Message Board Thread - "Setting RAF"

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Setting RAF JMcCurley 5/23/2011
When setting your reflected ambient temperature, how do you know what to set it as?
 
Re:Setting RAF dandersen 5/24/2011
Building science or level I courses teach you how to build and utilize a T-Reflect target. This device reflects thermal energy that is radiating towards your target which will alter the apparent temperature your camera is seeing.

To put this in "visual" perspective; in photography we can take a picture of a lightbulb which is emitting light. We can also take a picture of an object with a light shining on it. Where is the source of light coming from? In the first instance, the lightbulb or the subject in the photograph is producing the light. In the second instance the object is reflecting a light source. In thermal imaging we are not looking at visible light, rather emitted energy. The energy that the camera records is the sum of the energy the object is emitting as well as the energy that other objects in the general vicinity are radiating upon it (Hot or cold).

In order to correct your cameras apparent temperature measurement, you must remove the quantity of energy that is being directed towards the subject. We do this by using a temperature reflect target placed in the proper orientation with the subject exception and the camera subtracts this value from the total value (or apparent temperature) that the camera is recording, thus producing a corrected temperature.

The corrected temperature is the actual temperature of the exception. "Temperature Reflect" is only one variable that must be corrected to obtain a properly corrected temperature measurement.

One method of producing a temperature reflect target is to use crumpled tin foil placed in proper orientation with the exception, take a thermal reading of the average temperature of the target at an emissivity of 1 and enter that value in the camera.

To correct for all the other variables, I recommend further training to assist you in correctly making these adjustments to obtain an accurate quantitative temperature measurement.

There's a lot more to it than can be explained here.
 
Re:Setting RAF JMcCurley 5/25/2011
Thank you for your help
 
Re:Setting RAF Abbasalazar 6/11/2011
dandersen wrote:
g science or level I courses teach you how to build and utilize a T-Reflect target. This device reflects thermal energy that is radiating towards your target which will alter the apparent temperature your camera is seeing.

To put this in "visual" perspective; in photography we can take a picture of a lightbulb which is emitting light. We can also take a picture of an object with a light shining on it. Where is the source of light coming from? In the first instance, the lightbulb or the subject in the photograph is producing the light. In the second instance the object is reflecting a light source. In thermal imaging we are not looking at visible light, rather emitted energy. The energy that the camera records is the sum of the energy the object is emitting as well as the energy that other objects in the general vicinity are radiating upon it (Hot or cold).

In order to correct your cameras apparent temperature measurement, you must remove the quantity of energy that is being directed towards the subject. We do this by using a temperature reflect target placed in the proper orientation with the subject exception and the camera subtracts this value from the total value (or apparent temperature) that the camera is recording, thus producing a corrected temperature.

The corrected temperature is the actual temperature of the exception. "Temperature Reflect" is only one variable that must be corrected to obtain a properly corrected temperature measurement.

One method of producing a temperature reflect target is to use crumpled tin foil placed in proper orientation with the exception, take a thermal reading of the average temperature of the target at an emissivity of 1 and enter that value in the camera.

To correct for all the other variables, I recommend further training to assist you in correctly making these adjustments to obtain an accurate quantitative temperature measurement.

There's a lot more to it than can be explained here.
Question- WOuld this be the same when imaging a horse? I thought I was to set my RAF at 96.0 to 98. Please advise. Thank you.
 
Re:Setting RAF dandersen 6/12/2011
Why do you set it at thoes temps?

Because of your body heat?
 
Re:Setting RAF skid 6/24/2011
dandersen wrote:
you set it at thoes temps?

Because of your body heat?
What is the emissivity of a horse? Is there that much reflected energy?
 
Re:Setting RAF dandersen 6/25/2011
I did my level II field assignment on a horse and emissivity was .56. As transmittance is not an issue, there was significant reflectance in this case.

This emissivity is outside the expected range and was questioned by ITC, but the methodology utilized to obtain this emissivity was submitted, evaluated and accepted as correct.

This is an example of why it is imperative to make the necessary evaluations for temperature reflect and other atmospheric conditions and not just assume what they will be.

In most cases "apparent temperatures" are totally worthless. You cannot evaluate them for what they are, you cannot compare them to determine the temperature differential, you cannot use them for "maximum allowable temperature for the component".

This is not a "snap and shoot" technology. Outside of qualitative analysis, you must learn how to correct temperatures. (Or at least understand how they reflect the real world).

I.e. in one case where it doesn't matter is when you're 150° above ambient or comparative component plus or minus temperature correction. That's simply too hot regardless of what the actual temperature is.

Cylindrical objects (such as a cartridge fuse or your coffee cup)
have horizontal or vertical lines (depending on their orientation) that have different temperatures. Nine times out of ten when you see a thermal scan the temperature measurement is indicated at the center (hot line) of the object. This is reflection of the thermographer and the camera. You will also see hot or cold lines in some cases on the left and right of center. These are reflections of the environment. If you do not correct the apparent temperature in reference to the temperature reflect, the numbers are simply wrong.

In my opinion, there are all too many salesmen out there trying to sell a good thing as being too good to be true! "Camera owners" (untrained thermographers) will be the demise of this industry if there ever were to be one. A perfect example is veterinary applications. Thermal imaging got a black eye because of improper practices and techniques as well as inferior equipment. We are still trying to overcome this today.

When someone gets killed because of improper thermal imaging use, it will set back the industrial considerably (not to mention you will be the primary subject in a significant lawsuit).
 


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