Have you ever wondered what the size of your imager’s field of view is at a given distance? If you know the visual field of view specifications for a thermal imager, it is possible to calculate the size of your imager’s viewing area for any given distance using a scientific calculator. The formula for this calculation is:

{(tangent 1/2 viewing angle) x distance} x 2

To apply the above formula, follow these steps:

1. Determine your imager’s Field of View (in degrees) from the manufacturer’s specs.

2. Divide the value from Step 1 by 2

3. Use scientific calculator to determine tangent of number obtained in Step 2

4. Multiply number in Step 3 by distance from imager lens to object.

5. Multiply number in obtained in Step 4 by 2. This will be the width of the imager’s field of view at the specified distance.

Example: Calculate field of view for 16° lens at 25’.

(tan 8° x 25’) x 2 =

(0.140541 x 25’) x 2 =

(3.513525’) x 2 = ˜ 7.0’

If your imager specifies different Field of View values for horizontal and vertical, it will be necessary to calculate each value separately. Calculated values should be used for estimation purposes as actual values may vary slightly.

When performing infrared inspections of electrical distribution systems, many people identify the individual phases of polyphase circuits as A, B, and C; others frequently use 1, 2, and 3.

Confusion can arise with alphabetical or numerical labels particularly when switchgear enclosures are inspected from different perspectives e.g. front versus rear. Further confusion can occur when phase rotation has been modified or changed or, in some cases, mislabelled.

Reference errors can be avoided by using terms that cannot be confused such as Left, Middle, Right OR Upper, Middle, Lower. When using such terms, one should always reference where the image was taken from. For outside power lines references such as Street, Center, and Field may be used to identify phases without confusion.

Using the above simple terms can make your reports easier to understand and help to eliminate confusion when repairs are performed.

Thermal imging can often be used to help locate leaks from pipelines buried within concrete. For best reults, the subject piping should be heated as much as possible prior to imaging. Cold water lines may be heated by continuously flushing them with hot water. The amount of time required will depend upon the burial depth of the lines and the thermal conductivity of the concrete.

Once the lines have been heated, use your thermal imager to inspect the pathway of the pipe. Pipe leaks will appear as amporphously shaped warm areas instead of the well-defined lines caused by the pathway of the pipe. Suspected leaks may be marked directly on the concrete to direct excavation efforts required for leak verifcation and repair.

When imaging outdoors, it is best to perform infrared imaging at night to avoid interference from the sun.

Translated from tip submitted by Juan Nava, Cemex Mexico Planta Hermosillo.

Gracias Juan!

Thermal anomalies are not always as obvious as one might expect. Often, subtle thermal differences can be indicative of major problems. Because infrared thermography is a visual inspection technique, its effectiveness relies on the observation skills of the thermographer. Like any visual inspection technique, a thermographer must actively concentrate on the imagery displayed by their thermal imager.

Contrary to popular belief, humans are not inherently effective observers. Because humans tend to be casual in their observations, they frequently overlook subtleties. Whenever imaging, a thermographer’s eyes should always visually scan the monitor left to right and up and down while asking him/herself the following three questions:

1. What am I seeing

2. Why am I seeing this

3. Is this normal/reportable

While this approach may sound cumbersome at first, this practice will soon become instinctive and can help prevent you from overlooking the subtle thermal patterns that can be indicative of serious problems.

Traditionally, storage batteries for thermal imagers have been proprietary and available only from the imager manufacturer. Often, these special battery packs have cost hundreds of dollars each.

With a moderate amount of electrical skill and some homework, there are affordable power alternatives to be found in commercially available battery packs. To use an alternative battery, do the following:

1. Determine the required voltage of your imager.

2. Use a DC ammeter to determine the imager current requirements. If you know your imager’s power consumption in Watts, divide this number by the voltage required by your imager. Example: An imager that uses 12 Watts at 6 volts will draw 2 amps of current.

