Cause Analysis of interference in intelligent electromagnetic flowmeter
According to the characteristics of General intelligent electromagnetic flowmeter system, the interference sources of electromagnetic flowmeter are mainly discussed from the aspect of hardware optimization. For example, electromagnetic coupling and electrostatic induction are important sources of interference noise generated by intelligent electromagnetic flowmeter.
In the electromagnetic flow transmission, since the leads of the two electrodes are in an alternating magnetic field, induced electromotive force is generated in the closed loop of the leads when the transmission is energized.
This kind of interference signal is superimposed into the measurement signal, which affects the operation of the system.
Various excitation methods will bring different electromagnetic interference problems.
DC excitation mode is easy to generate polarization interference, AC excitation mode is easy to generate orthogonal interference (90 degree interference)In-phase interference (Power frequency interference)Wait.
Orthogonal interference refers to interference with a phase difference of 90 degrees from the flow signal.
When the intelligent electromagnetic flow transmitter adopts AC excitation mode, an alternating magnetic field will be generated, and a closed loop composed of electrodes, outgoing wires, measured media and input circuits of the converter will be generated, in the interference alternating magnetic field, the closed loop cannot be completely parallel to the magnetic lines generated by the alternating magnetic field of the transmitter, and there will always be a part of the alternating magnetic lines passing through the closed loop, thus an interference electromotive force is generated in the loop. In the electromagnetic flowmeter, measures are taken from the transmitter and converter to eliminate or suppress the interference of 90 degrees.
Intelligent electromagnetic flowmeter in-phase interference power frequency interference or common mode interference refers to interference signals that appear on the two electrodes of the transmitter at the same moment and have the same amplitude and phase.
When the flow rate is zero, that is, when the measured liquid is still, the measured in-phase signal is in-phase interference signal.
Electromagnetic flowmeter has many methods to suppress non-phase interference.
In terms of transmitter, the electrode and excitation coil are balanced and symmetrical in geometry, size and performance parameters, and are strictly shielded respectively to reduce the influence of distributed capacitance between the electrode and excitation coil. It is strictly prohibited to sweep steam and water through the instrument.