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Vision Tests and Thermography

Do you wear eyeglasses? Maybe you are used to going to the eye doctor annually and occasionally needing to update your prescription.    What you may not know is that, regardless if you wear eye glasses or corrective lenses, all adults, even those who have never needed glasses, have vision that begins to deteriorate with age.   The condition that makes our vision deteriorate is called presbyopia and it is caused by a hardening of the lens within our eyes.  It usually starts around the age of 40 and progresses slowly from there.

The onset of presbyopia can have an impact on your ability to perform high quality thermographic inspections as well.  If your eyes can’t clearly focus on the camera’s view screen, any adjustment you make to the image focus is going to be off. As many of us have learned in Level I training, focus is the most important foundational element of image quality as well as temperature measurement.  When your image focus is off, your image quality is poor and your temperature measurement is impacted.  Focus is essential in thermography.

Eye Chart

 

 

 

 

 

 

 

 

Luckily, we have a built in mechanism for checking our ability to see our camera’s view screen.  Most cameras have graphics that show up on the view screen.  A helpful hint: If those letters aren’t nice and sharp to your eyes, your near vision is off and your image focus will also be off. That’s something you want to correct sooner rather than later.

We recommend annual vision tests, such as the Jaeger vision test for thermographers.  It might be in the best interest of your program to include this recommendation in the written practice document of your thermography program.  There are a number of viable options out there for improving your near vision.  Many optical shops offer prescription safety glasses options. A number of safety glasses manufacturers have products that are normal safety glasses except for a small portion at the bottom of the lens where a magnifier is installed to assist in up-close reading.  Several products are rated in magnification powers just like over-the-counter reading glasses.  Those might be just enough correction to make a difference in your image quality.

Stay on top of your vision with an annual eye test, especially after 40 years of age.  Your camera can see clearly but the question is, can you?

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

What Kind of Hot is It?

The discovery that accurate temperature measurements are many times difficult in electrical applications of thermography can be a hard pill to swallow.  Electrical apparatus are often made from metal that’s bare, so emissivity is low, and thus temperature measurements are unreliable.

The good news is that despite this fact, electrical anomalies can be relatively easy to detect, but only if you know what you’re looking for.  The simple fact is that electrical circuits with current flowing through them will inherently generate heat.  It’s a byproduct of normal operation.  So when you inspect electrical apparatus, guess what?  It’s often hot. The important thing to determine is what kind of hot is it?

What do we mean by that?  It’s the pattern that’s important in the discovery of electrical system anomalies.  The lion’s share of abnormal heating in electrical system components is abnormal electrical resistance on a contact surface.  We discourage thermographers from saying “loose connections” because in truth there are many other causes for increased resistance, and in many cases the connection is plenty tight.  Something else could be  amiss.  Take a look at the image below.

What kinda hot is it?

What kinda hot is it?

Notice the pattern.  The area of the highest thermal energy is at the connection point, and the circuit gets cooler the further away from the contact point.  This thermal signature is most often associated with increased surface resistance at the contact surface.  The greatest amount of heat is generated at the point of resistance and then it conducts away from its point or origin, resulting in the telltale “trailing away” pattern.

So remember, in electrical applications it’s not usually a matter of how hot a thermal anomaly is, it’s what kind of hot it is.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

Transformer Cooling Tubes

There are many electrical applications for thermography.  Nearly every electrical apparatus in any type of facility is an excellent candidate for thermal inspection.  One of the easiest, and often safest, types of electrical apparatus to inspect are oil-filled transformer cooling tubes.

Usually visual access to transformer cooling tubes is readily available.  Often, inspection of transformer cooling tubes can be accomplished from well outside of clearance distances because they have such a large surface area. They’re usually several feet tall, and several inches wide, and since temperature measurement isn’t the goal of this type of inspection, IFOVmeas concerns don’t really apply.

Cooling tubes on oil-filled electrical devices, including transformers, operate on the simple principle of convective cooling.  The oil is the cooling medium for the internal windings, and as it increases in temperature, it decreases in density as many fluid mediums do.  The warmer oil is less dense and thus lighter than the surrounding cooler oil, so it tends to rise.  As the oil cools it becomes denser and it tends to sink and natural circulation results.

Transformer 1

In the image above, we can see four banks of cooling tubes on a transformer.  The three banks on the left have what is considered a normal thermal pattern, while the one on the right has an abnormal pattern.  Oil isn’t circulating in the right-hand bank of tubes.  There are several potential root causes for this type of pattern, such as low oil, flow obstruction, a closed valve, or perhaps the apparatus is out of level.

When this type of condition exists, the cooling capacity of the device is negatively impacted.  While in the cooler parts of the year, or when the device is lightly loaded, this might not be as great a concern.  Whenever this type of pattern is detected however, it should be reported so it can be addressed before it becomes more critical.