3. Select a battery with appropriate voltage and capacity. To determine how a battery will last with your imager, divide the Amp Hour rating by the current draw of your imager. A wide variety of rechargeable batteries are available through many professional video retailers.

4. Construct a fused power cord to connect your imager to your power supply making sure that the polarity is correct.

Constructing your own battery packs can save you money and result in longer run times between battery charges.

Proper planning prevents poor performance. This frequently repeated phrase has been applied to many disciplines and has application in thermography as well. One of the greatest appeals to thermography as a PdM tool is the wide range of potential applications. However, without planning the varied uses for thermography can cause one to lose focus and compromise program efficiency.

Using preplanned routes can improve inspection efficiency by serving as a roadmap for your inspection activities. When setting up inspection routes, keep the following in mind:

1. When possible, use established routes from other PdM technologies such as vibration analysis.

2. Routes should be of same class or hierarchy for subject equipment. As an alternative, establish routes based upon physical location.

3. Keep in mind requisite travel times between locations.

4. Establish routes to ensure that subject equipment will be under proper load.

5. Never include more equipment in a route than can be accomplished in a single work shift.

When following a route during an inspection, any equipment not inspected should be noted in the final project report.

Everyone has heard the fabled race between the tortoise and the hare in which the tortoise beats the hare. One of the morals of the story is that a steady pace may be more fruitful than erratic bursts of speed.

Thermographers who perform infrared inspections should keep in mind that a slow and steady pace can lead to victory. Working at an even pace can help to prevent overlooking the subtle temperature variations that often indicate serious problems. Purchasers of thermographic services should bear in mind that the best value is not in the fastest inspection time, but rather in the thoroughness and accuracy of the inspection.

When it comes to your next infrared inspection, beware of the hare. Inspections that are praised more for their swiftness today may be cursed in the future for their costly oversights.

Nearly all portable thermal imagers designed for predictive maintenance utilize storage batteries as a power source. As such, even the best thermographers are limited by the storage capacity of their batteries. When planning a project it is helpful to know how long your batteries should last.

Most batteries sold are rated in Amp Hours, a number used to indicate battery supply capacity. To determine how long a battery will last with your imager, divide the Amp Hour rating of the battery by the current draw (in Amps) of your image. For an imager that draws 2 Amps, a 6 AH battery will last 3 hours.

Depending upon their size, some batteries are rated in milliAmp Hours. To convert this number to Amp Hours, divide the mAH rating by 1000. Example: An 1800 mAH battery equals 1.8 AH

It is important to know that some imagers consume more power during start up. If so, this will shorten the expected run time of a battery from the calculation above. A battery’s storage capacity also decreases with age. If your batteries are providing extremely short run times, it may be time to replace them with new ones.

If you have inactive spots on the LCD screen in your infrared camera's monocular viewfinder, they are probably caused by sun damage.

When working outdoors, sunlight can easily enter an upturned viewfinder eyepiece. When this happens, sunlight can be magnified by the viewfinder optics permanently damaging or destroying your LCD screen.

To prevent such damage, always cover your imagers eyepiece to prevent sunlight from entering the viewfinder. Temporarily placing a cover such as a baby sock over the eyepiece until you are ready to image can help to avoid a ruining an expensive viewfinder.

Submitted by James Henry,
IMC Chemicals

If you are a thermographer who performs infrared inspections of electrical distribution systems, you are not alone and you never should be. Working alone near exposed, energized electrical equipment is not only dangerous, it is a violation of federal law!

Administered by OSHA, the Occupational Safety and Health Standards for General Industry, 29 CFR, Part 1910 apply to most thermographers working within the United States or its territories. Specifically, 1910 Subpart R covers the operation and maintenance of electric power generation, control, transformation, transmission and distribution lines or equipment. Covered facilities include utilities and equivalent industrial establishments.

According to Subpart R, prior to the commencement of work, medical and first aid supplies must be provided for, including persons trained in first aid and CPR when work is on or near exposed lines or equipment energized at greater than 50 volts. Since CPR cannot be self-administered, at least two people trained in first aid and CPR must always be present when working near most exposed energized equipment.

