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Several methods for adjusting sensitivity of vortex flow meter

When the vortex flowmeter has no liquid flow in the pipeline, the receiver counts abnormally due to the noise generated by the pipeline vibration, and the sensitivity of the instrument should be adjusted.

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1. Adjustment of amplifier gain

In general, it is not necessary to adjust the gain of the vortex flowmeter amplifier unless the sensor has been replaced. The amplifier gain is adjusted by the AMP potentiometer on the amplifier board A, and the amplified eddy current waveform is monitored on the oscilloscope. At low flow rate, the peak eddy current waveform is about 100mVP-P.

2. Adjustment of trigger level

An increase in the trigger level (the sensitivity at which the pulse occurs) decreases the sensitivity of the flow rate. When there is no liquid flow in the pipeline, the abnormal pulse caused by pipeline vibration and pulsating flow noise can be effectively dealt with by increasing the trigger level.

The trigger level can be adjusted by the TRG potentiometer on the vortex flowmeter amplifier board, and the peak value of the amplified vortex waveform can be converted into a pulse whenever it exceeds a pre-determined trigger level. As a result, the flow sensitivity is reduced by increasing the trigger level.

When the trigger level of 80mVP-P changes to 350mVP-P, the resulting sensitivity will be 80/350=1/4.4(sensitivity ratio) times.

When changing the sensitivity, the resulting small flow rate (the low limit of measurable flow rate) is about 1/(the square root of the sensitivity multiplied by the standard small flow rate).

3. Zero adjustment

The vortex flowmeter is correctly connected, and the signal with zero amplitude is input to the vortex flowmeter through the low-frequency signal generator, and the zero is adjusted to adjust the potentiometer. The display value of the digital multimeter should be 4mA.

4. Full scale adjustment

If you do not know the full scale frequency of the instrument, you can adjust the instrument by calculating the full scale frequency B through a large flow rate. The relationship is as follows:

fmax=KQQmax

With the correct connection, the vortex flowmeter uses the signal generator to output the signal to the charge amplifier, increase the input signal amplitude, convert the output square wave, and change the output frequency of the signal generator until the value displayed on the frequency meter is the full-scale frequency calculated according to the above formula. At this time, the fixed frequency is unchanged, and the range potentiometer is adjusted until the digital multimeter is 20mA.

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