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15/03/2004
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A rotary torque transducer has been developed that employs the latest software and hardware to give users a variety of communication options and is very compact. Dean Palmer reports
A technological breakthrough has occurred in the world of sensors that will grab the attention of machine designers and control engineers looking to measure power in drive shafts and other rotating machine elements. The new development is a rotary torque transducer that really does take data communications to the next level for users and is so compact that it’s hard to believe how the company actually managed to squeeze all the technology into such a small design space.
Sensor Technology, based in Banbury, is the company behind the new development. Bryan Lonsdale, founding director of the business, told Eureka: “Transducers have traditionally been provided with an analogue output voltage, which was fine 10 years ago, but users want more sophistication and functionality now. So we re-designed our existing range of torque transducers to a new ‘plug and play’ sensor which has built-in complex electronics that make it more connectable, and the product is around an eighth of the size of its predecessor.”
The new transducer range, Torqsense RWT310/320, is radically different from its predecessor, the 300 series and other sensors currently available on the market. First, it is smaller because the complex electronics are smaller and have been placed within the transducer itself, whereas normally the transducer and electronics are provided separately as two systems. Lonsdale continued: “It really is a radically different product we’re providing. Three years ago we simply couldn’t have sourced the required small sized electronics devices and circuit boards that make up the new sensors. The integration level of electronic components [driven by technological advances for mobile phones] has allowed us to radically reduce the overall size of the sensor.”
When questioned about the innovation behind the new sensor, Lonsdale remarked: “To my knowledge, nobody else can provide users with the ability to measure and analyse low speeds at such high resolutions in such a compact device.”
Unlike traditional slip ring transducers, the RWT sensors make use of a simple non-contact measurement technique of a radio frequency (RF) couple for power and signal communication. This means the device is mechanically straightforward and easy for machine designers, who up to now have had to put a lot of time and money into obtaining accurate torque measurements for production monitoring and machine control.
To achieve non-contact operation, SAW (surface acoustic waves) devices are used as frequency dependent strain gauges to measure the change in resonant frequency caused by strain experienced in the drive shaft. This measurement is directly related to the torque experienced in the rotating machine element. While SAW technology is certainly not new (Eureka covered Sensor Technology's first breakthrough SAW sensor back in September 1993), the way the technology has been applied to such a compact sensor is truly novel.
Inside the RWT sensors are two miniature processors, sourced from US-based electronics firm Sygnal. These in effect replace all the peripheral processors and chips, AC connectors and I/O devices that were used on the 300 series. The actual number of external chips has been reduced by 10 and the new sensor still has 128k of on-board flash memory, 8k of RAM and a very low power consumption of 25mA.
Sensor Technology started developing the new sensors in November 2002 and the first assembled device was ready in January this year. Lonsdale explained: “We started by analysing the capabilities of three or four different chip devices which took us several months to complete. The two processors we chose have different tasks within the sensor. One communicates with the SAW [surface acoustic wave] sensors, the other communicates with the outside world, digitally if required via a USB port.”
The current model has an impressive bandwidth of 5kHz but Lonsdale reckons the company should achieve 10kHz very shortly - that equates to around 10 times the normal bandwidth found in other ‘smart’ sensors. The sensors work between 11V and 32V, although Lonsdale hinted that a 44V version for the automotive industry was also in the pipeline.
The RWT sensor is very versatile in the way it communicates with external systems and devices. The sensor has several channels of output, for speed, torque, power and angle, which can be used simultaneously or separately. It has a digital RS232 output, an analogue option and even has a USB port for connection to a PC. Mark Jeffs, software engineer on the RWT, commented: “In May at the Hanover Fair in Germany, we will be launching a sensor which has an extra circuit board inside, will be no larger than the current one, but will have a wireless [Bluetooth] connection for communication to handheld devices. This is for customers that want to interrogate the torque measurements remotely.”
There is also a very impressive overload rating on the device. Most sensors on the market have a 200% overload rating but the RWT sensors currently have a 500% rating and Lonsdale said there are plans in place to extend this rating to 1000%.
There are three different body sizes available and seven corresponding shaft sizes. Torque ratings start from as low as 100mNm up to around 10,000 Nm. Obviously, the larger the torque rating required, the larger the shaft and body size will be.
The casing is CNC-machined aluminium and so fulfils all the relevant EMC regulations. Prices we are told start at £800 for the standard basic factory set sensor which has a 1V or +/- 5V output. The more advanced model will set you back around £1,450, but for this you get all the advanced user configurable features, additional software for averaging and scale changing. And if you're a keen user of National Instruments' LabView testing and instrumentation software, Sensor Technology is planning to bundle this with its sensors to customers who will be able to download the necessary drivers for their application from NI's website.
Sensor Technology has 25 employees, is privately owned (and funded) and turns over roughly £1m a year. A huge 50% of this revenue is ploughed back into R&D which helps keep the firm ahead of competitors. The company supplies most of its product to R&D labs, test and instrumentation companies and academic institutions but that looks set to change with the new sensors. Nick Hopkins, business development manager at the company, told Eureka: “OEM design engineers, machine designers, systems integrators, food and beverage engineers and automotive manufacturers should all be interested in the new sensor.”
According to Lonsdale, five years ago, the software within the new sensor wouldn’t have been a great deal of effort, the hardware would have been more of a challenge. “But today, the effort on the software is fifty-fifty and rising. It’s a new working culture for us which requires new disciplines and skills.” And according to Hopkins, “we spent around £150k developing the sensor over a period of 18 months, some of which is tax refundable [24%] from the Government.”
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Author
Tom Shelley
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