Efficient Plant June 2018 - 35

infrared inspections

Target Tips for
Thermographers

Jim Seffrin
Infraspection Institute

OBTAINING QUALITY DATA during an infrared (IR) inspection
hinges on the use of proper equipment, thermographer training, and
knowledge of the inspected system. Thus, it's imperative for thermographers to familiarize themselves with the construction and operation of
the object(s) to be imaged before inspections begin.
Prior to performing an IR 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
affect findings.
2. Discuss the reason(s) for conducting the infrared inspection
with the system end user (or client).
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 environmental conditions and infrared equipment are appropriate for
collecting accurate data.
6. Determine if a similar system is available for reference
purposes.
These pre-inspection practices can vastly improve the quality of collected data and help reduce errors. As always, work safely.

Jim Seffrin, a practicing thermographer with more than 30 years of experience
in the field, was appointed to the position of Director of Infraspection Institute in
2000. This article is based on two of his "Tip of the Week" posts on IRINFO.
org. For information on various workplace topics and infrared-related issues, as
well as upcoming training and certification opportunities, email
jim@infraspection.com or visit infraspection.com.

JUNE 2018

Get to know your target and how close to position yourself from it before beginning an inspection.

WHAT'S THE APPROPRIATE DISTANCE?
Among thermographers, one of the most frequently asked questions
is, "How close do I need to be to my target?" Answer: "It depends."
Determining the appropriate distance basically involves three factors:
target size, IR-equipment optics, and detector resolution.
With qualitative thermal imaging, the maximum viewing distance is
achieved when the object and any possible anomalies can be clearly
resolved. If a target can't be clearly distinguished, it will be necessary
to move closer or use a telephoto optic.
When using an imaging radiometer, obtaining accurate temperatures
will require substantially shorter distances than those for thermal imaging. Obtaining accurate quantitative data requires the radiometer's
spot-measurement size to be 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.
Since there's no means of correcting for errors caused by imaging
too far away from a target, it's crucial to always ensure appropriate
distance prior to recording images. EP
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Table of Contents for the Digital Edition of Efficient Plant June 2018