There are many opportunities to apply infrared to electrical apparatus, transformer cooling tubes just be one. As a thermographer,  look at the world around you with a thermal mindset and discover what you can see when you Think Thermally®.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner
 
 

 

Focus First

If you’ve had Level I Thermographic Applications training course you most likely heard the mantra of “Focus First!” from your instructor, and with good reason! Of all of the camera settings that can be adjusted by the camera operator, focus is by far the most important.  Focus is essential to both image quality and temperature measurement.

Focus First House 2Focus First House 1

 

 

 

 

 

 

 

 

 

Consider the images above.   The image on the right is of much higher quality.  While it’s fairly easy to discern that the object in either image is a house, the right hand image is crisper, and there is more detail because the focus is so sharply adjusted.  Most customers will notice image quality immediately, and the image on the left just wouldn’t be helpful to help illustrate thermal anomalies clearly.

Box 1

Box 2

 

 

 

 

 

 

 

 

 

Reviewing the next set of images above, one can determine that each contains a box used to measure the maximum apparent temperature of the detected anomaly.  In the left hand image, the focus is sharp and thus the detector elements are getting a clear representation of the amount of thermal energy being emitted from the surfaces within the area box.  This allows the detector to more reliably measure that energy and assign a temperature value to it.  In the right hand image, our focus is marred.  This effect reduces the clarity of the energy being projected onto the detector elements, resulting in a faulty measurement.

Clear, sharp focus is essential in thermal imaging.  It can be the difference between success and failure.  Remember and adopt the mantra of “Focus First!”, and use this tip to help you Think Thermally®.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

 

Infrared Cameras: The Answer my Friend is NOT Blowing in the Wind

Regardless if you’re inspecting buildings, roofs, or electrical or mechanical apparatus, when you have an abundance of air movement across a surface, there is an increase in heat loss or gain on that surface from convective cooling or heating.

Convective cooling is often discussed in many applications of thermography.  Often the result is cooling of anomalous conditions to the point that they’re not easily detectable.  Sometimes, however, when the temperature difference is large enough, the convective cooling can take place and thermal abnormalities are still detectable. The issue at hand, and the question that is posed to the thermographer, is the quantifiable impact that convection has on surface temperature. We want to know this because once the air movement slows or stops, the surface temperature will increase even if the object in question doesn’t change otherwise.

This phenomenon is well known to most thermographers who have had some type of formal training.  So, why are we bringing it up in this blog?  We’re trying to battle misinformation.  There are formulas that supposedly help thermographers calculate varying temperature measurement corrections when given certain velocities of air movement. Readers beware; don’t use these formulas or attempt to use them to correct temperature measurements as they are not accurate except in tightly controlled circumstances when examining one specific piece of equipment.

If you’ve taken a Level I Thermographic Applications course, the formula below should be familiar to you:

Q= h•ΔTA

This is Newton’s Law of Cooling.  It states that the amount of heat transferred convectively is dependent upon the Coefficient of Convective Cooling (h), the difference in temperature between the cooling medium and a point on the surface, and the area over which the transfer takes place.  The coefficient of convective cooling is dependent upon many variables, one of which is velocity.  Velocity however isn’t the only factor that impacts the value of h.  Orientation to flow, surface condition, geometry, and the viscosity of the fluid are all additional factors impacting h, so if the only one you can quantify is velocity you can’t know with any precision what h actually is.  The result is that any attempt to correct temperatures based on velocity alone are flawed, hence our aforementioned disclaimer urging thermographers not to use these formulas. There are a couple of “rules of thumb” that we will discuss in an upcoming blog post, so remember to check back often to learn more.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

Thermodynamics 101: Thermal Diffusivity Part III

This time we’re finishing up our discussion of thermal diffusivity before moving on to further discussion of thermodynamics.   Hopefully taking these topics a step at a time is doing its job and will allow you to absorb the knowledge more easily, and hold onto it longer.

In The Snell Group’s Level I course, we see several mathematical equations related to heat transfer.  We encourage you in class to not concern yourself with being able to calculate anything with them, that’s for Stefan, Boltzmann, Fourier and those guys.  As Level I thermographers, we need only to understand the relationships between the variables in these equations so we can better interpret what we see through our imagers.  Let’s look at this pesky formula again that we touched on in part one of this blog series: http://thermal-imaging-blog.com/?p=3602 :

Formula

 

 

Where:

k = Thermal conductivity

ρ = Density

Cp = Specific heat

This is a linear equation, so whatever happens on one side of the equal sign, also happens on the other side of the equation, and to the same degree.  If conductivity increases, so does diffusivity.  If either density or specific heat increases, diffusivity decreases.  Materials with higher conductivity will tend to be more diffusive than materials with lower conductivity.  Materials that are high density will tend to be less diffusive than materials that are less dense (with similar conductivity values, that is).

