How Delta T’s Understate Priorities
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How Delta T’s Understate Priorities
Tip written by: Infraspection Institute
For years, thermographers have traditionally reported apparent Delta T measurements when documenting their findings. Using a default emittance value between .8 and 1.0, apparent temperature measurements are recorded regardless of actual target emittance. While this methodology is fast and easy, it can lead to significantly understated Delta T repair priorities.
The temperature displayed by a radiometer is largely dependent upon the emittance and reflected temperature values entered into the radiometer’s computer. Typically, errors in either of these settings will cause temperature measurement errors that are exponential in nature and can cause large errors in reporting Delta T’s.
Example: Using an emittance value of 1.0 a thermographer measures the apparent Delta T between two, uninsulated electrical bus bars to be 44ºC. How much can observed temperature vary due to emittance values?
From the above, the following observations can be made:
- Emittance can have a significant impact on Delta T measurements
- The greater the variation between an object’s true emittance and radiometer settings, the more understated the Delta T
- Repair priorities may be significantly understated if accurate emittance values are not utilized
As there is no way to correct for errors introduced by apparent Delta T measurements, thermographers should utilize correct emittance values whenever possible. As always, all thermal anomalies detected during an infrared inspection should be investigated and proper corrective measures undertaken as soon as possible.
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