How Does an Ultrasonic Flow Meter Work?

Operation

• The ultrasonic flow meter consists of a pair of transducers located on a straight length of pipe. Each sensor transmits an ultrasonic signal through the pipe towards the other sensor. The flow of materials inside the pipe affects the frequency of the signal each sensor receives. The sensors measure the difference in frequency between each signal and calculate the rate of flow in the pipe based on this measurement.

Method

• The signals emitted from each transducer experience a shift in frequency relative to the motion of the fluid. This frequency shift occurs when the signals from each transducer encounter bubbles and particulate matter suspended in the fluid traveling through the pipe. To calculate the flow of the pipe you will need to carefully measure the distance between each sensor and know the diameter of the pipe. The distance between sensors is often measured in terms of the pipe diameter with most sensors requiring a distance greater than five times the diameter of the pipe between sensors.

Advantages

• Ultrasonic flow meters are available in stationary and portable models that clamp on to existing pipelines. This has the advantage of providing accurate flow measurements without interrupting the operation of the pipeline. Since this type of meter is a separate external device, it does not leak, change the pressure of the pipeline or affect its operation in any way.

Considerations

• Ultrasonic flow meters require specific conditions to provide accurate readings. This type of meter is only effective if the material inside the pipe contains bubbles or particulate matter to interact with the sonic waves the transducers generate. Sections of pipeline that contain valves, reducers, elbows or curves often produce inaccurate results, since the changing geometry of the pipeline interferes with the accuracy of the signal. The material of the pipe also impacts the accuracy of these meters and can reduce their accuracy to within 20 percent of the actual value.