交流励磁电磁流量计新型转换器设计
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摘要
电磁流量计是依据法拉第电磁感应原理来测量导电流体体积流量的流量仪表。转换器将传感器感应电动势信号转换成统一的标准电流输出或数字通讯信号,是电磁流量计的关键组成部件。转换器的设计主要涉及两个问题:一是由前端传感器励磁方式决定的信号处理方式,二是转换器抑制、消除各个干扰的处理能力。
工频励磁流量计测量窗口比较宽,而且可以测量液固两相混合液,可以弥补低频(1/8～1/32工频)矩形波励磁流量计只能测量液体流量的缺陷。但采用工频励磁会引入微分干扰、同相干扰,给转换器的设计带来很大难度。以前的转换器集成度不高,其稳定性、抗干扰性等各方面比较差,且体积庞大,无法满足当前工业生产现场的需要。
针对以上问题,本文设计了一种基于工频励磁的电磁流量计新型转换器,主要工作为:(1)着重解决转换器的抗干扰问题:提出了一种消除微分干扰和同相干扰的新方法,即通过三角函数关系来消除微分干扰和同相干扰,并采用集成电路实现了基于此方法的硬件电路;(2)对于参考信号的选取,采用变压器作为参考信号;(3)对于励磁频率波动导致流量信号和参考信号带来相位差不确定的问题,利用对称方法使得两信号相位差恒定;(4)对于电源电压幅值的波动带来的误差,利用除法器来消除。
实验表明:新型转换器提高了抗干扰性、零点的稳定性和测量精度。转换器还增加了液晶显示、实时时钟、RS-232接口等智能模块,使用方便,成本较低。
Electromagnetic flow meter (EMF) , which is based on Faraday's induction law, is an instrument to measure the volume flow of conducting fluid. As a key part of the EMF, the transducer which converts induced electromotive force signals into unified standard current output or digital communication signals. There are two problems for the transducer design. The one is the input signals processing mode in transducer, which is decided by the excitation pattern of front-end sensor, and the other one is the capability of transducer to inhibit and eliminate disturbance.
Compared with EMF excited by low frequency rectangle wave designed only for liquid flow measurements, EMF excited by power frequency has wider measurement bandwidth, and also can measure liquid-solid two-phase mixed flow, which cover the shortage of the former. But when power frequency excitation is adopted, it will incur differential interference and in-phase interference, and thus brings a large difficulty in transducer design. The traditional transducer with low integrity has disadvantages such as poor stability and anti-interference, huge size etc., which can not reach the requirements of industry production field.
In order to solve the problems mentioned above, a new transducer based on EMF excited by power frequency is designed. The main works in this thesis are as follows. (1) More emphasis is put on how to solve the anti interference, and a new method based on trigonometric function is proposed to eliminate the differential interference and in-phase interference. (2) In order to choose reference signal, innovative adopt transformer as reference signal. When transformer is chose as the source of reference signal, the circuit design is easy and the safety of circuit is improved. (3) Symmetry method is adopted to keep the phase difference constant, solving the problem of the uncertain phase difference between the flow signal and reference signal caused by excitation frequency fluctuation. (4) Divider is used to eliminate the error, which is caused by power voltage fluctuation.
The experiment shows that the new transducer's noise immunity, zero point stability and measurement precision are greatly improved, and some intelligent modules such as LCD display, real-time clock, RS-232 interface are also introduced, which makes the instrument convenient and low cost.
