When selecting an electromagnetic flowmeter, customers often focus on pipe diameter, flow range and liner material.
But there is another specification that is just as important:
Liquid conductivity.
A common question is:
“Why can’t an electromagnetic flowmeter measure any liquid?”
The answer is related directly to its measurement principle.
How Does an Electromagnetic Flowmeter Measure Flow?
An electromagnetic flowmeter works according to Faraday’s law of electromagnetic induction.
The sensor generates a magnetic field.
When conductive liquid moves through this magnetic field, an electrical voltage is generated.
The electrodes detect this voltage, and the transmitter converts the signal into flow velocity and flow rate.
In simple terms:
Moving conductive liquid → induced electrical signal → flow measurement
Therefore, the liquid must have sufficient electrical conductivity for the sensor to detect a reliable signal.
What Happens When Conductivity Is Too Low?
When liquid conductivity decreases, the electrical signal generated by the liquid becomes more difficult to detect reliably.
The flowmeter may therefore become more sensitive to:
electrical noise;
grounding conditions;
electrode condition;
external interference.
The result can be:
unstable readings;
weak measurement signals;
poor repeatability;
difficulty measuring very low flow;
inaccurate readings.
This does not necessarily mean that the flowmeter itself is defective.
The liquid may simply be outside the suitable conductivity range of the instrument.
What Is the Minimum Conductivity?
The exact minimum conductivity depends on the electromagnetic flowmeter design.
For example, some instruments may specify a minimum conductivity such as:
≥ 5 μS/cm
However, customers should always check the specification of the specific model rather than assuming that every electromagnetic flowmeter has exactly the same requirement.
Why Is Water Usually Suitable?
Most ordinary tap water and wastewater have sufficient conductivity for electromagnetic flow measurement.
This is one reason electromagnetic flowmeters are widely used in:
water supply;
wastewater treatment;
irrigation;
industrial water;
process water.
However, not all water has the same conductivity.
Very pure water, deionized water and some specially treated liquids can have much lower conductivity.
These applications should therefore be evaluated carefully before selecting an electromagnetic flowmeter.
Why Can’t Oil Usually Be Measured?
Most oils have very low electrical conductivity.
Because an electromagnetic flowmeter relies on the electrical signal generated by conductive liquid, ordinary oil is generally not suitable for a standard electromagnetic flowmeter.
For oil applications, other flowmeter technologies may be more appropriate depending on viscosity, flow range and required accuracy.
This is an important point during flowmeter selection:
The first question should not only be “What is the pipe size?” but also “What is the liquid?”
Can Conductivity Change During the Process?
Yes.
This can happen when:
two liquids are mixed;
chemical concentration changes;
water is diluted;
process composition changes;
cleaning water enters the pipeline.
If conductivity changes significantly, the measurement environment may also change.
In most suitable applications, conductivity remains well above the minimum requirement, so normal variations do not create a problem.
However, when the liquid operates close to the minimum conductivity limit, greater attention is required.
Low Conductivity and Low Flow
Low conductivity can become particularly noticeable at low flow rates.
At higher flow velocity, the generated measurement signal is stronger.
At very low flow velocity, the signal becomes smaller.
If the liquid also has very low conductivity, the measurement signal may become more difficult to distinguish from electrical noise.
Therefore, applications involving both:
very low conductivity + very low flow
should be evaluated carefully.
How Can You Check Whether the Liquid Is Suitable?
Before selecting an electromagnetic flowmeter, provide the supplier with:
liquid name;
approximate conductivity;
normal flow range;
minimum flow;
maximum flow;
operating temperature;
pipe size.
If conductivity is unknown, measuring it directly is preferable.
Do not simply assume that a liquid is conductive because it contains water.
Engineer’s Practical Advice
When an electromagnetic flowmeter shows unstable or inaccurate readings, check conductivity if the liquid is unusual or close to the instrument’s minimum conductivity requirement.
The troubleshooting process can be simple:
Check the liquid → Check conductivity → Check grounding → Check electrodes → Check installation
If conductivity is too low, adjusting parameters will not fundamentally solve the problem.
The better solution may be to select a flowmeter technology suitable for the liquid.
FAQ
Can an electromagnetic flowmeter measure water?
Yes. Most ordinary water has sufficient conductivity for electromagnetic flow measurement, but the actual conductivity should be considered for very pure or specially treated water.
Can an electromagnetic flowmeter measure oil?
Standard electromagnetic flowmeters are generally not suitable for ordinary oils because their electrical conductivity is too low.
Does higher conductivity mean higher accuracy?
Not necessarily. The liquid only needs to meet the flowmeter’s suitable conductivity range. Other factors such as installation, grounding and flow conditions also affect accuracy.
Why does my flowmeter become unstable with purified water?
Very pure or deionized water may have low conductivity. If the conductivity approaches or falls below the flowmeter’s minimum requirement, the signal can become weak or unstable.
What should I do if I don’t know the liquid conductivity?
If possible, measure the liquid conductivity or provide a representative liquid sample/specification to the flowmeter supplier for evaluation.
Final Thoughts
Conductivity is one of the most important selection factors for an electromagnetic flowmeter.
Remember the basic principle:
No sufficient conductivity → No reliable electromagnetic measurement signal.
Before ordering an electromagnetic flowmeter, do not only provide the pipe diameter and flow range.
Also confirm:
What is the liquid?
What is its conductivity?
Does the conductivity remain stable during operation?
These simple checks can prevent many measurement problems later.
Post time: Sep-01-2026