How to Troubleshoot Common Issues with Non-Contact Ultrasonic Flow Meters

Non-contact ultrasonic flow meters are increasingly popular due to their non-intrusive design, no pressure loss, wide measurement range, and cost-effective installation. Compared to vortex or electromagnetic flow meters, they offer significant advantages in many industrial settings. However, like all instruments, ultrasonic flow meters can encounter problems during operation. In this article, we'll explore several common issues and provide practical solutions to restore accurate and reliable flow measurement.
 

1. Unstable or Fluctuating Readings

Possible Cause:
Strong vibration from the pipeline or the presence of flow-altering devices such as valves or pumps immediately upstream or downstream of the sensor.

Solution:
Relocate the flow sensors away from the vibration source or install them upstream of any devices that disrupt fluid flow. For stable measurement, maintain sufficient straight pipe runs before and after the sensor location.
 

2. Inaccurate Readings or Large Measurement Errors

Common Causes and Fixes:

• Top or bottom sensor placement on horizontal pipes: Sediment or air bubbles may interfere with signal transmission.
  → Fix: Install sensors on the sides of the pipe instead of the top or bottom.

• Installation on downward-flowing pipe with incomplete filling:
  → Fix: Ensure the meter is installed on a fully filled section of the pipe.

• Flow disturbance devices in the sensor’s acoustic path (e.g., venturi tubes, orifice plates, valves):
  → Fix: Maintain a minimum upstream distance of 30D and downstream of 10D from such devices, or install the meter upstream of the disturbance.

• Mismatched pipe diameter and input value:
  → Fix: Adjust the entered pipe diameter to match the actual inner diameter of the pipe.

For a detailed guide on how ultrasonic flow meters work, refer to our article: How Does an Ultrasonic Flow Meter Work?
 

3. No or Very Low Flow Readings Despite Functional Sensors

Possible Causes and Solutions:

• Unclean pipe surface (paint, rust):
  → Fix: Clean the pipe thoroughly before installing the sensors.

• Rough or uneven pipe surface, or sensors placed on a weld seam:
  → Fix: Move the sensors to a smooth, weld-free section or polish the surface.

• Poor pipe roundness or internal surface roughness (common in cast iron pipes):
  → Fix: Use smooth pipe materials like steel, or avoid corroded and scaled sections.

• Testing ultra-pure or very low solid-content media:
  → Fix: Consider switching to a different flow meter type better suited for clean liquids.

• Installation on fiberglass-coated or jacketed pipes:
  → Fix: Remove the fiberglass coating and relocate the sensors.

• Sensor coupling issues (gaps, air bubbles):
  → Fix: Reapply ultrasonic coupling gel properly and ensure firm sensor attachment.

4. Flow Reading Increases When Valve Is Partially Closed

Problem:
The meter appears to show an increased flow when the control valve is partially closed.

Cause:
The sensors are installed too close to the downstream side of the control valve. When the valve is throttled, the flow velocity increases locally due to the reduced cross-sectional area.

Solution:
Move the sensors upstream of the valve by at least 30D, or maintain at least 5D of distance from the valve in the upstream direction.
 

Conclusion

Non-contact ultrasonic flow meters are reliable instruments when installed and maintained correctly. Most issues stem from improper installation, environmental interference, or inadequate coupling. By understanding these common causes and following the recommended solutions, you can ensure stable and accurate measurements in your application.
 

For more ultrasonic meter troubleshooting tips, Contact us for help!
 

FAQs

Q1: Can I install ultrasonic sensors on any type of pipe?
A: While they work on many materials, metal and smooth-surface pipes are ideal. Avoid placing sensors on fiberglass, heavily rusted, or insulated sections.

Q2: Why is my flow meter showing zero even though fluid is moving?
A: This may be due to poor coupling, air in the pipe, or installation on an unfilled or inappropriate pipe section.

Q3: How far should I place sensors from valves or pumps?
A: Maintain at least 30D upstream and 10D downstream of any flow disturbance for best results.

Q4: Do air bubbles affect ultrasonic flow measurement?
A: Yes, bubbles can scatter sound waves and lead to unstable or inaccurate readings. Try to install sensors where fluid is bubble-free and stable.