| Electromagnetic flowmeter, which is a kind of instrument for measuring the volume andflux of electric liquid,are composed of electromagnetic flow sensor , signal conversion part andcomputation part.It can be widely used in many fields,such as concrete,chemicalengineering,textile industry,metallurgy,mine industry,paper making, medicament,brewage andso on,especially in environmental protection.In electromagnetic flowmeter,the workingmagnetic field of the sensor is generated by excitation system.The excitation mode decides thecharacter of sensor's working magnetic field, electromagnetic flowmeter's antijammingability,and the capability to keep stability.Excitation technology is always an importantdirectiong to study.In nowdays,many companies take lowfrequence rectangular wave as theirmain excitation mode.Though this kind of excitation mode can get over direct currentpolarizing voltage, as a result of rectangular wave excitation exists level sudden change, effectof differential interference and inphase interference are introduced.The SNR of sensor's outputsignal obviously reduced in measuring low velocity of flow.This cause bad zeropoint stabilityand bad measuring veracity.In this paper,the pivotal technical problem in the design of electromagnetic flowmeter isfirst analyzed.The origin of differential disturbance and inphase disturbance are discussed.Inthe design of intelligent electromagnetic elowmeter, trapeziform wave excitation method isintroduced.It reduces dB/dt and minishes the influence of differential disturbance and inphasedisturbance.SCM and D/A chip are combined to produce trapezoidal wave.With softwarecontrol them.,the frequence of trapezoidal wave can be modulated.In signal processing part,pretreatment circuit,magnifying circuit,filter circuit will be designed,and how signals isprocessed will be analyzed. The paper demonstrates the feasibility to use trapezoidal wave toexcitated electromagnetic flowmeter.the signal processing circuit can achieve the expectantdemand.
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