When performing infrared inspections in the future, having a second CPR trained person along will not only satisfy OSHA requirements, it may save your life should an accident occur!

A specification commonly provided for thermal imagers is Instantaneous Field of View or IFOV. Many people mistakenly believe that IFOV values provide meaningful information about a thermal imager’s performance. Unfortunately, this is simply not true.

Originally developed for evaluating the optical performance of thermal imaging systems, IFOV values were intended to allow a user to calculate the minimum target size needed to achieve 50% probability of detection at any given distance. Using IFOV values to evaluate modern thermal imagers and radiometers is unreliable for several reasons:

1. To date, there is no accepted standard for determining IFOV. Consequently, imager manufacturers calculate IFOV values differently, making test results impossible to compare.

2. Because IFOV values are reported for a single pixel, they cannot be used to accurately calculate spot measurement size for imaging radiometers since accurate temperature measurement requires several pixels, not just one.

3. Stated IFOV values are traditionally reported at 50% radiance or less which is unreliable for both temperature measurement and accurate thermal imaging.

When comparing commercial infrared equipment specifications, one should simply ignore IFOV values and concentrate on meaningful specifications instead.

While it is often interesting to use a thermal imager to view ordinary objects, imaging the sun, arc welders and similarly hot objects should be avoided unless your imager has been built specifically for these applications. The reason for this is that the sensitive thermal detector that comprises the heart of any thermal imaging system can be destroyed by imaging very hot objects, even for brief periods of time.

To help avoid a costly detector replacement, only image objects whose temperatures are within the stated operating range of your imager.

Perhaps a sage corollary could be derived from Bruce Springsteen's epic song, Blinded by the Light:

... Mama always told not to image into the sights of the Sun...

A ruined detector assembly is NOT where the fun is.

Almost all handheld thermal imagers come equipped with neckstraps as standard equipment. If you utilize the neckstrap supplied with your imager to support or carry your imager, the following tips can help to avoid costly damage caused by an unexpected drop.

1) Many neckstraps are made of relatively thin material. Retrofit thin neckstraps with sturdier material.

2) Check your neckstrap frequently for wear. Neckstraps frequently become frayed where they attach to camera body eyes or snap hardware.

3) Be certain that your neckstrap ends are permanently sewn so that they cannot be pulled apart or separate accidentally.

4) Check snap swivels for condition. Replace worn or inferior hardware with quality materials.

5) Consider adding a second, redundant neckstrap in case the primary neckstrap fails.

6) Periodically check camera body eyes for wear and mechanical integrity. Over time, attachment points that mate with metal hardware can erode; mechanically fastened hardware on your imager can become loose.

Following the above tips can help prevent accidentally dropping your imager and could save you from a costly repair.

Over the past twenty years, a number of temperature severity guidelines that have been published by various organizations. When using these guidelines, you may compare similar components under similar load to each other OR compare the subject component to ambient. The former of these approaches is recommended since since ambient temperature can swing widely over time. Furthermore, it is often impossible to obtain an accurate ambient temperature for devices located within an enclosure once the enclosure has been opened for the infrared inspection.

One of the most conservative temperature guides can be found in the Maintenance Testing Specifications, published by the National Electrical Testing Association, Morrison, Colorado. According to the NETA MTS, temperature differentials greater than 15° C are categorized as, "Major discrepancy; repair immediately".

Other organizations publish less conservative temperature guidelines than the NETA MTS. Some guides require delta T's of 70°C or higher to qualify as items of immediate concern. When setting temerature limits, one should remember that temperature differentials cannot be utilized to predict time to failure for an electrical device. Therefore, all thermal anomalies detected during an infrared inspection should be investigated and proper corrective measures undertaken as soon as possible.

Capacitors are devices commonly found in AC electrical distribution systems where power factor correction is required. Like any electrical component, capacitors need to be regularly checked for proper operation. Infrared thermography can be used to rapidly inspect capacitors from a safe, remote distance.

