The choice of electromagnetic flowmeter is mainly the correct choice of the transmitter, and the converter only needs to be matched with it.
Choice of caliber and range
The diameter of the transmitter is usually the same as that of the piping system. If the piping system is to be designed, the diameter can be selected according to the flow range and flow rate. For electromagnetic flowmeters, the flow rate is suitable for 2 - 4m / s. In special cases, such as solid particles in the liquid, in consideration of wear, the optional flow rate is ≤ 3m / s, for easy to manage the fluid. Available flow rate ≥ 2m / s. After the flow rate is determined, the transmitter diameter can be determined according to qv= D2.
The range of the transmitter can be selected according to two principles: one is that the full scale of the meter is greater than the expected maximum flow value; the other is that the normal flow is greater than 50% of the full scale of the meter to ensure a certain measurement accuracy.
Temperature and pressure selection
There are certain restrictions on the fluid pressure and temperature that the electromagnetic flowmeter can measure. When used, the pressure used must be lower than the working pressure specified by the flowmeter. At present, the working pressure specifications of domestically produced electromagnetic flowmeters are:
Less than 50mm caliber, working pressure is 1.6MPa; 900 mm caliber, working pressure is 1 MPa;More than 1000mm caliber, working pressure is 0.6MPa.
If there are special requirements on the pressure resistance of the transmitter, you can negotiate with the manufacturer.
The operating temperature of the electromagnetic flowmeter depends on the lining material used, which is generally 5 - 70 ° C. Such as special treatment, can exceed the above range, such as the wear-resistant corrosion-resistant electromagnetic flowmeter produced by Tianjin Automation Instrument No.3. The transmitter allows the measured medium temperature to be -40 to 130 °C.
Selection of lining material and electrode tree material
The lining material and electrode material of the transmitter must be correctly selected according to the physical and chemical properties of the medium. Otherwise, the instrument will be damaged quickly due to the corrosion of the lining and the electrode, and the corrosive medium will easily cause an accident if it leaks. Therefore, the electrode and the lining material must be carefully selected according to the specific measurement medium in the production process.
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.
Vortex flowmeter installation method
1. The vortex flowmeter can only be measured in one direction. The installation should pay attention to ensure that the direction of the medium flow is consistent with the direction indicated by the flowmeter arrow.
2. The best installation method of the vortex flowmeter is vertical installation, and the medium passes through the flowmeter from bottom to top. Install the flowmeter on a vertical pipe with the flow direction from bottom to top.
3. When installing horizontally, the flowmeter must be installed in the high pressure zone of the whole system and ensure the corresponding outlet pressure; do not install at the highest point of the pipeline, because the highest point is often gas accumulation, the pipeline is not full, and the outlet cannot be directly emptied.
4. When measuring high temperature fluid, try to use vertical installation; if you have to install horizontally, please install the transmitter part of the flowmeter vertically downwards or horizontally to avoid excessive temperature; pay attention to air flow at installation location Or well ventilated.
5. Straight pipe section requirements: at least 15 times the pipe diameter before the flow meter and 5 times the pipe diameter after the flow meter. If there are elbows, indents, expansions and other sources of interference in front of the flowmeter, the diameter of the flowmeter should be 30–40 times, and the diameter of the flowmeter should be 6 times. The flow meter should be installed upstream of the regulator valve, pressure or temperature sensor.
6. When installing, pay attention to the pipe diameter should be slightly larger than or equal to the inner diameter of the instrument.
7. When using the sealing ring, the inner diameter of the sealing ring should be slightly larger than or equal to the inner diameter of the instrument, and the center of the sealing ring is at the center of the pipe.