How does the concept of thermal diffusivity impact thermographers in the field? Most often, the heat we’re interested in is developed internal to the object we’re inspecting.  How we “see” the heat is dependent upon how the heat gets from inside (where we can’t see it) to the outside surface (where we can).  The thermal pattern detected from the surface on of an object is going to be influenced by ambient conditions as well as variances in the operating parameters of whatever system the object is part of.  Likewise, the thermal characteristics of the material through which the heat flows will impact the pattern we detect.  Often, we will be more concerned with small areas of highly concentrated heat than we are with larger areas with an even heating pattern.  Consider though how an object would appear thermally if the object is very diffusive.  A “spread out” or diffuse pattern may be difficult to observe thermally but it doesn’t always mean there isn’t trouble.

Another common infrared application involves nondestructive testing, NDT, where the thermographer intentionally disturbs thermal equilibrium by adding or removing heat from a material and observing, thermally, subsurface anomalies.  Data collected during testing like this can identify purity of material, porosity and thickness.

Thermal diffusivity occurs in all materials whenever there is a transient event or thermal equilibrium is disturbed. Knowing its effects takes a careful eye and some basic understanding.  Hopefully you’ve gained some of that basic knowledge from this blog post.  Check back for our fourth and final installment of Thermodynamics 101 and Think Thermally®!

 

Think Thermally,

www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

Themodynamics and Diffusivity 101: Part II

We’re partly through our discussion of thermal diffusivity in our series on basic thermodynamics for the field thermographer.   It is not our intent to have the reader become an expert in heat transfer theory.  But it is important to understand the variables that effect thermal diffusivity and how this concept impacts the thermal world we may see in the field.

In The Snell Group’s Level II course we describe diffusivity with an analogy involving water, one of our favorite materials to discuss.  The example is given of a volume of water in a container, and a drop of red food coloring being added.  The red dot of food coloring expands as it mixes into the water.  Instead of the water turning a dark red like the single drop of food color is, the water takes on a pink hue, because the food coloring disperses throughout the sample of water.  It really is a great example of diffusion, and it illustrates what happens with heat energy as it diffuses through a material. You can see an example of this water experiment below with the red, representing the food coloring, gradually diffusing throughout the water within the container.

 

Water Container

 

Body Heat

Diffusivity is essentially “spreading out” or “drawing” of the heat energy.  Have you ever climbed into bed on a cool night and noticed that the covers were cool at first?  As you lay there, you begin to warm up but you will notice that if you change position, and move over to a spot in the covers where you haven’t been laying, that spot is cooler.  That is because your body heat hasn’t reached that area of the covers yet.   When you wake up the next morning, the whole bed is warm, even spots you’ve not been laying on.  That’s diffusivity at work. The heat from your body moves into the mattress, both linearly and non-linearly.  At first, the greatest amount of transfer is occurring linearly from your body to the mattress material.  However as you continue lying in bed, you are giving more heat energy to the mattress, and the heat begins to transfer within the material of the mattress in a non-linear fashion, with the mattress trying to reach thermal equilibrium.  By the time you’ve laid there all night, the mattress is pretty uniformly warm due to the heat energy being “spread out” or diffused into the mattress material.

We’ve got one more installment on Thermal Diffusivity, and then it’s on to more Thermo!

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

Auto Draft

If you’ve taken a basic Level I thermography course, you’ve already received a brief introduction to thermodynamics.  In Level II thermography courses, students get to dig a little deeper into “Thermo” (as we like to call it) in an effort to help advanced thermographers better understand why objects appear thermally they way that they do.  If you’re an engineer, some of this information is a refresher, but for other folks it’s brand new, and maybe it doesn’t all stick the first go around.   We’re going to explore some principles of thermodynamics in three, smaller blog installments because, like the old riddle suggests, you eat an elephant one bite at a time.

Diffusivity Part 1

Many of you have at least heard the term “thermal diffusivity” used, and if you have been to Level I or II course, you probably have even seen it demonstrated.  For those of you who haven’t been to a Level I or II infrared course, I need to issue a spoiler alert.  The Miracle Thaw demonstration illustrates how a highly thermally diffusive material will allow heat transfer to occur more rapidly than a material with lower diffusivity, because the heat transfer is occurring both linearly and non-linearly.  We give a brief description of the concept in our Level I course, but we largely leave it at that.

For those engineers out there, you may have seen the formula below before Thermal diffusivity, α, is used to describe or define heat transfer situations that are not at steady state, or said another way,  when temperature distribution changes with time.  It is related to the steady state variable thermal conductivity as shown in the equation below where k is the thermal conductivity.  Cis the specific heat and ρ is the density.  The product of the specific heat and the density of a material it’s thermal or heat capacitance and is based on the volume of a material.

