Liquid level & position monitoring with the British Army

The Terrier is a multi-function armoured digger, designed and built in the United Kingdom, to fulfill a wide variety of roles including obstacle and mine clearance, route opening and maintenance, digging-in, excavation and general engineer tasks.

Weighing 30 tonnes, Terrier can still reach speeds of almost 50mph. To ensure it can be used both night and day and provide operators with a full 360° surveillance capability, it is fitted with five on-board cameras and thermal imaging technology.

Potentially operating in combat zones – either with a crew or via remote control – dependable reliability is essential in such demanding and severe environments. Monitoring and controlling the sophisticated systems requires sensors that will also continue to function and provide reliable outputs in these challenging conditions.

Gill Sensors and Controls was asked to provide a suite of sensors for liquid level and position sensing, based on the proven reliability of their solid-state, capacitive and induction technologies.

Four custom designed liquid level sensors were produced for engine oil and coolant levels, along with transmission and final drive oil levels. Additionally, three non-contact linear position sensors were engineered for steering position, brake wear and final drive locations.

The liquid level sensors are all manufactured from stainless steel, with an integrated military specification D38999 connector. Varying in length between 125mm and 580mm, they have been developed for inverted mounting with an M22x1.5 mounting thread and a designed life expectancy of 30 years.

Sealed to IP67 and with an operating temperature range of -40°C to +125°C, the sensors also conform to severe environmental and Defence Standard EMC tests.

Another key challenge for all the sensors was the requirement for the negative supply and signal to be fully isolated from the sensors metal housing and able to withstand a 28V positive supply to the housing and sensor probe.

Of the three non-contact linear position sensors, two are adaptations of the Blade25 and Blade60 position sensor range. With heavy duty wiring and Mil-Spec connectors added, the standard product proved adept at coping with the tough environmental standards and operating conditions.

The third non-contact induction sensor was designed specifically to measure the position of the final drive secondary brake release mechanism. The dual purpose sensor measures the wear of the brake pads and the state of the secondary brakes (applied/released).

Having a measuring range of 5mm with an accuracy of +/-0.1mm, the Pulse Width Modulation (PWM) output voltage range was 0>4.2V with an output range of 10% to 90%.

Once again a life expectancy of 30 years was specified with an IP67 rating and -40°C to +125°C operating temperature range. As with all the other sensors, stringent environmental and Def-Stan EMC test limits are complied with.