Hollysys LM series PLC in the control system of the screw compressor applications

Pick to: this paper introduces the screw compressor control system consisting of PLC and instrumentation. This system is combined with the actual application, upgrade of screw compressor control system. Using results show that the system operation is reasonable, the real-time data record and display convenient intuitive, more security and stability of system operation. Keywords: hollysys LM series PLC; 1 introduction screw compressor screw compressor control system is widely used in mining, chemical, power, metallurgy, construction, machinery, refrigeration and other industries, has the advantages of high reliability and strong applicability, gradually replaced by other types of compressor. Statistics show that sales of screw compressor have accounted for more than 80% of all positive displacement compressor sales. The market share of screw compressor in the future, will still be growing, especially the oil-free screw compressor for faster development. The basic working principle of screw compressor 2 screw compressor belongs to positive displacement compressor. Screw compressor is equipped with a pair of gears in the cylinder helical rotor Yin and Yang, the two rotor has several concave tooth, the two counter-rotating with each other. Between the rotor and clearance between casing is only 5 ~ 10 silk, main rotor is also called Yang rotor or convex rotor, driven by the engine or motor, most of which driven by motor. The rotor is also called the Yin rotor or rotor, by the main rotor through the injection forming of the oil film drive, or by the main rotor side and concave rotor of the synchronous gear drive. Spiral rotor groove after suction mouth is full of gas. When the rotor rotation, the rotor groove casing wall closed, forming the compression chamber. When the rotor groove closed, lubricating oil is sprayed into the compression chamber, seal, cooling and lubricating effect. When the rotor rotating compressed gas mixture ( That is a mixture of lubricant and air) Vent, compressor chamber volume reduced to compressed gas mixture. When the compression chamber through the vent, mixture of oil and gas from compressor discharge, complete with a suction, compression and exhaust process. Screw compressor working cycle can be divided into three suction, compression and exhaust process. With the rotation of the rotor, each pair of mutually meshing tooth have do the same work cycle. 3 screw compressor control system hardware design early screw compressor control systems installed by the instrument box installed in the field instruments, no remote meter, by artificial site operation. Through the field of pressure, differential pressure switch and temperature switch with electric cabinet to control the start and stop of compressor operation. The temperature, pressure, differential pressure switch and electrical contactor, time relay, such as cooperate with each other, realize automatic protection chain function of the compressor, to ensure the safety of the compressor stable running. This kind of control mode are the obvious defects, because the operator can't specific details about the compressor running status, and poor stability of this kind of instrument, precision is low. In order to solve these defects, the hardware part of the control system by PLC, instrumentation, input devices, output devices, and touch screen, etc. Field data acquisition using remote meter, pressure transmitter, thermal resistance to replace the original pressure, differential pressure switch, temperature switch and the thermometer, realize the data remote transmission, improve the accuracy of measurement. Control part adopts PLC and HMI, powerful logic control based on PLC controller and PC record analysis function, friendly visual images, data display and operation, perfect the chain unit safety protection function, improve the operation control performance. Both can guarantee the safe operation of the centralized, and can make the operator details about running status of the unit. Screw compressor control system hardware structure diagram is shown in figure 1. Figure 1 screw compressor control system hardware structure diagram of programmable controller by hollysys company LM 3109, change I/O modules including 24 channel 24 VDC input / 16 channel relay output, can extend the biggest seven extension module, a user program storage space for 120 k bytes, useing keep area is 6 k bytes; With password protection and real time clock; The timer counter any point; Basic instruction 340, extension instruction for 47; Communication interface includes a RS232 and RS485; Support proprietary protocol ( RS232 only) / MODBUD RTU protocol/freedom. Touch screen is used in working state, data is alarm display and parameter setting and the remote control. 4 screw compressor control system software design of a screw compressor load adjustment by 6 solenoid valves. Each solenoid valve opening can be 25%, 50%, 75%, 100%. Compressor load time, work time less open first, then according to the four level were 25%, 50%, 75%, 100%, in turn, open it. Unloading compressor, work time more to uninstall first, and then according to the four level were 100%, 75%, 50%, 25%, in turn, closed. It is important to note that at 25% level, turn off the compressor, the delay time before closing 25% solenoid valve. Screw compressor control system of the main program flow chart shown in figure 2, loading and unloading flow chart shown in figure 3. Figure 2 main program flow of the control system of screw compressor tutu 3 screw compressor flow chart of load and unload 5
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