How Does a Magnetic Flow Meter Work?
The working principle of the magnetic flow meter is based on Faraday’s law of electromagnetic induction. This law states that when a conductor moves in a magnetic field, an induced electromotive force is generated at both ends of the conductor perpendicular to the magnetic field and the direction of movement. The magnitude of this electromotive force is proportional to the movement speed of the conductor and the magnetic induction intensity of the magnetic field.
When the conductive fluid passes through an insulating pipe with an inner diameter of D (unit: m) at an average flow rate of υ (unit: m/s), the pair of pipes is located in a uniform magnetic field with a magnetic induction intensity of B (unit: T). Due to the law of electromagnetic induction, an electromotive force E (unit: V) perpendicular to the direction of the magnetic field and the direction of flow will be generated on a pair of electrodes. This electromotive force E can be calculated by the formula E=BDv. At the same time, the volume flow rate qv (unit: m³/s) can be converted using the corresponding formula.
Electromagnetic flow meters need to be particular caution. According to data, about 2/3 of flow meter failures in actual use are caused by incorrect selection or installation. Therefore, key data must be carefully collected when selecting. Including the properties of the measured fluid, flow range, working pressure and temperature range. These data are crucial to ensure the accurate selection and stable operation of the electromagnetic flow meter.
The flow calculation formula is:
Q＝Vπ(D/2)²
Where,
Q represents the liquid flow rate in m³/h;
V represents the liquid flow rate in m/s, and its range is usually 0.1~15 m/s;
D represents the inner diameter of the pipe in mm.
Order Guide of Electromagnetic Flow Meter
Step 1: Collect data
1) Ensure that the actual maximum working pressure is lower than the rated working pressure of the flowmeter.
2) Verify whether the maximum and minimum operating temperatures are in line with the temperature range of the flowmeter.
3) Confirm whether there is a negative pressure situation.
4) Users can refer to the flow range table to select a suitable electromagnetic flowmeter. If the inner diameter of the selected electromagnetic flowmeter does not match the existing process pipeline, it may be necessary to reduce or expand the pipe. If the reduction is selected, the impact of the resulting pressure loss on the process flow needs to be evaluated.
5) From an economic point of view, a smaller-caliber electromagnetic flowmeter can be selected to reduce investment costs.
6) The economic flow rate needs to be adjusted for different fluids. For example, when measuring clean water, the economic flow rate range is 1.53m/s; for solutions that are easy to crystallize, it is recommended to increase the flow rate to 34m/s to use the self-cleaning effect to prevent deposition; and when measuring abrasive fluids such as slurry, the flow rate should be appropriately reduced to 1.0~2m/s to reduce wear on the lining and electrodes.
Step 2: Selection of electrode materials.
Appropriate electrode materials should be selected according to the corrosiveness of the measured fluid. You can refer to the relevant corrosion manual. For special fluids, it is recommended to conduct experiments to determine the best material.
Step 3: Selection of lining materials.
When selecting lining materials, it is necessary to comprehensively consider the corrosiveness, abrasiveness and operating temperature of the measured medium.
Step 4: Determine the protection level.
The protection level of electromagnetic flowmeters is usually divided into three categories:
IP65: This level of flowmeter can withstand water sprayed from any direction, with a water spray pressure of 30kPa and a water output of 12.5L/s. At a distance of 3 meters, the water inflow into the shell will not cause damage to the instrument.
IP67: This level of flowmeter is waterproof. Even if it is immersed in water for a short period of time, the water inflow into the shell will not affect the performance of the instrument.
IP68: This is a submersible protection. The sensor can be immersed in 1 meter deep water. After continuous diving, the water inflow into the shell will not cause damage to the instrument.