Capacitors are wound devices that are electrically connected between potential and ground. Capacitors used for power factor correction are generally encased in painted, rectangular steel canisters and often have two equal sized bushings for electrical connections. In a three phase circuit, there may be several capacitors connected to each phase.

The most common failures of capacitors are loose/deteriorated bushing connections, open circuits due to internal winding failure, and open supply circuits. When inspecting capacitors, be sure to:

1. Visually inspect capacitor bodies. Capacitors should not be misshapen/ swollen.

2. Thermographically inspect capacitor bodies. Capacitors should be warmer than ambient air temperature and exhibit equal temperatures across all phases.

3. Check bushing and wiring connections for hotspots.

Any thermal anomalies detected should be investigated and corrected as soon as possible. Capacitors operating at ambient temperature should be corrected immediately as imbalanced capacitance can be more detrimental than having no capacitors at all.

Everyone who has performed infrared inspections outdoors on sunny days is familiar with the problem of solar reflections. Compensating for solar reflections is usually accomplished by repositioning the thermal imager to change the viewing angle to eliminate the reflection. For objects exposed to strong sunlight, a more insidious problem can occur in the form of solar loading.

The concept of solar loading is familiar to everyone: objects exposed to the Sun will heat up. In general, dark colored objects absorb the most solar energy and heat faster than light colored objects. If an object absorbs enough heat from the Sun, significant thermal anomalies may be hidden and go undetected.

As there is no way to compensate or correct for solar loading, the most prudent course of action is avoidance. Solar loading can be avoided by imaging on cloudy days, at night, or early in the morning. Solar loading can also be overcome by shading an exposed target and waiting for the object’s temperature to return to normal.

Capacitors are devices commonly found in AC electrical distribution systems where power factor correction is required. Like any electrical component, capacitors need to be regularly checked for proper operation. Infrared thermography can be used to rapidly inspect capacitors from a safe, remote distance.

Capacitors are wound devices that are electrically connected between potential and ground. Capacitors used for power factor correction are generally encased in painted, rectangular steel canisters and often have two equal sized bushings for electrical connections. In a three phase circuit, there may be several capacitors connected to each phase.

The most common failures of capacitors are loose/deteriorated bushing connections, open circuits due to internal winding failure, and open supply circuits. When inspecting capacitors, be sure to:

1. Visually inspect capacitor bodies. Capacitors should not be misshapen/ swollen.
2. Thermographically inspect capacitor bodies. Energized capacitors should be warmer than ambient air temperature and exhibit equal temperatures across all phases.
3. Check bushing and wiring connections for hotspots.

Any thermal anomalies detected should be investigated and corrected as soon as possible. Capacitors operating at ambient temperature should be corrected immediately as imbalanced capacitance can be more detrimental than having no capacitors at all..

We’ve all heard the phrase, “A chain is only as strong as its weakest link.” When it comes to thermography, the weakest link is frequently not the test equipment but rather the thermographer.

All too often, many facility managers are led to believe that infrared imagers are fully automatic instruments that require nothing more than “point and shoot” operation. While thermography is a science, it is also an art or craft requiring a skilled human operator for both conducting the inspection and interpreting the data obtained.

In order to achieve maximum effectiveness, thermographers need to have an understanding of infrared theory, heat transfer concepts, equipment capabilities and limitations, and environmental conditions, as well being knowledgeable about the system(s) being inspected.

Whether you are setting up an infrared inspection program or maintaining one, thermographer training should not be overlooked. Obtaining quality training is an investment that can pay huge dividends by maximizing the effectiveness of thermographers and eliminating your weakest link.

Infraspection Institute offers Level I, II, and III training and certification for thermographers worldwide. Our infrared training programs meet the requirements for training of NDT personnel in accordance with the ASNT document, SNT-TC-1A.

