Variohm Eurosensor - PRODUCT NEWS

Image: Positek’s custom sensors shown in-situ for horizontal and vertical displacement measurement of expansion joints on a reinforced concrete motorway bridge.

Positek’s customised linear displacement sensors meet fast delivery and high specification for motorway structural monitoring

When a major UK-based structural health monitoring systems company were called in to urgently evaluate problematic expansion joints on a reinforced concrete motorway bridge, they required not just an extremely fast delivered solution for several linear displacement sensors but also a combined accuracy, temperature stability and environmental specification that would be beyond the capabilities of most suppliers.

Compounded by such restraints they contacted Positek Limited who pulled out the stops and within a one-week timescale delivered around forty custom-built sensors featuring a unique differential coil design with electronic temperature compensation and full IP68 protection. Based on Positek’s PIPS™ non-contacting sensor technology – a compelling alternative to LVDT and potentiometric displacement sensors – the long life and exceptionally durable sensors deliver consistently high accuracy linear position measurement in the harshest environments.

The expansion gap on a typical road bridge is expected to linearly expand and contract around 1 mm over a temperature range of -20 to +35°C. In order to precisely monitor abnormal non-linear gap movement in both vertical and horizontal planes and in real time, the overall accuracy offered by the sensor’s had to be excellent. Due to mechanical expansion as well as a temperature shift in the sensor electronics, it was decided to custom modify the standard coil design of Positek’s S115 series linear displacement sensor and integrate thermal drift compensation to boost precision and temperature stability.Image: Cutaway view of Positek’s differential coil design – provides higher accuracy and lower temperature drift

The standard PIPS coil design features a fixed reference coil, an active coil and a one-piece metal target. The custom modification introduces a second active coil in place of the reference coil with a metal target spanning both coils. This differential layout was further enhanced by modelling the sensor’s thermal coefficient and factoring the values into temperature compensation electronics that was integrated into main housing. Sensors with a 5 mm displacement range were supplied for the application and arranged vertically and horizontally on brackets supplied by the customer. The modified design can be supplied with displacement ranges as low as 1 mm. As well as improve the measurement linearity over the temperature range, the modification also increased the gain by a factor of three and reduced the electrical noise by two- to three-times - which was of benefit for the multiple measurement instrumentation system the customer developed for the application.

Image: The custom designed differential coil sensors are based on Positek’s S115 series waterproof and submersible linear displacement sensors.

Positek’s linear displacement sensors, even as standard components, offer environmental ratings up-to and exceeding IP68 protection levels and 10-bar submersible pressure endurance. The 35 mm diameter push-rod sensor used for this challenging measurement task was housed in 316 stainless steel and fully sealed to protect the sensor electronics against rain, road salt and sea water corrosion as well as the potential for frosts and high-humidity. The durable sensors also impress with standard shock and vibration specification values of 10g (IEC 68-2-6) and 40g (IEC 68-2-29) respectively. As with the standard PIPS technology design, this custom differential model is contactless and offers extremely long working life.

For this application, the custom sensors included industry standard 4…20 mA outputs with continuous proportional and absolute output with no need for additional signal conditioning. M8 rod-eye bearing fixings and cable gland/flying lead electrical connections facilitated straightforward commissioning. Positek’s linear displacement sensors are also available in a wide choice standard electrical outputs with various electrical connection options and calibrated output-to-length ratios.

Positek successfully manufactured and delivered the fully requested quantity of customised displacement sensors within the one-week timescale required by the customer to accommodate a scheduled maintenance closure of the motorway bridge.

UK-based Positek Limited – a Variohm Group member – is an ISO 9001-2015 qualified manufacturer with a comprehensive range of linear, rotary and tilt displacement sensors. Its patented PIPS technology is extensively used across a wide variety of challenging industrial and research-based position measurement tasks. With a comprehensive standard range and a fast-turnaround custom design service, Positek also offers a range of ATEX- and IECEx-qualified sensors for demanding monitoring and measurement tasks for intrinsically safe installation.

About POSITEK Ltd.
Acquired by the Variohm Group in 2019, Positek Limited was established over 25 years ago and today operates as an ISO9001:2015 certified designer and manufacturer of linear, rotary and tilt sensors with several specialist quality standard certifications including ATEX, IECEx, and CSA for both sensors and galvanic isolation measurement amplifiers. With its own patented non-contact inductive position sensor technology the specialist enjoys a high reputation for a fast-turnaround standard range as well as customised sensors and transducers that are extensively used in intrinsically safe, hazardous, automotive, submersible and other challenging environment measurement tasks. The extremely robust and highly accurate technology allows linear position measurement up to 1500 mm or more with compact form factor angular position measurement capabilities from between 5° and 160°. Application areas include, but are not restricted to, oil & gas, mining, medical, marine, hydraulic & pneumatic cylinder position feedback, tilt sensing on construction and heavy machinery, and more.

For more information, please contact:

Positek Limited
L6 The Link, Andoversford Industrial Estate, Cheltenham GL54 4LB
Graham Pattison
Tel : +44 (0) 1327 351004

About Variohm EuroSensor
Variohm EuroSensor is a manufacturer, distributor and supply chain partner providing complete sales and application support across a comprehensive range of position, force, pressure, load, and temperature sensor technologies - for demanding measurement applications across industry, construction, agriculture, motorsports, research and more.

About Variohm Holdings
Comprising four closely linked operating divisions, staffed by highly experienced motion and sensor application specialists with extensive knowledge of international standards; Variohm Holdings combines its considerable design and manufacturing capability with best of brand products and components from leading global partners to provide engineered solutions that are seamlessly and cost effectively integrated for your application.

For more information, please contact:-

Williams' Barn, Tiffield Road, Towcester Northants NN12 6HP United Kingdom
Tel: +44(0) 1327 351004
Fax: +44(0) 1327 353564

July 2021

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