As an execution amplification and expansion component of signal output, the intermediate relay plays an important role in the automatic control system. According to the regulations of the equipment periodic inspection system, necessary inspections and tests should be carried out regularly on the working status of the equipment. However, in on-site work, The detection of intermediate relays is a weak link that is easily overlooked. This article analyzes the necessity of PLC’s transformation of relay control circuits, focuses on the transformation of PLC’s relay control circuits, and finally puts forward relevant opinions and suggestions for the renovation project of PLC’s relay control circuits, providing guidance for the application of PLC in control circuits. Provide some reference.
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PLC is a programmable controller. It is a new industrial automation control device based on a microprocessor and developed by integrating computer technology, communication technology and control technology. The working process of PLC is generally divided into three stages: input sampling, program execution and output refresh. The completion of the above three stages is called a scan cycle. During PLC operation, because the scan cycle time is relatively short and the previous process has not yet executed the output, the following program terminates the action of the previous process, causing the automated production line to fail to operate normally. Timer (T) is an important aspect of the basic instructions of PLC. It can realize time-based control functions by relying on the internal clock pulse of PLC. The auxiliary relay (M) is a soft relay inside the PLC, which plays the role of logic transformation and logic memory in the PLC ladder diagram. This article uses the normally open contact of the timer and the auxiliary relay as the trigger condition to eliminate faults in automated production line control.
1 Analysis of PLC transformation of relay control circuit
First, determine the main circuit, input part and output part. The first is to determine the main circuit. In the process of using PLC technology, PLC can transform the relay control circuit. If there is no improvement and expansion of its functions, generally speaking, the main circuit will not change. Moreover, if there is no protection part in the circuit, the relevant staff must add it to the circuit. Also, if you want to expand the circuit function, you must redesign the circuit so that the circuit can adapt to new changes and requirements. The second is to determine the input part. The input information is the main information for controlling electrical appliances. Only by confirming the input information can we better grasp the contacts of the master control electrical appliances. The third is to determine the output part. The so-called output is the part that controls the execution of electrical appliances. In the process of using PLC technology to control relays, the execution part of controlling electrical appliances must be determined. The output part requires an AC control environment. If the PLC is not equipped with an AC interface, then the external interface of the intermediate relay should play the role of introducing AC power into the device.
Secondly, related matters that need to be paid attention to during the specific transformation process. The first step is to understand the specific tasks, understand the specific output and input devices, and draw the PLC wiring diagram before performing specific operations. Generally speaking, the contacts of the input part should use normally open contacts. Only in this way can some people who have just come into contact with PLC technology better understand this technology and further master the conversion between PLC programs and control schematic diagrams. Relations, however, use hard chaining for the output part, and the chaining part must be retained. The second step is to select the programming components. Generally speaking, the input part is replaced by X and the output part is replaced by Y. Pay attention to the one-to-one correspondence of the numbers for these two parts. The third step is to avoid short circuits and eliminate contact competition. Due to the characteristics and nature of the PLC’s scanning working method, competition may occur in some cases, which will eventually lead to phase-to-phase short circuit of the power supply. The occurrence of this situation will cause big problems, so competition must be eliminated and improved. security and stability[1].
Finally, there are two points that need to be paid attention to in PLC technology. The difference between PLC technology and relays mainly includes two aspects: on the one hand, the order of PLC cannot be reversed when scanning. It scans step by step according to certain steps. However, relay circuits can make all relays The contacts of the relay act simultaneously, which means that the sequence of the relay steps can be reversed. On the other hand, the PLC ladder diagram is a very strict QR code. There cannot be cross lines in the PLC ladder diagram. In addition, the contacts cannot be placed in a vertical position.
2 Auxiliary relay application examples
In PLC, the auxiliary relay (M) functions as an intermediate relay in the relay control system. The auxiliary relay cannot directly drive external loads and is only used for internal programming.
By downloading and debugging the program, it was found that the lifting cylinder of the unit station oscillated up and down and could not be completely reset, causing the subsequent program of the unit to be unable to run. After analysis, the error in this program is that because the lifting cylinder is a single electronically controlled cylinder, the normally open contact of the timer is closed instantaneously, and the spring of the lifting cylinder is reset. Since the reset time exceeds the scan cycle of the PLC, the lifting cylinder is set again. , thus causing the lifting cylinder to oscillate up and down. In order to completely reset the lifting cylinder, when the normally open contact of the timer is closed instantaneously, the auxiliary relay M0 is set, and the normally open contact of M0 is used as the trigger condition for cylinder reset, and M0 is reset at the end of the program. Through debugging, the station can operate normally [2].
3 Strengthen PLC opinions and suggestions on the transformation of relay control circuits
First, relevant personnel should strengthen their understanding of PLC technology and improve staff’s awareness of using PLC technology. In order to give full play to the role of PLC technology, you must first have a full understanding of PLC technology, master all aspects and requirements that need to be paid attention to, and various skills in the application of PLC technology. Moreover, you must also use PLC technology according to the requirements. , only in this way can the safety and rationality of the application of PLC technology be improved. In addition, relevant staff must strengthen their awareness of the application of PLC technology, actively use PLC technology in traditional line control, and use PLC technology to transform relay control lines.
Second, sufficient preparations must be made when using PLC technology. In the process of using PLC technology, you must first draw the PLC drawings and design the drawings scientifically and rationally based on the actual situation. Moreover, in the process of using PLC technology, you must be realistic and formulate a PLC operation plan based on the actual situation. In addition, relevant materials must be prepared during the process of PC transforming the relay control circuit, so that the PLC can smoothly transform the relay control circuit [3].
Third, certain rules and sequences must be followed when using PLC to transform relay control circuits. Since PLC technology has some new characteristics compared to traditional technology, certain rules and requirements must be followed in the process of using PLC technology.Keywords: Industrial Ethernet data transmission terminal