If the flow velocity is V [cm/s], the magnetic flux density is B [Gauss], and the pipe diameter is D [cm] then the induced electromotive voltage, E, will be E = BVD * 10-8 [volts]. The induced voltage is directly proportional to the flow velocity as long as the pipe diameter and the magnetic flux are constant. Therefore, by measuring the electromotive voltage, we can measure the flow rate of the water.

How do electromagnetic flow meters work?

The water flow meter in all TSI products uses an electromagnetic design. This is the proven technology for Fire Services and for taking measurements from fire hydrants. Because there are no mechanical parts in the water stream, the sensor is not affected by any debris and there is no pressure loss.

Magnetic coils are placed at the top and bottom of the pipe, setting up a magnetic field that is perpendicular to the direction of water flow. Water is conductive, so the flowing water breaks the magnetic field and generates a small electromotive voltage, perpendicular to the axis of the magnetic field and the flowing water.

Please refer to the figure below for a technical explanation:

If the flow velocity is V [cm/s], the magnetic flux density is B [Gauss], and the pipe diameter is D [cm] then the induced electromotive voltage, E, will be E = BVD * 10-8 [volts]. The induced voltage is directly proportional to the flow velocity as long as the pipe diameter and the magnetic flux are constant. Therefore, by measuring the electromotive voltage, we can measure the flow rate of the water.

If the flow velocity is V [cm/s], the magnetic flux density is B [Gauss], and the pipe diameter is D [cm] then the induced electromotive voltage, E, will be E = BVD * 10-8 [volts]. The induced voltage is directly proportional to the flow velocity as long as the pipe diameter and the magnetic flux are constant. Therefore, by measuring the electromotive voltage, we can measure the flow rate of the water.

Although the science behind it may seem complex, a TSI flow meter is easy to use. It is also highly accurate and totally reliable, which is essential in the firefighting environment. Other methods of measuring flow rely on a physical object such as a paddle wheel being placed in the water stream. In comparison this is inferior for the following reasons:

ELECTROMAGNETIC FLOW METERS PADDLE WHEEL FLOWMETERS
ACCURACY 98% accurate over a full  range of firefighting flow rates Less accurate and a narrow measuring range
RELIABILITY Highly reliable with a longer lifespan (no moving parts) Subject to wear and tear, and susceptible to damage (moving parts in water stream)
INSTALLATION Versatile. Can be installed anywhere on a firefighting pump Restricted locations due to turbulence impacting on accuracy. e.g. minimum of six pipe diameters needed after bend in pipe
GHOST READINGS * No Yes (paddles spin due to turbulence)

Electromagnetic measurement beats the paddle wheel method

Electromagnetic measurement beats the paddle wheel method

Why is accuracy of flow measurement important?

Modern firefighting techniques (fire suppression and fire extinguishing) use technologically advanced firefighting equipment, which requires specific pressure and flow rates to ensure that they operate as designed. Too little or too much water can put a firefighter’s safety at risk. Too little water and a flashover may not be controlled. Too much water and visibility may be severely impaired. TSI electromagnetic flow meters are highly accurate across the whole range of firefighting flow rates from 30-5000 LPM, thus ensuring these situations do not occur.