Infrared Training Center

Thursday, October 12, 2017

Use of the Wedge Method for Emissivity and Reflection Independent Temperature Measurement

By: Ralph Rudolph
R. Rudolph Consulting LLC @

clip_image002A technique called the Wedge Method or Roll Nip method is finding increased use in measuring strip temperatures in the metal production/processing industries as it is touted as providing the dual advantages of appearing to be independent of the material emissivity and the presence of any ambient reflected radiation. Basically, the concept is quite simple: Picture a horizontal steel strip that contacts and at least partially wraps around a large roll, usually a deflector roll used to change strip direction or a bridle roll used to set strip tension. Aim a radiation thermometer almost parallel to the strip into the gap formed between the roll and strip tangent point, as deep as you can go. (Viewing at an angle from the side is fine). This gap, as the claims state, can be treated as a blackbody with an emissivity of 1.0 (see Figure 1). Hence, you don’t have to worry about ambient radiation as reflectivity is 0.0 and you don’t have to worry about changing material emissivity. This is partly true and partly wishful thinking.

Blackbody conditions exist for a cavity if and only if all sides of the cavity are at the same temperature. If the roll being used has a very low thermal mass (heats up easily) and there is a large wrap around the roll and sufficient strip tension to allow heat transfer to occur between the strip and the roll, then the roll will heat up to near strip temperature over a time period, but because the roll has natural convection, conduction and radiation losses, the roll can never quite reach the strip temperature. Emissivity never reaches 1.0. It should be obvious that if the strip abruptly changes temperature, which can happen with strip thickness or furnace temperature changes, it will take time for the roll to change temperatures. Heat transfer between the two can take quite a while during which time the temperature reading from the wedge system will be quite inaccurate.

Wedge or cavity measurement method
Figure 1.

So, if a system is designed well, with a major roll wrap, low thermal mass roll, sufficient strip tension and steady long term operation (no major changes in strip temperature), this method can work as claimed (except that emissivity must be set somewhat lower than 1.0 to compensate for the roll being at a slightly lower temperature than the strip).

Given human nature, however, I’ve seen numerous instances where folks have not understood why the wedge method can work and who have misapplied it. Believe it or not, I’ve seen an instance where a so-called wedge method has been applied with zero roll wrap, with the strip simply passing over a support roll. And this system was (unfortunately) designed by the equipment provider who should have known better. I would guess that a majority of wedge method applications that I’ve seen have been poorly designed, with little attention paid to the amount of roll wrap or roll material and with little understanding of what occurs during changes in strip temperature.

There is a modification to the wedge method that can provide a significant improvement: Mount a second Radiation Thermometer to monitor roll temperature and compare this reading to that of the wedge RT. Using a PC with input and output cards (and most any older PC will work), abrupt deviations between the two readings which occur as strip temperature changes can be used to correct for errors. If accuracy is desired, it’s well worth the extra expense. You get what you pay for.

Tuesday, October 10, 2017

InfraMation 2018 is Headed to Austin, Texas

InfraMation, the world’s leading IR training experience and thermal imaging conference, is headed to Austin, Texas September 11-14, 2018.  Join other thermography experts from around the world at the downtown Hilton Austin to learn the latest thermal imaging techniques and applications while making valuable connections.

Learn more and register at

The best deals are now available for a limited time with our Super Early Bird options that include among other items a FLIR E8 thermal imager, the chance to win a FLIR E95 infrared camera, a FREE ITC Certification renewal, and up to $800 off your entire registration.  

More details coming soon including a Call for Papers for those who are interested in sharing their knowledge and experience with other industry professionals, plus sponsorship and exhibiting opportunities too.  Until then, follow us on Facebook ( and Twitter ( with the hashtag #inframation18 for the latest conference updates.

Wednesday, September 27, 2017

Furnace and Heater Tube Inspections

by Ron Lucier, ASNT NDT Level III

ITC logo registeredOne of the more challenging applications of infrared thermography is in the measurement of process heater and furnace tubes. In fact we get dozens of inquiries each year from our clients on this very subject. Since this is a very complex subject it is probably appropriate to start from the beginning.

Process Heaters
There are as many uses for process heaters as there are designs. The basic configuration consists of a shell (outer casing),   tubes (where the process fluid flows) and a heat source. These units are both thermodynamically and hydraulically complex.

Process heater or furnace diagram

In the simple drawing above we illustrate convective gas flow, which is turbulent, and radiant heat from the flame, refractory and other tubes – all non-uniform and time varying. When you view tube from an access port typically you can only see a portion of the tube or the tube at an oblique angle. Therefore, the odds are stacked against you from the start!

