How to get the most from your infrared camera investment

Infrared (IR) thermography is a fundamental asset in today’s predictive maintenance (PdM) and condition monitoring programs.

By Plant Engineering Staff September 30, 2003

By Leonard A. Phillips, FLIR Systems, North Billerica, MA

Infrared (IR) thermography is a fundamental asset in today’s predictive maintenance (PdM) and condition monitoring programs. How can you ensure that the IR camera system you buy will meet your current and future needs and yield maximum return on investment? Purchasing the right infrared camera can yield a total payback in a single incident.

However, purchasing on price alone can be a waste of time and money, or worse — it can compromise your plant’s reliability or safety.

Choosing the right infrared camera for your application requires understanding the full range of target variables, which include size, distance, infrared characteristics, and environmental factors. It also requires understanding these target parameters in terms of camera sensitivity, resolution, and overall accuracy.

Why measure temperature?

The temperatures and changing temperatures over time of electrical and mechanical targets in your plant serve as the basis for your condition status reports and for actions that you recommend. This could mean anything from no problems noted to tightening a fuse or shutting the factory down to avoid a potential fire or explosion. Your name is on your reports. The credibility of your PdM program, and sometimes the safety of your facility, depends on the accuracy of the data behind your recommendations.

How much accuracy do you need? How much can you afford?

An IR camera must deliver accurate temperature measurements over a wide range of ambient conditions. If a voltmeter gave incorrect answers in hotter or colder parts of your facility, you would throw it away.

Likewise, if an infrared camera produces temperature measurements that vary with ambient temperature, or cannot measure some of the more challenging targets in your facility, it is not a good value at any price.

Measurement resolution is extremely critical to accuracy and can be described as the smallest target spot size whose temperature can be reliably and accurately measured by the camera. The farther the operator moves away from a target, the smaller the target appears and the more challenging it is to accurately measure.

Taken a step further, measurement resolution is the ability of the camera to accurately measure the temperature of a certain diameter target spot at a particular distance. The ratio of the maximum distance at which a camera can accurately resolve and measure a minimum spot size to the spot size itself is called the camera’s maximum distance-to-spot size ratio or simply spot-size ratio. Cameras that have interchangeable lenses can change their spot size ratio by changing camera optics. That’s why PdM applications in most facilities require lens interchangeability.

The camera optics project the image in their field of view onto the focal plane array (FPA) detector. The FPA detector converts the projected image into an electrical signal, which is interpreted by the camera’s scanning and processing electronics as a thermographic image. In practical terms, the bigger the projected image of a target of interest is, the more accurately it can be measured. As a result, a telescopic lens is required to magnify distant objects and a wide-angle lens is needed to focus on nearby objects or to survey large areas quickly.

If the same camera must be used to inspect an electrical connection on a utility pole 40 ft away and a section of 16-gauge wire in close quarters that require the camera to be only 18 in. away, different lenses are required to accommodate both targets. That’s why lens interchangeability is a must-have capability.

Try before you buy

Camera specifications are generated under laboratory conditions. To confirm that a camera system performance meets your needs, insist on a demonstration at your facility and on typical targets — and ideally in the hands of your own thermographer. Use the camera on targets that truly test its performance. Test it on small, distant targets as well as on hot and cold targets. Use it in hot and cold areas to be sure it can deliver accurate measurements under different ambient conditions. Your reputation and the health and safety of your facility depend on your decision.

Description of lenses

The following images of a utility disconnect were taken from the same position and camera. Each image was produced using a different lens as indicated:

7 deg field of view — extreme telescopic with minimum working distance of 19.69 ft

12 deg field of view — telescopic with minimum working distance of 6.56 ft

24 deg field of view — standard with minimum working distance of 1.64 ft

45 deg field of view — wide angle with minimum working distance of 0.66 ft

80 deg field of view — very wide angle lens with minimum working distance of 0.66 ft

Note: All lenses can focus on targets from the minimum working distance to infinity.

Be sure to choose a camera system that can focus and resolve targets at your actual working distances. Compare the minimum working distances and the relative magnification of the target taken by the different lenses.

To accommodate small nearby objects as well as similar objects at much greater distances, a camera system that includes interchangeable lenses is a must.