Instrumentation Monthly Test | Measurement | Control
The growing trend towards non-contacting absolute sensors for linear and angle position measurement continues with a number of technologies which each provide application dependant advantages. As well as the obvious benefits of longer working life and reduced maintenance that such wear-free sensors bring, these technologies can be relatively diverse in terms measurement range, resolution, accuracy and repeatability. Furthermore, other factors such as electrical and mechanical interfacing, performance in hostile environments and overall price vs. performance are also varied. This article discusses three alternative non-contacting sensor types from Variohm EuroSensor’s German distribution partner, the sensor and transducer specialist Novotechnik.
Inductive position transducers
Novotechnik’s LS1 series inductive position transducers feature the NOVOPAD non-contacting inductive absolute measurement principle and with a small 18 x 18 mm cross section are offered as a wear-free alternative to small rod-type linear potentiometers. The robust and durable technology has an exceptionally long service life potential – in excess of 100 million operations – and can be used in the most extreme environments such as steering and position display or feedback for agricultural machinery or construction equipment. An integrated signal processing function provides an absolute current or voltage output signal with a measurement range from 25 to 200mm in a choice of integrated return spring or with a backlash-free ball coupling for push-pull use. Full range repetitive accuracy is better than 0.025 % and the combination of 12 or 13-bit resolution and linearity to +/- 0.1 % makes the LS1 series a good choice for high precision use. An integrated teach-in function with a status LED provides a useful calibration feature that can be built into the customer’s machine set-up without additional equipment, and the inductive sensor technology is unaffected by magnetic fields. Cable and connector versions are available
Magnetostrictive position transducers
Novotechnik’s TP1 series covers standard linear measurement ranges between 50 mm and 4.5 metres and is available with a choice of a guided position sensor or a contactless system which uses a floating sensor for completely wear-free mechanical use. The NOVOSTRICTIVE technology is ideal for long travel range position display or feedback and can provide a 1 micron resolution and linearity to 10 microns over its full range. With up to IP68 protection and high resilience to shock and vibration, the sensor can provide a more rugged alternative to glass scale encoders, for instance for machine tools. Variants of this technology can also be used for in-cylinder positon feedback for fluidpower applications. The TPI has extremely high resistance to interference and is available with analogue current and voltage interfaces as well as SSI and Novotechnik’s own DyMoS® protocol which can provide velocity as well as position information. This flexibility maximises use and versions are also available with an incremental quadrature interface that can replace backlash- and hysteresis-prone rotary encoder solutions for long linear movements.
Non-contact multiturn rotary sensors
In the past multiturn angle sensors have used gearing for the rotation counter which is subject to wear and backlash or have relied on continuous power-on or battery back-up to maintain positional information in memory. Both these principles have proven to be unsuitable for industrial or automotive use – being too expensive, too large or too complex for the application. Novotechnik has developed a new absolute non-contacting principle that combines a single turn angle detection and a separate turn detection in a compact package which is able to measure angles across multiple turns with high resolution and accuracy. The GMR (Giant Magneto-Resistance) technology is used in its RSM2800 series sensors, providing analogue, SSI and SPI interfaced electrical angle measurement from 720° up to 5760° in 360°steps (2 to 16 turns). With independent linearity to +/- 0.03 %, GMR is a true power-on system where absolute position value is non-volatile. Two-channel versions are also available for redundant safety-relevant applications. The compact and robust sensors have a nominal housing diameter of only 30 mm with straightforward two-hole mounting and push-on or slotted shaft coupling. The sensor is particularly suited to automotive engineering for electronic drive and steering systems as well as packaging and printing machinery or demanding angle measurement applications as a more robust and longer life solution for wirewound potentiometers or optical encoders.