工频励磁流量计测量窗口比较宽,而且可以测量液固两相混合液,可以弥补低频(1/8～1/32工频)矩形波励磁流量计只能测量液体流量的缺陷。但采用工频励磁会引入微分干扰、同相干扰,给转换器的设计带来很大难度。以前的转换器集成度不高,其稳定性、抗干扰性等各方面比较差,且体积庞大,无法满足当前工业生产现场的需要。
针对以上问题,本文设计了一种基于工频励磁的电磁流量计新型转换器,主要工作为:(1)着重解决转换器的抗干扰问题:提出了一种消除微分干扰和同相干扰的新方法,即通过三角函数关系来消除微分干扰和同相干扰,并采用集成电路实现了基于此方法的硬件电路;(2)对于参考信号的选取,采用变压器作为参考信号;(3)对于励磁频率波动导致流量信号和参考信号带来相位差不确定的问题,利用对称方法使得两信号相位差恒定;(4)对于电源电压幅值的波动带来的误差,利用除法器来消除。
实验表明:新型转换器提高了抗干扰性、零点的稳定性和测量精度。转换器还增加了液晶显示、实时时钟、RS-232接口等智能模块,使用方便,成本较低。
Electromagnetic flow meter (EMF) , which is based on Faraday's induction law, is an instrument to measure the volume flow of conducting fluid. As a key part of the EMF, the transducer which converts induced electromotive force signals into unified standard current output or digital communication signals. There are two problems for the transducer design. The one is the input signals processing mode in transducer, which is decided by the excitation pattern of front-end sensor, and the other one is the capability of transducer to inhibit and eliminate disturbance.
Compared with EMF excited by low frequency rectangle wave designed only for liquid flow measurements, EMF excited by power frequency has wider measurement bandwidth, and also can measure liquid-solid two-phase mixed flow, which cover the shortage of the former. But when power frequency excitation is adopted, it will incur differential interference and in-phase interference, and thus brings a large difficulty in transducer design. The traditional transducer with low integrity has disadvantages such as poor stability and anti-interference, huge size etc., which can not reach the requirements of industry production field.
In order to solve the problems mentioned above, a new transducer based on EMF excited by power frequency is designed. The main works in this thesis are as follows. (1) More emphasis is put on how to solve the anti interference, and a new method based on trigonometric function is proposed to eliminate the differential interference and in-phase interference. (2) In order to choose reference signal, innovative adopt transformer as reference signal. When transformer is chose as the source of reference signal, the circuit design is easy and the safety of circuit is improved. (3) Symmetry method is adopted to keep the phase difference constant, solving the problem of the uncertain phase difference between the flow signal and reference signal caused by excitation frequency fluctuation. (4) Divider is used to eliminate the error, which is caused by power voltage fluctuation.
The experiment shows that the new transducer's noise immunity, zero point stability and measurement precision are greatly improved, and some intelligent modules such as LCD display, real-time clock, RS-232 interface are also introduced, which makes the instrument convenient and low cost.
引文
[1]魏金汇,肖秀芳.电磁流量计及其应用[J].炼油化工自动化,1997,2:62-68.
[2]黄宝森.电磁流量计[M].北京:高等教育出版社,1988:1-195.
[3]纪常杰,周润才.如何选择合适的流量计[J].国外油田工程,2001,17(9):9.
[4]蔡武昌,马中元.电磁流量计[M].北京:中国石化出版社,2004,30-34.
[5]蔡武昌.电磁流量计的现状和进展[J].世界仪器与自动化,1998,2(4):40-43.
[6]李素蓉.行业差异性与市场份额分配浅析[J].中国仪器仪表,2003,5,4-5.
[7]鲁崇恭,马中元.带微机电磁流量计转换器的研究[J].计量学报,1992,1:52-58.
[8]蔡武昌.电磁流量计应用近况和技术发展[J].炼油化工自动化,1997(4),52-56.
[9]D.Reily,GEdmunds.Development of an electromagnetic flowmeter for cryogenic fluids[J],USA:NASA Lewis Research Center,1964.
[10]VCushing.Electromagnetic flowmeter for insulating liquids[C].Proc,19~(th)IEEE IMTC,Anchorage,2002:103-108.
[11]Z.Z.Yu,A.T.Peyon,M.S,Beck Imaging system based on electromagnetic tomography(EMT)[J].Electromagnetic Letter,1993,29(7):625-626.
[12]Zhang XiaoZhang.Reconstruction of flow patterns by means of electromagnetic induction [C].FLOMEKO,1996:82-84.
[13]Zhang XiaoZhang.2D analysis for the virtal current distribution in an electromagnetic flow meter with bubble at various axis positions[J].Meas,Sci,Technol,1998,(9):1501-1505.
[14]张宏建,管军.基于电磁感应原理的多电极流量测量方法[J].计量学报,2004,25(1):43-46.
