Application of Siemens 300CPU and Aoyuexin 300PLC in Air Compressor Pneumatic Control System
1 Introduction
As the air source equipment of the pneumatic control system, the air compressor's stability and reliability during operation are directly related to production safety. Since most of the early electrical controls were relay circuits, they were prone to aging during long-term operation, thereby reducing sensitivity, and frequent shutdown failures during operation, which would affect normal production. The use of programmable controller technology to transform the control of the air compressor overcomes the shortcomings of the traditional pure relay control circuit. It can not only complete the control of the switch quantity, but also realize the control of the analog quantity. Meet the system's requirements for control accuracy and safety.
2 System working process
2.1 Working process of air compressor unit
After the equipment is powered on, the system first checks the operating conditions of the air compressor. When the cooling water pressure and the air compressor crankcase oil pressure meet the requirements, the 1# machine is started, and the 2# machine is used as a backup. The startup methods are all The y-δ starting mode is adopted, and the y-δ starting delay is 6 seconds. After starting, the air storage tank starts to inflate. When the air storage tank pressure reaches the set value of 0.7mpa, the air intake valve of the air compressor closes and the machine runs dry. When the pressure of the air storage tank drops to 0.65mpa, the intake valve opens and the air is charged again. When the pressure of the gas storage tank drops to the set value 0.55mpa due to failures and other reasons, and the 1# machine is in a shutdown state, the 2# machine starts and runs normally. The operating principle is the same as that of the 1# machine, and the gas storage tank continues to be inflated . When the pressure of the gas storage tank drops to 0.55mpa, and the 2# machine is in a shutdown state, the 1# machine starts and runs normally. At the same time, the normal running time of the two machines is 12 hours. That is to say, when one machine runs for 12 hours, no matter whether it is faulty or whether the pressure of the gas tank is lower than 0.55mpa, it will be shut down. And start another machine.
2.2 Working principle of gas drying equipment
Two compressors share a gas drying equipment. After the athermal gas dryer is turned on, the tower a first performs adsorption operation, and the tower b performs regeneration operation. Under the set timing control, the intake solenoid valve a2 is opened and a1, b1, and b2 are closed. The compressed air enters the tower a from the bottom through the a2 valve. During the upward transportation, the moisture in the gas is absorbed by the adsorbent in the tower. The dry gas enters the gas storage tank through the shuttle valve c. At the same time, after a2 is opened, b1 is opened with a delay of 10 seconds, and the residual gas in tower b is used to move from top to bottom to remove the The small points are taken out from the b1 valve and emptied through the muffler. The 10 seconds of its opening is for tower b desorption. After a delay of ten minutes after the opening of a2, the solenoid valve b2 opens, while valve a2 is closed, and tower b is inflated. After ten seconds, valve a1 is opened. The water in tower a is taken out to desorb tower a, and the valve a1 is closed after a delay of ten seconds. At this time, because the pressure in tower a drops and the pressure in tower b increases, the shuttle valve c closes the exhaust port a and opens the exhaust port b. In the same way, after the b2 valve is opened for ten minutes, the a2 valve is opened, the b2 valve is closed, and the delay is ten seconds, and the b1 valve is opened to make the b tower perform desorption operation. In this way, the two towers operate alternately to dry the gas.
Figure 1 Working principle of air compressor unit
3 System control requirements
3.1 Control requirements for air compressors
(1) Turn on the power before starting up, all the status indicators installed in the control room and on-site will light up, showing the current status.
(2) Press the start button, the air compressor starts in the y-δ mode, the solenoid valve of the air inlet opens, and the air storage tank is inflated. In addition, when starting, two machines are not required to run at the same time, but either one can be run first.
(3) If the machine is running for more than 12 hours or fails, the standby machine will start and run.
(4) During operation, if water pressure or oil pressure is insufficient, stop immediately and give instructions.
(5) Press the stop button to stop.
