Target Tips for Thermographers

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.

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

2. 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.

3. Discuss the reason(s) for conducting the infrared inspection with the system end user (or client).

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

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

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

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.

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

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.