Precision Electronics and Laser Optics Expand Thermal Applications
- Sunday, 01 December 2013
Thermal imagers allow a user to see an object’s heat signature, and heat provides an entirely different set of performance data than the visible spectrum available to the naked eye. A fully radiometric camera will calculate a temperature value for every pixel seen on screen. The technician uses the thermal colors on screen to look for differences in temperature, between previous states or like components, without actually coming into direct contact with the device under test.
With a capable infrared camera and an understanding of thermodynamics, the user can discover and often diagnose issues that are unseen. Infrared thermal imaging is typically more accessible and more affordable than radiography, acoustic ultrasound, eddy current analysis, vibration analysis, and other advanced inspection technologies. As a result, thermography has become a mainstay of manufacturing, industrial and commercial maintenance, research and development, and materials analysis.
In this article, we will explore the importance of ease of use, enhanced image quality, and an integrated development approach in today’s thermal imaging applications. Complexity, cost, and image quality used to be barriers to use. Now, thanks to new improvements, a completely different and far broader set of users can take advantage of infrared technology.
Ease of Use
The evolution of thermal imaging systems follows that of most electronics: Capabilities, accuracy, sophistication, and ease of use have increased as size and weight have decreased. Early systems used cooled sensors to get the best thermal image, requiring tanks of liquefied gas, such as nitrogen, to be present.
An imager using earlier technology was both more expensive and difficult to operate in a portable environment, due to size, power consumption, and warmup time. Infrared imagers have gone from laboratory bench-top, to truckmount, to heavy portable, to lightweight portable. While not as mature as other semiconductor devices, such as the microprocessor, a handheld thermal imager is nonetheless a complex device, using precision electronics to acquire and process the infrared signal.
Multi-spectral image combination tech nology also now adds an infrared image with a visible light image in nearperfect alignment: The user can see the device under test through a partiallytransparent infrared image (see Figure 1). The technology provides visual context for where a temperature abnormality is located in the physical environment. The capability transfers through to the captured images, so that a third party not present at the original point of measurement can feasibly interpret the data. Captured images can be shared wirelessly and through direct download to PC, and then further manipulated in software.
As today’s electronic devices become increasingly wireless and more interconnected, it is not surprising that infrared and other measurement devices are following suit. Many newer thermal imaging systems now connect wirelessly with other measurement tools, such as current clamp meters, contact temperature meters, and multimeters. The resulting information provides additional context about why a thermal anomaly may be occurring, and corroborating evidence about the root cause, thus producing a more credible diagnosis.
The biggest challenge to infrared image quality has not been pixel resolution, but rather image focus (see Figure 2). If your image is out-of-focus, important details, of course, will be blurred or might even be unrecognizable. For an infrared camera, however, there is an added level of impact, in that the focus also affects the temperature measurement calculation. The imager does not actually measure temperature; it calculates temperature based upon the amount of infrared energy being focused on to the microbolometer, along with the input of some other variables (emissivity, transmissivity, reflected background temperature, etc.). If the focus is off, less infrared energy is detected and registered by the sensor and subsequently used for radiometric calculations. Therefore, the displayed apparent temperature could appear lower than it would if the image is in proper focus.