Optical EngineeringEquivalent temperature differences with respect to ambient temperature difference as a function of background temperature
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The performance evaluation of a thermal imager includes the comparison of a measurement to some specified temperature differential. It is uncommon to find a specification that is a function of absolute temperature. Since detectors respond to differential power, equivalent temperatures are presented with respect to an ambient (25°C background) differential temperature as a function of background temperature. The changes in the equivalent temperature difference are shown to be significant in both the near and far infrared regions ofthe spectrum. A simple curve is obtained to estimate the equivalent temperature difference for the far infrared region. The curve shape of the near infrared region varies too significantly to obtain any simple and accurate curve fit. The current thermal imager test methods should be reevaluated and specified in terms of background temperature.