Message Board Thread - "Odd settings required to reach actual temps"

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Odd settings required to reach actual temps RobertC 2/9/2009
I shot a pump and got a max temp of 141F with a flange temp of 120 or so.

I used the defaults 1.0 emissivity and a background of 68.

Later, I went down with a contact thermocouple and actual flange temp is 96F.

Reshot and got the same values, SO I reset E to .91 and background to the painted concrete temp of 58F.

My 96F point went to an apparent 125F

So I got wqeird and just entered random numbers.

When I ended up at 277 for background, my pump flange was close to actual.

Why?

This is with a Fluke TI55FT, and I am brand new at this, but my LevelII couldn't make much sense of it either.
 
Re:Odd settings required to reach actual temps InDemand Inc. 2/10/2009
Do you have any pics?
 
Re:Odd settings required to reach actual temps TDLIR 2/10/2009
Robert,
from your post, it clearly shows that proper training (Level 2 for temp meas.) is much needed.

There are many reasons why you get what you get with IR temps. Level 2 training will explain all of these variables and you will get a better understanding. Understanding ir temps and also understanding contact temps is important.

I cannot speak for the ability of your level 2 to understand temp accuracy with ir and contact thermometers. But proper training will answer many of your questions.

just my thoughts.
 
Re:Odd settings required to reach actual temps Doctir bob 2/12/2009
There are several reasons an IR camera reading will disagree witht a contact thermocouple reading. I start from the most likely to the least likely, assuming the thermographer understands how to measure temperature with his/her IR camera:

1. Thermocouples get the temperature of the thermocouple. Contact resistance between the thermocouple and the surface frequently results in values on warm targets reading lower on a thermocouple than on an IR camera. Done properly with a well-calibrated, well-designed IR camera, I believe the IR camera reading gives a truer surface temperature value more than the thermocouple reading in this type of application.
2. IR camera measurement and thermocouple measurement done in different locations at different temperatures.
3. Thermocouple response time can be several seconds to minutes depending on the design. If one doesn't wait long enough the contact thermocouple hasn't reached its maximum value on a warm surface.
4. IR camera doesn't compensate for changes in its own internal temperature. Reads fine when at the same temperature as when calibrated. Reads not so good when its in a warmer or colder environment. Very manufacturer dependent. FLIR cameras don't have this problem. I cannot speak for others.
5. IR camera is out of calibration.
6. Thermocouple is out of calibration.
7. Thermographer is unfamiliar with how to find Treflect (background temperature).
8. Thermographer is unfamiliar with how to measure emissivity of target. Typically for painted targets such as motor housings, the emissivity is 0.95.
9. Thermographer is unfamiliar with the relationship between Treflect (background temperature) and emissivity.
 
Re:Odd settings required to reach actual temps manuel-thermoimagen 2/12/2009
10. IR Camera Out of Focus.
 
Re:Odd settings required to reach actual temps manuel-thermoimagen 2/12/2009
10. IR Camera Out of Focus.
 
Re:Odd settings required to reach actual temps RobertC 2/16/2009
Doctir bob wrote:
re several reasons an IR camera reading will disagree witht a contact thermocouple reading. I start from the most likely to the least likely, assuming the thermographer understands how to measure temperature with his/her IR camera:

1. Thermocouples get the temperature of the thermocouple. Contact resistance between the thermocouple and the surface frequently results in values on warm targets reading lower on a thermocouple than on an IR camera. Done properly with a well-calibrated, well-designed IR camera, I believe the IR camera reading gives a truer surface temperature value more than the thermocouple reading in this type of application.
2. IR camera measurement and thermocouple measurement done in different locations at different temperatures.
3. Thermocouple response time can be several seconds to minutes depending on the design. If one doesn't wait long enough the contact thermocouple hasn't reached its maximum value on a warm surface.
4. IR camera doesn't compensate for changes in its own internal temperature. Reads fine when at the same temperature as when calibrated. Reads not so good when its in a warmer or colder environment. Very manufacturer dependent. FLIR cameras don't have this problem. I cannot speak for others.
5. IR camera is out of calibration.
6. Thermocouple is out of calibration.
7. Thermographer is unfamiliar with how to find Treflect (background temperature).
8. Thermographer is unfamiliar with how to measure emissivity of target. Typically for painted targets such as motor housings, the emissivity is 0.95.
9. Thermographer is unfamiliar with the relationship between Treflect (background temperature) and emissivity.
Well, turns out my level II was sending me on a mission to learn.

Camera is brand new, focus is sharp, Thermocouple was just cal'ed. Emissivity is right.

#7, and 9 are my strong candidates.

Got to call Fluke about the internal temp compensation.

And I am going to get a pice of brushed aluminum from the shops tomorrow.

Thanks for the guidance.
 


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