Liquid ultrasonic flow meters are widely appreciated for their non-invasive nature, high accuracy, and versatility in fluid measurement. However, like all precision instruments, they can occasionally encounter operational problems. This article outlines common faults that may occur in liquid ultrasonic flow meters and provides effective troubleshooting methods to restore optimal performance.

1. Inaccurate Readings

Possible Causes:

  • Presence of turbulence caused by nearby fittings such as Venturi tubes, orifice plates, vortex, turbine meters, or partially closed valves.
  • Mismatch between the meter’s input pipe diameter and the actual pipeline.

Solutions:

  • Reposition the sensor away from flow-disturbing equipment—ideally 30D upstream and 10D downstream of such devices.
  • Modify or match the flow meter pipe diameter to the pipeline.

2. Sensor Working, but No or Low Flow Velocity Detected

Possible Causes:

  • Pipe exterior has residual paint or rust that hasn’t been cleaned.
  • Sensor installed over weld seams or uneven surfaces.
  • Poor pipe roundness, rough internal surfaces, or pipe scaling.
  • Low particle density in the measured medium or use of ultra-clean liquids.
  • Sensor mounted on fiberglass or plastic pipes.
  • Sensor installed over a casing, which weakens ultrasonic signal transmission.

Solutions:

  • Clean and smooth the pipe surface before installation.
  • Avoid weld seams and irregular surfaces.
  • Use metal pipes with smooth inner walls and avoid liners if possible.
  • Avoid installing sensors on casings or fiberglass; if necessary, use clamp-on sensors with appropriate compensation features.

3. Poor Coupling Between Sensor and Pipe

Possible Causes:

  • Gaps or air bubbles in the coupling interface between sensor and pipe.

Solutions:

  • Re-clean and re-install the sensor.
  • Sand or smooth the pipe surface; relocate if near welds.
  • Apply fresh and adequate coupling gel.
  • Avoid installation over coated, insulated, or encased pipe sections.

4. False High Readings When Valve Is Partially Closed

When the flow control valve is too close to the sensor and partially closed, the increased local flow velocity may be misinterpreted by the flow meter.

Solution:

  • Install the sensor at least 30D upstream or 5D downstream of the control valve to ensure stable flow conditions.

5. No Flow Measurement Despite Proper Setup

Possible Causes:

  • Change in fluid properties or presence of vapor due to high temperature.
  • The medium’s temperature exceeds the sensor’s limits.
  • Coupling gel has aged or dried up.
  • High-frequency electrical noise interference.
  • Data loss or software crash in the computing unit.

Solutions:

  • Confirm the medium is in liquid state and within operating temperature limits.
  • Reapply coupling agent if dry or aged.
  • Shield the device from high-frequency sources or use filters.
  • Reboot the device or restore settings from backup.

Conclusion

While ultrasonic flow meters offer numerous advantages, they can be sensitive to installation errors, environmental conditions, and pipe irregularities. By understanding these common issues and applying the appropriate troubleshooting measures, users can maintain the accuracy and reliability of their measurement systems.

For more detailed guidance on how ultrasonic flow meters work or selecting the right flow meter for your application, Click for help.

FAQ:

Q1: Can I install an ultrasonic flow meter on a plastic pipe?
Yes, but signal strength may weaken. Use suitable sensors and coupling methods designed for plastic materials.

Q2: What’s the ideal upstream and downstream straight pipe length?
Typically, 30D upstream and 10D downstream is recommended for stable readings.

Q3: How often should the coupling gel be replaced?
It’s good practice to inspect the coupling gel every 6–12 months and replace it if dry or degraded.

Q4: What causes sudden signal loss in ultrasonic flow meters?
Common reasons include air bubbles, worn coupling agent, or strong electrical interference.