Learning PLC, not only should only learning software, hardware - also need to learn

by:Coolmay     2020-06-19
Actually PLC controller is only part of the electrical system in the factory, if the factory understand into a human body, the PLC is factory of the brain, the brain through the eyes, nose and other signal input is analyzed, the final motion control of limbs, etc. So the eyes, nose and limbs are equally important.

eyes correspond in a factory? Is the input signal, such as close to switches, photoelectric switch, various sensors detect the external state of the device; Limbs is the output signal, corresponding to the motor in the factory, cylinder and so on direct drive device of the equipment. So both input and output are equally important. Learning PLC, not only should only learning software, hardware, also need to learn is more important than software and hardware, so for the learning of PLC controller, Hardware electric circuits of the study are also important, you don't attend.

let's talk about the next input signal, we can be classified in order to study;

a, digital quantity input signal

factory of input signal in the digital quantity; That with just two states, is a discrete quantity, in the program corresponding to the '1' and '0'. Are close to switches, photoelectric switches, liquid level switch, etc. , basically switch, two words are the digital quantity. So let's talk about how they are connected to the PLC and the matters needing attention.

1, the digital quantity of sensors in principle can be divided into two kinds of NPN and PNP, corresponding to different connection of PLC, try not to mix, some trouble, do not know can go to in the previous articles I have a look. In fact, the output voltage is different, has no effect for programming.

2 from the wiring, digital sensors can be divided into two wire and 3 wire system, the difference is that whether will be 24 v - is needed The sensor.

3, digital sensors can be divided into from the function of normally open ( 没有) And normally closed ( NC) , this is similar to relay, often open the sensor did not trigger in the program is 0, triggered in the program is 1; Normally closed sensor did not trigger is 1 in the program, when triggered in the program is 0, the need to remember. 4 detection function, such as proximity switch need close to detect metal, photoelectric sensor need keep out, didn't require a liquid level switch, safety grating needs no obstructions, etc, among which we can also in learning in the future, which used to talk about. For digital sensors we remember these.

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analog input signal input signal, some trouble with current signal; A voltage signal. Is a representative of the continuous state, is a discrete quantity, and then the common analog input signals are in the factory, test temperature, pressure, flow rate, etc. You need to pay attention to is; 1, not all of the testing temperature, the pressure sensor are analog quantity, the factory also has some nodes temperature sensor and pressure sensor, refers to the pressure or temperature reaches a certain or some other number, and a switch output signal of sensor itself, this is the digital quantity.

2, analog sensor wiring has some trouble, there are two wire system, there are four wire, now home with three wire system. Refers to two wire sensor, power supply and signal Shared two wires, four wire sensor is the power supply and signal, respectively, with two wires. Three wire system is on the basis of the four wire of the power supply to the signal of negative short connect together, so only three lines. Siemens S7 - 200 / S7 - 200 smart/s1200 is generally four wire system, namely, power supply and signal, and can select signal types in the hardware configuration.

3, there are some specific analog need to use a specific device or module, PLC 4 - the generally acceptable 20ma,0- 10 v, etc. , and tests on high temperature thermocouple or weighing sensor and so on because of working principle, generally only the mv level voltage signal, so you need to use a specific module or instrument, it is also need to accumulate experience. Three, the digital quantity,

1 analog input signal, such as using high-speed pulse encoder input, etc.

2, there are some very high precision sensors, for example, in the west, such as keyence sensor with high resolution, because the resolution of the analog quantity is not enough, so you need to use the communication or other means for connection to reach the precision of the sensor itself.

3, there are some kind of sensor or other equipment with the library files, direct call the library files can be read out data.

we say again signal output: a digital output, we said before the PLC controller have one advantage is to use 220 v or 380 v, 24 v control digital output refers to '0' '1' two states, generally control the ordinary motor, solenoid valve, etc. , digital control output is good, as long as logic no problem.

two analog output, some of the discrete devices, such as regulating valve, hydraulic proportional amplifier and so on need some control of gradual change, the devices are commonly need feedback value for closed-loop control or PID, later have the opportunity to take you to do this aspect of practice.

three communication control, some of the frequency converter or you need to use the communication control, such as servo drive, and in fact is that on the one hand; PLC programming is not difficult, difficult is familiar with the need to control device. It has some difficulty, need very strong self-learning ability. For learning PLC, not only need to make the program and debug to get a lot of experience, also need very strong self-learning ability, in the process, sometimes a experienced people words can save a lot of time for you, so also want to use the power of the Internet more.

electrical system is a set of knowledge system, for the novice, need a a knowledge learning, finally become own knowledge network, will achieve mastery through a comprehensive study to become a master.


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