Programmable controller is widely used, so it has a strong practical significance. For programmable controller, we have heard more or less, but we may not know the characteristics of programmable controller. In this paper, the four characteristics of PLC will be introduced. If you are interested in PLC, you may as well read on.
1、 Rich functions
The function of PLC is very rich. This is mainly related to its rich instruction system for processing information and internal devices for storing information.
It has dozens or hundreds of instructions. It can deal with all kinds of logic problems and calculate all kinds of data. It can do whatever ordinary computer can.
Its internal relays, equivalent to intermediate relays, are more numerous. Memory a bit can be used as an intermediate relay, how not much!
It also has many counters and timers, which are beyond the reach of relay circuits. Small box or module, its internal timer, counter up to hundreds, thousands. This is also because as long as you use a word in the memory and add some flag bits, you can become a timer and counter, so there are so many.
Moreover, these internal devices can also be set to maintain or not maintain power loss, that is, reset after power on. In order to meet different use requirements. These are also difficult to achieve by relay devices.
Its data storage area can also be used to store a large amount of data, hundreds, thousands, tens of thousands of words of information can be stored, and, after power failure, it will not be lost.
The programmable controller also has abundant external devices, which can establish a friendly man-machine interface for information exchange. It can input program, input data, read program and read data. Moreover, reading and writing can be carried out on the picture with both pictures and texts. After the data is read out, it can be transferred and printed. Data input can be typed in, can be read in, and so on.
The programmable controller also has communication interface, which can link or connect with computer to exchange information with computer. It can also be networked to form a larger and more extensive control system than a single machine.
Programmable controller also has powerful self-test function, which can carry out self diagnosis. The results can be recorded automatically. This adds transparency and convenience to its maintenance.
The abundant functions make it possible for the wide application of PLC, and also create conditions for the automation, remote control and intelligent control of industrial system.
Programmable logic controller (PLC) has many functions, which other electric controllers don’t have and the traditional relay control circuit can’t match.
2、 Easy to use
It is very convenient to control the system with PLC. This is because: first of all, the establishment of PLC control logic is the program, using the program instead of hardware wiring. Programming is more convenient than wiring. Changing the program is more convenient than changing the wiring!
Secondly, the hardware of PLC is highly integrated and has been integrated into various miniaturized modules. Moreover, these modules are matched and have been serialized and standardized. All kinds of control system required modules, programmable controller manufacturers have spot supply, can be purchased on the market. Therefore, the hardware system configuration and construction is also very convenient.
It is because of this that the word “Ke” can be used in PLC. As for software, it is not difficult to program. For hardware, its configuration is variable and easy to change.
Specifically speaking, PLC has five aspects of convenience
(1) Convenient configuration: according to the needs of the control system, determine which PLC to use, which type, which module to use, and how many modules to use. After confirmation, order and purchase in the market.
(2) Easy to install: PLC hardware is easy to install and assemble. The external wiring has a connector, which is easy to connect. When replacing the module, the connector can be installed on the new module, and there is no need to connect again. Do not connect any internal wires, as long as you make some necessary dip switch settings or software settings, and compile a user program to work.
(3) Programming convenience: Although there are no actual relays, time relays and counters in the PLC, these devices exist through the program (software) and system memory. The number of them is unimaginable for relay control system. Even if it is a small programmable controller, the number of internal relays can be counted in thousands, and the number of time relays and counters can also be counted in hundreds. Moreover, the contacts of these relays can be used indefinitely. There are so many logic devices in PLC that users can’t feel any limitation when using them. The only consideration is the entry and exit points. No matter how much this internal in out point is used, it doesn’t matter. The control points of large-scale programmable controller can reach more than ten thousand points. How can there be such a large real system? If it’s not enough, it can also be controlled online without any restrictions. The instruction system of programmable controller is also very rich, which can easily realize the control of various switching values and analog values. The programmable controller also has a memory area to store data, which can store all the information to be saved in the control process In a word, due to the strong function of PLC, the limitation of its function in control system is not PLC itself, but people’s imagination or other supporting hardware facilities.
The peripherals of PLC are very rich. There are many kinds of programmers, which are convenient to use. There are also data monitors, which can monitor the work of PLC. There are many softwares using PLC, not only ladder diagram language similar to relay circuit design, but also basic language, C language and even natural language. These also provide convenience for programmable controller programming.
The program of PLC is easy to store, transplant and reuse. After the program of PLC used in a certain type product is perfected, all the products can be used. Produce one, copy one. Compared with the relay circuit, the equipment needs wiring and debugging, which is much easier and easier.
(4) Easy maintenance: This is because:
① The PLC works reliably, and there are few failures, which greatly reduces the workload of maintenance. This will be further introduced when we talk about the third feature of PLC.
