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.