Why are heater tubes of interest anyway?
Heater tubes 1There are several reasons for inspecting tubes. Qualitatively slag (scale) buildup on the outside of the tube can be readily identified. Buildup on the inside of the tube (coking) is a bit more difficult but commonly performed. In both cases the slag or coke prevents the transfer of heat into the process fluid. In the case of slag buildup, the process fluid may not be sufficiently heated, affecting downstream processing. The case of coking on the inside of the tube is more serious. Since the coke has an increased resistance to heat transfer, the tube surface temperature increases. After all it is the flow of the process fluid that is keeping the tube “cool” in the first place. In fossil boilers this is called “DNB” – Departure from Nucleate Boiling and is usually caused by flame impingement, which initiates a layer of steam on the inside of the tube. The external tube surface, unable to conduct its heat to the water, increases dramatically, causing a failure (opening) in the tube.

Wednesday, September 20, 2017

Blower Door Inspection for Air Infiltration in a Remodeled Cottage

By Tom Coffey, Infrared Training Center 

ITC logo registeredA small cottage (700 sq. ft) outside of Knoxville, TN was completely remodeled from January to March 2010. It was an existing cinder block structure with no insulation except ½ inch of airspace between the nailers and the block wall as well as the empty block core. The R value of existing building walls was approximately 2.97. After the remodel an R-value was calculated and determined to be 12.6

2 x 4 studs were used to build the interior walls the insulated with 4” of backed fiberglass bat insulation. Old windows were removed and new double pane sash type windows installed during the remodel.

The house was depressurized to approximately 50 Pascal and allowed to equalize for 30 minutes. A thermographic scan was performed after the equalization period. Infiltration was found around the sash windows where the top and bottom pieces join in the corners of the windows.

Picture1 Picture2

There was some expected infiltration around the front door which was missing a sweep on the bottom of the door. Also infiltration was found at the attic access.

Picture3 Picture4

All of these small problems are easily correctable and will be done as time permits.

The installation of the blower door took approximately 30-45 minutes. Reaching the right depressurization took another 30 minutes and the IR scan took another 45 minutes. For a house this size, allowing for the small footprint I did not do an air exchange calculation. The purpose of this exercise was to determine if the house remodel and adding insulation was sufficient to keep the house at a comfortable level during East Tennessee summers and winters. It was determined during the remodel process that R-13 insulation in the walls and R-19 insulation in the ceilings would be sufficient for the weather conditions in this area of the country.

Wednesday, September 13, 2017

Getting Started with R&D Thermography Online Course

ITC logo registeredVideo tutorials on IR Camera Properties and getting started with ResearchIR. For any SC camera including A300, A320, SC645, SC6000, SC6700, and SC7000, SC8000 cameras.  There is NO CHARGE for this FREE  course.

Includes information on:

  • Camera Technology
    • Cooled vs Uncooled Thermal Cameras: Field of View
    • The difference between cooled & uncooled thermal detectors?
    • Cooled vs Uncooled Thermal Cameras: Speed
    • Cooled vs Uncooled: Sensitivity
  • FLIR ResearchIR Max
    • Connecting to the Camera
    • Image Enhancement
    • Image Subtraction
    • Recording Data
    • Triggering
    • Super Framing
    • Analysis Tools
    • Analysis Charts
    • Measurement Functions
    • Sharing Data
    • File Extraction Tool
  • FLIR ResearchIR and MATLAB
    • FLIR Thermal Face Detection and Tracking in Matlab
    • Opening FLIR Movies with Matlab Software
    • Connecting FLIR Systems GigE Cameras to MATLAB
    • Applying MATLAB Filters in FLIR ResearchIR Max Software

   Course Registration and Information

Thursday, September 7, 2017

IR finds Yellow Jackets Nest in House

by Sanin Mulic, Barber Foods

After attending my level one instruction during the week, and ITC wetting my appetite for thermal imaging, I returned home with my company's P-65 camera.  I decided to scan my own house to practice what I was taught all week.  All looked good until I went upstairs and noticed a bright spot on the inside wall.  I took several images of the spot and come Monday, I talked to two level 2 associates about what I had found.  There were several possibilities and I was told to take several more shots at different times to see if it moved or varied in temperature.   When we found it never moved I suggested that it might be insects (wasps, hornets, etc.) and talked with one of the other thermographers who would bring in a stethoscope to see if  I could hear them before opening up the wall.

Wasps  Wasps-vis 
Thermal image of the wasp nest (left).

