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Previously, torque sensors required a complicated array of slip rings connected to the rotating drive shaft of the machine under test, but Torqsense provides a non-contact means of taking readings.

In use, a couple of pads are glued to the side of the driveshaft and a Torqsense unit mounted close by.

The Torqsense then starts monitoring torque and feeding it as a data signal to the Scada control system.

The pads are tiny little piezoelectric combs encased in plastic.

The combs are designed to open or close under the torque effect of their rotational speed on the drive shaft.

The greater the torque, the more the distortion.

The Torqsense unit emits a low powered radio frequency signal towards the combs, which reflect it back to the Torqsense.

The reflected signal comes back at a changed frequency, the change being proportional to the distortion of the combs, and thus to the torque in the drive shaft.

The physical phenomenon that deforms the combs is called the Surface Affect Wave (SAW).

Sensor Technology used this phenomenon to develop a method of torque monitoring, the non-contact nature of which promised to be attractive to working engineers.

Charles Austen Pumps (CAP) has recently upgraded its test facilities with Surface Acoustic Wave (SAW) equipment from Sensor Technology.

CAP manufactures pumps individually designed to meet specific customer requirements.

The cyclic nature typical in pump operation tends to induce torsional oscillations in the drive shaft, which can have an adverse effect on performance if unchecked.

CAP has recently built a test station based on Sensor Technology’s SAW sensors.

Advantages of SAW techniques include a broader signal bandwidth than other analogue-based technologies and elimination of electronic interference.

CAP found that it often also proves far lower cost, is simpler to use, is more reliable and has a wider operating range than contact alternatives.

Torqsense transducers are used in monitoring the constantly changing flow characteristics of materials such as tomato ketchup, chocolate, pasta sauce and chicken tikka massala as they are mixed.

To date, real-time control has been virtually impossible due to the non-uniform nature of the food, which may contain particulates, fibres, vegetables, meat, nuts, raisins, biscuits and so on.

To achieve real-time control, the Torqsense has to be able to detect the changes with sufficient sensitivity, yet be robust enough for regular wash downs and general industrial abuse.

It must not compromise hygiene standards and regimes either.

Torqsense has been found to meet all these requirements and is being used in by a number of food processors.

Often the key requirement is to mix sufficiently to achieve a uniform dish, but not to waste time and energy by over-mixing.

This can be done by monitoring the torque on the mixer’s shaft, as it will move to a steady state (within the characteristics of the given recipe) once fluid uniformity is achieved.

Nuclear precision gearboxes supplied to the nuclear industry have to be guaranteed to never fail prematurely, so testing them off-line is a vital function for Centa Transmissions.

A test rig has been developed in which a motor drives the test unit against a load created by an industrial disc brake.

The test runs initially for three hours at the full working load, and is then increased to 300 per cent load for another hour.

At the heart of the rig is a Torqsense that constantly monitors the torque in the gearbox, generating a performance profile that can be compared with the ideal performance standard.

The duty the gearboxes are destined for takes place in an environment where reliability has to be 100 per cent.

They are used in completely automated scoop mechanisms that collect small amounts of ‘high-activity liquor’ from the reactor cooling systems.

This is sealed into thick-walled ceramic flasks for long-term storage until the radioactivity has decayed to safe levels.

This is at the very core of the nuclear plant where a component or system breakdown would mean shutting down all operations for months, automated/unmanned removal of the faulty parts, sealing into a secure flask and automated installation of a replacement.

Torqsense is also helping analyse recipe mixing properties in a project that could slash development costs in the food and plastics industry and help nanotechnology advances in the pharmaceuticals world.

Research and development is being carried out at the University of Bradford to develop a miniature mixer (5-25g batch) that incorporates a set of integral instruments to monitor the properties of materials as they are being mixed.

The instruments work in real-time during the mixing process and their output is captured to a PC for analysis.

Software is being written so that the analysis can be performed simultaneously with the mixing and perhaps even used to interactively control the mixer itself.

One of the key parameters to be measured is the torque of the mixing element, as this will become constant once mixing is complete.

This is measured by a Torqsense non-contact sensor that offers the development team the great advantage of not requiring complex and delicate slip rings, making the mixer easier to build (and rebuild between trials) and far more robust in operation.

High-performance torque measurement is also helping to improve the energy efficiency of industrial (and domestic) washing machines.

Process plant manufactures are redesigning machines to reduce power consumption.

In horizontal axis washers (front loaders in domestic parlance), the load, the wet laundry, is lifted on one side of the axis and falls on the other side.

This is a dynamic where regenerative energy recovery is very attractive if it can be practically achieved.

A test rig has been built that subjects washing machine systems to extensive tests using an industry-standard inverter to simulate the various washing cycles and so on.

A critical element of the programme was the ability to make continuous accurate torque measurements, and for this Torqsense is ideal.

The time saving in setting the transducer, compared to installing a slip-ring-based sensor, over a big project is measurable and significant.

By measuring the torque change, the exact moment when to switch the drive from power to regeneration and make the most of the potential energy released by the falling load could be defined.

Given that the motor could be rotating at up to 1,500rpm, this called for very accurate data collection and equally responsive control programmes.

This technique has proved so worthwhile that it will be built into next generation washing machines.

With industrial sized loads, energy savings of 20-30 per cent may be achievable.

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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