ultrasonic flow meter advantages

Transit-time ultrasonic flow meters are usually considerably more accurate than Doppler measurement.  However, Transit-time fails to measure fluid flow accurately when there are bubbles and particles in the fluid stream which blocks the sound wave reaching across the pipe to measure its transit time.  Most ultrasonic manufactures use low frequency sound pulses to measure the transit time there by severely limits their accuracy when bubbles/particles reach between 1-2% concentrations. These products are often time low cost and for relatively clean and stable fluids gives users a smart solution in terms of a cost benefit ratio. Very few manufacturers’ employee ultrasonic technologies that can measure less than 5-10%, while only one manufacturer, Smartmeasurement Inc. from USA has a patented technique that can measure accurately fluid flow of up to 30% bubbles/solids in stream Transit time ultrasonic flow meters are used in the vast majority of flow application due to its superior technology in obtaining excellent accuracy versus Doppler technology as well as its ability to measure liquids with up to 30% solids and bubbles in the flow stream.

SmartMeasurement’ s AlsonicDSP family of ultrasonic flow meters that use Digital Signal Processing techniques and their patented “fine time measurement technologies” that involve sound waves to be beamed at picoseconds to ensure accurate measurements of liquids that contain solids or gas bubbles. The AlsonicDSP product line are used in both fixed and portable application as well as more complicated Area Velocity open channel techniques for sewers, small channels and rivers.

The AlsonicDSP product line flow transmitters use Cross Correlation to erase noise and make 3-d cross sections of the flow profile’s travel speed through a pipe. It also allows users to use a Fast Fourier Transform technology, which allows for two signals to use the same frequency. This increases the accuracy of the flow rate measurement. Finally, the AlsonicDSP ultrasonic product line flow meters can be used to measure fluids that contain up to 30 percent gas bubbles or solids.

Doppler technologies are only used where the fluid which has a high concentration of solids and bubbles in the flow stream and often times cannot measure fluid flow accurately, due to its unique technique in using particle or bubble velocities in the flow stream to measure the overall flow rate of the fluid.  Since particles or bubbles in a stream flow at different speeds, it is impossible for this technology to measure all the particles/bubble velocities to calculate the true average flow in a flow stream.   Doppler technologies are only used where Transit-times techniques fails which is where there is a very high concentration of particles/bubbles.
Both Doppler and Transit-time techniques have transducers that can either be inserted into a pipe or on the outside of a pipe. Typically, the transducer is inserted into a pipe when the pipe is not uniform in size or the pipe is too thick due to corrosion or pipe insulation. Digital signal processing has made it possible to use a transmitted signal via the use of digital signal coding. Digital signal processing alleviates many of the problems caused by noisy environments. Most transit time ultrasonic flow meters require that the process either be clean, meaning there are few solids or gas bubbles in a liquid, or has no trapped liquid in a gas, and the piping must be closed. However, to alleviate some of its inaccuracies, transit-time ultrasonic meters can also use in multiple path configurations to achieve higher accuracies.

Historically the market is moving away from Doppler to transit time technologies because transit-time techniques are continuing to improve while Doppler technologies remain stagnant. Currently, over 90% of ultrasonic fluid measurement uses transit-time ultrasonic technologies of various scan frequencies, unique algorithms, noise cancellation techniques. Transit-time measurements are used from low cost hot/cold water meters to large channels and rivers in more complicated open channel measurement using multipath techniques. The wide variety application usages of transit time measurement mean they are mass produced making them much cheaper than Doppler as only a few manufactures remain.  Most ultrasonic flow measurement applications are liquids that are relatively clean with less than 1-2% concentration of bubbles or solids in a flow stream.  However, users often don’t know if they have excess bubbles or particles in their flow stream and often times user higher scan technologies with higher accuracies. Smartmeasurement is the only manufacturer that uses both low frequency transit-time technologies and high frequency technologies as well as Doppler techniques.