With onset of warmer weather, the harshness of winter is but a fading memory for most. Left undetected, the damage caused by winter’s fury is a reality that can lead to premature roof failure. Fortunately, an infrared inspection of your roof can detect evidence of problems before they can get out of hand.

Performed under the proper conditions with the right equipment, an infrared inspection can detect evidence of latent moisture within the roofing system often before leaks become evident in the building.

The best candidates for infrared inspection are flat or low slope roofs where the insulation is located between the roof deck and the membrane and is in direct contact with the underside of the membrane. Applicable constructions are roofs with either smooth or gravel-surfaced, built-up or single-ply membranes. If gravel is present, it should be less than ½” in diameter and less than 1” thick.

For smooth-surfaced roofs, a short wave (2-5.6 µ) imager will provide more accurate results especially if the roof is painted with a reflective coating. All infrared data should be verified by a qualified roofing professional via core sampling or invasive moisture meter readings.

Thermography is a versatile nondestructive test technique that has a wide variety of applications. In short, thermography can be applied to any situation where knowledge of heat patterns and associated temperatures across a surface will provide meaningful data about a system, object, or process.

In thermography, there are two basic approaches to evaluating data. Qualitative thermography or thermal imaging relies on observing thermal patterns and noting any inexplicable differences or anomalies. Quantitative thermography adds non-contact temperature measurements to thermal images.

Many systems produce heat as a byproduct of operation. Such systems include electrical distribution systems, machinery and insulated structures. These systems are generally inspected during normal operation once line-of-sight access is obtained.

Thermography can also be applied to systems that do not produce heat as a byproduct of operations by actively heating and/or cooling the target and observing the resulting images. Systems that are candidates for active thermography include building facades, low slope roofing systems, storage tanks and composite materials.

When heated or cooled properly, thermal patterns caused by changes in the thermal conductivity or capacitance of the subject system can provide evidence of internal structures, water infiltration, or contaminants. The use of active thermography is growing, especially for inspection of composite materials used in the aircraft, aerospace, and marine industries.

One of the most frequently asked questions in thermography is, “How close do I need to be to my target?” The answer depends upon target size and the type of data that are desired.

Appropriate distance is largely dependent upon three factors: target size, IR equipment optics, and detector resolution.

With qualitative thermal imaging, the maximum viewing distance is achieved where the object and any possible anomalies can be clearly resolved. If a target cannot be clearly distinguished, it will be necessary to move closer or to use a telephoto optic.

When using an imaging radiometer, obtaining accurate temperatures will require substantially shorter distances than those required for thermal imaging. Obtaining accurate quantitative data requires that the radiometer’s spot measurement size is smaller than the area being measured. If it is determined that the radiometer’s spot size is larger than the area being measured, it will be necessary to move closer or use a telephoto optic calibrated for the imager.

Because there is no method for correcting for errors caused by imaging at excessive distances from a target, it is imperative to always ensure appropriate distance prior to recording images.

Many facilities undergo regularly scheduled shutdowns for preventive maintenance. Performed prior to shutdowns, infrared inspections can help to point out potential problems in electrical and mechanical systems and allow for more effective use of resources during a shutdown.

When planning a scheduled outage, it is a good practice to schedule infrared inspections four to six weeks prior to the outage. Doing so can uncover hidden problems and allow for scheduling of additional requisite manpower and/or obtaining replacement parts prior to the shutdown. Infrared inspections can also save money by helping to direct maintenance efforts where they will be most needed during the planned outage.

Pre-outage infrared inspections should be performed with subject equipment energized and operating under normal load. Inspections should be performed by trained and certified thermographers who are familiar with the equipment being inspected.

A follow-up infrared inspection of all repaired/retrofitted equipment should be performed within 48 hours of repair or installation to confirm that repairs were effective.

For more information on training and certification, or to obtain a copy of the Guideline for Infrared Inspection of Electrical and Mechanical Systems, please contact Infraspection Institute at 609-239-4788 or visit us online at www.infraspection.com.

