Vortex flowmeter troubleshooting
Fumed Silica,Micro Silica,Aerosil Fumed Silica,Aerosil Silica Henan Minmetals East New Materials CO. LTD. , https://www.eastspecialitysilica.com
1. Judgment and processing of vortex flowmeter fault (signal output when there is no flow after power on)
(1) The power supply valve is not open with a signal output 1 Shielding or grounding of the sensor (or detection element) output signal leads to external electromagnetic interference;
2 The instrument is too close to the electromagnetic interference caused by strong electric equipment or high-frequency equipment.
3 installation pipeline has strong vibration;
4 The converter's high sensitivity is too sensitive to the interference signal;
The measures to be taken are to strengthen shielding and grounding to eliminate pipeline vibration adjustments and reduce the converter's sensitivity.
(2) The vortex flowmeter power supply in the intermittent operation state of the vortex flowmeter without shutting off the output signal does not return to zero. This phenomenon may be caused by the same reason as the first (1) phenomenon, which may be the influence of pipeline oscillation and external electromagnetic interference. The sensitivity of the converter should be lowered to increase the trigger level of the shaping circuit to suppress noise. The latest price of the vortex flowmeter overcomes the false trigger during the interval.
(3) Turn off the downstream valve output in the energized state. The output of the upstream valve does not return to zero. The output of the upstream valve is zero. This is mainly due to the influence of the fluid pulsation pressure upstream of the misfiring flowmeter. If the vortex flowmeter is mounted on a T-branch and the upstream supervisor has pressure pulsations or is a pulsating power source (such as a piston pump or Roots blower) upstream of the vortex meter, the vortex pressure causes false vortex flowmeters signal. The solution is to install the downstream valve upstream of the vortex flowmeter and close the upstream valve during shutdown to isolate the pulsating pressure. However, the upstream valve should be kept away from the vortex flowmeter and ensure sufficient straight pipe length.
(4) Off-state upstream valve output does not return to zero. Only on the downstream valve output is zero. This type of fault is caused by disturbances in the pipe flow disturbance from the vortex street flow downstream of a meter. In the pipe network, if the straight section of the downstream vortex flowmeter is short and the outlet is close to the valve of other pipelines in the pipe network, the fluid disturbance in these pipes (such as the valve opening, closing, frequent operation of the regulating valve in other downstream pipelines). ) Passed to the vortex flowmeter detection element caused a false signal. The solution is to lengthen the downstream straight section to reduce the effects of fluid disturbances.
2. Vortex flowmeter fault judgment and processing (no output signal after power flow)
There are several reasons for this failure:
(1) Power supply disconnection The power supply is not actually applied to the converter ie the converter is not operating;
(2) The power cable is connected incorrectly;
(3) The signal line disconnection signal between the detection element and the converter input terminal is not added to the preamplifier input terminal;
(4) Some component of the converter (such as amplification circuit, filter circuit, shaping circuit, output circuit, etc.
(5) No flow or flow in the pipeline is too small;
(6) Blocking of pipelines, Qingdao Aobo LUGB high-temperature vortex flowmeter detection element was stuck;
(7) Damage to the force detection element;
Six out of the above seven failures are hard faults that are relatively easy to find and the processing method is relatively simple. The fifth kind of trouble is more troublesome especially the reason that the trouble of "the flow is too small" is involved in the list selection problem if not because the valve opening degree is too small. To completely solve the problem, it is necessary to reselect the instrument with the appropriate range to reduce the diameter of the process piping.
3. The vortex flowmeter output (or indication) signal does not change with the flow rate. There are several reasons for this failure:)
Fault judgment and processing (after power-on, through-current (1) due to poor grounding of the shielding layer of the signal line or improper selection of grounding points. External electromagnetic interference is very serious (for example, 50Hz power frequency interference) completely suppresses the weak vortex signal output signal Being flooded by noise, then adjusting the opening of the valve and the gain of the meter will not help.
(2) The connection between the detection element and the converter is broken. The input of the preamplifier is open or the detection element has a signal line shorted to ground. This causes the preamplifier to lose serious unbalanced common-mode interference and the vortex signal The output is suppressed by noise interference and the output is completely disturbed.
(3) The gain of the preamplifier is too high to generate self-oscillation. The output is locked at the free-running frequency.
The faults caused by the above three aspects are caused by electrical reasons. Only strengthen shielding and grounding. Reasonable traces can reduce or eliminate interference.
(4) 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 The output signal is the vibration frequency signal. Adjusting the valve opening also does not change the output.
The solution is to use vibration reduction measures (pipe anti-vibration seat, fixed pipe) to clarify the direction of vibration of the vortex flowmeter sensor around the tube axis ±90 °C to detect the sensing element sensitive direction and the direction of the vibration can be reduced Small vibrations affect the mouth or properly reduce the gain and trigger sensitivity of the preamplifier. Take the above measures to eliminate the vibration effect.
