Specialists in motorsport engineering, BERU F1 Systems started its data acquisition projects with a strain gauge designed for use in Formula One. The company developed a microprocessor-controlled gauge that is able to compensate for temperature changes. Using a temperature sensor and a microprocessor with an extensive look-up table detailing how the sensor responds at different temperatures, a calibrated product was created that was up to 10 percent more accurate than available products on the market. BERU F1 Systems designs the mechanical basis of each strain gauge specifically for each application to ensure that it gives the most accurate and reliable results. When multiple parts are required, each gauge is then calibrated across the full range of loads and temperatures it is likely to meet, in the company's computer-controlled oven. The advantage is that multiple parts can be made pre-calibrated saving valuable processing and analysis. The company is then able to take a client's component design and redesign it to incorporate the sensor. Latest examples include NASCAR suspension, World Rally Car drivetrain and damper loadcells for this year's Scuderia Ecosse Ferrari F430GT at Le Mans. The strain data taken from such devices in suspension rod ends gives teams valuable insights into the behaviour of their cars with data downloaded to a logger on the vehicle or sent via telemetry to the engineers. Recent developments in electronic components have permitted BERU F1 Systems' engineers to significantly reduce the size of the suspension sensors so it can even match the aerodynamic profile of the wishbone.

Racing developments

As well as producing sensors embedded in the vehicles themselves, BERU F1 Systems also works closely with its racing clients to help them measure strain during the development process of new vehicles. As well as providing essential information for developing the car, the results from this early testing phase can be extrapolated from, to assess what is happening to the components not being directly tested on the production models. This application provides useful information for all car designers, not just those in racing. Vehicle manufacturers are becoming more attracted to this method. For example, the company has produced some equipment for a low-volume, high-performance road vehicle maker to help them with powertrain development and testing. The results can be used to analyse a suite of characteristics to increase performance or efficiency. Traction control, differential settings and gear shift points are some examples that can be optimized.The strain gauges can be used to monitor gearshifts in race cars. The strain gauge tells the engine management system when a gearshift is being attempted, and can be calibrated to suit how hard each driver pushes the gear lever, preventing accidental shifting, increasing engine life. The sensors provide a throttle blip during which gearshifts can be made, allowing the driver to keep the throttle pedal floored. With experience of harsh environments, the company believes that the robust solutions have potential in other sectors. Sensors mounted in rally car driveshafts endure over 5kN of torque in temperatures up to 120°C, making the products very applicable to aerospace and defence projects. It has also created an electronic tyre pressure monitoring system for the world's fastest road car, the Bugatti Veyron. In this application, traditional OEM systems struggled to endure the 100°C temperatures and 1000G centrifugal forces. The company is hoping this expertise will allow it to expand into other areas needing accuracy and a a good understanding of strain.

How a strain gauge actually works

A strain gauge is a resistor made from foil that is bonded to a dielectric backing (insulator). When the strain gauge is bonded to a material and the material is stretched or compressed it will change in resistance. This change in resistance can be used to measure the amount of force that causes the material to stretch or compress. This is done by converting resistance change into a voltage and is achieved by connecting four strain gauges into what is known as a Wheatstone bridge. When a number of strain gauges are configured into a Wheatstone bridge, they can be used for precise measurement. Voltage applied to a Wheatstone bridge (typically 5 or 10 volts) will create an output, usually in millivolts (mV). If a force is applied to the material that the Wheatstone bridge is bonded to, it will compress or stretch, and that produces a change in the Wheatstone bridge output expressed as mV/V (mV output from the bridge per unit Voltage input). This mV/V output is then calibrated by applying a known force (kilograms, pounds or Newton's) and the part can then be used as a sensor. A strain gauge can be mounted onto almost any material sample, the most typical being steel, aluminium and titanium.