 0, when close to 1. And input to the PLC controller input means external variables, provided by the external device a switch signal, transmission to the PLC. This is our switch input.

DI equipment is probably our most common. Such as our common variety of button.

button types are divided into a lot of kinds, such as our motor start, stop, reset, etc. , and our scram button, selector switch, proximity switch, etc. , these buttons from the structure is basically the same, there is nothing but buttons with lamp, some with no lights, have a plenty of the reset, a plenty of self-locking, but outside the output data is on or off, namely 0 and 1 at the other.

switch output, DI points with us on the contrary, it is sent to the PLC equipment device signal, this signal point is also divided into and off, such as our equipment remote start, through our PLC output, output a start signal, the coil or absorption, can through the PLC control the action of the corresponding equipment, the switch quantity is the same with us, the state of the output is 0 or 1.

analog input is our production process parameters, such as temperature, pressure, flow, level, vibration, etc. , there are a lot of, this parameter is a numerical change more, have corresponding range, such as 0 100 degrees Celsius, 0 1. 6 mpa, while in the process of production, the process of instrument to detect the corresponding physical quantities, by processing the physical value is transformed into the PLC can identify current signal and voltage signal, such as 4 - 20mA,0- 10 v, this is what we call the analog input.

analog output and DO some about the same, only is a range of output current or voltage value, at last, through equipment is converted to the corresponding equipment need analog, commonly used in frequency converter, adjusting valve control equipment, through the output frequency of frequency converter is controlled, such as 4 - 20 ma, 0 for the inverter 50 hz, or 0 for the regulator The opening of 100.

communication is inside the PLC should be a little bit complicated level, communication is divided into many kinds of protocols, different equipment, supported by the protocol type may not be the same, such as described above AO point frequency converter, can also be controlled by agreement, and the communication will basically take PLC com port, or the 485 interface, is not the same as switch points and simulation.

for PLC, basically the common variables as stated in the appeal, and at the time of programming, we need to build a variables, the PLC of the location of the internal and external equipment, then according to our equipment movement logic, carries on the programming, the operation of the equipment internal procedures can be converted to action. Program is equivalent to our logical thinking, variable is filling our application of a material, so a lot of programmers before programming will be needed to establish the program variables, or the point table, then according to some tables for next work.

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