An electromagnetic flowmeter is a type of flowmeter that uses magnetic fields to measure flow rates. The magnetic field is 15 times stronger than that of the conventional tube and is therefore capable of penetrating much deeper into the process fluid than the electrodes can. A number of advantages of this type of flowmeter are its low initial costs and the fact that it requires only sensors to replace when they wear out. Here are some of these advantages:
Magnetic flow tube
To use an electromagnetic flowmeter, a conductive fluid must be passed through a magnetic flow tube. The speed of the fluid, average liquid velocity, and the magnetic field strength all affect the voltage generated by the flow. Two electrodes, one on each side of the flow tube, sense the voltage, and the amount of flow is proportional to the difference between the two. Magnetic flow meters do not require long straight runs and can be installed in short meter runs.
There are two types of magnetic flow tubes. The short form magmeter has an OD of just under 500 mm. The magnetic flow tube is typically made of PFA or another material with similar specifications. However, the liner material can be damaged when overtorqued flange bolts are used. Liner protectors are available to prevent this damage.
Magnetic flowmeters must be located away from electrical radiation, cathodic protection systems, and other sources of electrostatic interference. The presence of liner protectors prevents shifting of the magnetic flowmeter sensor. If the electrodes 30 shift, the process fluid F will leak around them and potentially damage the insulators 50. Shifting can also cause the electrodes to short against the conduit walls 48. Liner protectors for electromagnetic flowmeters are typically secured to the magnetic flowmeter sensor using mechanical fasteners that are placed through the liner.
Magnetic flowmeters have two types of electrodes. One type uses a non-contacting metal sandwiched between two layers of liner material. This design is available in sizes under eight inches, and has ceramic liners. It is better suited to applications with severe coatings. However, it is important to match the inner diameter of the flowmeter to the inner diameter of the process pipes that it connects to.
Before installing an electromagnetic flowmeter, check its electrical and mechanical specifications. It should be installed on a pipe with a lining that is insulated from the environment. The transmitter and the metal pipeline should be connected by threads, flanges, or metal wires. The pipe should be grounded so that no grounding resistance is generated. Electric welding, for example, will create an interference potential that will interfere with the operation of the flowmeter.
The pipe must be straight and at least one pipe-length-long to meet the requirements. The medium should be flowing through the entire pipe at the installation position, otherwise the medium will stick to the electrode. To solve this problem, half of the flow pipe should be raised.