Wednesday, September 30, 2009

Quick and Easy Solution to Emissivity Problems

"We've received the camera and so far it's been good in that department. I am concerned however about emissivity. In my application, I'm filming the inside of a computer system which is a small, tightly packed space with different materials and emissivities. Because thermography is something new to me, I'm not sure how much of a role emissivity plays in throwing off my measurements. I could attach a thermocouple to each component to verify the readings on the thermal cam, however that's very time consuming and given the limited amount of time I have with this instrument, it doesn't make sense. I've read that there's emissivity sprays that will help with this issue but don't know if that solution is any better or cost effective. Do you have any cheap and quick solutions for my problem?"

Yes, emissivity can play a big role in your temperature measurement accuracy, especially if you are trying to measure shiny metals. Here is what I would do:

1. Set camera emissivity to 1.0
2. Use some slightly crinkled aluminum foil and place next to your target(s).
3. Using the area mode of your camera set to average temperature, read the apparent average temperature of the aluminum foil. (Be careful that you don't reflect your own heat reflection of the foil).
4. Enter this temperature as the reflected temperature in your camera.
1. Use some Liquid Paper brand correction fluid.
2. Place a small amount on your targets.
3. Set your camera emissivity to 0.95
4. Measure the temperature of your target(s)
Cautions and Caveats
• When using these techniques make sure that the correction fluid will not damage your components.
• Use a small amount of correction fluid. Changing the emissivity of small shiny components from less than 0.1 to 0.95 will greatly affect the heat transfer from these components, and thus affect their temperature. So the smallest amount of emissivity improver that you can measure is the amount to use. This is easy on FLIR systems cameras, just make sure that the emissivity improver is large enough to fill the cursor circle on the spot tool. Anything smaller will not be measured correctly.
• There are more sophisticated ways of doing this automatically for all materials on a PCB through software. Please contact a FLIR Systems Scientific Segment Engineer regarding Altair software.
• If you don't understand emissivity and reflected apparent temperature terms, get some training! A good place to start is this web based course, Thermography Basics.

How can one tell if the imager needs calibration?

Most manufacturers suggest that an IR camera be serviced with a calibration check annually, like many other instruments. The checklist below outlines the FLIR annual service program.

FLIR 14 POINT INSPECTION & CALIBRATION PROGRAM
1. Perform a complete operational check
2. Fusion calibration and laser alignment, when applicable
3. Verify all internal cable and PCB connections
4. Clean viewfinder and check optics
5. Upgrade internal camera software to latest revisions
6. Perform minor repairs
7. Verify and/or re-equalize as needed each temperature range for image uniformity
8. Verify standard lens calibration (others or special engineered lenses, optional)
9. Verify ambient temperature compensation as needed
10. Re-calibration to ensure it meets factory specification
11. Calibrate temperature ranges up to +1,500°C, when applicable
12. Perform quality approved acceptance test procedure
13. Provide calibration label with next due date
14. Provide calibration certificate (optional, extended calibration certificate with measured values)

Here is a quick way you can check your camera calibration in the field:
1. Measure the temperature of a MELTING ice cube. The reading should be 0 C +/- 2 C.
2. Measure the temperature of boiling water (if you are near sea level). Reading should be 100 C +/- 2 C

Tuesday, September 22, 2009

Thermography Weatherization Certification course earns BPI CEUs

The Weatherization certification course has been approved by BPI for 16 CEUS. It was previously approved by RESNET for 32 CEUS.

The 4 day certification course is intended to give the student a depth of the knowledge necessary to perform IR surveys of single or multifamily dwellings to identify weatherization issues. The class covers IR camera operation, and basic report generation, fundamentals of IR science and heat transfer principles. IR Weatherization surveys techniques, tips and tricks, and application examples.

Monday, September 21, 2009

How does the Lexus Driver Attention Monitor Work?

Here is how Lexus describes their Driver Attention Monitor:

"Mounted on the steering wheel column, a driver-monitor camera is part of the Advanced Pre-Collision System (APCS). It’s designed to recognize when the driver isn’t facing forward. If a frontal collision seems likely and the Driver Attention Monitor senses that the driver is not facing forward, a warning tone will sound, followed by a flashing light. "

While I don't have detailed specifications of the system, I believe that the system employs a near IR camera, working at the same wavelengths as an infrared remote control to view the drivers head. There might be an infrared LED providing illumination for the camera at night.

So I don't think this system is a LW IR camera as is typically used for thermography.

Friday, September 11, 2009

New Web Course: FLIR 600 Series Basics

This course provides an introduction to the operation of all variants of the FLIR 600 series cameras. These include the P620/640/660 and the B620/640/660. You will need to have your camera with you in order to obtain the maximum benefit from the camera operation exercises.

We highly recommend taking this course prior to taking the Thermography Basics, Building IR Basics, Level I, Weatherization, or Building Science courses.

Who should take this course: Users of FLIR 600 series cameras.

Prerequisites: No prior knowledge of thermography or infrared cameras is assumed.

Availability: This course is an on-demand self paced web based training course available 24 hours a day, 7 days a week. You can begin as soon as you enroll.

Thursday, September 10, 2009

Inspecting Concrete Block Walls with Thermography

General principles of thermodynamics and heat transfer can be used to explain how voids can be detected by infrared thermography. For most applications, solar energy (sunlight) is permitted to strike the exterior of the wall and heat the surface.
"I have a client who wants me to image a building block wall in search of voids where rebar was incased in concrete as part of the strengthening process. Is there a particular protocol you can point me to that will satisfy the building inspector that no voids exist?"

Solar energy striking the wall is absorbed by the masonry. Hollow or insulated cells create a thermal break or barrier within the cell causing the exterior face shell to heat rapidly. In contrast, the solidly grouted cell acts as a heat sink permitting energy to be conducted through the wall. The emitted energy of the exterior surface is therefore higher in locations of voided cells than that of solid cells. This emitted energy pattern is visible with an infrared camera. This method provides very crisp contrasting data, but is totally dependent on weather conditions and the availability of direct sunlight.

In the daytime, wall sections filled with grout will appear cooler than the other sections. At night, sections with grout will appear warmer than the rest of the wall.

CMU wall section during the day
CMU wall section at night

See these two white papers presented at the InfraMation Conference below:

Use of infrared thermography as a standard in the quality assurance and quality control of grouted masonry construction

Thermographic evaluation of concrete masonry walls: have they been properly reinforced?

Wednesday, September 9, 2009

Tips to find moisture in wall cavities and insulation

"I'm looking for moisture in wall cavities and insulation, all in the interior of homes. I can't even see the studs let alone the screws."
To find moisture in building materials, the infrared camera must see a temperature difference on the surface being viewed: no temperature difference, no detection. The question is; under what conditions can a temperature difference due to moisture occur?
The most common scenario for moisture detection involves a temperature difference due to the evaporation of water from a surface. When water evaporates, the surface will become cooler. In order to evaporate well, the air dewpoint temperature should be lower than the air temperature, the lower the better.

If the relative humidity where you are trying to inspect is 90%, you are not going to get much evaporation, hence not much cooling, hence very low temperature differences that might not be spotted with your IR camera. In such a situation, use a dehumidifier in the room to lower the humidity (it also adds heat to the room which raises the temperature and also lowers the humidity as well).