 

Formula

 

 

 

The SI unit of measurement for thermal diffusivity is m2/s, and essentially it’s a measurement of thermal inertia, or more simply put, how quickly material moves heat throughout its volume.

When discussing thermal conductivity, most of us consider heat energy moving linearly through a material, from the side where heat is applied to the other side.  Many of the demonstrations we use in class reinforce this concept.  When heat is applied evenly across a surface, the transfer will tend to be more linear than if the heat is applied in a more concentrated, non-linear fashion. Another important point to keep in mind involves the direction of heat flow.  Heat energy moving through the volume of a material can be triggered by adding or removing heat energy. In transient heat transfer situations, the kind we might experience in the field as thermographers, diffusivity of a material plays a part in how the heat will move through the objects we’re inspecting.

 

This important concept, once mastered, will help you as a thermographer in the field. Check us out next time for another installment on Thermodynamics 101 and Think Thermally®!

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner
 
 

Exposing Electrical Panels

Whether it’s high rise office buildings, hospitals, or an industrial facility, the approaches to accomplishing an infrared electrical scan vary as much as the locations.  One universal thread throughout these inspections is the manner in which most electrical maintenance folks expose panels for inspection.

Exposed

 

Most industrial grade panels have a two part cover but these configurations can, and do, vary from one manufacturer to another.  We commonly see an outer cover that has the enclosure door built in and held in place by a number of fasteners.  Once this outer cover is removed, many panels have what’s called a deadfront.  A deadfront usually describes the inner most layer of covering internal to an electrical apparatus that covers the energized circuit parts.  However, the electrical industry has sort of unofficially come to call what is essentially an inner panel cover, or bus cover, a deadfront.  This cover is usually the piece of sheet metal that has slots cut in it allow for the faces of the individual circuit breakers to show.

Removing the outer cover will reveal the breaker wire-to-lug connection points for each circuit.  So, if you have a wire-to-lug anomaly, you’d be able to view it only with the outer cover removed.  If you leave the deadfront in place, what is not visible is the bus-to-breaker connection point, where power is distributed from the panel’s internal bus work to the individual circuit breakers. Often, high resistance will develop in the termination points where each circuit is initially installed, the wire-to-lug junction.  However, any connection point in the circuit is a potentially failure point, including the breaker-to-bus connection.

Take the extra step, and removed that deadfront.  It only takes a few additional minutes but can add value to your electrical inspection.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner

 

Mechanical IR Safety

There’s a lot written about electrical safety as it applies to infrared inspections.  The danger of electric shock and exposure to arc flash hazards must be considered when inspecting electrical apparatus with thermography. What isn’t discussed nearly as often are the hazards associated with mechanical infrared inspections, of which there are many.

Roller Bearing

Roller Bearing

 One area of concern is inspecting rotating equipment.  Whether, its bearings, motors, couplings or belt drive components, special care should be taken when working around rotating assets. Even devices driven by fractional horsepower motors generate an enormous amount of torque and can cause serious injury if your clothing, hair, body parts or even the strap on your camera get caught in them.

 In many facilities, couplings and belt drive components are guarded for safety purposes and as such may not be readily available for inspection.  If removal of a guard is necessary for inspection purposes, it’s advisable to first de-energize the rotating device in question, if possible. Another option is to utilize a good thermal mirror (polished aluminum for example) and place it below or at an angle where you can view the component’s reflection.  While temperature measurements will probably not be accurate, the qualitative image will tell you a great deal.

Thermography is also very useful for inspecting high temperature systems such as boilers, steam lines, and kilns.  Special care should be taken in high temperature areas for a number of reasons.  Thermal imaging cameras often have not-to-exceed operating temperatures, which can be easily encroached upon in high temperature areas.  Additionally, the surfaces being inspected could be of sufficient temperature to cause serious burns if bodily contact is made.

 Sometimes steam lines and even boiler skins are coated with a low emissivity material to reduce radiant heat loss, and the danger to personnel is that these surfaces can often feel like they aren’t very hot–even with your hand held as close as an inch away.  Once contact is made however, radiation isn’t the mode of heat transfer any longer and severe burns can occur. Also of concern in high temperature areas is heat exhaustion.  Exposure to high temperature areas should be limited to short periods of time with time in between to cool off and re-hydrate.

So please remember to be safe during mechanical inspections.  Attention to detail and following proper inspection procedures can help you stay safe while you Think Thermally®.

 

Think Thermally,
www.thesnellgroup.com
The Snell Group, a Fluke Thermal Imaging Blog content partner