Displacement and temperature sensors get smaller and smarter

Paul Boughton

Chris Jones discusses some of the latest applications and innovations in non-contact displacement measurement and infrared temperature sensors for the automotive and motorsport markets.

Current trends indicate that smaller, more compact, more intelligent displacement measurement sensors are now required, particularly in high performance motorsport and automotive applications.

With pressure on motorsport teams and passenger vehicle manufacturers to minimise the weight of onboard systems and therefore reduce fuel consumption and vehicle emissions, the requirement for extremely compact sensors is now a critical factor, especially if installation space is also restricted. This is also true for integration – both in terms of electronics and building more intelligence into the sensor itself, without the need for any bulky, separate controllers. This means that displacement and laser profile sensors are more frequently required to perform signal conditioning directly in the sensor, therefore reducing component count, whilst offering faster measurement speeds.

Micro-Epsilon has been developing non-contact displacement measurement and infrared temperature sensors for automotive and motorsport applications for more than 40 years. These sensors are used in almost every conceivable area of a vehicle, as well as for R&D, test cells, production and for on-vehicle testing. Applications range from measuring the wear on brake discs and clutches, to measuring turbocharger speeds, engine piston displacement, valve lift, ride height and monitoring the temperature profile of tyres.

Manufacturers of automotive turbochargers, for example, now require measurement systems to test the performance limits of their products. Measurement systems are required to monitor the temperature and speed of the blades on the turbine wheel. Due to increasing material stresses and higher speeds (up to 400,000rpm), turbocharger blades are now made from either aluminium or titanium, which presents a challenge in terms of measurement technologies. Titanium is a very poor electrical conductor and so eddy current sensors cannot be used easily on titanium. However, using special linearisation and advanced electronics, measurement systems have been developed (such as Micro-Epsilon’s turboSPEED sensors) that are able to accurately measure the speed (and temperature) of both aluminium and titanium turbocharger blades over the complete speed range – in both multiple test cell and on-vehicle testing. These sensors are robust, resistant to oil and dirt, extremely compact and slim, with the latest versions measuring just 3mm in diameter.

Miniature cylinders and actuators

Miniaturisation of sensors is equally important in other areas. Hydraulic and pneumatic cylinders, valves and actuators, for example, are becoming ever smaller and therefore require more compact, ultra slimline position sensors for measuring displacement and piston position. More robust, pressure-resistant position sensors are now required.

Compared with traditional methods of measuring displacement and piston position in hydraulic cylinders and valves (ie LVDTs and Magnetostrictive sensors), Micro-Epsilon’s EDS series of sensors is much more compact in both its length and diameter. It uses a non-ferrous aluminium outer sleeve as its target, which can be easily integrated into the piston rod. This enables the sensor body to be a solid rod rather than a traditional LVDT style with a hollow sensor body and plunger, making it easier for OEMs to assemble and much more robust and reliable in harsh (on-vehicle) environments.

The sensors are manufactured from a pressure-resistant stainless steel (up to 450bar), can operate to 165˚C and withstand extreme vibration and shock levels. The sensor electronics and signal conditioning are completely integrated in the sensor flange using very compact electronics. Compared to an LVDT with similar measurement range, EDS sensors are typically 50 per cent shorter and much narrower in body diameter.

For such compact sensor geometries, it is necessary to use external electronics. However, the electronics are also very compact, typically 20 x 30 x 45mm (long) and it is not necessary to match sensor to electronics like many other sensor solutions, ie the sensor and electronics are interchangeable.

Another benefit of such a compact design is that the length of the hydraulic cylinder does not have to be increased in order to accommodate a larger sensor (which would increase weight and the overall space envelope). These sensors operate without any contact between the moving parts and are wear-free.

Ride height

Measuring ride height is also important in many motorsport applications. Non-contact laser displacement sensors can now be mounted to the wheel of a vehicle, with the laser window pointing down towards the ground or racing track. From here, these high speed sensors are able to accurately measure and monitor the ride height of the vehicle or motorcycle as it travels around the track. Suspension characteristics and engine power mapping can also be adjusted in order to optimise vehicle performance, whilst reducing energy consumption.

For measuring the temperature profile of vehicle components, Micro-Epsilon has developed a range of extremely compact thermal imaging cameras. These operate at high speed data capture of up to 120Hz full frame rate, re-transmit either full temperature data or provide alarm limits for pre-set events such as overheating or maximum hot spot. This high speed data capture and re-transmission of full temperature image information allows play back at a later date – an important feature in many automotive R&D and failure diagnostics work.

The thermoIMAGER TIM160, for example, can be fixed into position in an automotive production line or R&D test cell lab in order to monitor the temperature profile of target materials or objects. The cameras are even being used for on-vehicle testing and to monitor hotspots on vehicle cooling systems, radiators and electrical terminals.

As well as thermal imagers, compact, infrared temperature sensors can be mounted to the chassis, tyres, brake discs, engine and power train – almost anywhere on a vehicle where temperature needs to be measured. Sensors even come with integral software that allows the user to change the emissivity of the infrared temperature sensor to suit different target materials such as steel, carbon or rubber.

Blue laser sensors

For vibration and displacement measurements on hot glowing targets, for example in an engine powertrain, it has traditionally been a challenge to use displacement sensors due to the target being very hot and even glowing red on or near to the exhaust section.
Red laser displacement have tried to perform these types of measurements, but with red-hot glowing objects, a conventional red laser has a high signal interference from the surface of the thermocouple, because it emits the same or very near wavelengths of light as the red laser.
To overcome this limitation, Micro-Epsilon has developed a Blue LED Laser Sensor family, which operates at a wavelength of 405nm. This wavelength is far from the red part of the visible spectrum, which means it is easier to filter this type of emitted light from the target, ensuring very stable signals. This is a world first for high accuracy laser triangulation sensors and not only works with on red glowing surfaces but also on white hot glowing targets.

Measuring brake disc wear

When a vehicle stops or slows down, the brake discs need to absorb and dissipate the entire kinetic energy of the vehicle. The high amount of energy absorbed during vehicle braking transforms into heat, which makes a brake disc glow red hot under load. The shape of the brake disc can deform during braking as higher energy is absorbed. The full extent of this deformation or disc wear can also be measured using Blue Laser Sensors.

Using a conventional red laser sensor would result in a high signal interference from the brake disc surface, because it emits the same or very near wavelengths of light as the red laser. Even white hot glowing ceramic discs can be measured using Blue laser technology, which ensures very stable signals. Blue Laser Sensors can measure red glowing metals up to 1,600 deg C and silicon up to 1,150˚C, with no loss in measurement specification.

Chris Jones is Managing Director at Micro-Epsilon UK, Ellesmere Port, Cheshire. UK. www.micro-epsilon.co.uk