Magnetic flow meters, also known as mag flowmeters, are the go-to choice when it comes to flow measurement in applications involving conductive or water-based liquids. These devices are particularly suitable for wastewater and dirty liquid environments where traditional flow meters with moving parts may not be effective. This article will delve into the workings of mag flow meters and their various applications.
Understanding Faraday’s Law:
The underlying principle behind the operation of magnetic flow meters is Faraday’s Law. This scientific law states that the voltage induced across a conductor moving at right angles through a magnetic field is directly proportional to the conductor’s velocity. To put it simply, the flow of a conductive fluid through a magnetic field generates a voltage that can be measured and used to determine the flow rate.
The Formula:
Faraday’s Law can be expressed through the formula E = V x B x D, where:
– E represents the voltage generated in the conductor
– V symbolizes the velocity of the conductor (fluid)
– B denotes the magnetic field strength
– D represents the length of the conductor (distance between the electrodes in the case of mag flow meters)
Application to Mag Flow Measurement:
For the application of Faraday’s Law in flow measurement using magnetic flow meters, it is important to note that the fluid being measured must be electrically conductive for the principle to hold true. According to Faraday’s Law, the signal voltage (E) is directly dependent on the average liquid velocity (V), the magnetic field strength (B), and the length of the conductor (D).
In the case of wafer-style magnetic flow meters, a magnetic field is established across the entire cross-section of the flow tube. This means that the measuring element of the mag flow meter is exposed to the hydraulic conditions throughout the entire flowmeter’s cross-section. On the other hand, insertion-style flow meters radiate the magnetic field outward from the inserted probe.
Factors for Magmeter Selection:
Before selecting a magnetic flow meter for your specific application, consider the following key questions:
1. Is the fluid conductive or water-based?
2. Is the fluid or slurry abrasive?
3. Do you require an integral display or remote display?
4. Do you require an analog output?
5. What are the minimum and maximum flow rates for the flow meter?
6. What are the minimum and maximum process pressures?
7. What are the minimum and maximum process temperatures?
8. Is the fluid chemically compatible with the flow meter’s wetted parts?
9. What is the size of the pipe?
10. Is the pipe always full?
