June 20, 2016 qtechimaging

Application Story

THE CHALLENGE OF MEASURING HEAT AT HIGH SPEEDS

How do you measure the heat of an object that is moving fast or changing temperature rapidly? Traditional temperature measurement tools such as thermocouples or spot pyrometers don’t offer the resolution or speed needed to fully characterize high speed thermal applications. These tools are impractical for measuring an object in motion – or at the very least, provide an incomplete picture of an object’s thermal properties.

In contrast, an infrared camera can measure temperature across an entire scene, capturing thermal readings for each pixel. Infrared cameras can offer fast, accurate, non-contact temperature measurement. By choosing the correct type of camera for your application, you will be able to gather reliable measurements at high speeds, produce stop-motion thermal images, and generate compelling research data.

SPOT VS. BROAD AREA MEASUREMENT

Measuring temperature across a broad area, instead of spot by spot, can help researchers and engineers make better-informed decisions about the systems they’re testing. Since thermocouples and thermistors require contact, they only provide data from one location at a time. In addition, small test subjects can only fit a few thermocouples at one time. Attaching them may actually change the temperature reading by acting as a heat sink. Non-contact measurement is possible with a pyrometer – also called an infrared (IR) thermometer—but just like thermocouples, pyrometers only measure a single point.

Infrared cameras produce images from the radiation emitted by objects above absolute zero. By providing a temperature measurement for each pixel, researchers are able to see and measure temperature across a scene without contact. Because IR cameras offer more data than thermocouples or pyrometers and can track changes in temperatures over time, they work well for research and engineering purposes.

COOLED VS. UNCOOLED INFRARED DETECTORS

There are two types of infrared detectors: thermal and quantum. Thermal detectors such as microbolometers react to incident radiant energy which heats the pixels and creates a change in temperature that is reflected in a change in resistance. These cameras do not require cooling and cost less than quantum detector cameras.

Cooled quantum detectors are made from Indium Antimonide (InSb), Indium Gallium Arsenide (InGaAs), or Strained Layer Superlattice. These detectors are photovoltaic, meaning photons strike the pixels and are converted into electrons that are stored in an integration capacitor. The pixel is electronically shuttered by opening or shorting the integration capacitor.

“Quantum detectors are intrinsically faster than microbolometers – and the main reason for that is the microbolometers have to change temperature,” explains Dr. Robert Madding, President of RPM Energy Associates. A pioneer in the infrared industry, Dr. Madding has more than 35 years of experience in infrared thermography applications and training.

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