Non-contact temperature measurement specialist Land Instruments International is seeking a patent for a technique that ensures the continuous accuracy of its FTI Mv radiometric thermal imager when used for medical purposes.
Applications for thermal imaging are to be found in almost every medical and research field where body temperature is an issue, from chiropractic clinical evaluations and diagnosis of conditions such as Reynaud’s Syndrome to studies of wound healing and blood flow through transplanted tissue.
In all cases the uncertainty and repeatability of the temperature information required depends on calibration data such as sensitivity and ambient drift for the imager’s 19,200 pixel focal plane detector array (160 x 120), all of which update at frame rates of 25 per second and greater.
These data can compromise the calibration of traditional imagers, causing other manufacturers to limit claims for the temperature measurement accuracy of their product to +/-2% or 2°C. For the user, it also means that the imager must be returned to the manufacturer so that the calibration can be verified at regular intervals.
Land says its answer to this shortcoming is to combine the FTI Mv’s infrared detector array with two high-stability, P100i blackbody temperature reference sources, so that the imager can be calibrated continuously, on-line to provide reliable temperature measurement at any point in the scene being viewed. Accuracy is said to be improved to +0.5°C, with repeatable temperature measurements down to +0.2°C, both traceable to the ITS-90 National Standard.
This thermographic calibration method is said to have a number of other advantages. It eliminates ‘cold junction’ effects caused by variations in the detector temperature relative to the target; lenses and windows can be exchanged without transmission variations; any losses caused by the length and type of cable used are eliminated; and calibration of the image input card in the PC does not drift with temperature and time.
It is also possible to keep the imager in use when re-calibration is required, by verifying the calibration of the system using a platinum resistance thermometer, which can be returned to the laboratory without loss of direct traceability to ITS-90.