The vortex flowmeter is a relatively precise flow measuring instrument. Its working principle is the process of converting the Karman vortex street into flow data from the measuring sensor to the flow amplifier. In the process of use, it sometimes appears that the vortex flowmeter has been powered but there is no flow on the liquid crystal display but there is flow on the remote signal. When this kind of failure occurs, we must proceed from the following aspects examine.1. After the instrument is energized, the valve does not open, and there is indeed a signal output①. The sensor output signal of the vortex flowmeter is shielded or there is external electromagnetic interference when the flowmeter is grounded; ②, there is electromagnetic interference generated by large electromechanical equipment or high-frequency equipment around the instrument during installation; ③, vortex flowmeter There is strong vibration in the installation pipeline; ④, the sensitivity of the sensor’s receiving signal is too high;For the above faults, corresponding measures need to be taken to enhance the shielding and grounding of external interference, strengthen the pipeline to eliminate pipeline vibration, and adjust the sensor to reduce the sensitivity;2. The power supply of the intermittent vortex flowmeter is not cut off, and there is a signal output after the valve is closed.This type of failure is similar to that caused by pipeline vibration or external electromagnetic interference, and the treatment method is the same as above.3. When the instrument is energized, the signal output when the upstream valve is closed is zero, and the signal output when the downstream valve is closed is not zero.The reason for this kind of failure is mainly caused by the pulsating pressure of the upstream fluid. When the vortex flowmeter is installed on a T-shaped branch pipe, and the upstream main pipeline has pressure pulsation, or there is a power source that generates pulsating pressure, this At times, a false signal will be generated due to the pressure pulsation.Treatment method: The downstream valve needs to be installed upstream of the vortex flowmeter. The upstream valve can be closed to isolate the pulsating pressure when the machine is stopped, but the premise is that there must be a certain straight pipe distance from the instrument;4. The signal output of closing the upstream valve is not zero when the power is on. The signal output of closing the downstream valve is zero. This type of fault is caused by the fluid disturbance in the pipeline. Generally, if the distance between the downstream straight section of the vortex flowmeter is relatively long in the pipeline Short and the outlet is close to other valves, at this time, due to the fluid disturbance in the pipeline, it will be transmitted to the detection element of the vortex flowmeter to cause false signals;Solution: It is necessary to lengthen the distance of the straight pipe section of the meter to eliminate the fault caused by fluid disturbance.After solving the above problems, how to adjust the sensitivity of the vortex flowmeter?1. Adjustment of trigger levelThe increase of trigger level (sensitivity of pulse generation) will reduce the sensitivity of flow. When there is no liquid flowing in the pipeline, abnormal pulse generation 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. Whenever the peak value of the amplified vortex waveform exceeds the predetermined trigger level, it can be converted into a pulse. Therefore, as the trigger level is increased, the flow sensitivity will decrease.2. Zero point adjustmentCorrect wiring of the vortex flowmeter, input a signal with zero amplitude to the vortex flowmeter through the low-frequency signal generator, adjust the zero point to adjust the potentiometer, the display value of the digital multimeter should be 4mA.
Correct wiring, 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 calculated according to the above formula The full-scale frequency.
Post time: 21-09-21