Electromagnetic Flowmeter Selection and Installation Primary applications
Published on：2015-3-3 10:43:10 Hits：
Reasonable selection and correct installation of electromagnetic flowmeters, for ensuring the accuracy of measurement, to extend the life of the instrument is very important. Here the principle of electromagnetic flowmeter selection, installation conditions and use precautions to make a brief introduction.
(A) the principle of electromagnetic flowmeter selection
Electromagnetic flowmeter selection, mainly the correct selection of the transmitter, while the converter can only ancillary.
1. Caliber and range of choice
Transmitter caliber usually use the same caliber and piping systems. If the piping system to be designed according to the flow range and flow can be selected caliber. For electromagnetic flowmeters, the flow rate to 2-4m / s is more appropriate. In special cases, such as a liquid with solid particles, taking into account the wear, optional common velocity ≤3m / s, for easy attachment of a fluid management. Optional velocity ≥2m / s.
The transmitter's range can be selected based on two principles: First, the meter full scale value is greater than the expected maximum flow; the second is the normal flow meter greater than 50% of full scale, in order to ensure a certain degree of accuracy.
2. Selecting the temperature and pressure
Electromagnetic flowmeter can measure fluid pressure and temperature is a certain limit. The selection, use of pressure must be below the specified operating pressure of the flow meter. At present, the domestic production of electromagnetic flowmeter working pressure specifications:
Less than 50mm diameter, working pressure of 1.6MPa;
900 mm diameter, working pressure 1MPa;
Greater than 1000mm diameter, working pressure of 0.6MPa.
Such as pressure transmitters have special requirements, you can consult with the specific manufacturer. Some manufacturers have been able to manufacture pressure of 32MPa electromagnetic flow transmitter.
Electromagnetic flowmeter operating temperature depends on the lining material used, typically 5-70 ℃. Such as special treatment, may exceed the above range, such as Tianjin Automatic Instrument Factory production of wear resistant electromagnetic flowmeter. The transmitter allows the measured medium temperature of -40 ten 130 ℃.
3. Trees lining material and electrode material choice
Lining material and electrode material transmitter must be properly selected according to the physical and chemical nature of the medium, otherwise the instrument due to corrosion of the lining and the electrodes and quickly damaged, and highly corrosive media once the leak easily cause accidents. Thus, the production process must be based on the specific measurement medium, electrodes and careful selection of the liner material.
Installation (two) electromagnetic flowmeter
To ensure accuracy of electromagnetic flowmeters, proper installation is very important.
① transmitter should be installed in the interior dry and ventilated place. Avoid installation in environments where the temperature is too high, should not be subject to strong vibration, try to avoid the equipment with a strong magnetic field, such as large motors, transformers. Avoid installation in a corrosive gas. Installation site easy to repair. This is to ensure the normal operation of the transmitter of the environmental conditions.
② measured media in order to ensure full measuring tube inside the transmitter, variable Diego is best mounted vertically, flow from bottom to top. Especially for liquid-solid two-phase flow, must be mounted vertically. If the site only allows horizontal installation, you must ensure that the two electrodes at the same level
③ transmitter should be installed at both ends of the valve and bypass.
④ electromagnetic flow transmitter electrode measured by a few millivolts ac potential, the potential of the liquid inside the transmitter is based. In order to make the liquid level transmitter with the potential to stabilize and fluids to keep such potential, in order to ensure stable measurement, the transmitter housing with a metal pipe at both ends should be well grounded, the converter housing should also be grounded. Grounding resistance should not be greater than 10, can not be shared with other electrical equipment grounding wire. If the transmitter can not guarantee a good contact with the housing and the metal pipe, with metal wires to connect them. Then grounded.
⑤ In order to avoid signal interference signal between the transmitter and the converter must be shielded wire transfer. Do not allow the signal and power cables in parallel on the same cable pipe. Signal cable length is generally not exceed 30 m.
⑥ converter installation site should avoid AC and DC magnetic field and vibration, ambient temperature of -20 a 50 ℃, does not contain corrosive gases, relative humidity less than 80%.
⑦ To avoid the influence of flow velocity relative measurement, the flow control valve should be set at the transmitter downstream. For transmitters small diameter, the center distance from the electrode because the meter inlet end several times to have the equivalent of the length of the diameter D, so you can not do the provisions of straight pipe upstream. But for larger diameter meter typically due 5D upstream straight pipe above and downstream straight pipe requirements generally do not do.
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