【作者】 蒋程军；

【导师】 高宗海；

【作者基本信息】 西安理工大学 ， 精密仪器及机械， 2008， 硕士

【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。更多还原

【Abstract】 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.更多还原