[15]凌志浩,吴勤勤,张心泉.应用广泛的交流励磁磁场电磁流量计[J].造纸装置与设备,2006,25(6):53-54
[16]Raker R,Deacon J.The behavior of turbine vortex and electromagnetic flow meters[J].The Chemical Engineer,1984,(3):13-15.
[17]A.Kolin,An A.C.Induction Flowmeter for Measurement of Blood How in Intact Blood Vessels,Proc,Soc,Expt,Biol,1941:235.
[18]穆志坚,李大成.电磁计量技术[M].北京:机械工业出版社,1988:214-224.
[19]G.Y.Tian,G.P.Lucas.Numerical Simulation Modeling for Velocity Measurement of Electromagnetic Flow Meter[J].Institute of Physics Publishing,2006:36-40.
[20]王刚.低频矩形波励磁电磁流量计设计[D].重庆:重庆大学,2005:16.
[21]王国强,吕波,张小章.非对称流动对电磁流量计输出的影响[J].计量技术2003,(10):3-5.
[22]王新堂.励磁信号控制技术及其在电磁流量计中的应用[J].电测与仪表,1995,(7):21-23.
[23]Jea-eun CHA,Yeh-chan AHN.The performance of Electromagnetic flowmeters on a liquid metal two-phase flow[J].Nucl.sci.Technol.2003:3-4.
[24]潘祥明.电磁流量计及其普遍方程式[J].仪器仪表学报,1989(4):34-35
[25]高小朋,杜鸿雁.电磁流量计的干扰产生及其抑制和消除[J].计量技术,2007,No 3.
[26]王俭.电磁流量计低频正弦波励磁方法的研究[D].浙江:浙江大学,2006:16-17.
[27]李小京.电磁流量计放大滤波电路设计[J].化工自动化及仪表,2000,27(2):50-52.
[28]唐惠强,佘艳.基于MSCl211的电磁流量计的硬件设计[J].仪表技术与仪器,2007(12):50-51.
[29]Paul Horowitz,Winfield Hill,THE ART OF ELECTRONICS[M].北京:电子工业出版社,2005.
[30]CA3140[K],Intesil Corporation,1999.
[31]康华光.电子技术基础模拟部分[M].北京:高等教育出版社,2002.
[32]Four-Channel,Four-Quadrant Analog Multiplier of MTL04[K].ANALOG DEVICES.
[33]张国雄.测控电路[M].北京:机械工业出版社,2001.
[34]Low-pass filter of MAX280[K].MAXIM.
[35]李小京,王萍.用相关法改善电磁流量计低流速性能[J].化工自动化及仪表,2004 31(6):66-67.
[36]何立民.单片机高级教程[M].北京:北京航空航天大学出版社,2001.
[37]ICL7135 ANALOG-TO-DIGITAL CONVERTERS[K].Texas Instruments,1999.
[38]TIMEKEEPER M41T0 RAM[K].STMicroelectronics.
[39]OCMJ4X8C资料[EB/OL].www.GPT.com.cn.
[40]徐爱钧,彭秀华.Keil Cx51 V7.0单片机高级语言编程与μVision2应用实践[M].北京:电子工业出版社,2004.
[41]蔡屋昌,孙淮清.流量测量方法和仪表的选用[M].北京:北京化学工业出版社,2001:141-143.
[42]张太明.提高电磁流量计测量准确度的方法[J].计量技术,2007(9):24-26.
[2]黄宝森.电磁流量计[M].北京:高等教育出版社,1988:1-195.
[3]纪常杰,周润才.如何选择合适的流量计[J].国外油田工程,2001,17(9):9.
[4]蔡武昌,马中元.电磁流量计[M].北京:中国石化出版社,2004,30-34.
[5]蔡武昌.电磁流量计的现状和进展[J].世界仪器与自动化,1998,2(4):40-43.
[6]李素蓉.行业差异性与市场份额分配浅析[J].中国仪器仪表,2003,5,4-5.
[7]鲁崇恭,马中元.带微机电磁流量计转换器的研究[J].计量学报,1992,1:52-58.
[8]蔡武昌.电磁流量计应用近况和技术发展[J].炼油化工自动化,1997(4),52-56.
[9]D.Reily,GEdmunds.Development of an electromagnetic flowmeter for cryogenic fluids[J],USA:NASA Lewis Research Center,1964.
