1. Elimination of differential interference and power frequency interference
Differential interference and power frequency interference signal often exist in pipeline flowmeter signal, which is low in signal processing circuit
It is difficult to filter out power frequency interference completely by pass filtering.Synchronous sampling and power frequency compensation technology can be used to suppress
Power frequency interference and power frequency fluctuation are mixed into the potential of the flow signal to produce power frequency interference and effectively divide and differentiate
Interference.Synchronous sampling technology, sampling start time lags excitation signal 1/4 cycle, its pulse width as the power frequency
Even times of the period, eliminating differential interference while making the average value of power frequency interference in the potential of the flow signal equal to zero
Eliminate the influence of power frequency interference;The frequency fluctuation compensation of power supply is to ensure the dynamic fluctuation of frequency in excitation electricity
Source and sampling pulse can be adjusted synchronously, truly realize synchronous sampling technology and synchronous excitation technology, synchronous A/D rotation
The influence of differential interference and power frequency interference is reduced.
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 zero-drift signal will be transmitted between the circuits at all levels of amplification. After multiple levels of amplification, it will become a larger signal at the output end
Because the useful signal output from the sensor is weak, zero drift may drown the useful signal, so that the circuit has no
The law works normally.Therefore, in order to suppress zero drift, the differential circuit input of three operational amplifier is adopted to achieve large internal resistance
To suppress the introduction of common-mode signals.After the first stage amplifier circuit, the isolated capacitor is used to filter the baseline zero drift and prevent the DC signal from being too large to exceed the input range of A/D conversion.
3. Other measures to remove interference
The orthogonal interference caused by "transformer effect" of pipeline flowmeter sensor is eliminated by "transmitter zero adjustment method".
In terms of software design, digital filtering technology, power-off protection technology and software instruction redundancy measures can effectively improve the reliability of the input microprocessor digital.
