Sensing solutions

6 March, 2008

The applications in which sensors and transducers are used is growing daily, and they are being adopted across all industry sectors. Recent examples include the film industry, automotive, military and aerospace. Transducers from Variohm Eurosensor, for example, were chosen during the production of the last James Bond movie, Casino Royale.

EMP Designs is a design consultancy and systems integrator which specialises in motion systems, with a major area being the film industry. The company supplies motion base positioning and control systems for the industry, however as the high cost of delays and the complex schedules means equipment reliability is of the utmost important, the company regularly chooses Variohm for linear position and cable-extension transducers.

In a typical filmed scene, several hydraulically actuated motion bases may be synchronised with CGI and movie cameras for carefully choreographed stunts and action sequences which involve precise positioning of heavy objects or even large structures that sink. To provide positional feedback for the model platform in the film, six Variohm PT8420 cable-extension position transducers, suitable for use in harsh conditions, were selected. The IP68 rated PT8420 housings were mounted in the water below the motion base with stainless steel extension cables connected to the moving part of the submerged hydraulic cylinders.

Accuracy and reliability
EMP Designs also produced a three-axis control system to provide ‘pick up and use’ usability – where a scaled replica model of the motion base and a simple three-button control console are used to input, record and playback complex sequences. The manually controlled scaled model input mechanism includes a fixed base and a moving platform with three Variohm ELP series linear position transducers placed at exact corresponding positions to the hydraulic actuators on the full sized motion base. These provide a potentiometer output against position which is transferred through the controller to each axis to produce a move within the capability of the system. Unlike a standard joystick solution, this simple mechanism not only allows the operator to fully envisage and perform moves without specialist ‘gaming skills’ but simplifies the control software, keeping production costs to a minimum.

According to EMP Designs, it chose the ELP series slimline linear position transducers to maintain high accuracy and reliable position feedback in a compact form factor that helps to reduce the overall size of the scaled model.

Ejection seat testing
Sensors are also being used to help with the deployment of aircraft ejection seats. Martin-Baker has been manufacturing ejection seats for many years, and all current seats use a small rocket to propel the seat and occupant out of the vehicle fast enough to avoid collision with the fin and high enough to allow the parachute to deploy effectively even in ground level ejections. However, ensuring that the rocket burn, usually of around 400ms, provides sufficient thrust to provide a safe escape is a critical part of the design process.

As a result, each new rocket design is tested using a Kistler Instruments dynamic multicomponent force plate mounted in a test enclosure to measure the duration and thrust produced by the burn. Here, a highly reliable force measuring system which can maintain accuracy under difficult operating conditions is required as over 10,000lbs of thrust is combined with the corrosive atmosphere in the test enclosure.

When the motor under test is fired, considerable vibration levels are produced, yet the Kistler force plate allows force data to be acquired at a sample rate of 25,000 per second. The thrust against time data allows the design engineers to calculate both the speed of ejection and, most importantly, the maximum acceleration the occupant will experience, explains the company.

To keep the acceleration within the range the human body can withstand, initial movement of the seat is created by a low powered system so the seat is already in motion when the rocket motor fires. This limits the g-force loading to an acceptable level.

As well as testing new rocket motor designs, the Kistler force plate is also used for propellant life testing and inproduction QA sample testing for seat and canopy separation rocket motors.

Commenting on the benefits, Stuart Driver, Martin-Baker’s environmental test manager, said: “Mounting a rocket motor on the Kistler force plate takes only minutes and, as the data connections are permanently in place, we can carry out a comprehensive test routine quickly with total confidence in the data. Although the rocket motor is a small part of the ejector seat, it is the one component that must operate to full specification every time.”

Surveillance
The Lebanese National Defence Ministry has ordered six Pharos XLR3+ Long Range Multisensor Surveillance Platforms from Cedip Infrared Systems to provide its Naval forces with 24/7 long-range surveillance & reconnaissance capabilities in all weather conditions. The supplied PHAROS XLR3+ Platforms will be equipped with a long range thermal imager to give night capabilities and a high performance CCD camera with powerful zoom for daytime operation. These feature a twoaxis platform that may accommodate different types of sensors to ensure they meet even the most demanding of customer requirements.

The PHAROS XLR3+ standard configuration is based on the Cedip ADAMANT LR long range thermal imager. Operating in the 3-5µm (MWIR) spectral band, this thermal imager is field proven for the maritime environment and hot climates, offering a full TV format resolution (640 x 512). The triple field of view optical lens provides the ability to survey perimeters up to 25km distant with optimised flexibility. The head of the PHAROS XLR3+ is engineered to withstand the harsh marine environment and meets IEC60945 standards. It includes a wash/wiper system and internal heater to prevent misting on windows.

Selected for its high performance, compactness and operational robustness, the PHAROS XLR3+ provides outstanding operational effectiveness for applications including border and coastal surveillance, protection of sensitive sites, vessel traffic management, protection of fisheries exclusion zones and law enforcement, claims the company.