Common on-site monitoring issues with the transit-time ultrasonic flowmeter

Ultrasonic flow meters mainly rely on the sound velocity of the liquid to be measured to calculate the flow rate. However, sound velocity of the liquid will be affected by two common factors, liquid temperature and chemical concentration.

1. Liquid temperature has to be stable.

The temperature of the liquid will obviously affect the change of the speed of sound. If the temperature is unstable, the speed of sound will also be unstable, resulting in difficulties in flow monitoring which will reduce repeatability and accuracy.

2. The drastic changes in liquid concentration have a huge impact on ultrasonic flow monitoring. 

All chemicals in a liquid may affect the flow rate because of its impact on the sound velocity. Therefore, it is recommended to know or measure the liquid’s sound velocity before measuring flow rate to prevent inaccurate measurement.


In practice, when a user mixes chemicals in with the liquid, it will cause the liquid sound velocity fluctuates resulting in difficulty in flow monitoring. In addition, if the chemicals are unevenly distributed, the sound velocity will fluctuate at different locations.



For accurate results, liquid temperature and concentration must be controlled and stable.


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