(5) The "locking" of the vortex flow signal to the vortex signal does not underestimate the destructive effect of the pulsating flow on the vortex stability separation without effective suppression of the pulsating flow. If the pulsating frequency coincides with the frequency of the vortex signal, the vortex signal may be " "Locking" near this frequency will not change the frequency of the valve and meter sensitivity output signal.
The solution is to absorb or reduce the fluid pulsation during the design and construction of the instrument's installation piping as described in the first section of this chapter.
4. Vortex flowmeter fault judgment and processing (the output signal is irregular and unstable)
Irregular signals are mainly manifested in the pulse signals output by vortex flowmeters. Irregular pulse widths are often uneven. There are sometimes multiple waves and sometimes leak waves. When frequency signals are used to measure the signal frequency, the frequency values ​​are clearly displayed. ; Analog output signal indication value is unstable when large or small.
The reasons for this phenomenon are more often discussed separately.
(1) Electrical reasons The influence of electromagnetic interference The interference noise and the vortex street signal are superimposed to make the signal strong or weak. The plug-in vortex flowmeter manufacturers warranty the output pulse signal with multiple waves and leakage waves. In addition, the pre-amplifier's filter parameter settings, gain and sensitivity adjustments will not be suitable for multi-wave and leakage.
(2) The reason of the detection element is that the detection element is contaminated, the dampness sensitivity is reduced, the output signal is weakened, and the leakage wave is caused;
The sensitivity of the detection element is too high. Some useless disturbances The subvortex and fluid noise outside the main vortex are detected to cause multi-wave phenomenon, which leads to poor contact of the component leads, looseness of the detection components, etc., resulting in large and small signals.
(3) Installation reasons The meter's measuring tube and piping do not have the same concentricity and the gasket protrudes inside the tube when installed, causing fluid disturbances and generating additional vortices;
The measuring tube is not full of liquid and the vortex cannot be separated regularly;
The installation location of the instrument and the power source are too close to the pipe vibration and flow field disturbance;
The length of the upper and lower straight pipe sections of the installation pipeline is less than the disturbance of the baffle to influence the stability of the vortex street.
(4) The reason of a process is that the flow in the pipe is unstable;
(5) Causes of fluids Blocks, slugs, or ribbons in the fluid impact, a coiled body, and a vortex in the detection element cannot be stably separated;
There are two-phase flow or multi-phase flow type multi-variable vortex street signal instability;
When measuring the liquid flow, the working pressure is low, the flow velocity is high, and cavitation may occur.
Some of these failures can be resolved by adjusting the parameters of the instrument; some need to work closely with the customer, adjust the process, and change the position of the instrument to solve the problem; while others are problems with the selection of the table, for example, serious multiphase. The use of vortex flowmeters for flow, dirty, and pulsatile flow is inappropriate.
5. Vortex flowmeter fault judgment and processing (large measurement error)
The causes of the large measurement errors are also multi-faceted.
(1) Instrumentation reasons The meter factor K has changed over the verification period;
Set parameters (such as measuring tube inner diameter, standard state density, and meter factor) are incorrect;
The zero drift or span adjustment of the analog conversion circuit is incorrect.
The power supply has deviated too much from the rated value or the ripple is too large.
These kinds of reasons will directly bring measurement error to the instrument. The instrument should be promptly sent for inspection and checked in time to check various parameters set. Correct the zero point and range of the instrument to keep the instrument in good condition.
(2) The reasons for installation are not enough for the length of the upstream and downstream sections.
The inner diameter of the measuring tube of the instrument deviates greatly from the inner diameter of the piping;
Install different hearts and seals inside the convex tube;
Flow direction of the instrument is reversed;
The detection element is covered by impurities;
Detecting sensitivity reduces the small flow rate meter;
Leakage of pipes (for example, small leaks installed in underground pipes are not found) Valve leakage Leakage of by-pass valves Causes a small cumulative flow (total);
There are two-phase flow and pulsatile flow affect the accurate measurement;
The change of the geometric parameters of the deposits on the inner wall of the measuring tube and the occurrence of the corrosive body on the occurrence body changes the meter coefficient and causes the measurement error.
From the above analysis of various phenomena, it can be seen that improving the accuracy of measurement is the common wish of the customer and the manufacturer. If a large measurement error is found, the cause must be found in time and the instrument must be calibrated to reduce the losses caused by the inaccurate measurement.
6. Vortex flowmeter fault judgment and processing (measurement pipeline leakage)
Leakage through the long-term application measurement pipeline is also a common cause. The reasons may be:
(1) The pressure in the tube is too high;
(2) If the temperature of the fluid in the tube is too high or the temperature of the fluid in the tube changes too quickly, the fastener may loosen easily;
(3) seal failure;
(4) The body or test element is corroded;
Leakage of the measuring pipeline should be promptly repaired to avoid accidents.
7. Vortex flowmeter fault judgment and processing (sensors send abnormal abnormal whistling sound)
(1) Excessive flow rate causes chatter in the body or the detection element;
(2) cavitation in the pipeline;
(3) Loose body or detection element;
When this phenomenon occurs, in order to avoid damage to the generating body or detection element, the valve should first be adjusted to reduce the flow rate of the flow and further investigate the cause.