When an ultrasonic flow meter displays flow velocity but no flow rate, it often leaves users puzzled. This issue is common in industrial applications, and it typically means the meter can measure fluid speed but cannot convert it into flow or cumulative values.

To troubleshoot effectively, let’s understand the core principle first:

Flow = Velocity × Pipe Cross-Sectional Area
The flow meter measures velocity (m/s), then multiplies it by the pipe’s cross-sectional area—calculated from your input parameters like diameter, wall thickness, and material—to compute volume flow (m³/h or L/min). If cumulative flow does not increase, the problem lies in the area calculation or integration process.

Common Causes and Solutions

1. Low Flow Cutoff Setting (Small Signal Cutoff)

Cause:
All flow meters have a low flow cutoff value to eliminate errors from zero drift or minor leaks. If the measured velocity is lower than this cutoff, the meter will show zero flow and stop totalizing, even if velocity is displayed.

Solution:

  • Go to the settings menu and find Low Flow Cutoff.
  • If your normal flow is 0.3 m/s and cutoff is 0.5 m/s, the meter will not totalize.
  • Reduce the cutoff to 0.1 m/s or ensure your operating flow stays well above the cutoff.

2. Incorrect Pipe Parameter Settings

Cause:
If the pipe inner diameter is wrong, the cross-sectional area calculation is incorrect. Example: Actual ID = 100 mm, but input = 150 mm → incorrect area → incorrect flow.

Solution:

  • Check settings for pipe outer diameter, wall thickness, and material.
  • Verify units (mm vs inches).
  • Use actual measurements (e.g., caliper) instead of relying on memory or labels.

3. Totalizer Disabled or Reset

Cause:
Totalizer may be disabled or reset unintentionally, stopping cumulative flow calculations.

Solution:

  • Check display for cumulative status (e.g., “TOTAL ON”).
  • Enable totalizer in settings and confirm it’s active.

4. Sensor Installation Issues

Cause:
Even with velocity readings, improper installation can cause incorrect flow calculations. Common issues include:

  • Sensor placed too close to elbows, pumps, or valves (causing turbulence).
  • Dried coupling gel or uneven application reducing signal strength.

Solution:

  • Ensure straight pipe runs: 10D upstream, 5D downstream (D = pipe diameter).
  • Reapply coupling gel and remove air bubbles.
  • Check signal strength and quality (should generally be above 60%).

5. Incorrect Fluid Parameters

Cause:
Wrong fluid type or temperature setting can impact sound speed compensation, slightly affecting flow calculations.

Solution:
Verify fluid type, temperature, and density settings match actual conditions.

6. Hardware or Software Faults

Cause:
Rare, but possible. Issues include main board errors or loose output wiring.

Solution:

  • Restart the flow meter.
  • Reset to factory defaults (after backing up parameters).
  • Contact manufacturer for technical support.

Quick Diagnostic Flow

  • Is instantaneous flow = 0? → Check Low Flow Cutoff.
  • Is instantaneous flow very small? → Check pipe parameters.
  • Is cumulative flow not increasing? → Check totalizer status.
  • Signal weak? → Fix installation issues.
  • Still not working? → Reset or call support.

Final Thoughts

If your ultrasonic flow meter shows velocity but no flow, the root cause is often a parameter configuration error, low flow cutoff, or installation problem. Start with easy checks like cutoff settings, then move to pipe dimensions and installation. Only after ruling out these should you suspect hardware failure.

For more detailed guides, check our related resources:

By following these steps, you can quickly restore accurate flow measurement and avoid costly downtime.