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Influence of Dielectric Conductivity on Electromagnetic Flowmeter

Jan 10, 2017

At  present, the electromagnetic flowmeterconversion circuit input  impedance has been greatly improved, the measurement of conductive  liquid is usually not due to changes in dielectric conductivity caused  by errors, but for a certain converter input impedance, the measured  conductivity of the medium there is a The lower limit value can not be lower than the lower limit value.

The conductivity of the measured medium is too large to adapt. For  example, when the conductivity exceeds 10-1 (S / cm) or so, it will  reduce the flow signal, change the indication value, indicating the flow  value is less than the actual flow value. This  is due to the electromagnetic flow transmitter, the magnetic field is  finite, the measured conductive liquid flow through only a limited  magnetic field, in order to produce induced electromotive force e. Therefore,  the induced electromotive force e, which represents the flow signal, is  the result of the conductive liquid cutting the magnetic field lines of  the magnetic field portion, and the conductive liquid other than the  ends of the magnetic field does not make any contribution to e. On the contrary, because they are also connected with the two electrodes, it also constitutes a part of the external circuit. When  the transmitter and the converter are connected together, this part of  the external circuit and the converter input impedance in parallel and  become the transmitter load. When  the conductivity of the measured medium is large, the resistance of the  external circuit is small, no matter how high the input impedance of  the converter, the parallel results will depend on this part of the  liquid outside the circuit, thus reducing the transmitter and conversion  Between the transmission accuracy.

Therefore,  the electromagnetic flowmeter, the dielectric conductivity is not  affected by a certain range, the measured dielectric conductance string  can not be too large nor too small. With  the development of electronic technology, converter input impedance of  the progress, will be able to reduce the measured dielectric  conductivity of the lower limit.