At present, there are two types of commonly used vortex flowmeters: piezoelectric detection type vortex flowmeter and capacitance detection type vortex flowmeter.
The main problems existing in the use of street flowmeters are: (1) inaccurate or always unable to indicate the instrument; (2) the indication fluctuates in a wide range and cannot be read; (3) the indication is accurate when the flow is large, but inaccurate when the flow is small; and (4) when the flow changes, the instrument indication does not change.
2. Analysis of Main Problems and Solutions
2.1 Type Selection Problems
In the selection of some vortex flowmeters, due to the inaccurate data provided or the change of process conditions after the design selection, the instrument selection is too large, resulting in poor use effect. Therefore, in order to ensure that the flow velocity is sufficient when the fluid flows through the whirlpool body, the Reynolds number of the fluid must be greater than 4,000 when the fluid flows in the pipeline, so as to ensure that the energy generated by the whirlpool has sufficient strength. At the same time, the temperature, density and dirty degree of medium should be considered when selecting the type, and the appropriate instrument should be selected.
2.2 Installation Problems<
(1) If the matching between instrument inner diameter and pipeline inner diameter exceeds the allowable range, the measurement error will be large. In order to ensure the measurement accuracy of the instrument, it is necessary to ensure that the inner diameter of the instrument matches the inner diameter of the pipeline when the instrument is installed. The ideal state is that the inner diameter of the flowmeter and the inner diameter of the pipeline are completely equal, but in fact this state can not be reached. When the error between instrument caliber and pipeline inner diameter is less than 3% of instrument caliber, if the pipeline inner diameter is larger than instrument caliber, the instrument does not need to be corrected. If the pipeline inner diameter is smaller than instrument caliber, the influence of pipe diameter matching can be eliminated by modifying instrument coefficient K.
(2) Requirements for straight pipe sections at entrance and exit.
After the installation of the vortex flowmeter, the uniform and stable flow velocity distribution must be ensured, which is one of the most important conditions for the normal operation of the instrument. Therefore, in order to ensure the uniform and stable distribution of the fluid flowing through the surface, it is necessary to ensure that the straight pipe section of the inlet and outlet has sufficient length when the instrument is installed. When there is no sudden change in pipe diameter and no secondary flow can be formed, the straight pipe section at the entrance must satisfy: not more than 10-times; the straight pipe section at the exit of DN (pipe diameter) must satisfy: not less than 5-times; when DN (pipe diameter) flows through elbows, shrinkage pipes, valves and other throttling and resistance components, the fluid produces strong disturbance, the longer straight pipe section must be considered, the straight pipe section at the entrance is (15-18) & times; DN (pipe inner diameter).
(3) The influence of improper installation position.
When considering the convenience of maintenance, maintenance and inspection, it is necessary to avoid installing in places with large vibration. Vortex flowmeter can't overcome the influence of vibration interference of pipeline itself, especially at low flow rate or zero flow rate, which will directly affect the accuracy of output signal. If it can only be installed in the place where the pipeline has strong vibration, effective methods must be taken to overcome or eliminate the vibration effects of the pipeline and equipment, so as to ensure the normal use of the instrument. Therefore, it is necessary to install anti-vibration rings on the upstream and downstream of the vortex flowmeter or to install anti-vibration joints.
2.3 Reasons for tuning PID parameters
The inaccuracy of parameter setting results in the wrong indication of the instrument and the wrong calculation of full scale frequency of the secondary instrument. If the fullness frequency is similar, the instrument indication is not accurate for a long time. If the fullness frequency is greater than the calculated fullness frequency, the instrument indication fluctuates in a wide range and cannot be read. At the same time, the inconsistency of parameters in various data also affects the final determination of parameters, so this problem is solved by re-calibration and comparison of parameters.
3 concluding remarks
Only reasonable selection and correct installation can ensure the normal use of the instrument and accurate measurement. In addition, the probe of vortex flowmeter should be cleaned regularly to avoid affecting the normal measurement, check the grounding and shielding regularly, and eliminate external interference. The capacitive vortex flowmeter used at present has the characteristics of simple structure, convenient installation and maintenance, wide application range, wide measuring range ratio (45:1), convenient configuration and strong adaptability to the environment, which is difficult to compare with other flow meters.
