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Sensor Technology has supplied its Torqsense non-contact digital torque monitoring system to Ferrotec, a provider of bespoke sealing products.

Ferrotec is able to optimise ferrofluid materials for extreme performance requirements and incorporate them into bespoke vacuum system designs.

‘About half of our work is to bespoke design and we have to test every seal to the nth degree to meet out customers’ specifications,’ said Jeff Lewcock of Ferrotec.

To test the feedthrough, it is mounted onto a vacuum chamber that is connected to a helium leak detector.

Helium is then spayed onto the feedthrough and the leak rate is observed during static and dynamic running.

As part of the test, the starting and running torque of the seal are measured and the power loss through the seal is calculated.

These readings allow Ferrotec to troubleshoot the individual seal and analyse the design’s performance.

‘With the sort of tolerances we work to, we needed a torque sensor that didn’t add any extra drag to the whole seal mechanism, so we were delighted to discover Sensor Technology’s non-contact Torqsense,’ added Lewcock.

Inside the torque sensors, two tiny piezo frequency resonating combs are fixed to the shaft and supplied with power via a radio signal.

The combs ‘open up’ as torque is applied to the shaft, changing their resonating frequency.

As a result, the resonant frequency of the returning radio signal is an indication of the torque within the seal.

A wireless radio-frequency non-contact coupling is used to supply power and interrogate the combs.

Since it is non-contact, the Torqsense torque sensor exerts no drag on the test piece and, as it is fundamentally a digital system, it has a broader signal bandwidth than other analogue-based technologies.

Electromagnetic interference is eliminated, making it suitable for Ferrotec’s needs.

Torqsense can test the seals of super-high-performance vacuum systems.

The ultimate fields of precision manufacture, such as electronics, biophysics and thin-film deposition, where tolerances are measured in atoms, are often conducted in a hard vacuum to remove airborne contaminants and to avoid the performance-reducing effects of tiny air movements.

However, most vacuum chamber designs require seals for rotary drive shafts (called rotary feedthroughs) and ‘feedthroughs’ for the passage of materials, components, tools and finished products.

In high-vacuum applications, conventional seals are unlikely to achieve the performance specifications required, so magnetic fluid seals are used.

A ferrofluid is a stable colloidal suspension of sub-domain magnetic nano particles in a liquid carrier.

The particles, which have an average size of about 100 angstrom (10nm), are coated with a stabilising dispersing agent (surfactant), which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid.

Sensor Technology

Sensor Technology are manufacturers of TORQSENSE Transducers, the world’s first low cost non-contact rotary torque transducers designed for OEM applications. Rotary torque measurement has always been difficult and expensive.

The patented method uses a surface acoustic wave device as a frequency dependent strain gauge and measures the change in resonant frequency caused by the applied strain in the shaft.

The signal is transmitted via an RF couple from the rotating shaft to a fixed pick-up.

By using a frequency-based device, the signal bandwidth is increased, and the problem of electronic interference common with analogue signals is eliminated. The torque sensors are designed to operate direct from a PLC or a PC.

They require minimum length of shaft, have low inertia, no physical contact between shaft and housing, wide bandwidth, high resolution and accuracy resolution to better than one part in a million, and excellent noise immunity.

The technology lends itself to design of OEM transducers for specific customer applications. Applications include automotive, manufacturing machines, condition monitoring where knowledge of torque is critical, torque control of tightening procedures, and monitoring of viscosity during mixing where consistency is required. The technology replaces existing types of rotary torque sensors by providing better performance at a lower price.

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