The Electromagnetic Insertion Flowmeters are based on the same technology as the more traditional full-bore electromagnetic flowmeters (usually called mag meters) namely Faraday's Law of Electromagnetic Induction:
When a conductive liquid moves through a magnetic field, it produces a voltage directly proportional to the velocity of the medium.
The essential differences between the two types of flowmeters are their installation and the positioning of the electrodes that allow this voltage to be measured:
Contrary to some ideas sometimes held, insertion-type electromagnetic flowmeters offer excellent accuracy, sometimes even better than that offered by full-bore flowmeters.
In the case of Single Point Flowmeters, this accuracy requires that installation instructions be followed, and often that velocity profiles be produced during commissioning.
This operation consists in carrying out punctual velocity measurements, by progressively raising the probe from the bottom to the top of the pipe; it then makes it possible to apply to the measurements which will be obtained from the flowmeter a 'profile' coefficient taking into account the dispersion of velocities inside the pipe, to improve the accuracy of the average velocity.
These flowmeters may also require more frequent checks and re-calibrations, but these operations are facilitated by the concept of mounting insertion flowmeters.
Full Profile Flowmeters, which have several sets of electrodes from the bottom to the top of the pipe, have the advantage of permanently taking into account this dispersion of velocities and the variability of profiles according to hydraulic regimes (turbulent, laminar or transient regimes).
It is also understandable that this multi-point measurement can offer, especially in cases of disturbed and non-uniform regimes, a better accuracy than that of full-bore flowmeters.
However, the arrangement of the electrodes along the flowmeter body, as well as the method of calibration, are important to ensure this accuracy, especially at low velocities/flow rates.
Our partner, Flow-Tronic, has favoured more demanding design choices in manufacturing, which allow to optimize the accuracy of the measurement of the average flow velocity: