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Using an Isotherm Feature

The more things change, the more they remain the same. This timeless observation is especially true when referring to the isotherm feature found on today’s modern thermal imagers.

The isotherm feature found on modern thermal imagers is somewhat of a relic having been around for over 25 years. In simple terms, an isotherm feature allows a thermographer to visually highlight areas exhibiting a similar apparent temperature on the imager’s monitor screen.

Originally designed for the monochrome imagers of the 1970’s, an isotherm is a user-definable, high-contrast overlay generated by an imager’s on-board computer or within image processing software. Prior to the advent of imagers with multi-color displays, the isotherm feature was a necessity for defining areas exhibiting similar temperatures. For other imagers, it was a requisite part of measuring temperature.

With modern thermal imagers capable of providing multi-color imagery and direct temperature measurement, it would seem that the isotherm is a feature due for extinction. There are, however, several instances where an isotherm may still be useful. Among these are:

• The ability to define areas operating within a defined temperature range
• A preset temperature alarm that automatically appears when an object exceeds user-defined temperature limits
• A highlight color that defines hot/cold areas on monochrome images

One should be aware that accurate use of an isotherm is dependent upon proper use of the imager. When using an isotherm, one should practice proper measurement techniques giving particular consideration to viewing angle, spot measurement size and emissivity settings.

Infrared equipment selection and operation are two of the many topics covered in all Level I Infraspection Institute Certified Infrared Thermographer® training courses. Level I training is available at several locations each month and through our Distance Learning Program. For information on thermographer training including course locations and dates, visit us online at www.infraspection.com or call us at 609-239-4788.