Application of new PID control method in high and low temperature laboratory The implementation of PID control in high and low temperature laboratory involves more professional knowledge. Therefore, it is necessary to analyze the structure and composition of the control system, clarify the temperature control principle, and design a control system that meets the requirements. In order to promote its better application, continuously improve the control level of high and low temperature laboratories, and create favorable conditions for the smooth implementation of the test.
First, the PID control system structure The high-low temperature laboratory PID control method discussed in the paper is based on the PID control system. The system is mainly composed of PC and PLC. The control of the refrigeration unit and heater is completed through the control cabinet. At the same time, under the control of PLC, the PPI cable is used as the free port communication medium of the upper computer, and the graphic display and data are managed in combination with the field data. Under the control of the system, the temperature can be adjusted to the range of -100 ° C ~ +200 ° C, and the accuracy is controlled at ± 1 ° C.
The main circuit in this control system is an important part, and the number and characteristics of the controlled equipment need to be comprehensively analyzed during design. The two refrigeration units designed in this paper are M1 and M2, which are controlled by contactors K1 and K2 respectively. In order to ensure the uniformity of the temperature in the test chamber, the K3 contactor is used to control the indoor fan. In addition, K4 and K5 are responsible for controlling the two heaters and controlling their heating using a solid state relay SSR.
At the same time, the S7-200 is used as the CPU module of the PLC, and the expansion module uses the EM231. The pt100 sensor in the entire system acquires the temperature in the chamber through the EM231. In order to ensure the measurement accuracy, the three-wire connection method is used in the design. In addition, Q0.1 and Q0.0 at the output are responsible for controlling two refrigerators, while Q0.3 and Q0.4 are responsible for controlling two sets of electric heaters, and Q5 controls the illumination in the test chamber.
The temperature control algorithm is responsible for the upper PC, and the calculation result is transmitted to the PLC under the support of the PPI. The heating of the electric heater is controlled by Q1.0 through the SSR.
Second, the principle of PID temperature control
The implementation of PID temperature control is mainly carried out under the PID algorithm, and it is necessary to carefully analyze the PID parameter setting in combination with the control process to construct a special PID parameter generation system. The system consists of a rising section T1, a constant temperature section T2, a cooling section T3 and a constant temperature section T4. In order to meet the test temperature control accuracy requirements, to ensure that the actual temperature control curve is better matched with the set curve, it is especially important to do the PID parameter tuning. This paper constructs a PID parameter generation system, and determines the control parameters of the temperature control section by the following matrix:
It is convenient to program the PID parameter generation system on the host PC. In addition, for some special parameters, it needs to be determined in the debugging system. In addition, the system operation needs to use the bit-type output to meet the system output requirements based on the incremental PID algorithm, that is, in the period T time, based on the reference PID output normalization result, determine the SSR conduction. time.
Third, the application of PID control system In order to ensure the better application of PID control system in high and low temperature laboratory, the application should pay attention to the following content:
1. Prepare for application The PID control system designed in this paper has a complicated structure and involves a lot of professional knowledge. The normal operation of the system directly affects the application effect. Therefore, the application should be fully prepared to strengthen the technical research and ensure the PC. The functions of communication between the machine and the PLC, control of the test chamber temperature, and data management editing curve are smoothly realized. First, when communicating between a PC and a PLC, the PPI cable is mainly used to connect the COM and free ports of the PC and PLC to provide an information transmission channel for both. Secondly, when controlling the temperature of the test chamber, the PID parameter generation system and the PID control algorithm are mainly applied. Therefore, it is especially important to study the PID control algorithm to ensure the rationality of the algorithm. Finally, the experiment will generate a large amount of data, and the application needs to apply a special database to manage the graphics and data information generated by the experiment. At the same time, the curve editing function is realized by means of the curve editing program. In addition, in order to facilitate the operation of the test personnel, the application should be designed with a friendly interactive interface, in line with the tester's operating habits.
2. Writing a reasonable software program To ensure the good application of the new PID control method in high and low temperature laboratories, professional software system support is required. The written software needs to implement the following functions: (1) Failure during the test, automatic detection and alarm (2) It can realize the management of the database and has the report printing function; (3) It can display the temperature curve in real time and support zooming; (4) The number of input chillers, heaters and related parameters can be set freely. Test the requirements for temperature control.
3. Do a good job of software and hardware debugging After completing the hardware and software design, in order to find out and solve the problems in the system operation in time, the software and hardware debugging work should be done. On the one hand, clear debugging operations. The designer should combine the high and low temperature laboratory control requirements and the various functions of the system, clarify the details of the commissioning operation, and carry out the commissioning work according to certain procedures and specifications. On the other hand, solve the bad problems in the system in time. In the debugging work, once the problem is found, it should be carefully analyzed whether it is a hardware problem or a software problem, analyze the cause of the problem, and solve it in time to ensure the smooth implementation of each function.
Finally, the designed system is applied to the temperature control in the test chamber, which is not only easy to operate, but also has the control precision to meet the expected requirements, and has good promotion value.
IV. Conclusion High and low temperature laboratories are commonly used equipment for industrial production and scientific research. In order to ensure the smooth progress of relevant tests, active methods have been actively adopted to continuously improve the control accuracy and level of test chambers, which has become a hot topic in the industry. The new PID control method discussed in this paper is based on the newly designed system. The following conclusions are drawn through research:
(1) The PID control system designed in this paper is mainly composed of PC and PLC. In addition to ensuring normal communication between the two, the temperature control principle should be clarified. This paper provides support for the realization of temperature control through PID parameter generation system and PID algorithm.
(2) In addition to the hardware design in the design, the normal operation of the system also needs software system support. Therefore, the rationality of the software design should be ensured according to the test requirements.
(3) Applying the PID control system designed in this paper to the high and low temperature laboratory, it is not only easy to operate, but also powerful in function, and the control precision meets the test requirements, which has high promotion and application value.
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