Message Board Thread - "SUN REFLECTIONS IN DAY TIMES"

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SUN REFLECTIONS IN DAY TIMES PKS 1/12/2004
We are using AGEMA-550 camera for doing thermography in 400/220/132/33/11 KV switch yards.
We set the ambient temperature of air & humidity in a approximate method depending on the weather condition. For most of our customer we used to do it in the day time. We know it is better to do the outside job in night or the time at which sun influence is not much more, but this is not possible at all times. So, when we are doing the survey in the day times, we are observing the reflection in our image, even a solid bus bar with out any joint showing more than 100°C.But as per AGEMA, SRX filter is in bulit in the camera which will filter the heat due to sun influence at the 3.5 micron only. So what we are thinking that the reflection may be at very low wave length region, which not getting filtered by existing filter. But the moment we are changing our direction of location or angle of location, we are able to eliminate maximum problem due to reflection. But we are still in doubt that taking reading during day time for outside equipment may be not more accurate. Is there any method of doing the survey in day time without affecting the accuracy?

Plaese get into my queries & your reply in this regard with proper justification will be highly appreciated?

Q1. Shall we use Thermometer & Hydrogauge for measuring the ambient temperature & himidity for the above job? As per my knowledge we can not measure accurately the Tamb by our IR camera.

Q2. Shall we use the recent method for Tamb by which we will focus to the sun at e=1 and measure the temperature that will be our Tamb & after setting Tamb then to measure the temperature in day time.

Q3. AGEMA does not have any parameter like atomsphere temperature setting, which is different from Tamb as per recent news. How the atomsphere temperature & ambient temperature affect the temperature reading?

PRASHANTA
 
re:SUN REFLECTIONS IN DAY TIMES Gary Orlove 1/14/2004
The sun is a powerful infrared radiator and emits energy in all IR wavebands. However, the relative amount the sun emits reduces as the wavelength increases, just as Planck's law says it should.

So,as we move out to longer wavelengths the amount of energy that reflects from the sun compared to the energy emitted by our targets gets smaller. This means that IR cameras that view in the longer wavelengths would be "bothered" less by solar reflections.

So LW (8-13 µm) IR cameras “see” the least amount of reflected solar energy. This makes surveys easier for the operator as the true "hot spots" are easier to find.

This doesn’t mean that you can’t use a SW camera for inspections during daytime. Thousands of successful thermographers have proven otherwise; but you do have to be a bit more careful about the solar reflections. The key to discovering if a “hot spot” is a reflection is to move the infrared camera. Reflections will appear to move on your target surface, but a true hot spot will remain in the same position.

Q1. Shall we use Thermometer & Hydrogauge for measuring the ambient temperature & humidity for the above job? As per my knowledge we can not measure accurately the Tamb by our IR camera.
A: The "ambient" temperature setting in your AGEMA 550 camera actually refers to what we now call Reflected Apparent Temperature. The air temperature and the humidity are only used to correct for the infrared radiance reduction caused by atmospheric attenuation. The error this causes is quite small compared to using incorrect T reflected and object emissivity settings. For most measurements I wouldn’t worry about it (unless you are looking through high temperature, high humidity atmosphere at targets at great distances.) You can measure the T ambient air temperature with cardboard. See http://www.infraredtraining.com/community/boards/thread/213/.

Q2. Shall we use the recent method for Tamb by which we will focus to the sun at e=1 and measure the temperature that will be our Tamb & after setting Tamb then to measure the temperature in day time.
A: NO NO NO! Do not point any infrared camera at the sun. You risk damaging your detector at great repair expense to you. Instead use aluminum foil to measure T reflected as discussed in http://www.infraredtraining.com/community/boards/thread/195/.

Q3. AGEMA does not have any parameter like atmosphere temperature setting, which is different from T amb as per recent news. How the atmosphere temperature & ambient temperature affect the temperature reading?
A: You are right, the 550 only has distance and relative humidity parameter settings in order to correct for atmospheric transmission loss. Set the relative humidity to the correct value. For short distances and normal humidity the relative humidity can normally be left at a default value of 50 %.

You might consider taking an infrared training course which will answer all these questions and more; and will provide instruction on proper survey techniques and image interpretation.

Gary Orlove
Infrared Training Center
 


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