Electrode: Its function is to extract and induce a proportional induced inductive potential signal. The electrodes are typically made of non-magnetically conductive stainless steel and are required to be flush with the liner so that the fluid passes unimpeded. It should be installed in the vertical direction of the pipe to prevent deposits from accumulating on it and affecting the measurement accuracy.
Enclosure: Made of ferromagnetic material, it is the cover of the distribution system excitation coil and isolates the interference of external magnetic field.
Lining: A complete electrical insulation lining on the inside of the measuring tube and on the flange sealing surface. It directly contacts the liquid to be measured, and its function is to increase the corrosion resistance of the measuring catheter and prevent the induced potential from being short-circuited by the metal measuring tube wall. Most of the lining materials are PTFE plastics and ceramics that are resistant to corrosion, high temperature and wear.
Converter: The induced potential signal generated by the liquid flow is very weak and is greatly affected by various interference factors. The function of the converter is to amplify and convert the induced potential signal into a unified standard signal and suppress the main interference signal. Its task is to amplify the induced potential signal Ex detected by the electrode into a unified standard DC signal.
Vortex flowmeter common fault
1. The measurement range of the vortex flowmeter is large, generally 10:1, but the lower limit of measurement is limited by many factors: Re>10000 is the most basic condition for the operation of the vortex flowmeter. In addition, it is also responded by the vortex. The signal, the vortex frequency f is also small, and it also makes signal processing difficult. The upper limit of measurement is the frequency response of the sensor and the frequency limit of the circuit. Therefore, the flow rate range must be calculated and calculated according to the flow rate of the fluid. The environmental conditions on the site are complicated. In addition to the conditions such as ambient temperature, humidity, and atmosphere, electromagnetic interference should also be considered.
2, vibration is also a big enemy of this type of instrument. Therefore, care should be taken to avoid mechanical vibrations, especially the lateral vibration of the pipe (perpendicular to the pipe axis and the vertical vortex generating body axis). This effect cannot be suppressed and eliminated in the design of the flowmeter structure. Since the vortex signal is equally sensitive to the influence of the flow field, it is not suitable for the length of the straight pipe section to ensure the flow conditions necessary for stabilizing the vortex street. Even the capacitive and ultrasonic type with strong anti-vibration performance guarantees that the fluid is a fully developed one-way flow, which is not negligible.
The medium temperature also has a great influence on the performance of the vortex flowmeter. For example, the pressure stress type vortex flowmeter cannot be used for a long time at 300 °C, because its insulation resistance is rapidly reduced from 10-100 MΩ at normal temperature to 1-101 Ω, and the output signal is also small, resulting in deterioration of measurement characteristics. In the measurement system, the sensor and the converter should be installed separately to avoid long-term high temperature affecting the reliability and service life of the instrument. The vortex flowmeter is a relatively new type of flowmeter. It is in the development stage and is not very mature. If it is not properly selected, the performance will not work well. Only after reasonable selection and correct installation, it is necessary to carefully and regularly maintain during the use process, accumulate experience, improve the predictability of system failure and the ability to judge and deal with problems, so as to achieve satisfactory results.
Vortex flowmeter selection
(1) Selection of vortex flow transmitter
In the measurement of saturated steam, VA type piezoelectric vortex flow transmitter is adopted. Because of the wide range of vortex flowmeter, in practical applications, it is generally considered that the flow of measuring saturated steam should not be lower than that of vortex flowmeter. The lower limit, that is to say, the fluid flow rate must not be less than 5 m/s. According to the size of the steam, the vortex flow transmitters with different calibers are selected, and the caliber of the transmitter cannot be selected by the existing process pipe diameter.
(2) Selection of pressure compensation pressure transmitter
Since the saturated steam line is long and the pressure fluctuates greatly, pressure compensation must be adopted. Considering the corresponding relationship of pressure, temperature and density, only pressure compensation can be used in the measurement, because the saturated steam pressure of Mingtong Company is 0.3-0.7MPa. Range, the range of pressure transmitter can be selected 1MPa.
(3) Display instrument selection
Display instrument intelligent flow display instrument with voltage regulation compensation, instantaneous flow display and cumulative flow accumulation function.