Application of Emerson Inverter and PLC in constan

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The application of Emerson Inverter and PLC in constant liquid level control

Abstract: This paper introduces the application of Emerson Inverter EV2000 Series in constant liquid level variable frequency energy-saving control of xuanliu well in steel plant

key words: frequency converter ultrasonic liquid level meter PID constant liquid level control data transmission radio station

Preface: the xuanliu well water system of Baotou steel strip plant supplies production water for the rolling line, and the whole water system operates circularly. In order to ensure the water level in xuanliu well, some centers are called microcomputers) the wood-based panel universal experimental machine ensures the basic balance, and the circulating water in the pool is pumped out by 5# pump (110KW) to prevent water overflow. Since the original system adopts soft start, the speed cannot be adjusted, and the control of water level depends on human attendance, which is controlled by opening and closing valves. Otherwise, at low liquid level, the pump will be vacuumized and the pump body will be damaged (cavitation); High liquid level will flood the water pump room and cause power failure. For this reason, we design a frequency conversion constant liquid level control system. The ultrasonic liquid level detector (Baxter company) is used for liquid level detection, and the liquid level closed loop is formed through the internal PID of the frequency converter to realize the automatic constant control of the liquid level

1. The composition of frequency conversion constant liquid level control system

the pump motor of the system is 110KW, four levels, and the speed is 1480r/min. Evt1100p series general frequency converter is used as the control core of water pump motor in the design. Fbson-y-05-n series ultrasonic level detector produced by Baxter Industrial control company is used for liquid level detection, with AC220V power supply and integrated installation. The maximum range can reach 5 meters, and the maximum actual detection water level is 1.85 meters. The schematic diagram of the system is shown in Figures 1 to 3

an ECB is used for simple relay interlocking. In addition to interlocking with the old system, there is also a simple start, stop and alarm of the frequency converter. The system is also equipped with an ECB, which communicates with a data transmission radio (Modbus) through serial port to realize interlocking with another water pump room (clean ring pump room). When there is a high liquid level alarm in xuanliu well, it is transmitted to the clean ring pump room through PLC and data transmission radio, and the operator determines the start and stop of the water pump (because the two are too far away and are not suitable for cable laying, wireless data transmission is adopted). The PLC in xuanliu well is set as the master station, and the PLC in Jinghuan is set as the slave station. The data transmission radio adopts two pt6080 36000 KVA submerged arc furnaces, two sets of 50 ton intermediate frequency electric furnaces and one set of 50 ton AOD refining furnace produced by Shenzhen kelixun. The radio is a module with large power and small volume designed by using advanced single-chip microcomputer technology, radio frequency technology and digital processing technology. The experimental results show that the half duplex data transmission radio adopts SMT new technology and high-quality components. It has strong anti-interference ability, exquisite and firm, compact structure and convenient installation. Data and voice are compatible, and data transmission can take priority. RS232, RS485 and TTL interfaces can be selected to adapt to wide range. See the following schematic diagram:

2. Variable frequency constant liquid level control parameters and working principle:

2.1 EV2000 general technical specifications:

2.2 to achieve constant liquid level control in xuanliu well, we use the given potentiometer as the liquid level setting, and the feedback adopts the ultrasonic liquid level meter (transmission output MA). Make pressure closed-loop regulation through the PID regulator inside the frequency converter. The parameters of the frequency converter are set as follows:

fp 01=0 parameter write protect selection, All parameters can be rewritten

f0.00=3 given as VCI simulation given

f0.03=1 terminal operation

f0.04=0 steering is positive

f0.08=1 load is fan type

f0.10=15 acceleration time

f0.11=15 deceleration time

f0.14=1 v/f curve setting (power 2, pump load characteristics)

f5.00=1 closed loop operation is effective

f5.01=1 given as VCI

f5.02=1 feedback as CCI (pay attention to line adjustment changes), Ultrasonic output

f5.09=20 minimum quantitative corresponding feedback (4mA, 20% relative to 20mA)

f5.12=0.10 proportional gain

f5.13=0.05 integral time

fh 00=4 four pole motor

fh 01=110 power 110kw

internal PID control block diagram of frequency converter:

2.3 ultrasonic parameter setting

a, measurement mode selection: distance measurement

b, measurement range: cm

c, response speed selection: slow

d, safe level: maintain

ultrasonic Working Voltage 220VAC, output signal is ma

in order to reliably detect liquid level, the response speed of ultrasonic transmitter must be slow. This is because too fast response speed will cause disturbance of external interference signals, which will make the liquid level signal change too fast and affect the normal operation of the equipment. Slow down, but you don't know? So as to output the actual stable current signal after the signal is comprehensively averaged

3. Actual operation effect

after a period of on-site operation, the effect of variable frequency constant liquid level operation is very good. When a liquid level height is set with a potentiometer, the frequency converter operates in a constant liquid level control mode. When the liquid level is set to 70cm, the actual liquid level in the xuanliu well is basically constant between cm. When the liquid level is lower than 70cm, the frequency of the frequency converter decreases until it finally stops at the lowest operating frequency (20Hz). This is because if the operation frequency of the frequency converter is too low, the lift of the water pump is not enough, and the motor power is wasted, which is not conducive to energy-saving operation. Setting the minimum operating frequency can make the pump lift meet the requirements (circulating water in xuanliu well will not cause the liquid level to be too low and the pump to vacuum under the lowest operating power). The frequency of frequency converter generally reaches about Hz during production, so the energy-saving rate is very high (about 40%), and the constant liquid level control greatly reduces the labor intensity of operators. When the liquid level is too high for some reason, EC20 PLC and data transmission radio can also provide signals for the superior pump station to realize the interlocking control of the water system of the pump station, ensure the normal production water supply requirements, and greatly save electric energy (more than 35%), which is a model project for the energy saving and consumption reduction project of Baotou Steel

the attached schematic diagram is as follows:


① EV2000 series general frequency converter Emerson Energy Co., Ltd.

② new PID control and its application Machinery Industry Press Tao Yonghua

③ EC20 user manual Emerson Energy Co., Ltd.

④ general frequency converter and its application Machinery Industry Press Han Anrong

⑤ Baite industrial control field instrument selection manual Fuzhou Fuguang Baite automation equipment Co., Ltd (end)

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