3.2 Control requirements for gas dryer
The control of the gas dryer is synchronized with the operation of the air compressor, and is turned on together with the power supply of the air compressor, and its start is controlled by the main contactor of the air compressor.
4 System hardware design
4.1 System configuration
This design uses Siemens 300CPU, and the I/O ports use OYES-SM321 and OYES-SM322 digital input/output modules and OYES-SM331 analog input modules to expand sequentially on the second SM port of its No. 3 expansion slot .
4.2 Expansion unit I/O distribution and wiring
Assign the expansion ports of Aoyuexin 300PLC, and the definition of I/O ports is shown in the attached table.
For the acquisition of switch signal, when the air compressor is running at high speed, it must have a good cooling system and lubrication system to avoid damage to the machine caused by the heat generated during the operation. Therefore, water pressure and oil pressure are the first considerations. The pressure switch is used to collect these quantities and connected to its digital input module sm321, the starting address is 100.0-100.3. The collection of analog quantity is mainly used to test the pressure of the gas storage tank to control the operation of the air compressor. These quantities need to be collected with a pressure transmitter, and the pressure of 0-1mpa is converted into a current signal of 4-20ma and sent to the analog input module SM331, whose starting address is 672-687. The hardware wiring is shown in Figure 2.
For the y-δ start of the air compressor, although it has been interlocked between km2 and km3, km5 and km6 in the software program design, for the safety of its operation, it is interlocked again in the hardware connection. Lock to ensure that a short circuit will occur due to contact ablation or other faults that cannot be disconnected when starting. The gas dryer part has four solenoid valves, which are controlled by km1 and km4 after the power is turned on. Once the machine #1 or #2 is started, the gas dryer will start to work. Below the tower a The a2 valve is opened, and the a tower works first. Then work according to the aforementioned working principle. Using km1 and km2 to control this part can ensure the synchronization of the gas dryer and the air compressor.
5 Software design
5.1 Air compressor control
Design its operating program based on the working principle of the air compressor. Turn on the machine and check its water pressure and oil pressure. When these conditions are met, the 1# machine will start and begin normal operation. It should be noted here that the start of the 2# machine in the movement, because it is controlled by the timer on the one hand, but also by the pressure control of the gas storage tank, when the pressure of the gas storage tank is lower than 0.55mpa, this Explain that the 1# machine is faulty, so the 2# machine is started, but this is the same as the initial condition of the 1# machine. When the machine is turned on, the pressure of the gas storage tank is 0, and both machines can run, so the pressure transmission is required here. The controller and km1 and km4 jointly control the startup. km1 and km4 are respectively connected in series with pressure transmitters to control the interlocking operation of the two machines. The running ladder diagram of the main and standby machines is shown in Figure 3. The start of 1# machine is controlled by i672 and q108.3, and the start of 2# machine is controlled by i672 and q108.0. In this way, when the pressure is lower than the set value 0.55mpa, the two machines will not start at the same time.
Figure 3 Air compressor ladder diagram
5.2 Gas dryer system control
The ladder diagram of the air compressor gas dryer system controls the gas dryer mainly based on the starting conditions of the two air compressors. As a common part, no matter which machine starts, it requires gas drying operation. Therefore, it is not necessary to design the start and stop buttons in the gas drying ladder diagram, but through q108.0 and q108.3, namely 1#, 2# machine km1 and km4 to complete its control.
6 Conclusion
After this transformation, during the operation of the air compressor, the number of visits to the site by the operator is reduced. By directly observing the working condition of the air compressor in the central control room, the alarm signal can be sent to the abnormal situation on the spot. Respond quickly, instead of waiting until other pneumatic control equipment has an insufficient air pressure alarm before discovering that there is a problem with the air compressor system. After more than a year of operation, except for the mechanical failure of the equipment, there were basically no control problems, which fully met the design requirements. The use of Aoyuexin PLC is cost-effective and the control of the air compressor makes it easy to operate, and the safety and stability during operation are further improved.
