(A) the principle of selection of electromagnetic flowmeter

Electromagnetic Flowmeter Selection of the main transmitter is the correct choice, and the converter only needs to be supporting them.

1. Calibre and range of choice

Transmitter diameter pipeline system and are generally selected the same calibre. If the pipeline system to be designed, will be under the scope of traffic flow and to choose calibre. For electromagnetic flowmeter, the flow rate to 2-4 m / s more appropriate. In exceptional circumstances , Such as liquid with a solid particles, taking into account the wear and tear, optional common velocity 3 m / s, for easy management of the fluid. Optional velocity 2 m / s.

The transmitter can range to choose two principles: First, full instrumentation is expected to range greater than the maximum flow value and the other is larger than the normal flow meter full range of 50 percent, to guarantee the accuracy of measurement.

2.choice of Temperature and pressure

Electromagnetic flowmeter to measure the fluid pressure and temperature there is a certain limit. Selection, the use of pressure must be less than the pressure of work flow meter. At present, the domestic production of electromagnetic flowmeter pressure of work specifications for:

Less than 50mm calibre, work pressure to 1.6 MPa;

900 mm calibre, work pressure for 1 MPa;

more than 1000 mm calibre, work pressure to 0.6 MPa

pressure on the transmitter there are special requirements, should be made with the manufacturer specific consultations. Some manufacturers have been able to create pressure of 32 MPa electromagnetic flow transmitter.

Electromagnetic Flowmeter depends on the temperature used by the lining material, generally 5-70 . As do special treatment, could exceed the scope of the above, such as Tianjin Automatic Instrument Factory production of wear-resistant corrosion-resistant electromagnetic flowmeter. Transmitter allows Tested medium temperature of -40 10 130 .

3. Tree-lined electrode material and the choice of materials

ransmitter of the lining material and electrode materials must be based on physical and chemical properties of the medium to correct choice, or instrument because of the lining and electrode corrosion and damage quickly, but once the corrosive strong media leak easily lead to accidents. Therefore, the production process must be based on the specific measurement of the medium, carefully chosen and the lining of the electrode material.

(b) the installation of electromagnetic flowmeter

To ensure the accuracy of electromagnetic flowmeter, correct installation is very important.

transmitter should be installed in indoor dry-ventilated place. Avoid installed in the local environment temperature is too high, should not be subject to strong vibration, as far as possible to avoid a strong magnetic field equipment, such as large motors, transformers, and so on. Avoid installed in a corrosive Gas occasions. Locations to facilitate maintenance. This is to ensure the normal operation of the transmitter environmental conditions.

to ensure that the transmitter in the measurement of a measured medium, and change again and again for the best vertical installation, the flow of bottom-up, particularly for liquid-solid two-phase, must be installed vertically. Permitted only if the scene level, you will need to ensure that Two electrodes in the same horizontal plane

transmitter should be installed at both ends of valves and bypass.

electromagnetic flow transmitter of the electrodes measured by a few mV AC potential, is the transmitter, based on the potential of liquid in order to make liquid potential and stability of the transmitter and maintain fluid and other potentials, to To guarantee stability measurement, and the metal shell of the transmitter should be good at both ends of the earth, converter shell should also be grounded. Grounding resistance can not be greater than 10, and other electrical equipment can not be the grounding line sharing. If we can not guarantee that the transmitter cover and good contact with metal pipes, metal wires of their link to more reliable ground.

in order to avoid interference signals, between the transmitter and a signal converter to be shielded by wire transfer. Does not allow the signal cables and power lines parallel to the pipe on the same cable. Signal cable length generally should not exceed 30 m.

converters should avoid reference to the installation site, DC strong magnetic field and vibration, temperature to -20 1 50 , does not contain corrosive gases, relative humidity of not more than 80 percent.

to avoid measuring the relative velocity at impact, the flow control valve should be installed in the lower reaches of the transmitter. Transmitter of the small-calibre, because the electrode from the center to the flow meter import terminal have been equivalent to the distance several times the length of the diameter D Therefore, on the upper reaches of straight pipe can not provision, the larger the flow meter diameter, 5 D in general should be above the upper reaches of the straight, the lower reaches of the general requirements of paragraph not straight.