3503E Trionex Digital Input Module

When a conductor at 3503E moves perpendicular to a magnetic field, a voltage is generated perpendicular to the magnetic flux lines and the direction of motion. This phenomenon is known as electromagnetic induction, and it is a fundamental principle in the operation of all electromechanical generators. In a generator mechanism, the conductor involved is usually a coil (or set of coils) made of copper wire. However, there is no reason why the conductor should be made of copper wire.

Any electrically conductive substance in motion, even a liquid, is sufficient to generate an electromagnetic voltage. Electromagnetic induction is therefore a suitable method for measuring the flow of liquids. In a practical sense, only liquid flow is measurable using this technique. Gases must be heated to a plasma state before they can conduct electricity, so electromagnetic flow meters cannot be used for most industrial gas flow streams.

3503E In order to successfully deduce the volume flow rate from the induced voltage, several conditions must be met.
The fluid must be a reasonably good conductor of electricity (note: if the conductive fluid contains some non-conductive solids, this is also possible; the conductive fluid surrounding the non-conductive solids still provides the electrical continuity between the electrodes required for induction).
The pipe must be completely filled with fluid to ensure contact with the two probes and to ensure flow through the entire cross-section of the pipe
The flow tube must be properly grounded to avoid errors caused by stray currents in the liquid.
The first condition is careful consideration of the process liquid prior to installation. The manufacturer of the magnetic flowmeter will specify the minimum conductivity of the liquid to be measured.

The second and third conditions are met by the correct installation of the magnetic flow tube in the pipeline. 3503E must be installed in such a way that the flow tube (without air holes) is completely flooded. The flow tubes are usually installed with the electrodes transverse to each other (never perpendicular!). Therefore, even momentary gas bubbles do not disrupt the electrical contact between the electrodes and the liquid flow. Magnetic flowmeters show several advantages over other types of flowmeters. Since the induced voltage is only proportional to the vertical velocity of the conductor, in this case the velocity of the fluid along the centre line of the flow tube. Therefore, magnetic flowmeters do not require long upstream and downstream pipe diameters as do orifice plates, which is a great advantage in many piping systems.