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Blog #059 – Your THERMOGRAPHY COMFORT LEVEL – NETD. What is it and why is it important?

When shopping for an IR camera one needs to match up certain features of the camera to the investigative needs of the thermographer.  So, we need to understand and look at “camera specifications” which are found in the “spec sheets”.  The most expensive thing you can do is get a camera that doesn’t fit your needs.  For example, is there a difference in the needs of a thermographer who is performing inspections on high ∆T (temperature difference) items (such as motors, electrical, etc) verses the thermographer who is performing inspections on small ∆T surfaces (interior/exterior building surfaces) ?  Yes!  This is where we become concerned about the “sensitivity” of the detector array in the camera.  Performing inspections on surfaces that have a 100 degree F differential does not require the same sensitivity as performing inspections on surfaces that have a 2 degree F differential.  For example, evaporative cooling usually results in a drop in temperature of only a few degrees F.  The more sensitive the detector array, the easier it will be to locate such issues.  When you look at a spec sheet for a particular camera, look for “thermal sensitivity” or the NETD (noise equivalent temperature differential).   You’ll usually see something like this:  ≤0.1 °C at 30°C target temp. (100mk);  or ≤0.07 °C at 30°C target temp. (70mk);  or ≤0.05 °C at 30°C target temp. (50mk).  The lower the number, the more sensitive the camera.  The 50mK infrared camera detector array is much more sensitive than the 100mK detector.   You’ll notice, too, that the lower the number the more expensive the camera.  I would not recommend a camera that has an NETD higher than 100mK. 

 The ASNT (American Society of NonDestructive Testing) says: “The noise equivalent temperature difference is also the primary index of the infrared thermographic system.  This index indicates the temperature resolution and shows the minimum detectable temperature difference appearing on a target surface whose emissivity ε is nearly equal to 1.0”…  “A smaller value indicates better temperature resolution of the system.”

 The images below show the capability of highly sensitive infrared cameras and this is what you need to perform a thorough job in building diagnostics.

Taken with a Fluke 70mK Ir camera

Taken with a Fluke 70mK Ir camera

 Notice that the framework is only .2° F (2/10 of a degree) cooler and the effect of the hot water pipe is less than a 2 degree F rise in temperature.

Fluke 50mK detector

Fluke 50mK detector

This image was taken with a Fluke Ti32 infrared camera  with a 50mK detector array.  Notice the detail and the sensitivity.  This camera can detect and collect greater detail which helps the thermographer who is performing energy audits home inspections and moisture investigations.

How’s your comfort level in thermography?
(The above comments represent my opinion).

Rod Hoff / Restoration Consultants Inc
Thermography Instructor / IR camera sales
3284 Ramos Circle, Sacramento CA 95827
toll free 888-617-3266 ext 301
fax 916-736-1134

Provider of Fluke TiS, TiR, TiR1, Ti, Ti25, TiR27, Ti27, TiR29, Ti29, TiR32, Ti32, TiR3, and TiR4 infrared cameras.


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About infrarod

Rod Hoff is a Thermographer and instructor with Restoration Consultants, Inc. He teaches a two-day IR class in moisture and building envelope investigations. A graduate from Florida State University, with a degree in education, he received his formal training in Thermography from Snell Infrared and Restoration Consultants, Inc.

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