PLC automatic control system is adopted to realize

Using PLC automatic control system to realize automatic control of air compressor station

under the condition that air-jet looms are widely used in cotton textile enterprises, the construction of air compressor station is an important auxiliary project. The main equipment equipped in all air compression stations in Tianjin textile park are centrifugal air compressors and refrigerated air dryers, which form a compressed air supply system through air storage tanks, connecting pipes and valves, and are equipped with cooling system, instrument air system and computer detection system, so as to ensure the gas demand of different pressures and loads with the air compression station as the production line. On this premise, ensuring qualified gas supply quality, meeting stable gas supply pressure, and automatically adjusting gas supply flow are the basic tasks of automatic control of air compressor station. With the continuous improvement of automation level, the discussion on the construction of unattended air compressor station is an inevitable topic in the development process

necessity of automatic control of air system

it is applied to the air compressor station of cotton spinning No. 1 Factory of Tianfang Investment Holding Co., Ltd., which is equipped with 4 sets of 70m3/min, 4 sets of 53m3/min, 2 sets of 48m3/min, 4 sets of 43m3/min centrifugal air compressors and 1 set of 42.5m3/min screw air compressor, and is equipped with refrigeration dryer with corresponding processing capacity. The CMC controller of the air compressor equipment can automatically control and protect the operation of the host, automatically prompt work information, have fault alarm and protection shutdown functions, can automatically load or unload according to the size of air consumption, and is equipped with LCD display for on-site observation of various process parameters and equipment status. It has rs422/485 communication interface, and can realize the complete connection with the computer monitoring system in the field control room

at present, the automatic control system of the air compressor station can mostly measure metal and non-metal materials, engineering structures, mechanical part characteristics, etc. under various conditions through Siemens S7. 300 programmable controllers collect the real-time operation data of some air compressors into the PLC control system through rs422/485 communication interface, and transmit the data to the computer in the field control room for display, so as to replace the traditional instruments. However, the air compressor was not controlled

the CMC controller of the air compressor equipment can control a single air compressor well, but it does not have the overall regulation ability of the air compressor system. In the air pressure system, compared with the adjustment of a single air compressor, the overall automatic regulation of the air pressure system is more important:

■ a single air compressor cannot guarantee the stability of the overall air supply pressure of the air pressure system, while the overall automatic control of the air pressure system can effectively maintain the stability of the air pressure in the system

■ overall load balancing and reducing exhaust venting can save more energy and labor costs. 29 new chemical materials in the fields of special rubber, engineering plastics, membrane materials, electronic chemicals and so on are listed in the category of advanced basic materials

■ it can realize unmanned operation, and automatically start or load the air compressor according to the actual needs to maintain the system pressure

■ it can record the operation data and alarms of the air compressor at fixed time, such as trip, surge, communication failure, pressure, etc

in the existing PLC system, the overall regulation function of the air pressure system is not realized. Since the CMC controller of the air compressor provides rs422/485 communication interface, all data acquisition and control functions are realized through the communication interface. Compared with the original control system, there is no need to increase the investment of hardware equipment, but only need to improve and increase the control software to realize the overall control of the air compressor system

in addition to the air compressor equipment, the refrigeration dryer matched with the air compressor can also be integrated into the rs422/485 network to realize the full automatic control of the air compressor air supply equipment

automatic control of other systems in the air compressor station

in addition to the air compressor air supply system, other systems in the air compressor station also need automatic control, such as water circulating cooling system. The control method of these systems is different from the air pressure air supply system, which mainly adopts the traditional control mode. The automatic control of the system can be realized by using the instrument to collect the required operating parameters, conduct data processing, analysis and calculation, and output the control signal to the actuator

automatic control has the following advantages:

■ simple operation, can realize unattended

■ good real-time adjustment prevents human factors from lagging behind

■ high reliability

■ reduce the burden of staff

■ save labor costs

parameters to be controlled and possible control methods

control requirements for air compressor station; (1) high and low pressure air supply pressure control (automatic start and stop control of the unit); ⑵ automatic drainage control of the system; ⑶ circulating water level control and automatic dosing control; (4) parameter control of required compressed air temperature, circulating water temperature, etc

the overall automatic control of the air compression system can generally be achieved by one of the following two methods:

⑴ PLC system is used for communication and control

⑵ Ingersoll Rand or its own control software can be used

the first method has high reliability and is suitable for industrial control systems. When the monitoring computer fails, PLC can also carry out automatic control according to the set program

"west wind" overwhelms "east wind". The second method is to control through the computer of the control system to conduct separate analysis and calculation. It has good flexibility, but the disadvantage is that if there are faults such as computer crash, it may affect the normal operation of the system. Fortunately, the general recovery of computers often does not take much time

in addition to the automatic control of the air compressor and gas supply system, the air compressor station can establish an equipment control network with the refrigeration station and heating station system to realize centralized control, or connect with the factory control center, and the controller of the control center can monitor in real time and remotely, so as to realize real unattended

system composition

for the above discussion, if it is necessary to realize the overall automatic control of the air compressor station, many mature PLC automatic control systems can be selected. Now take the PLC automatic control system of ZH company as an example

the automatic control system adopts Siemens s series programmable controller, with rs422/485 network interface, and supports MODBUS and other related network communication protocols. The system can use special industrial communication network technology to implement remote connection. The automatic control equipment of the air compressor station can establish the implementation scheme of the hierarchical control network after integrating various factors according to the actual production situation, the characteristics of each equipment, and the possible problems, as shown in Figure 1

■ hardware configuration

field instruments, controlled equipment, actuators, equipment with serial communication interface (e.g. empty