impeller.net The Online Pump Magazine

26.04.2004

Ultrasound Helps Optimise Drive Designs

A bespoke pump maker is using ultrasound waves to efficiently model drive torque and thus contain development costs to within predictable limits. Charles Austen Pumps has recently upgraded test facilities with Surface Acoustic Wave (SAW) equipment from Sensor Technology, a recognised leader in the field.

Charles Austen Pumps manufactures pumps individually designed to meet specific customer requirements that cannot be satisfied by off-the-shelf units. Over the three generations that this family firm has been operating it has continually honed its skills at accurately predicting development costs and working within budgets, and has become adept at using advanced techniques such as SAW analysis.

Much of its work comes down to optimising drive dynamics to produce the desired characteristics, be it a smooth flow in a critical medical situation, ultra low noise for pumps in home and office installations, or the guaranteed extra long life of pumps in inaccessible locations.

The cyclic nature typical in many pumps’ operation tends to induce torsional oscillations in the drive shaft, which can have a significant adverse effect on performance if unchecked, and this is where much of Charles Austen Pumps’ development effort is focussed, as technical Manager Brian Glover explains:

“We have recently built a new test station based on Torqsense, Sensor Technology’s SAW sensor, and it is proving it’s worth time and time again. Many years ago we used a simple torque arm and scales when developing prototype, then we moved on to slip ring technologies which were expensive and difficult to use because they induced a frictional load of their own.

“Techniques based on Surface Acoustic Waves began to emerge about 10 years ago and we embraced these with considerable success.”

SAW provides non-contact monitoring of instantaneous rotary torque, allowing accurate modelling of the load changes. Charles Austen Pumps built its own test stand and it served them well for many years.

“The state of the SAW art has now moved onto a higher plane, so last year we decided to tap into Sensor Technology’s expertise and develop a new cutting edge test rig. They supplied us with a Torqsense unit and helped with designing and building the rig.”

In essence a Torqsense is a frequency dependent strain gauge operating at ultrasound frequencies. It consists of a transducer mounted on the shaft, which monitors variations in resonance frequency of a drive shaft as the torsional load varies and transmits a radio frequency signal to an adjacent pick up.

Torqsense embraces all the advantages of SAW technology, including a broader signal bandwidth than other analogue based technologies and elimination of electronic interference. As Charles Austen Pumps found, it often also proves far lower cost, simpler to use, is more reliable and has a wider operating than contact alternatives.

Glover sums up: “Our reputation is based entirely on the quality of our engineering, and our business on the ability to accurately forecast development cost for each job. Sensor Technology has helped us build a new facility that makes our drive engineering accurate, predictable and reliable, or put another way we are moving from a black art to an exact science!”

Source: Sensor Technology

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