Good question, this is a question people often ask 👍
I useSimplified version + Technical versionIt's easier to understand from two perspectives.

In short (remember this sentence first).

👉 Electromagnetic flow meters always prefer fluids that conduct electricity..
Pure water and oil have very low (or almost no) conductivity.Therefore, no quantity can be produced.

Please explain the principle more clearly.

Electromagnetic flowmeters rely on Faraday's law of electromagnetic induction:

Fluid (= conductor)
Flowing in a magnetic field
→ Voltage will be induced
→ Voltage magnitude ∝ Flow velocity ∝ Flow rate

The concept of the formula is:
E = B × L × v

Here's the problem 👇

👉 The fluid itself must be a conductor.Only then can voltage be generated.

Why is the amount of "pure water" insufficient?

Pure water (deionized water, RO water)
👉 Extremely low conductivity(Close to 0 μS/cm)
Electromagnetic flow meters typically require:
- Minimum conductivity approximately 5～20 μS/cm(Look at the brand)

👉When conductivity is insufficient, the following will occur:

The induced voltage is too small
Noise is greater than signal
The signal is fluctuating or simply displays 0.

So it's not broken, it's...The physical principle itself doesn't work..

Why is the amount of "oil" insufficient?

Oils (hydraulic oil, lubricating oil, diesel oil, etc.):

almost Completely non-conductive
Flowing in a magnetic field
👉 No induced voltage will be generated at all

result:

The electromagnetic flow meter is "completely imperceptible".
Just like air 😅

What quantity of these fluids should be used?

Here's a reference table to help you remember it quickly 👇

fluid type	Suitable for flow meters
pure water	UFM ultrasound,TMFM Coriolis Force
oil	Gear typeFRV Turbo,TMFM Coriolis Force
Acid and alkali solutions, wastewater	FMG electromagnetic flowmeter (best suited)
High precision requirements	TMFM Coriolis Force

A one-sentence summary (for engineers)

Electromagnetic flowmeters are not incapable of measuring liquids, but they are incapable of measuring "non-conductive liquids".

If you encounterOn-site selection, specification sheet issues, or actual measurements not meeting the required values.Tell me what fluid you're measuring, its concentration, and temperature, and I can directly help you determine which type of flow meter is more reliable.