Setting the scene for sensors  By Robin Butler of Sherborne Sensors

Robin Butler of Sherborne Sensors examines the series of sensors available in the marketplace and explores the applications they can be deployed in.

Sensors are an integral component of any measurement and automation application to ensure accuracy, reliability, efficiency and communications capability. This has fuelled research and development into the sensors industry and the continued innovation in sensors technology has ensured a thriving market and a growing demand for custom solutions.

According to analyst firm Frost & Sullivan, the sensors market in Europe is estimated to reach $19 billion by 2016, creating opportunities for technological advancements and ultimately new applications for sensors. 

Ultra-reliability and long-life precision sensors such as inclinometers, accelerometers and load cells enjoy an unrivalled status within the sensors industry and are critical for use in industries spanning aerospace, military and defence, transport, construction and civil engineering, to name but a few.

Inclinometers
Inclinometers can measure horizontal and vertical angular inclination to very high levels of precision and output the data in the form of analogue or digital signals. Inclinometer technology has broadened the scope of sensor applications in recent years and there is a wide array of standard products available.

Customised products can offer the customer many advantages including performance specifications to meet exacting requirements and enabling the direct fitment into applications. This results in better performance with both time and expense saved in the installation process. (Picture: The T820 Series Inclinometer ).

Below are listed some typical inclinometer applications
1) Military Fire Control Systems - require robust sensors which can deliver precision measurements following exposure to severe levels of mechanical shock from the firing process.
2) Rail Track Monitoring - to survey rail tracks to determine deterioration and the need for safety critical maintenance.
3) Satellite Communications - used on ship, vehicle and land based antenna applications to track communication satellites.
5) Civil Engineering - to monitor movement over time of bridges, buildings and other large structures.
6) Continuous Casting Monitor - to ensure guide tracking is within dimensional tolerances to ensure continuous and quality production.

Accelerometers
Accelerometers measure linear acceleration and deceleration of dynamic systems. These can be used in the development phase of projects to ensure design calculations correlate with actual measurements in the application and also in the safe operation and control of equipment in service.

The careful selection of an accelerometer is essential to ensure its frequency response is matched to the application requirements. Products are available with bandwidths up to many kHz and some specialist low frequency accelerometers to measure down to DC levels (0Hz). (Picture: The A640 Series Accelerometer).

Some typical examples of accelerometer applications include
1) Aircraft Health Monitoring - acceleration levels applied to aircraft structures in service are monitored for determining the safe flying life of the aircraft.
2) Civil Engineering - low 'g' range accelerometers utilised to monitor accelerations induced into bridges and other structures to check design calculations and long term critical safety.
3) Railway - control of braking and cornering of trains to ensure safety and passenger comfort.
4) Flight Simulators - to control actuation systems to ensure the programmed 'g' levels are achieved.
5) Accident Data Collection - acceleration data recording for future reference in the event of an accident or incident.

Load Cells
A load cell is a transducer that is used to convert a force into an electrical signal and offers measurement of tension, compression and shear forces. The majority of today's designs use strain gauges as the sensing element, whether foil or semiconductor, and feature low deflection and high frequency response characteristics, which are especially beneficial for both materials testing and high‐speed load measurement applications, particularly where peak forces are being monitored. 

Load cells are available in many physical shapes and forms to suit particular applications and forms of loading. Miniature form and very low force ranges are invariably available as custom designs where specific customer applications require them. (Picture: The U2000 Series Load Cell).

Some of the major load cell applications include
1) Aerospace - Fatigue testing of airframe structures, internal engine forces and ejector seat force measurements.
2) Paper Mill - bearing force load cells to monitor and maintain correct roller tension.
3) Marine - hoist loads, platform retention, towing forces and mooring loads and systems.
4) Civil engineering - bridge lifting/weighing, vehicle/crane load monitoring and earthquake force monitoring
5) Pharmaceutical Industry - to control the compressive forces during tablet manufacture during many millions of cycles.

For further information, e-mail: sales@sherbornesensors.com or view website: www.sherbornesensors.com  Refer to page 377

Embedded coil technology
radically improves temperature stability
and miniaturisation of displacement sensors

Precision sensor manufacturer Micro-Epsilon has developed a unique technology for use with eddy current and capacitive displacement sensors. These new technologies and manufacturing methods enable a wide variety of custom sensors to be produced, which are not only capable of operating in higher temperatures, but which also benefit from low thermal expansion (thermal drift) and extremely compact conditioning electronics, making it ideal for the aerospace sector.

Micro-Epsilon's new Embedded Coil Technology (ECT) represents a technological breakthrough in eddy current sensor design and manufacture, enabling the previous limitations of using eddy current sensors to be overcome. Due to its ultra-compact design and by using new inorganic materials in its construction, the new eddyNCDT ECT sensors provide almost unlimited scope in terms of the external design and geometrical shape of the sensor. This means the sensors can be adapted to suit virtually any application requirements.
 
EddyNCDT ECT sensors offer extreme mechanical robustness, resulting in longer service intervals and higher temperature stability. In addition, the complete circuit electronics can now be integrated into the sensor itself, providing an even more compact measurement solution for OEMs and machine builders. The sensors are also suitable for harsh operating environments, including high vibration, impact shocks and high operating temperatures as high as 350 deg C.
 
Sensors have been produced with extremely low thermal drift and with temperature errors of less than 20ppm/K (parts per million per degree Kelvin).
 
Chris Jones, Managing Director at Micro-Epsilon (UK) Ltd comments: "Embedded coil technology has enabled us to produce custom-specific designs for OEMs. ECT eddy current sensors are already being used in a variety of applications, including the alignment of mirror segments on giant reflector telescopes; for use in ultra-high vacuums or clean rooms in semiconductor manufacturing; and for measuring the grinding gap on refiners used in paper mills. We are also developing specific solutions for the aerospace and defence sector."
 
"Using our electronics expertise from within the Micro-Epsilon Group, we were able to develop extremely compact electrical circuits, which allowed us to manufacture the sensor with integrated electronics in the sensor head. We are therefore able to produce a single or multiple sensor channel arrangement in one sensor body," he adds.
 
Custom capacitive sensors
As well as eddy current sensors, Micro-Epsilon has also designed capacitive displacement sensors that make use of ECT. The capaNCDT ECT sensors are manufactured using a new type of production process. Similar to the eddy current ECT method, by embedding the electronic components in an extremely stable carrier material, significantly better temperature stability can be achieved compared to conventional capacitive displacement sensors.
 
CapaNCDT ECT sensors can withstand operating temperatures as high as 200 deg C, as well as very low temperatures down to -269 deg C. Similar to eddyNCDT ECT sensors, the capacitive versions are extremely compact. Micro-Epsilon's capaNCDT CSH-FL, for example, has an installation height of just 4mm.
 
For further information on Micro-Epsilon's ECT eddyNCDT and capaNCDT ECT displacement sensors, e-mail: info@micro-epsilon.co.uk  Refer to page 279