A pioneering naval weapons alignment system powered by electronic sensor technology heralds a fresh wave of British innovation in military and naval applications, says Mike Baker, managing director at Sherborne Sensors.
Digital signal processing
In the early nineties, British engineer Jonathan May challenged convention with his work in developing a ship-borne weapon alignment system, in order for naval vessels to align their weapons more quickly, more accurately, and at a lower cost than previously needed. May remained convinced there was a better way to approach weapons system alignment, by combining the approaches of the US Navy and Royal Navy, and using electronics and signal processing. He founded Electronic Measurement Systems Ltd. (EMS) to pursue the concept further and designed a new tilt system employing higher ranged electronic sensors with more accurate custom electronics. Lighter and more user-friendly, May’s Computerised Electronic Tilt Angle Measuring System (CETAMS) comprised a set of up to eight inclinometers linked via a single electronics module to a laptop PC.
The ship’s Master Level Datum, located on the ship’s founding plate, acts as the reference platform and a sensor is placed on it. The remaining sensors are secured on the other platforms of the weapons system. This allows simultaneous measurement of all the ship’s platforms and calculation of the errors between them.
The inclinometers were specially modified by Sherborne Sensors to enhance the accuracy of the device and provide a low output impedance drive suitable for driving the long cables without interference. Furthermore, the measurement of each tilt takes just 10-15 seconds, with the system using a signal processing algorithm to calculate the tilt of each inclinometer.
CETAMS made it possible to perform a test in under an hour, whereas previously a tilt test could take three or four days to complete. Crucially, as the system compensates for small movements during measurement, it enables tilt tests to be performed while the ship is alongside dock without impacting on other activities taking place on board.
The key component of the system is the Sherborne Sensors’ dual axis sensor. Early prototypes were made to incorporate two analogue sensor heads into a single unit with room to insert the digitising electronics. In addition to improved accuracy, May wanted to keep track of each inclinometer so that recorded scale factor and offset adjustments could be linked to the sensor itself. This required adding intelligence to the inclinometer and non-volatile storage on additional circuit boards. It was just after the first working prototypes of the new sensor assembly had been commissioned that the DSIC, a dual axis digital inclinometer, became available. The new DSIC had all the functionality being designed into May’s new sensor assembly, but in only two thirds of the space occupied by its prototype.
Consequently the EMS systems, based around the DSIC, can offer an improved measurement capability and greater functionality for a wider range of applications. The dual channel capability means that both standard tilt test measurements and accurate plane alignment such as that used for mast alignment are supported. Furthermore, each sensor head has its own serial number that can be read remotely, which means that whenever an inclinometer is connected to the system, it can immediately be identified.
When the sensors are being secured to weapons components and other metal structures on board ship, it is possible for the base to pick up grease and dirt, or be knocked causing roughened feet. This could result in a change to the zero tilt offset, introducing a fixed error. However, by measuring the offset of a device and storing its value linked to the serial number, such errors can be compensated for in the system software.
Four years on from the initial system upgrade and 18 months since adopting the DSIC, EMS has delivered a new CETAMS unit to the AWD Alliance for the Australian Navy, and also received orders from the Canadian Navy. This has enabled EMS to further establish a firm footing as a military contractor. EMS hopes to collaborate with military, naval, and shipyard customers on other innovative technologies that employ highly-customised, dual-axis inclinometers.
Sherborne Sensors is a global leader in the design, development, manufacture and supply of high-precision inclinometers, accelerometers, force transducers and load cells, instrumentation and accessories for civil engineering, industrial, military and aerospace customers. Products are supplied under the AS9100C Quality Accreditation and are renowned for their ultra-reliability and long-life precision within critical applications. www.sherbornesensors.com