Theory and Performance

What is a Magnetic Flow Meter?

A magnetic flow meter (mag flowmeter) is a volumetric flow meter which does not have any moving parts and is ideal for wastewater applications or any dirty liquid which is conductive or water based. Magnetic flowmeters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions). Magnetic flowmeters are also ideal for applications where low pressure drop and low maintenance are required.

Principle of Operation
The operation of a magnetic flowmeter or mag meter is based upon Faraday's Law, which states that the voltage induced across any conductor as it moves at right angles through a magnetic field is proportional to the velocity of that conductor.

Faraday's Formula:
E is proportional to V x B x D where:

E = The voltage generated in a conductor
V = The velocity of the conductor
B = The magnetic field strength
D = The length of the conductor

To apply this principle to flow measurement with a magnetic flowmeter, it is necessary first to state that the fluid being measured must be electrically conductive for the Faraday principle to apply. As applied to the design of magnetic flowmeters, Faraday's Law indicates that signal voltage (E) is dependent on the average liquid velocity (V) the magnetic field strength (B) and the length of the conductor (D) (which in this instance is the distance between the electrodes).In the case of wafer-style magnetic flowmeters, a magnetic field is established throughout the entire cross-section of the flow tube (Figure 1). If this magnetic field is considered as the measuring element of the magnetic flowmeter, it can be seen that the measuring element is exposed to the hydraulic conditions throughout the entire cross-section of the flowmeter. With insertion-style flowmeters, the magnetic field radiates outward from the inserted probe (Figure 2).

Magmeter Selection
The key questions which need to be answered before selecting a magnetic flowmeter are:

•	Is the fluid conductive or water based?
•	Is the fluid or slurry abrasive?
•	Do you require an integral display or remote display?
•	Do you require an analog output?
•	What is the minimum and maximum flow rate for the flow meter?
•	What is the minimum and maximum process pressure?
•	What is the minimum and maximum process temperature?
•	Is the fluid chemically compatible with the flow meter wetted parts?
•	What is the size of the pipe?
•	Is the pipe always full?

Advantage as follows

1.No movable and throttle components in the pipe, so there is no extra pressure loss, the effort of saving energy is observable.

2. High performance in the aspect of anti-clogging, especially apply to measuring the solid-liquid two phases medium, such as wastewater, slurry and paper pulp.

3. As the inductive signal exists in the whole magnetic field, it can be regarded as the average value of the cross section of the pipe. So the upstream straight run is short relatively, just 5D.

4. Just the liner of the pipe and electrode surface contact with the liquid, so choosing right material for liner and electrode can realize the requirements of anti-abrasion and corrosion-proof.

5. The inductive voltage signal is precise proportional to the average velocity.

6. The measurement result has nothing to do with the liquid pressure, temperature, density, conductivity (no less than the lowest limit) and some other parameters, so the measurement accuracy is high and reliable.

Structure features

1. Quick respondence and good stability.

2. High accuracy: ±0.5% or ±1.0% as normal, ±0.25% under special calculation.

Repeatability: ±0.5% or ±1.0% as normal

3. Double-cavity structure separates the electronic part from the wire connection terminal.

4. Super low EMI switch power source, suitable for wide range of power voltage.

5. High-definition background-light and extended-temperature LCD displayer, easy to operate.

6. Support bus digital communication output, RS485, RS232C, HART, BRAIN, MODBUS etc.

7. Measure and accumulate the flow rate of bidirectional fluid