I couldn’t wait, so that night armed with a drill, a can of flying insect killer, and the enthusiasm of a new thermographer,  I went up to the room; my pet cat, who loves to lay in the window there, had to investigate with me too.   I approximated where the hotspot was and drilled a 1/8 “ hole through the wall board. As I removed the drill bit, about 8 to 10 yellow jackets came charging through the hole and I started to spray the bug spray at the hole.  By this time, the yellow jackets were in an attack mode and I started to swing at them in defense.  Out of the corner of my eye I saw my cat speeding to the door with his tail bigger than I have ever seen it.  I finally killed the last one, sprayed about 1/3 of the can, and plugged the hole; but not before being stung twice.  I went outside and saw a swarm just outside the window. I drilled a second hole a few inches above it and knowing what was going to follow,  I had the spray ready to go as soon as the drill came out.  I sprayed about 1/3 of the can and then plugged the hole. I returned several hours later and the swarm was gone.  I climbed a ladder and found a small hole where they were coming and going.  I plugged that from the outside.  As I came back inside I saw my cat peaking from around the door as if to ask “Is it safe to come out now?”

After a few days I took another thermal image and there was no evidence of the yellow jackets remaining.  I submitted this investigation as my level one field report and it passed, but the memory of this initial experience will last a long time (the cat won’t forget it either!)

No-wasps no-wasps-vis
No wasps after removal.

Tuesday, August 29, 2017

Why does my Infrared Camera read higher than my Infrared Temperature Gun?

 ITC Logo TM 250 The answer is, in a word, resolution. Take a look at the image below.

7-20-2010 1-48-44 PM

The infrared camera is able to locate and measure much smaller objects than an IR temperature gun. Note the spot measurement on the infrared image; its reading is 250 F. Contrast that to the average area measurement typical of an infrared gun at a reading of 184 F. The gun is averaging all the hot areas along with the cold areas of the grating we see in the image.

Another common question is why the IR camera reads a higher temperature than a contact temperature probe? Contact temperature probes require an extremely good contact in order to read a decent temperature. In fact these probes measure their own temperature, so if the heat transfer is not good from the substrate, and the probe sensor is colder than the surface, the temperature will be lower. Also remember that contact thermometers act as heat sinks, sucking heat out of a surface.

Wednesday, August 23, 2017

IR Pictures Through a Grating or Mesh

Question from a customer: “Scanning through the steel grating I read a temperature 5 to 15 degrees Celsius lower than scanning without the grating. I know it is to do with the steel grating but I was wondering why.”
Great question. Let’s take a look at a typical situation with and without a grating, and then placing the grating at different distances to the camera.
The distance between the fuse and the camera remains constant, and the camera is always focused on the fuse. The only changes are the insertion of the grating, and the distance of the grating from the infrared camera.
Figure 1. Looking at a fuse directly with no grating. Max temperature is 51.4 C.
Figure 2. We have inserted the grating close to the fuse.
Max temperature dropped to 51 C, a small error.

Friday, August 18, 2017

What does Sensitivity (NETD) mean when applied to a Thermal Imager?

Sensitivity expresses the ability of an infrared camera to display a very good image even if the thermal contrast in a scene is low. Put another way, a camera with good sensitivity can distinguish objects in a scene that have very little temperature difference between them.
Sensitivity is most often measured by a parameter called Noise Equivalent Temperature Difference or NETD, for example, NETD @ 30 C : 80mK. A Kelvin degree is the SI base unit of thermodynamic temperature equal in magnitude to a degree Celsius, so mK means thousandths of a degree (80mK = 0.080 K).
What is NETD? NETD is defined as the amount of infrared radiation required to produce an output signal equal to the systems own noise. This is a noise rating of the system and should be as low as possible. We are not talking about how loud the system is here!!! We are talking about electronic noise that we translate into a temperature difference at an object temperature of 30 C (86 F).

Tuesday, March 7, 2017

New Online Course - FLIR ONE Basics


This course will introduce you to the operation of the FLIR ONE infrared camera. This course is a self paced on-demand web course, you can start as soon as you enroll and you can stop and continue where you left off at any time. This is NO CHARGE for this course.
The goal of this course is simple: By the end of this course, you will be able to operate a FLIR ONE camera. Our instructional video will familiarize you with the basic camera functionality.
Who should take this course: This course is intended for users of the FLIR ONE camera or anyone interested in purchasing one.
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.
We highly recommend you take a thermography course after finishing this basics course. We offer the On-Demand Introduction to Level I and Thermography for Home Inspectors classes here, or Level I, Residential Energy Auditing, or Level I - Building Investigations Courses available at .


  • Get Expert tips on IR camera operation
  • Explore the user interface buttons and menus
  • Learn how to operate the camera using a video and slide format to explore functions
  • See examples of applications for the FLIR ONE


  1. Getting to Know your FLIR ONE (Online Lesson)
  2. Next Steps (Online Lesson)
  3. Course Evaluation and Certificate Generation (Online Lesson)


  1. FLIR ONE Basics