Selecting, Specifying, and Purchasing Infrared Imagers

The right imager is a necessity for a successful infrared inspection program.

Buying a thermal imager can be a daunting task for seasoned thermographers. It can be especially difficult for less experienced users. Knowing how to correctly specify and choose proper test equipment can help avoid a costly purchasing mistake.

As infrared thermography gains wider acceptance, its use is increasing. With the availability of lower cost microbolometer imagers, thermographers have more choices than ever before.

Procuring an imager is a challenge for many reasons: the initial purchase price can run up to tens of thousands of dollars, no imager is capable of performing all imaging applications, imager performance varies widely, performance specifications are not always available or comparable, and making an incorrect purchase can be costly.

Before purchasing an imager, assess present and future needs, obtain and compare manufacturer specifications, and take time to thoroughly evaluate the imager where it will be used. This step-by-step approach is designed as a guide to the purchase process from initial consideration to final decision. In general, the most important considerations are listed first.

Determine appropriate spectral response

Prior to selecting an imager, determine the application(s) for the imager. Whenever possible, consideration also should be given to potential future applications.

One of the most important performance criteria for infrared equipment is spectral response. Manufacturers generally select one of two infrared wavebands in which equipment will operate. Imagers that operate in the near infrared (shortwave) have spectral responses of 2-5.6 microns. Imagers that operate in the far infrared (longwave) have spectral responses of 8-14 microns.

Spectral response is a permanent characteristic of the equipment and cannot be changed. Selecting equipment with proper spectral response is important because many applications are wavelength specific. Choosing equipment with an incorrect spectral response may result in inaccurate data. Table 1 shows recommended spectral responses for preventive and predictive maintenance applications.

Evaluate objective specifications

Objective specifications describe performance characteristics for a specific imager model. These specifications are not changeable and will, in many cases, determine whether an imager can be used to accomplish an inspection successfully. Objective specifications are usually available from the manufacturer’s product data sheets.

To best compare the objective specifications among thermal imagers, refer to the manufacturer’s published data for the imager and develop a spreadsheet noting as many specification values as possible. When completed, the spreadsheet will allow relevant comparisons among the imagers. Some of the most important objective specifications are listed in Table 2. Other relevant objective specifications may be added.

Determine performance specifications

Performance specifications refer to how an imager operates in the field as well as the history of the model line. Historical information is usually available from the manufacturer; performance history is best obtained from references provided by those who already own equipment. The manufacturer’s representative should be willing to provide the names of users who may be contacted for equipment reference. Some of the performance criteria to be considered include:

• Length of time the imager has been in production. It may be wise to delay purchasing a recently introduced model until after it has proven to be reliable in similar installations.

• References from actual users of the subject imager.

• Opportunity to try a loaner unit or rent the imager before purchase. Manufacturers may credit short-term rental fees toward the purchase price. Be certain to thoroughly try the imager under the exact conditions that will be encountered in the job.

• Software options available for the camera. Be certain that selected software is capable of performing the desired analysis.

Check service and warranty information

In general, service and parts, including calibration procedures, can be obtained only from the equipment manufacturer. So the success of an infrared program can be greatly affected by the ability of a manufacturer to service and support the infrared equipment because service is not available from third parties. Prior to purchase, consider the following:

• Manufacturer’s experience in building and servicing infrared equipment and capability to provide future service

• Recommended service or calibration frequency and anticipated costs

• Expected delivery time for any required repairs

• Length of warranty and covered parts

• Location of equipment service centers

• Loaner/rental availability during repair periods

Evaluate for subjective characteristics

Subjective characteristics include how the imager feels to the operator. Comfort will be important because considerable time may be spent with the chosen imager. When evaluating an imager, consider the following:

• Are imager controls easy to use and understand?

• Is the equipment designed to be rugged and durable?

• Is the imager ergonomically comfortable?

• Will the size or weight of the imager present problems for long-term usage?

• Is the imager display clear and free of noise and distortion? Although this is one of the most important considerations when selecting an imager, there is no methodology for assigning an objective value to image quality.

• Is the imager display adequate and compatible with operator’s safety glasses or other personal protective equipment such as hard hats, face shields, hoods, respirators, etc.?

• Is the imager display viewable in direct sunlight?

Equipment cost

From a performance standpoint, cost should be the least of the considerations when purchasing equipment. Equipment that cannot accomplish a task is no bargain at any price. For many infrared cameras, cost is negotiable as are items such as extended warranty and service contracts. For a comprehensive list of equipment manufacturers, visit www.irinfo.org.

Once the final selection has been made, be sure to get quality certification training for the thermographers. For new users, training should include infrared theory and heat transfer concepts, equipment operation, image capture and analysis, standards compliance, application-specific inspection techniques, documentation of findings, and temperature measurement techniques. MT


This e-mail address is being protected from spambots. You need JavaScript enabled to view it is the director of the Infraspection Institute, 425 Ellis St., Burlington, NJ 08016; (609) 239-4788

Table 1. General Recommended Spectral Responses For Preventive and Predictive Maintenance

Application

2-5 microns

8-14 microns

Indoor electrical systems

X

X

Outdoor electrical systems

 

X

High-temperature targets

X

 

Highly reflective targets

X

 

Boiler/heater tubesgas fired

X

 

Boiler/heater tubescoal fired

 

X

Long-distance imaging

 

X

Smooth-surfaced roofs

X

 

Gravel-surfaced roofs

X

X

Glass

X

 

Plastics

X

 

 

 

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Table 2. Comparison Of Objective Specifications

 

Imager 1

Imager 2

Imager 3

Environment

 

Operating temp. limits

 

Imaging

 

Spectral response

 

Visual field of view

 

Detector type

 

Detector size

 

Cooling type

 

Focus

 

Min. focus distance

 

Imager frame rate

 

Visual camera

 

Image display

 

Display type

 

Color palettes

 

Measurement

 

Measurement range

 

Thermal sensitivity

 

Emissivity correction

 

Spot measurement size1

 

Temp. measurement tools

 

Reflected temp. comp.

 

Accuracy

 

Data storage

 

Storage media

 

File format

 

Images stored

 

Voice recording

 

Power source

 

External power

 

Battery type/run time

 

Optical accessories

 

Lens options

 

Filter options

 

Data interface

 

Video format

 

Video output

 

Physical

 

Dimensions

 

Weight with battery

1 For information on determining spot measurement size, refer to the Guideline for Measuring Distance/Target Size Values for Quantitative Thermal Imaging Cameras, available from Infraspection Institute, Burlington, NJ.

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