Thermographic Improvements Benefit Automotive Industry
- Sunday, 01 April 2007
Other applications of quantitative thermography in automotive industry typically use high-performance infrared imagers with cooled InSb and MCT technologies. These applications usually are described as “fast” and/or “high-resolution” thermography, and deal with thermal characterization, non-destructive testing (NDT), and stress analysis.
With each new year, automobiles consume more electricity as consumer demand for electronics and improved performance escalates. Some of these electrical parts govern safety-critical systems, and therefore, have to be tested carefully during the design process, often by the Tier 2 or 3 automotive part suppliers, prior to shipping to the final assembly plant. One example is an electronic monitoring system that reduces CO2 production by an internal combustion engine.
This automotive component manufacturer used a Titanium IR camera from Cedip Infrared Systems with G1 and G3 lenses to evaluate the part design by monitoring the thermal generation of the part as electric current was increased to 200 Amps within <200 ms. The magnifying germanium lenses (G1 and G3) allowed the Titanium IR camera to measure and record transient events at 4-μm resolution on the small electronic part, identifying hot spots in the component and possible design flaws.
The first step of measurement is to evaluate local emissivity. Using Altair software Cedip researchers are able to create a full-field map of emissivity, which can be applied either to real-time images or recorded video. The resulting corrected temperature map has been used by automotive researchers to redesign components based on hot spots and thermal gradients.
Designing new and more effective automotive brakes also depends on careful temperature measurements. Braking effectiveness is linked to pad and disc temperatures, both overall temperature as well as temperature gradient across the brake pad surface, to avoid stress and permanent deformations. The difficulty of making such temperature measurements is due to the wide range of temperatures encountered (20°C to 900°C) and disk brake rotation speed.
Using Titanium IR camera systems, automotive engineers can meet both requirements thanks to three special features. The camera has very precise external trigger modes to handle image acquisition from fast-moving targets. Titanium also combines four temperature ranges to extend traditional IR sensing ranges from 300-400°C, upwards to temperature bandwidths of 1000°C. Finally, although the Titanium is sensitive to a broad band if IR radiation — 1.5 to 5.1 μm — using bandpass filters at 2 μm reduces the camera’s sensitivity to changes in emissivity, yielding a more accurate temperature reading.
Another example of thermal imaging in automotive design and manufacture is tires. Tire tests are different from rotating brake tests. The temperature range for tire testing is less than brake testing, falling within 20°C to 80°C. Temporal synchronization for this application is more stringent. Integration time, which is the time of accumulating photons for measurement, should be as short as possible to avoid smearing. It is widely understood that long-wave infrared (LWIR, 8-12 μm) cameras have shorter integration time at 20°C than mid-wave infrared (MWIR, 2-5 μm) cameras. The Titanium 530 IR camera uses a LWIR cooled MCT detector to provide a thermal image with very low thermal resolution (NEDT= 25 mK) and integration time less than 50 μs. The camera’s Hypercal mode allows users to give priority to anti-smearing, similar to the fastshutter “sports” setting on many digital cameras. The system automatically adapts its calibration curve and its Non Uniformity Correction table to compromise between acquisition time and objective temperature measurement. Finally, Titanium IR camera systems also can record external analog signals (speed, pressure, temperature, etc.), helping users build a more in-depth picture of thermal behavior.