② Even if the PLC fails, the maintenance is very convenient. This is because programmable controllers are equipped with a lot of fault signals. For example, if the battery voltage of the programmable controller supporting memory data is insufficient, there will be a low voltage signal indication. Moreover, the PLC itself can record the fault condition. Therefore, it is easy to diagnose the fault of PLC. At the same time, it is very simple to diagnose the fault. Troubleshooting can be carried out according to the module, and the spare parts of the module can be purchased in the market, so it can be simply replaced. As for the software, it will not break down after debugging, as long as it is adjusted according to the use experience to make it perfect.
(5) Easy to use: programmable controller is used for a certain device. If the device is no longer used, the programmable controller can be used for other devices. As long as the program is adapted, it can be done. If there is a big difference between the original device and the new device, some of its modules can be reused.
3、 Reliable work
It is very reliable to control the system with PLC. This is because the programmable controller has taken a lot of measures in both hardware and software to ensure that it can work reliably. In fact, if the PLC is not reliable, it can not be used in the industrial environment, it will not be a PLC.
(1) In terms of hardware:
The input and output circuits of PLC are electrically isolated from the internal CPU. Its information is transmitted by optocoupler or electromagnetic device. Moreover, the CPU board also has anti electromagnetic interference shielding measures. Therefore, it can ensure that the operation of PLC program is free from external electric and magnetic interference, and can work normally.
Most of the components used in PLC are non-contact and highly integrated, and the quantity is not too much, which also provides the material basis for its reliable work.
In the mechanical structure design and manufacturing process, in order to make the programmable controller work safely and reliably, many measures have been taken to ensure that the programmable controller can withstand vibration and impact. The ambient temperature can be as high as 50 ℃ and some programmable controllers can be as high as 80-90 ℃.
Some programmable controller modules can be hot standby, one host works, the other host also runs, but does not participate in the control, only for backup. Once the working host fails, the hot standby can automatically take over its work.
There is further redundancy, using one out of three design, CPU, I / O module, power module are redundant or part of them. Three sets work at the same time, and the final output depends on the results of most of the three decisions. This can make the probability of system failure almost zero, and make sure. Of course, the cost of such a system is very high, and it is only used in particularly important occasions, such as the crossing control system of railway station.
The working mode of PLC is scan and interrupt, which can ensure it can work orderly and avoid the “risk competition” of relay control system, and its control result is always determined; moreover, it can deal with the control in an emergency, which can ensure the timely response of PLC to the emergency and make the PLC work reliably.
In order to monitor whether the running program of PLC is normal, the monitoring program of “watchdog” is set in PLC system. When running the user program, first clear the “watchdog” timer and start timing. When the user program runs through a cycle, check the timer value. In case of timeout (generally less than 100ms), the alarm will be given. Serious timeout can also make the PLC stop working. Users can take corresponding emergency measures according to the alarm signal. If the timer does not time out, the starting process will be repeated and the PLC will work normally. Obviously, with this “watchdog” monitoring program, the normal operation of PLC user program can be ensured, and the “dead cycle” affecting the reliability of its work can be avoided.
There are many instructions to prevent and detect faults in the PLC to generate the prompt signal of whether the important modules work normally or not. The working condition of PLC and the system controlled by PLC can be monitored by compiling corresponding user program to ensure its reliable operation.
Every time the PLC is powered on, it needs to run the self-test program and initialize the system. This is the configuration of the system program, the user can not intervene. When there is a fault, there is a corresponding error signal prompt.
It is the strong reliability measures of PLC in software and hardware that ensure the reliable operation of PLC. Its average time between failures can be more than tens of thousands of hours, and the average time to repair is also very short when there is a failure, just a few hours or even a few minutes.
Some people have done a questionnaire about why to use PLC. In the answer, most users take the reliable operation of PLC as the main reason for choosing it, that is, the reliable operation of PLC is the first choice.
4、 Cost effective
The use of high and new technology will bring huge social and economic benefits, which is the embodiment of science and technology as the first productive force and the vitality of high and new technology. So is programmable controller.
Although the first investment of using PLC is larger, it is economical to use PLC in the long run. This is because:
Although the investment of using PLC is large, it has small volume, small space, less investment of auxiliary facilities, less power saving and operation cost, reliable work, less shutdown loss, simple maintenance, less maintenance cost, and can be used again and bring added value, etc., from which greater returns can be obtained. Therefore, in most cases, its benefits are considerable.
The above is the small series of “programmable controller” related content, through this article, I hope you have a certain understanding of the four characteristics of programmable controller. Finally, Xiaobian sincerely thanks for your reading. Every time you read, it is a great encouragement to Xiaobian. Finally, I wish you a wonderful day.