An electromagnetic flowmeter works according to Faraday’s law of electromagnetic induction. When a conductive liquid flows through the magnetic field generated by the sensor, a small voltage is induced between the electrodes. The converter detects this voltage and calculates the flow velocity. Therefore, the liquid must have sufficient electrical conductivity for the flowmeter to generate and detect a reliable measurement signal.
When the conductivity is low, the induced signal becomes more difficult for the converter to detect reliably. The problem is not necessarily that the electromagnetic induction principle stops working, but that the useful flow signal becomes relatively weak compared with electrical noise and other interference. As a result, the displayed flow rate may become unstable, particularly at low flow velocities.
Low conductivity can also make the flowmeter more sensitive to electrode polarization and electrical noise. Since the electrodes are in direct contact with the liquid, the electrical characteristics of the liquid-electrode interface become increasingly important as conductivity decreases. External interference, grounding problems, or poor signal cable installation may therefore have a greater influence on the measurement.
The effect becomes more noticeable when low conductivity is combined with very low flow velocity. A low-conductivity liquid already produces a relatively weak measurement signal, and a low flow velocity further reduces the induced voltage. Under these conditions, the signal-to-noise ratio can become poor, resulting in unstable readings, zero-point fluctuations, or difficulty maintaining a reliable flow indication.
This is why electromagnetic flowmeters have a minimum conductivity requirement. For example, a particular instrument may specify a minimum conductivity such as 5 μS/cm, but the actual requirement depends on the flowmeter design and manufacturer. The manufacturer’s specified conductivity range should always be checked before selecting the instrument.
It is important to note that conductivity is different from corrosion resistance or water quality. A liquid can be chemically aggressive but electrically conductive, while another liquid may be chemically mild but have very low conductivity. For example, many aqueous solutions are suitable for electromagnetic measurement, whereas some oils and hydrocarbons have extremely low conductivity and generally cannot be measured reliably using a conventional electromagnetic flowmeter.
Temperature can also affect conductivity. Some liquids become more conductive as temperature increases, while their conductivity may decrease as temperature falls. Therefore, when the conductivity is close to the instrument’s minimum requirement, it is important to consider the actual operating temperature, rather than relying only on a conductivity value measured under laboratory conditions.
When troubleshooting a flowmeter with unstable readings, it is therefore useful to check:
Medium conductivity → Operating temperature → Actual flow velocity → Pipe-full condition → Air bubbles → Grounding → Electrical interference.
In short, low conductivity reduces the reliability of the electrical signal generated by the flowing liquid. When the conductivity is too low, the useful signal may become too weak relative to noise and interference, causing unstable or inaccurate measurements. For this reason, the medium’s conductivity should always be confirmed before selecting an electromagnetic flowmeter.
Post time: Aug-24-2026