Theory behind EBT
Experts have confirmed that there is a correlation between the eye canthus temperature (tear duct area) and core temperature. The tear duct is a small area and you need to put enough pixels on it to make a good measurement. The lower resolution cameras with fixed focus aren’t optimized for this task. Even with the recommended cameras, you’ll find that maximum reported temperature is a function of distance so you will want to set your alarm limits and do your screening at a fixed distance. Higher resolution will give you better stand-off distance and ability to detect smaller features. A 320×240 pixel camera can safely accomplish the mission.
How can a thermal camera be used for EBT detection if the accuracy is only specified as ±2 °C?
Most of our thermography cameras have the same accuracy specification. This value refers to the absolute accuracy of the camera when measuring temperature. When using the cameras for EBT detection, the absolute temperature is not important and we care more about the relative temperature instead. When measuring the relative temperature between two data points, the inaccuracies can be accounted for.
Consider the screening mode that some of our cameras offer. This mode requires you to take a reference temperature of a healthy person’s face first. Then, the screening mode will alarm if an individual’s face temperature is more than 2 °C above the reference temperature. In this sense, the camera is only measuring a temperature difference which will negate any inaccuracies in the final reading. It is recommended to update the reference temperature every 15 min in order to have the best results.
What object parameters should I use?
The emissivity of human skin is typically taken to be 0.98. It is good to set other parameters accordingly. When using a camera for EBT detection, the distance is usually very small so the atmospheric parameters can be ignored.