Key points
- Magmeters need conductivity; ultrasonic meters do not.
- Clamp-on ultrasonic installs without shutdown.
- Magmeters tolerate solids and slurry better; ultrasonic transit-time prefers clean liquid.
- Both have no moving parts and no pressure loss (inline).
How each one measures
An electromagnetic meter applies a magnetic field across the pipe; the moving conductive liquid induces a voltage proportional to velocity, picked up by electrodes, which is Faraday's law. An ultrasonic transit-time meter sends sound pulses with and against the flow; the time difference is proportional to velocity (background).
Side-by-side comparison
| Criterion | Electromagnetic | Ultrasonic (transit-time) |
|---|---|---|
| Liquid must be conductive | Yes (≥2–50 µS/cm by model) | No |
| Typical accuracy | ±0.5% of reading (±0.3% selected) | ±1% inline; ±1–2% clamp-on, installation-dependent |
| Solids / slurry | Good with suitable liner | Limited; Doppler type for high solids |
| Installation | Spool piece, pipe cut | Inline or clamp-on without cutting |
| Large pipes (>DN1000) | Heavy and costly | Clamp-on cost barely changes with size |
| Straight run | ~10 D up / 5 D down | Often longer; profile-sensitive |
| Typical uses | Water, wastewater, chemical, pulp | Oils, DI water, HVAC retrofit, surveys |
Selection rules
- Is the liquid conductive above the meter's minimum? If not, use ultrasonic, turbine or Coriolis.
- Can you shut down and cut the pipe? If not, use clamp-on ultrasonic.
- Does it carry solids or slurry? Then use electromagnetic with a PU or rubber liner.
- Is it for billing or permit records? An electromagnetic meter with a verified calibration is usually preferred.
Related questions
Which is more accurate?
In most water applications, an inline magmeter: its reading is less sensitive to velocity profile than a clamp-on ultrasonic installation.
Can ultrasonic meters measure wastewater?
Transit-time meters struggle with heavy solids and bubbles; Doppler ultrasonic or electromagnetic meters are better suited.
Sources and further reading
Product specifications quoted here are summarised from Supmea datasheets. Confirm the figures for your exact model before final design.