- SM magmeters
- Technology
How magmeters measure the flow of conductive liquids with no moving parts
Magnetic inductive flow meters, commonly known as magmeters, utilize the principles outlined in Faraday's law of induction to accurately measure the flow of conductive liquids in various industrial settings.
Faraday's law
Faraday's Law says that when a conductor moves through a magnetic field, it creates a voltage. This voltage depends on how fast the conductor is moving, among other things such as the strength of the magnetic field. In the case of a magmeter, the conductor is the fluid flowing through the pipe.
Required fluid properties
Conductivity
All magmeters require a minimum conductivity of the medium for the technology to measure flow. Medium conductivity of at least 20 µS/cm is required for the SM family. Media with conductivity below the 20 µS/cm threshold produce low induction voltages, making it difficult or impossible to distinguish the difference between the signal voltages and noise voltages. Typically, fluid with at least 25 % water has a high enough conductivity for the SM magmeter to function properly.
Viscosity
The specified medium viscosity for use with the SM magmeter is < 70 mm²/s (40 °C). Practically, higher viscosity fluids will result in a larger pressure drop through the meter and a minor impact on accuracy.
Temperature
The medium temperature specification depends on the SM model. Please refer to the datasheet for that detail.
Medium temperature can be higher than specified when the ambient temperature is relatively low. For example, the SM is used in brewing applications for media temperature around 185 °F, but the ambient temperature is only around 70 °F. A general rule of thumb is for every degree the ambient temperature is lower than the maximum, the medium temperature can be one degree higher. This is valid for media temperature up to about 190 °F maximum.