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technical article
Common sense of vortex flowmeter
2012-1-16 10:50:23

Vortex flowmeter installation, use and maintenance


传感器接受二次仪表的12VDC供电,采用压电晶体元件检测旋涡分离频率. The vortex flowmeter sensor receives 12VDC power from the secondary meter, and uses a piezoelectric crystal element to detect the vortex separation frequency. The probe body installed inside the cylinder feels the pressure generated by the vortex on both sides of the rear of the cylinder

Pulse, the piezoelectric crystal element embedded in the probe body feels the effect of this strain force to generate an alternating charge, and the sensor processes and outputs a pulse signal of a certain amplitude to the secondary instrument. This pulse signal and flow through

The flow rate of the pipeline is proportional. This proportional relationship is determined by the K coefficient of the sensor. The K coefficient is generally calibrated by the manufacturer. The K coefficient represents the number of pulses sent by the sensor for each flow unit flowing through the pipeline.

The secondary meter is a SK series single-chip 908-based flow display meter. After receiving this pulse signal, on the one hand, the pointer-type ammeter displays the instantaneous flow rate, and on the other hand, the 8-digit digital display shows the cumulative flow rate or

Accumulated time, on the other hand, can output 4-20 mA or 0-10 mA signal to the regulator or recorder for use. The secondary meter sets parameters based on the K factor and flow range of the sensor.

Main problems

的题目。 Title of vortex flowmeter . Mainly: ① Indications are not accurate for a long time; ② There is no indication at all times; ③ The indications fluctuate widely and cannot be read; ④ The indications do not return to zero; ⑤ No indications at small flows;

Therefore, the indication is inaccurate when the flow rate is small; 指示 the indication change cannot keep up when the flow rate is changed; ⑧ the K factor of the meter cannot be determined, and the data are inconsistent in many places.

Analysis and solution of main problems

The analysis and solution of these problems are complicated, and there are different levels of problems from installation, parameter setting, daily maintenance, and operating environment. Many problems are related to each other, and some problems are solved.

Need to wait for a certain process running time, so it brings great difficulties to the solution of the problem. Some problems are caused by different reasons, and some reasons are related to different problems.

Summarize the main causes of these problems, mainly related to the following aspects:

(1) Selection issues. Some vortex sensors have been selected in a large size or after design and selection due to changes in process conditions, which has made the selection larger. The actual selection should choose the smallest size possible to improve measurement.

The reason for this is mainly related to the problems ①, ③, ⑥. For example, a vortex street pipeline is designed to be used by several equipments. Because some equipment of the process is sometimes not used, the current actual flow rate is reduced.

Due to international use, the size of the original design is too large, which is equivalent to improving the lower limit of the measurable flow rate. The indication of the small flow rate of the process pipeline cannot be guaranteed. It can also be used when the flow rate is large.

Changes in process conditions are only temporary). Can be combined with parameter re-setting to improve the accuracy of the indication.

(2) Installation issues. The main reason is that the length of the straight pipe section in front of the sensor is not enough, which affects the measurement accuracy. The reason for this is mainly related to topic ①.


(3) Reason for parameter setting direction. Due to the wrong parameter, the instrument indication is wrong. The parameter error makes the secondary meter full-scale frequency calculation wrong. The reason for this is mainly related to the problems ① and ③. Full-scale frequency difference

The inaccuracy of the indicator makes the instruction inaccurate for a long time. The actual full-scale frequency is calculated to make the indicator fluctuate widely and cannot be read. The inconsistency of the parameters on the data affects the ultimate determination of the parameters.

The calibration and the comparison with each other determine the parameters and solve this problem.

(4) Secondary instrument failure. This part has many faults, including: once the instrument circuit board is disconnected, the range setting has a single bit display that is bad, the K coefficient setting has a single bit display that is bad, making it impossible to determine the range setting and the K series.

This part of the reason is mainly related to topics ① and ②. The problem was solved by fixing the corresponding fault.

(5) Four-line connection problem. Some circuits look good on the surface of the circuit. Carefully check that some connectors have actually loosened and caused the circuit to be interrupted. Although some connectors are tightly connected, they are fastened to

The line is interrupted, which also causes the circuit to be interrupted. This part of the reason is mainly related to topic ②. The corresponding line problems were solved, and the existing problems were also solved accordingly.

(6) The problem of the connection between secondary instruments and subsequent instruments. The mA output circuit of the secondary meter is interrupted due to the problem of the subsequent meter or the inspection of the subsequent meter. For this type of secondary meter, this part of the main reason

It should be related to topic ②. Especially for subsequent recorders, if the recorder is damaged for a long time and cannot be repaired, be sure to pay attention to shorting the output of the secondary meter.

(7) There is no indication of the loop due to the secondary instrument flat axis cable failure. Due to the long-term operation and the influence of dust, which caused the flat shaft cable failure, the problem was solved by cleaning or replacing the flat shaft wire.

(8) For the problem ⑦, the main reason is that the secondary instrument display meter head ’s coil fixing screw is loose, which causes the meter head to sink, the pointer and the case friction is large, and the action fails.

(9) Use environmental issues. Especially the sensor part installed in the ground well, due to the high ambient humidity, the circuit board gets wet. This part of the reason is mainly related to the problems ② and ②. Through corresponding technological transformation measures,

The sensor with high ambient humidity has re-separated the probe part from the conversion part and switched to a separate sensor, which improves the working environment. The instrument has been running well a few days ago.

(10) Because the on-site adjustment is not good, or because of actual changes after adjustment. Due to poor on-site vibration and noise balance adjustment and sensitivity adjustment. Or due to the situation on site after a period of operation after adjustment

The further changes in the cause of the instruction title are mainly related to the questions ④ and ⑤. Use an oscilloscope, coupled with the process running conditions, readjust.

(11) The reason why the question 提出 was raised separately is that this question has affected the analysis and solution of the question for a long time. Because the K-factor calibration conditions are not available, the K-factor can only be based on the information provided by the manufacturer.

Some changes caused the K-factors in the several materials provided to be inconsistent, which affected the problem solving. By looking for conditions to re-calibrate, or through repeated modification and comparison, the same instrument parameters were finally determined.

to sum up

(1) Because the determination of the K-factor is very important in the entire link of the vortex street, the correctness of the K-factor directly affects the accuracy of the circuit, the replacement of parts of the instrument, and the wear of the process pipeline, etc., may all affect the K-factor. .

However, enterprises lack calibration methods and capabilities. They can only send out calibration. Due to the impact of process operation, it takes 5 to 6 days to remove the vortex street from the pipeline and it is difficult to meet the process, so the K coefficient cannot be determined. .

This year, through the transformation of the flow meter room, although the calibration conditions of the smaller diameter vortex streets have already been provided, there is still nothing to do with the larger diameter vortex streets. In the future, you should pay attention to the on-site calibration method of vortex streets and use standard frequency.

Rate and portable ultrasonic flowmeter, measure the instantaneous flow in the pipeline and the pulse output frequency of the sensor, and calculate the K factor on the spot.

的探头,检查中曾发现,个别探头检测孔已被污物堵塞,甚至被塑料布裹住,影响了正常丈量。 (2) The probes of the vortex flowmeter should be cleaned regularly. It was found during inspection that the detection holes of individual probes have been blocked by dirt or even covered with plastic cloth, which has affected the normal measurement.

(3) Regularly check the grounding and shielding conditions to eliminate external interference. Sometimes the indication is due to interference.