Visit our Magmeters / Electromagnetic Flow Meter Category Page to see our product selection.

Magnetic flow meters have been commercially available since the mid 1950's, measuring the flow of water and a wide range of other electrically conductive liquids, including corrosives, slurries and sludge in closed pipe systems.

Today, Instrumart offers a full range of magnetic flow meters, including: wafer-style, flanged-style and ceramic flowtubes, with a wide range of liners and electrode materials, as well as insertion and electrodeless designs.

These primary heads are offered with integrally-mounted or remote (field) mounted signal converters featuring both pulse and 4-20mA output signal options (RK20 Series).

In addition to offering you relatively "clog-free" obstructionless flow measurement with no moving parts to wear out or pressure drop to overcome, this cost-effective technology also offers you a variety of other advantages, such as:

  • Easy to install
  • Low cost
  • Minimum maintenance
  • Linear analog output
  • Insensitivity to specific gravity, viscosity
  • Pressure, Temperature, etc.
  • Ability to measure flow of a wide range of difficult-to-meter fluids, such as corrosives, slurries, and sludges
  • Insertion-style probe with exclusive Venturi Tip offers greater economy, especially for large pipe sizes

Applications

  • Water & Waste Water
  • Pulp & Paper
  • Cellulose
  • Pharmaceuticals
  • Food & Beverage
  • Cosmetics
  • Mining
  • Chemical Processing
  • Agricultural Fertilizer
  • Liquid Feed Batching

Operating Principal

Faraday's Law of Electromagnetic Induction is the underlying principle of operation for magnetic flow meters. This law states that the magnitude of the voltage induced in a conductive medium moving through a magnetic field and at right angles to the field is directly proportional to the product of the strength of the magnetic flux density (B), the velocity of the medium (V), and the path length (L) between the probes.

E = constant x B x L x V
Where; E = The voltage generated in a conductor
V = The velocity of the moving conductor
B = The strength of the magnetic field
L = The length of the conductor path (The distance between probes)

In other words, the faster a wire is passed through a magnetic field, at right angles to the field, the more voltage will be induced.

Full Flowtube-type Magnetic Flow Meter

To apply Faraday's Law to Full Flowtube-type Magnetic Flow Meters, it is assumed that the fluid being measured is adequately conductive.

Full Flowtube-type 
	Magnetic Flow Meter

As the liquid flows through the pipe, it passes through the magnetic field (B) within the flowtube. As it passes through the influence of the magnetic field, a voltage is induced between the two electrodes, imbedded within the sidewalls of the flowtube. The distance (D) between the two electrodes is fixed (constant). The strength of the magnetic field (B) is also constant. Therefore, the only variable is the induced voltage (E), which is proportional to the velocity of the flowing liquid (V).

Insertion magnetic flow meter

To apply this principle to Insertion Magnetic Flow Meters, it is assumed that the fluid being measured is adequately conductive (above 1 S/cm).

The output signal voltage (E) is dependent on the average liquid velocity (V) and the distance between the two electrodes (D), located in the notch of the venturi tip at the end of the insertion probe.

In the case of the insertion magnetic flow meter, the magnetic field is confined within the tightly directed notch (flow channel) of the exclusive venturi tip. Therefore, the measuring element is physically isolated from swirling cross currents and other random hydraulic conditions that may be taking place throughout the cross sectional area of the flow tube.

Selection Factors

Several factors should be reviewed concerning liquids to be metered by magnetic flow meters.

Conductivity

Even water varies in conductivity, due to the various ions present.

Deionized water and distilled water are not adequately conductive.

Chemical and/or pharmaceutical solutions are often not adequately conductive. The concentration level of the solutions can also affect conductivity. Therefore, this variable should also be considered.

Temperature affects conductivity. Therefore, the temperature of the liquid being considered should also be known.

The key, and only constant rule is that liquid conductivity must be above minimum S/cm requirement specified for individual product.

Acids/Caustics

Generic descriptions of chemical solutions may not adequately describe all component substances. Detailed descriptions should be confirmed to select chemically compatible materials of construction.

Velocity

The liquid velocity should be maintained within the specified flow range of the meter for proper operation. However, applications monitoring abrasive slurries, sludge or greases will require special consideration.

Abrasive Slurries

Mildly abrasive slurries can be handled by magnetic flow meters. Flow velocity should be maintained at 6 ft/sec or slower to minimize the risk of abrasion damage. However, velocities should not be allowed to fall below 4 ft/sec to prevent suspended solids from settling out of the flow stream.

Sludge and Greases

Sludges and grease-bearing liquids should flow at higher velocities (approximately 6 ft/sec minimum) to minimize coating of electrodes.

Flow Table

The following tables can be used to convert flow velocity to volumetric flow rate (range) in specific (nominal) pipe diameters.

Meter size in Inches
Velocity = 1 ft/s
Meter size (in) Flow rate US GPM Meter size (in) Flow rate US GPM
1/10 0.024480 10 244.80
1/8 0.038250 12 352.51
1/4 0.038250 14 479.81
3/8 0.15300 16 626.69
1/2 0.61200 20 979.21
3/4 1.3770 24 1410.1
1 2.4480 28 1919.2
1 1/4 3.8250 32 2506.8
1 1/2 5.5080 36 3172.6
2 9.7921 40 3916.8
2 1/2 15.300 48 5640.2
3 22.032 56 7677.0
4 39.168 64 10027
5 61.200 72 12691
6 88.128 80 15667
8 156.67    
Sizing a flowtube

Example:
Velocity = ft/sec
Nominal Pipe Diameter = 6"
Desired measuring range = 1,000 US GPM (Flow Rate)

6" Meter size = 88.128 US GPM
v= 1,000 US GPM / 88.128 US GPM X 1ft/sec
v= 11.35 ft/sec

Meter size in Meters
Velocity = 1 ft/s
Meter size DN mm Flow rate m3/h Meter size DN mm Flow rate m3/h
2.5 0.017671 250 176.71
4 0.045239 300 254.47
6 0.10179 350 346.36
10 0.28274 400 452.39
15 0.63617 500 706.86
20 1.1310 600 1017.9
25 1.7671 700 1385.4
32 2.8953 800 1809.6
40 4.5239 900 2209.2
50 7.0686 1000 2827.4
65 11.946 1200 4071.5
80 18.096 1400 5541.8
100 28.274 1600 7238.2
125 44.179 1800 9160.9
150 63.617 2000 11310
200 113.10    
Sizing a flowtube

Example:
Velocity = meters/sec
Nominal Pipe Diameter = DN150
Desired measuring range = 200 m3/h

DN150 Meter size = 63.617 m3/h
v= 200 m3/h / 63.617 X 1m/sec
v= 3.144 m/sec

Visit our Magmeters / Electromagnetic Flow Meter Category Page to see our product selection.