A clamp-on ultrasonic flow meter needs stable acoustic transmission through the pipe wall and the liquid. If the signal is unstable, the ultrasonic path is being disturbed by installation issues, pipe conditions, or flow characteristics.
Possible causes:
  • The transducers are mounted at the wrong spacing or on an unsuitable pipe surface.
  • Pipe parameters such as material, wall thickness, diameter, or liner are entered incorrectly.
  • The pipe is not completely filled.
  • Air bubbles, solids, heavy turbulence, or deposits interfere with the ultrasonic signal.
  • Coupling quality between transducer and pipe is poor.
  • The pipe surface is contaminated with paint, rust, scale, or other deposits that block acoustic contact.
Transducer installation and mounting approach:
  • Mount transducers on the side of the pipe – avoid mounting on top of the pipe, as gravity can create air gaps between the transducer and the pipe surface, blocking acoustic transmission.
  • Prepare a smooth, clean pipe surface – remove all paint, rust, scale, and other deposits from the mounting area; the surface must be smooth and in direct contact with the transducer for proper coupling.
  • Apply adequate coupling gel – use enough high-quality coupling gel to ensure complete acoustic contact between the transducer and pipe; poor coupling is a common cause of signal loss and instability.
  • Verify transducer spacing and orientation – confirm correct transducer spacing and mounting angle according to the installation guide; incorrect spacing will degrade signal strength.
System and process verification approach:
  • Recheck all entered pipe data – verify the pipe material, wall thickness, diameter, liner type, and selected mounting method match the actual installation.
  • Ensure the pipe is completely full – the pipe must be full at the measuring location; partially filled pipes cause unstable or missing signals.
  • Avoid unsuitable measuring locations – do not install meters in pump discharge zones or highly disturbed sections; move to a hydraulically calmer section if turbulence is excessive.
  • Inspect the process – check for entrained air, suspended solids, internal scaling, lining effects, or other flow disturbances that interfere with ultrasonic transmission.
  • Test signal quality – review the signal strength indicator on the meter; a weak or fluctuating signal confirms an installation or process issue.