The ultrasonic flow sensor is a non-invasive volume flow measurement tool, which employs one of two basic principles of operation, namely transit-time and Doppler Effect technologies:
Transit-Time Ultrasonic Flow Meters
Ultrasonic transit-time flow meters rely on the frequency difference between upstream and downstream times of flight of an ultrasonic pulse that is projected into and across the pipe. This shift in frequency is proportional to the flow velocity. Transit-time flow meters will not operate with dirty or bubbly liquids and are therefore typically used for clean and ultra-pure flows.
Doppler Ultrasonic Flow Meters
An ultrasonic Doppler flow meter employs the frequency shift of an ultrasonic signal when it is reflected by suspended particles or gas bubbles in motion. This shift in frequency is proportional to the flow velocity. As such, Doppler flow meters are commonly used in dirty applications such as waste water.
Ultrasonic Flow Sensor Advantages
• Non-invasive and easy to install technology
• No process contamination
• Applicable to corrosive fluids
• Low maintenance as no moving parts
• Zero pressure drop
• Can detect zero flow
• Applicable to small and large (up to 5 metres) pipes
• Portable, battery powered units available for remote or field applications
• Sensors available for pulsating flows
• Insensitive to changes in temperature, viscosity, density or pressure
Ultrasonic Flow Sensor Limitations
• Can suffer from pipe-wall interference
• Accuracy may be affected by any air spaces in the pipe
• May be incompatible with certain pipe materials eg concrete, fiberglass and plastic lined pipes
• Restricted to applications with clean, bubble free fluids (transit-time meters)
• Flows must contain particulates or bubbles of a minimum concentration and particulate size (Doppler meters)
• Accuracy may be affected by particle-size distribution and any relative velocity between particulates and the fluid (Doppler meters)
• Not suitable for very low flow velocities (Doppler meters)
Being non-instrusive, ultrasonic flow sensors have a wide variety of applications in the water, waste water, heating, ventilation and air conditioning, petroleum and general process markets.
© iCenta 2016. Specialists in precision flow meters, level sensors, instrumentation & control.