According to the characteristics of the electromagnetic flowmeter transmitter, the converter must have the following performance.
1. Stable linear amplification The electromagnetic flowmeter requires a linear amplifier with high stability to amplify a few millivolts of flow signal to a sufficiently high level.
2. Can distinguish and suppress various interference signals For orthogonal interference, except that the interference adjustment mechanism of the transmitter in the submerged electromagnetic flowmeter is zero, the anti-jamming mechanism must also be set in the converter to eliminate the remaining in the transmitter. Orthogonal interference signals. Otherwise, these remaining orthogonal interference signals are also amplified by the main amplifier, which affects the instrument operation. The method of suppressing the orthogonal interference of the converter is to identify and separate the orthogonal interference signal amplified by the main amplifier, and then feed it back to the input end of the main amplifier to cancel the orthogonal interference signal coming in from the input end.
For the in-phase interference, the reason for the generation of the mountain is more complicated, and the method of suppression is more. In the transmitter, the electrode and the excitation coil are symmetrically balanced in any shape, size, and performance parameters. Do not strictly screen 9, in order to reduce the influence of the distributed capacitance between the electrode and the excitation coil. In addition, a single, good grounding is highly desirable. Reducing the grounding resistance can reduce the in-phase potential due to spurious and turbulent currents. In terms of converters, it is also necessary to increase the ability of the instrument to resist in-phase interference. Usually, a differential amplifier circuit is used in the preamplifier stage of the converter. This is due to the use of a high common-mode rejection ratio of the differential amplifier, which suppresses the in-phase disturbance signal entering the input of the electromagnetic flowmeter converter from being amplified. If the constant current source circuit is added in the pre-differential amplifier stage of the converter, the in-phase interference can be better suppressed.
3. A sufficiently high input impedance converter must have a sufficiently high input impedance to overcome the influence of the internal resistance change of the transmitter and improve the measurement accuracy http://.
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