The electromagnetic flowmeter has been a tried and trusted, maintenance-free industrial flow
measurement device for many years. It is based on Faraday’s law of induction, where a voltage
is induced in a conductor when it moves within a magnetic field. The conductive fluid passing
through the flowmeter forms the moving conductor, and the induced voltage is proportional to the average flow velocity. Fluids with conductivities of 5 micro-siemens/cm and above can be accurately measured by the SAFMAG. Advantages of using electromagnetic flowmeters include unrestricted pipe cross-section and independence of density and fluid viscosity. Performance is unaffected by changes in process pressure, temperature and fluid conductivity. All of this, plus a linear output signal, make the SAFMAG an ideal flowmeter for a wide variety of applications.
The SAFMAG utilises a new generation multitasking microprocessor to handle all functions simultaneously. Low power electronics technology reduces total power consumption, therefore realising small power backup systems. The SAFMAG’s rugged design and reliability make it the obvious choice when it comes to flow measurement of conductive fluids. Two versions of the signal converter are available:
- ACMPU for use on all slurries, pulps and pastes providing a stable, accurate reading of flow with these traditionally difficult applications.
- DCMPU for use on all other general applications, the pulsed dc technology and continuous automatic rezeroing, making it the recommended choice in these applications. The simple design of the SAFMAG enhances reliability. The flowtube housing is fully welded and pressure tested to ensure a complete seal against moisture and other contaminates. The field wiring is isolated in a separate terminal box, sealed from the coil housing to ensure that the coil housing is not contaminated by possible conduit entry infiltration. User friendly, self-explanatory input or interrogation of measurement data is done directly on the converter by means of a 4-button keyboard. An easily readable illuminated 2-line display is used to display the flowmeter data. Flow rate and flow total are continuously displayed. Configuration data is stored in nonvolatile EEPROM memory.
Electromagnetic flowmeter performance can be compromised by stray currents present in the piping or process fluids. Proper connection of the flowtube to reference the process fluid potential is important. The first rule to be observed is that the flowmeter body and the fluid should be at the same potential. The SAFMAG is supplied with a grounding electrode for this purpose. In process fluids with low conductivity or in cathodic protection situations, it is recommended that two grounding rings located at the upstream and downstream faces of the flowtube are used to ensure a positive process ground.
The flowtube size is an important consideration as it affects flow velocity. It is often necessary to select a meter that is smaller than the adjacent piping to ensure the fluid velocity is suitable for the meter. The following table shows guidelines for sizing meters in different types of applications, although operation outside these limits may also give acceptable performance.