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Blog #021 – 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.

Fluke infrared camera detector 70mK

Fluke infrared camera detector 70mK

This image was taken with a Fluke infrared camera which has a 70mK detector array.  Notice the sensitivity.  It is picking up a temperature difference of 2/10 of 1 degree F.   

Fluke infrared camera with 50mK detector array

Fluke infrared camera with 50mK detector array

This image was taken with a Fluke Ti32 with a 50mK detector array.  Notice the fine detail and sensitivity.  There is only 3/10 of 1 degree F between the nail and the siding.

We all have budgetary constraints.  Maybe a way to look at is over the long period of use.  Take the number of years that you plan on using your camera (a minimum of 5 years) and divide the number of months into the price difference of getting the better camera.  A $2,000.00 difference divided by 60 months is $33.33 per month.  Many feel that the better camera with more detail is worth it.  But, as long as you have a camera with a 100mK or lower dector array you’ll be fine.

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
rhoff@restcon.com

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

See DEMO www.moistureview.com/demo.html

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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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