Three anti-interference methods for electromagnetic flowmeter

The electromagnetic flowmeter is an instrument that applies the principle of electromagnetic induction to measure the flow of conductive fluid according to the electromotive force induced by the conductive fluid through the applied magnetic field. The electromagnetic flowmeter will encounter certain interference problems during use, and today we will come to specific Introduce the anti-interference measures of the electromagnetic flowmeter, hope to help everyone.

1. Differential interference and elimination of power frequency interference

Differential interference and power frequency interference signals are often present in the signal. Low-pass filtering in the signal processing circuit is often difficult to completely filter out power frequency interference. Mingyu uses synchronous sampling and power frequency compensation techniques to suppress the flow signal potential. The mixed power frequency interference and power frequency power frequency fluctuations generate power frequency interference, and effectively eliminate differential interference. Synchronous sampling technology, the sampling start time lags the excitation signal by 1/4 cycle, and the pulse width is an even multiple of the power frequency cycle. Eliminate the differential interference and make the average value of the power frequency interference in the flow signal potential equal to zero to eliminate the influence of power frequency interference; the frequency fluctuation compensation of the power frequency power supply is to ensure the dynamic fluctuation of the frequency, and the excitation power supply and the sampling pulse can be adjusted synchronously. Realize synchronous sampling technology and synchronous excitation technology, synchronous A/D conversion, reducing the influence of differential interference and power frequency interference.

2, zero drift elimination

The so-called zero drift is when the input signal of the sensor is zero, the output of the amplifier is not zero. The signal of zero drift will be transmitted between the circuits of each stage of amplification. After multi-stage amplification, it becomes a larger signal at the output. Since the useful signal output from the sensor is weak, the zero drift may overwhelm the useful signal, so that the circuit can not work normally. Therefore, in order to suppress the zero drift, the differential circuit input of the three operational amplifier is used to realize the weak signal acquisition of the large internal resistance. In order to suppress the introduction of common mode signals. The first-stage amplifier circuit uses a DC blocking capacitor to filter out the zero drift of the baseline to prevent the DC signal from being too large and exceeds the input range of the A/D conversion.

3. Other measures to remove interference

For the orthogonal interference generated by the "transformer effect" of the electromagnetic flowmeter sensor, the "transfer zeroing method" is used to eliminate.

In terms of software design, digital filtering technology and power-down protection technology and software instruction redundancy measures can effectively improve the reliability of the input microprocessor.