1. The vortex flowmeter is connected to the power supply, the valve is not opened, and there is a signal output.
Solution: ①The shielding or grounding of the output signal of the sensor (or detection element) is poor, which induces external electromagnetic interference; ②The meter is too close to strong current equipment or high-frequency equipment, and electromagnetic radiation interference in the space will affect the meter; ③Install the pipeline There is strong vibration; ④The sensitivity of the converter is too high, and it is too sensitive to interference signals; the measures to be taken are to strengthen shielding and grounding, eliminate pipeline vibration, and adjust to reduce the sensitivity of the converter.
2. For vortex flowmeters in intermittent working conditions, the power supply is not interrupted, the valve is closed, and the output signal does not return to zero; the main reason may be the influence of pipeline oscillation and external electromagnetic interference.
Solution: Lower the sensitivity of the converter and increase the trigger level of the shaping circuit to suppress noise and overcome false triggers during intermittent periods.
3. When the power is on, turn off the downstream valve, the output does not return to zero, and close the upstream valve to return to zero. This is mainly due to the influence of the pulsating pressure of the upstream fluid of the flowmeter. If the vortex flowmeter is installed on a T-shaped branch and there is pressure pulsation in the upstream main pipe, or there is a pulsating power source (such as piston pump or Roots blower) upstream of the vortex flowmeter, the pulsating pressure causes the vortex flow False signal.
Solution:Install the downstream valve to the upstream of the vortex flowmeter, and close the upstream valve during shutdown to isolate the influence of pulsating pressure. However, during installation, the upstream valve should be as far away as possible from the vortex flowmeter and ensure sufficient straight pipe length.
?
4. Under the power-on state, the output of the upstream valve will not return to zero when the upstream valve is closed, but the output of the downstream valve will return to zero. This fault is caused by the disturbance of the fluid in the pipe, and the disturbance comes from the downstream pipeline of the vortex flow meter. In the pipe network, if the downstream straight pipe section of the vortex flowmeter is short and the outlet is close to the valves of other pipes in the pipe network, the fluid in these pipes will be disturbed (for example, the valves in other downstream pipes are frequently opened and closed, and the regulating valve is frequently Action) to the vortex flowmeter detection element, causing false signals.
Solution:Lengthen the downstream straight pipe section to reduce the influence of fluid disturbance.
5. After energization and current flow, the output (or indication) signal of the vortex flowmeter does not change with the flow rate. Because the shielding layer of the signal line is poorly grounded or the grounding point is not selected properly, the external electromagnetic interference is very serious (such as 50Hz power frequency interference). The weak vortex signal is completely suppressed, and the output signal is completely submerged by noise interference. At this time, adjusting the valve opening and the gain of the instrument will not help. The connection between the detection element and the converter is disconnected, the input end of the preamplifier is open, or the detection element has a signal wire that is shorted to ground, causing serious imbalance in the input of the preamplifier, common mode interference takes the opportunity to make people, vortex street The signal is suppressed by noise interference, and the output is completely controlled by interference. The gain of the preamplifier is too high, causing self-oscillation, and the output is locked at the self-exciting frequency.
Solution:The above faults are caused by electrical reasons. Only by strengthening the shielding and grounding, rationally routing, reducing or eliminating interference, the normal operation of the instrument can be restored.
?
6. The strong vibration of the pipeline (or environment). When the vibration direction is consistent with the sensitive direction of the instrument detection element, the vibration completely suppresses the vortex signal, and the output signal is the vibration frequency signal. The output cannot be changed by adjusting the valve opening.
Solution:Adopt vibration damping measures (adding pipeline anti-vibration seat, fixed pipeline), clarify the direction of vibration, rotate the sensor of the vortex flowmeter around the pipe axis by ±90 ℃, and adjust the sensitive direction of the detection element to be perpendicular to the vibration direction. Reduce the impact of vibration or appropriately reduce the gain and trigger sensitivity of the preamplifier. Take the above measures to eliminate the impact of vibration.
?
7、 The "locking" of pulsating flow on the vortex street signal. Without effective suppression of the effect of pulsating flow, the destructive effect of pulsating flow on the stable separation of vortices should not be underestimated. If the pulsating frequency coincides with the frequency of the vortex street signal, the vortex street signal may be changed. "Lock" is near this frequency, at this time adjust the valve and instrument sensitivity, the output signal frequency will not change.
Solution:Take measures to absorb or reduce fluid pulsation during the design and construction of the installation pipeline of the instrument.
?
8、The meter exceeds the verification period, and the meter coefficient K has changed; the set parameters (such as the inner diameter of the measuring tube, the standard state density and the meter coefficient) are wrong; the zero drift of the analog conversion circuit or the range adjustment is wrong; the power supply is too large to deviate from the rated value Or the ripple is too large.
Solution:Send the meter for inspection quickly, check the various parameters set in time, and calibrate the zero point and range of the meter regularly to maintain the integrity rate of the meter.
?
Want to know more about the precession vortex flowmeter, thermal gas mass flowmeter, electromagnetic flowmeter, vortex flowmeter, turbine flowmeter, ultrasonic flowmeter, please pay attention to the official website of Hollysys Industrial Control Instruments.
