When measuring the temperature of a person with a thermal camera, apart from temperature reading indication, the operator also gets a colour pattern picture, clearly showing the relativity of the different temperatures in the frame. It is therefore easier to identify people who have fever with a thermal camera than identifying those who have a relatively high facial temperature compared to others in a group.
Traditional temperature measurement involves an instrument that makes contact with the surfaceto be measured. This is not ideal for use in mass screening as these thermometers are relatively slow and require sterilisation between uses to safeguard against cross contamination.
Non-contact thermometers measure surface temperature. If the temperature of the human body is 37 degrees Celsius, the face, which is exposed to the atmosphere that removes heat from the face, will naturally show a reading below 37℃. This difference in temperature is often factored into the results of infrared thermometers that are specifically for fever detection. Even then, results cannot be recklessly taken at face value, as there are other factors influencing skin temperature differently from person to person. Variations in skin colour equals minor variations in emissivity, which will in effect result in different readings. Equally, make-up on a person’s face would make a difference in emissivity, and even at the same temperature of the body, the temperature of the face measured by the device would be different. For those with more perspiration on the face than others, the temperature measured by the device will appear relatively lower, as the evaporation of perspiration will cause the skin to cool down. Because of the factors that influence skin temperature, the measured value should not be considered an absolute temperature value, but should be recognised as a relative temperature value for the purpose of detecting a person with fever.
After selecting a person whose face temperature is relatively higher with a thermal camera, the temperature of the identified person should be confirmed by using an ear thermometer to determine whether the person has a fever or not.
R&C Instrumentation has introduced the CG320 Thermal Imaging Camera originally designed for military use; it now also has a model for fever detection. The device has an alarm output that can be connected to a warning sound or lamp and comes standard with data processing software. Find more information on www.randci.co.za