Solid Coupling Answer to Ultrasonic Flowmeter Questions

01 February 2008

When discussing the relative merits of the operation and installation of a clamp-on ultrasonic flowmeter one of the most commonly raised questions relates to the physical mounting of the sensors.

Solid coupling answer
Solid coupling answer

Whilst manufacturers differ in their approach to mechanically mounting the sensors to the pipeline, offering systems varying from simple straps or chains through to more complex frames, brackets and clamps the result sought is the same; to obtain a good contact between the surface of the sensor and the pipe.

In order to achieve a better bond between the sensors and the pipeline all companies have to make use of some kind of coupling compound to remove any air from the interface point. The problem with this has always been selecting the best component for the application as atmospheric conditions, temperature and the measurement application can all affect this choice. Some gel-based substances are water-based and they are easily degraded by condensation and even if oil-based media are used, high temperatures can cause the compound to break down. Furthermore as the flowmeters are often used on food, beverage or pharmaceutical applications it is essential to use something approved for these types of environments.
In order to ensure that the sensors are correctly mounted Katronic Technologies have traditionally used three types of coupling gel, each of which is applicable to a certain temperature range. In spite of this and the fact that Katronic have no reported incidents of failure owing to a loss of coupling customers are occasionally concerned that this could be an issue, particularly on measurements where there is a strong likelihood of condensation or adverse weather conditions. To this end, Katronic have introduced a new coupling system designed to give the best possible installation conditions and provide the customer with the confidence they would expect from a conventional metering system.

Rather than using a jelly-based substance the new coupling is based on the use of a variety of different solid pads, which conduct the ultrasonic signals and ensure that there is the best possible interface between sensor and pipeline. The normal precautions associated with any ultrasonic application still need to be taken, however the solid pads have proved to be an excellent alternative and the best solution for applications where an extra confidence factor is required.

The use of a solid coupling technique has also allowed Katronic to branch into other areas of ultrasonic metering where previously a clamp-on flowmeter might not have been used. Solid coupling is used on the new Waveguide Sensor Assembly that allows the use ultrasonic flowmeters on systems up to 450°C.

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