Message Board Thread - "Reflected apparent temperture measurement (RAT)"

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Reflected apparent temperture measurement (RAT) PKS 12/26/2003
How a aluminium foil is used to measure the reflected apparent temperature.Why we are setting e=1, why not some other value like 0.88? What will be ambient temperature during the above measurement? If we are taking measurement in furnace tubes, how a aluminium foil will be kept in line with our target?What should be the thickness of aluminium foil?
 
Reflected Apparent Temperature (RAT) Bernie Lyon 1/5/2004
The aluminum foil is used as a diffuse infrared reflector. It reflects the background radiation, which may be called Background, Tamb, T Reflected, or T surroundings; this depends on which infrared camera you are using. (Spot radiometers and some infrared cameras do not have the ability to correct for background radiation.)
Aluminum is a great reflector of infrared radiation. That is why it makes a great infrared mirror. The aluminum is placed in the same plane as the target and it reflects the background radiation to the camera.
Here is an example which may help explain the concept:
Let's say you are looking at a panel and behind you is a hot boiler which has an emissivity of 0.95. You place the aluminum foil in the same plane as the panel and set the emissivity of your infrared camera to 1.0. Then, measure the Reflected Apparent Temperature (RAT). I would recommend that you use the area mode set to average temperature to obtain this reading. Let's assume that you obtain a temperature reading of 340 degrees F. This is not the true temperature of the boiler because the emissivity of the camera is set to 1.0 and there is no compensation done.
The Reflected Apparent Temperature that you enter into the camera is in degrees, but the camera is more concerned with the radiation. If you replaced the boiler with a large blackbody simulator set at a temperature of 340 degrees F, you would get the same amount of radiation. The Reflected Apparent Temperature is a reading you get when the emissivity of the camera is set to 1.0.
In the example mentioned above, the Reflected Apparent Temperature is 340 degrees F. This would be entered as Tamb for some cameras, such as a PM595, or PM695. This is NOT the same as the ambient temperature. The ambient temperature is the temperature of the air around the target of interest. In this case the ambient temperature may be 80 degrees F. Ambient temperature, along with distance and relative humidity, may be used with infrared cameras to compensate for atmospheric attenuation.
The thickness of the aluminum foil is not critical. Ordinary aluminum foil, such as that used for cooking, is fine. However, I would not use “space blanket” material that is found in sporting goods stores used for hikers and campers. This material is very thin and may be somewhat transparent in the shorter infrared wavelengths.
For furnace tubes, it is not practical to get the Reflected Apparent Temperature using aluminum foil. If you want to determine the Reflected Apparent Temperature in the furnace, observe the wall opposite the tubes. Imagine a pool table to determine where the RAT is coming from. (The angle of incidence is equal to the angle of reflection.) If you are observing tubes on the right side that are 5 feet away at an angle of 30 degrees, then the source of radiation is from the left side 10 feet away; assuming that you are looking through a view port that is equal in distance from the left and right sides. Point your camera in this direction and measure the RAT.
Measuring boiler tube temperatures is one application where the RAT is higher than the target. It is important to get this value correct in order to get good temperature measurements on the tubes.

 
Explanation of terms? innie 2/11/2008
I am currently doing a project looking at the temperature patterns of the equine back before and after a chiropractic adjustment as part of my dissertation, using a ThermoCam E320.

I am very new to this and was wondering if anyone could explain abit about the different setting on the camera? What they mean, how it is measured and how or if I need to change the settings before imaging.

If I have understood it right, emissivity in horses is about 0.98? This is also the set emissivity value on the camera. Reflected Apparent Temperature is set to 20 degrees, as is Relative Humidity, while Atmospheric Temperature is set to 30 degrees. What do these terms mean, will I need to change these settings before the pictures are taken? And in that case how is this done?

Much appreciate any answers!

Innie
 
Re:Reflected apparent temperture measurement (RAT) Andrew Szelc 2/11/2008
innie wrote:
rrently doing a project looking at the temperature patterns of the equine back before and after a chiropractic adjustment as part of my dissertation, using a ThermoCam E320.

I am very new to this and was wondering if anyone could explain abit about the different setting on the camera? What they mean, how it is measured and how or if I need to change the settings before imaging.

If I have understood it right, emissivity in horses is about 0.98? This is also the set emissivity value on the camera. Reflected Apparent Temperature is set to 20 degrees, as is Relative Humidity, while Atmospheric Temperature is set to 30 degrees. What do these terms mean, will I need to change these settings before the pictures are taken? And in that case how is this done?

Much appreciate any answers!

Innie
You may also want to see a very good paper dealing with the Reflected Apparent Temperature issue.
This is: "Don't let the RAT bite you!" by Mikael Cronholm, ITC Sweden.

http://www.infraredtraining.com/store/infra2002.asp

Regards,
Andrew
 
Re:Reflected apparent temperture measurement (RAT) HITECHSOLUTIONS 2/24/2008
Innie,
Before you make a fool of yourself in front of your client I would take a Level 1 Certification in Infrared. You can't rely on what the camera has there settings on. It depends on alot of things. Please talk to Gary Orlove from the ITC.
 


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