When performing an infrared inspection, obtaining quality data relies on the use of proper equipment, thermographer training and knowledge of the system being inspected. It is imperative that a thermographer be familiar with the construction and operation of the object(s) to be imaged before the inspection begins.

Prior to performing an infrared inspection of an object for the first time, a thermographer should:

1. Become familiar with system construction by reviewing appropriate drawings or blueprints noting insulation materials located on, or within, the subject system and how they might impact findings.

2. Discuss with the end user the reason(s) for conducting the infrared inspection.

3. Review any previous inspection reports and operational data to determine history of the subject system including past problems.

4. Ascertain that the system is under normal operating conditions and how its operation is likely to affect thermal signatures.

5. Ensure that line-of-sight access is available and that environmental conditions and infrared equipment are appropriate for collecting accurate data.

6. Determine if a similar system is available for reference purposes.

Following the above can vastly improve the quality of collected data and help to reduce errors in reporting. As always, remember to work safely.

With most thermal imagers capable of displaying images in monochrome or multicolor, many new thermographers ask which color palette is the best choice for effective imaging. The answer will depend on a number of factors including application, delta T associated with the exception, and personal preference.

Because it is usually less confusing than multi color palettes, grayscale may be better suited for some applications. Additionally, applications that have a large delta T associated with exceptions or where target recognition is important may be better suited for grayscale imaging. Such applications include electrical distribution systems, building envelopes inspected from the interior of the structure, and low slope roof inspections.

Multicolor palettes offer an advantage when imaging targets having a small delta associated with exceptions or when imaging targets with several discrete temperature zones. Typical applications include mechanical systems, refractory systems, building envelopes inspected from the exterior, and medical/veterinary applications.

For hardcopy reports, printing monochrome images can result in lower cost than multicolor reports. Lastly, the choice to use monochrome or multicolor is largely a matter of personal preference. Thermographers should always use a palette which best represents the observed thermal patterns and provides data that are easily understood.

With tremendous emphasis placed upon the sophistication of today’s modern thermal imagers, it’s easy to forget the basics of thermal imaging. Regardless of imager age or sophistication, there are several basic concepts that can vastly increase the accuracy and success of an infrared inspection.

1. Select the proper spectral response imager for the application.

2. A clear line of sight to the target is required with no obstruction of the imager lens.

3. Imager optics must be clean and calibrated to the imager being used.

4. Target should be dry and at a stable temperature.

5. Imager focus is imperative to accurate diagnosis and temperature measurement. Be sure to focus imager and the viewfinder as well.

6. Knowing the construction, operation and characteristics of the system being inspected is vitally important to anticipating thermal patterns and performance.

7. Adverse atmospheric conditions such as wind, humidity, or solar reflection and solar loading should be avoided.

8. For electrical and mechanical equipment, the systems must be energized and under load; for structural inspections, a delta T of 10 C (18 F) is desired.

9. Discriminating small temperature differentials across targets with low emittance values can prove quite difficult.

10. Whenever safely possible, cross reference observed infrared temperature values with accurate contact temperature readings.

When performing any infrared inspection, be certain to take all necessary safety precautions and always work safely..

With the advent of digital storage media, nearly every modern thermal imager is capable of storing images electronically. For thermal imagers that do not have image storage capability, there are inexpensive and readily available solutions.

For thermal imagers having a video output jack there are two options for image storage. The first option utilizes a VCR to record desired imagery. Videotape allows for recording of moving objects and/or dynamic processes. Videotape is inexpensive, readily available, and special equipment is not required for playback. Still images can be captured from videotape using a video capture board available for most personal computers.

The second option utilizes a digital recorder that accepts a standard video input. With a digital recorder, single frames of data may be captured to digital media such as PC cards. Camcorders having a digital snapshot camera feature may provide the best solution of all. Several currently available models allow a thermographer to record to videotape and/or to capture still images from the video input. Additionally, the daylight snapshot feature of the camera may be used to capture high quality daylight images.

Once images have been recorded, they can be directly imported into a PC for storage or incorporation into written reports