Sherborne Sensors Limited - PRODUCT NEWS

Delivering sensors with military precision

Despite the impact of the downturn and spending cuts in many defence markets, innovation and investment in inclinometer technology has continued to broaden the scope of sensor applications in military platforms, and address the need for precision, repeatability, and survivability

The core sensor technology powering inertial inclinometers to measure angle relative to gravity has remained relatively unchanged for several years, and has been field proven in a wide range of defence applications. Yet the need to consistently deliver measurement precision and repeatability, under the harshest operating conditions and often in space restricted applications continues to drive the need for further customisation.

According to analyst firm Frost & Sullivan, the sensors market in Europe earned revenues of $12.5 billion in 2009 and it estimates the market will reach $19 billion by 2016. Meanwhile, in the US, demand for sensors, transducers, and associated equipment is forecast to increase 5.2 percent annually to hit $12.3 billion in 2014, according to research by Publications. This rise will be spurred by economic recovery from a weak base in 2009, says the company, with the aerospace/military market seeing moderate growth and benefiting from technological innovations and increased shipments of sensor-containing equipment.

At the same time, there has been renewed focus on revisiting tried and trusted sensor solutions to solve new technological challenges. One recent example is the Helicopter Alert and Threat Termination - Acoustic (HAALT-A) project in the US, where commercial sensors were reconfigured onto a helicopter airframe to acoustically detect incoming fire and localise the shooter(s). Since an established sensor design was used, a fully-developed and detailed deployment package was delivered within seven months of the contract award.

Survivability and mission assurance
A servo inclinometer is an extremely sensitive transducer that converts angle of tilt into an electronic signal, and is able to determine horizontal and vertical inclination with high precision. A torque balance flexure servo inclinometer essentially consists of a pendulum and unbalanced mass that aligns itself with the Earth's gravitational field, the deflection of the pendulum being proportional to the sine of the angle of tilt. Typically, the pendulus mass is mounted on a flexure suspended coil that rotates within a magnetic field provided by a permanent magnet not dissimilar to that employed in a dc motor. The pendulus mass's position is detected by an electronic proximity sensor, and the resulting error signal is used to feed current back into the moving coil restoring the pendulus mass to its original position. The restoring current is itself the analogue signal of the sine of the angle of tilt.

For applications demanding precision and repeatability several orders of magnitude greater than conventional open loop inclinometers, a closed-loop torque balance servo system is preferred, and delivers resolutions to 0.1 arc second (0.00003°). Closed-loop, torque balanced servo inclinometers are extremely robust, and can offer high precision after withstanding severe levels of mechanical shock and vibration. Survivability via robust design is essential for sensors deployed within military platforms. And all the components on a platform must perform to specification within the defined environment if 'mission assurance' is to be delivered.

Techniques employed by sensor-based devices to enhance survivability while maintaining accuracy include fluid damping and mechanical stops. The latter is invoked within an inclinometer (or accelerometer) to prevent damage when a device is exposed to acceleration beyond its calibrated range of operation. Meanwhile, fluid damping employs a specialised viscous fluid that encapsulates the mechanical servo mechanism in order to provide both shock protection and to act as an additional filter attenuating unwanted background vibration that ensures highly accurate output signals. Fluid damped servo systems are available for applications demanding the most robust sensors, and offer up to 1,500g of mechanical shock protection.

Electronic damping is added in the form of active low pass output filters to maximise the useable frequency range of the inclinometer if critically damped. Alternatively the response can be over-damped to further attenuate the effects of environmental vibration and shock on the signal output. In military environments, the sensor often has to operate reliably within a background of electro-magnetic interference due to the proximity of other electrical or electronic equipment. Additional filtering is therefore provided to ensure this electromagnetic compatibility.

Meeting military demands
Sensor devices are employed in defence applications where 'situational awareness' is critical - i.e. to provide the user with as much information as possible concerning their present circumstances in order to take the most appropriate action. Today, sensors play a crucial role in enabling this situational awareness, and there has been a huge increase in the volume of information being made available to military personnel as a result. Significant military applications for inclinometers are:

* Fire control aiming systems. Demand robust sensors able to deliver precision measurements after exposure to severe levels of mechanical shock from the firing process. The reliability of the sensors performance over many years is paramount in these harsh operating environments.

* Naval ship communications - antenna alignment to satellites. Precise total error bands in two axes are achieved over wide operational temperatures by thermally compensating the sensors outputs at specific temperatures. Precision, robust, and environmentally protected sensors are required to withstand the rigours of these applications.

* Military vehicle systems - including mobile communication and weapon guidance system levelling. It is imperative such vehicles are accurately levelled when stationary to ensure their onboard systems are correctly referenced. The robustness of the inclinometers during transit over rough terrain is also essential to ensure the sensors' precision is maintained.

The scope of applications for inclinometers within military platforms is extensive and all demand the highest levels of precision, repeatability, ruggedness and reliability. Precision measurement capability describes the need for the sensor to be able to accurately translate the exact angular position of the platform to which it is affixed during or after being exposed to severe environmental conditions. The demands placed upon the sensor in many defence applications will often call for a customised design based on proven technology that fully addresses the specific requirements of the application.

Pathway Forward
Sensors will continue to pervade all aspects of daily life, but especially in the defence markets. This trend is driven mainly by the need for end users to have ever more precise and diverse information about the environments in which they are operating. Minimisation of size, form factor, and weight has become necessary given that the cost associated with carrying extra weight and/or increasing the size of the overall form factor can be significant in reducing the ability of the military platform to carry out its primary mission.
As a result, industry investment will continue to increase to further develop existing technologies so they can adapt to ever more stringent requirements. As in most cases, this pathway is more cost effective than developing, testing, and fielding a new technological solution. Fortunately, many existing sensor technologies have proven their capabilities in the field, are familiar to end users and, with incremental improvement, offer core capabilities that can meet operational demands for many years, if not decades, to come.

About Sherborne Sensors:
Sherborne Sensors is a global leader in the design, manufacture and supply of high-precision inclinometers, accelerometers, force transducers and load cells, rotary encoders, instrumentation and accessories for industrial, military and aerospace customers. Products offered under the Sherborne Sensors brand are renowned for their ultra-reliability and long-life precision within critical applications. Recent acquisition of synergistic technologies by Sherborne Sensors within our inclinometer and force and load cell offerings has allowed customers to benefit from expanded product lines, with added benefits of engineering support, global sales presence, repair, refurbishment and calibration services, stocking programs, and continuous product improvement.

For more information, please contact :-

Robin Butler
Sherborne Sensors Limited
1 Ringway Centre, Edison Road, Basingstoke RG21 6YH United Kingdom
Tel: +44 (0)1908 673 868
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November 2011

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