[10]VCushing.Electromagnetic flowmeter for insulating liquids[C].Proc,19~(th)IEEE IMTC,Anchorage,2002:103-108.
[11]Z.Z.Yu,A.T.Peyon,M.S,Beck Imaging system based on electromagnetic tomography(EMT)[J].Electromagnetic Letter,1993,29(7):625-626.
[12]Zhang XiaoZhang.Reconstruction of flow patterns by means of electromagnetic induction [C].FLOMEKO,1996:82-84.
[13]Zhang XiaoZhang.2D analysis for the virtal current distribution in an electromagnetic flow meter with bubble at various axis positions[J].Meas,Sci,Technol,1998,(9):1501-1505.
[14]张宏建,管军.基于电磁感应原理的多电极流量测量方法[J].计量学报,2004,25(1):43-46.
[15]凌志浩,吴勤勤,张心泉.应用广泛的交流励磁磁场电磁流量计[J].造纸装置与设备,2006,25(6):53-54
[16]Raker R,Deacon J.The behavior of turbine vortex and electromagnetic flow meters[J].The Chemical Engineer,1984,(3):13-15.
[17]A.Kolin,An A.C.Induction Flowmeter for Measurement of Blood How in Intact Blood Vessels,Proc,Soc,Expt,Biol,1941:235.
[18]穆志坚,李大成.电磁计量技术[M].北京:机械工业出版社,1988:214-224.
[19]G.Y.Tian,G.P.Lucas.Numerical Simulation Modeling for Velocity Measurement of Electromagnetic Flow Meter[J].Institute of Physics Publishing,2006:36-40.
[20]王刚.低频矩形波励磁电磁流量计设计[D].重庆:重庆大学,2005:16.
[21]王国强,吕波,张小章.非对称流动对电磁流量计输出的影响[J].计量技术2003,(10):3-5.
[22]王新堂.励磁信号控制技术及其在电磁流量计中的应用[J].电测与仪表,1995,(7):21-23.
[23]Jea-eun CHA,Yeh-chan AHN.The performance of Electromagnetic flowmeters on a liquid metal two-phase flow[J].Nucl.sci.Technol.2003:3-4.
[24]潘祥明.电磁流量计及其普遍方程式[J].仪器仪表学报,1989(4):34-35
[25]高小朋,杜鸿雁.电磁流量计的干扰产生及其抑制和消除[J].计量技术,2007,No 3.
[26]王俭.电磁流量计低频正弦波励磁方法的研究[D].浙江:浙江大学,2006:16-17.
[27]李小京.电磁流量计放大滤波电路设计[J].化工自动化及仪表,2000,27(2):50-52.
[28]唐惠强,佘艳.基于MSCl211的电磁流量计的硬件设计[J].仪表技术与仪器,2007(12):50-51.
[29]Paul Horowitz,Winfield Hill,THE ART OF ELECTRONICS[M].北京:电子工业出版社,2005.
[30]CA3140[K],Intesil Corporation,1999.
[31]康华光.电子技术基础模拟部分[M].北京:高等教育出版社,2002.
[32]Four-Channel,Four-Quadrant Analog Multiplier of MTL04[K].ANALOG DEVICES.
[33]张国雄.测控电路[M].北京:机械工业出版社,2001.
[34]Low-pass filter of MAX280[K].MAXIM.
[35]李小京,王萍.用相关法改善电磁流量计低流速性能[J].化工自动化及仪表,2004 31(6):66-67.
[36]何立民.单片机高级教程[M].北京:北京航空航天大学出版社,2001.
[37]ICL7135 ANALOG-TO-DIGITAL CONVERTERS[K].Texas Instruments,1999.
[38]TIMEKEEPER M41T0 RAM[K].STMicroelectronics.
[39]OCMJ4X8C资料[EB/OL].www.GPT.com.cn.
[40]徐爱钧,彭秀华.Keil Cx51 V7.0单片机高级语言编程与μVision2应用实践[M].北京:电子工业出版社,2004.
[41]蔡屋昌,孙淮清.流量测量方法和仪表的选用[M].北京:北京化学工业出版社,2001:141-143.
[42]张太明.提高电磁流量计测量准确度的方法[J].计量技术,2007(9):24-26.