Non-Contact Human Temperature Measurement
Body temperature measurement has advanced over the years with the developments in thermometer technologies, resulting in improved measurement accuracy and better tools for monitoring. Thanks to advancements in sensor development, it is now possible to measure the surface temperature of the objects even without any physical contact. This non-contact temperature measurement technique is widely popular in factory floors to scan objects for elevated temperatures. However, these technologies are also useful in research, medical applications, and group temperature screening.
Public officials and healthcare providers are already relying on these tools to fight the ongoing COVID-19/Coronavirus pandemic. These non-contact thermometers are helping them in screening people in public places for high temperatures that may have resulted due to virus infection and isolate them to prevent spreading the disease.
However, it is essential to note that non-contact medical thermometers are different than their industrial counterparts. Also, similar to other measurement tools, these devices can generate inaccurate readings too. Fortunately, there are ways through which you can reduce measurement errors and ensure better accuracy.
But before we discuss the factors to consider for measurement accuracy, let's get a better understanding of the major types of thermometers available in the market and find out the purpose of each.
Types of Thermometers
There are two fundamental types of thermometers for temperature measurement – clinical contact thermometers and non-contact thermometers.
Clinical contact or medical thermometers
These are the most commonly used temperature measurement devices that can produce accurate results within 30 seconds. Medical thermometers use mercury or are either digital. Mercury thermometers are more or less obsolete since mercury is toxic and can lead to death in case the thermometer glass breaks.
A digital thermometer is more prevalent today, and it is comprised of a temperature sensor and electronic components to display temperature in a numerical value. In most cases, measurement is carried out by placing the thermometer's temperature sensing tip inside the mouth, rectum, or armpit.
There are even temporal artery thermometers, also known as forehead thermometers that measure the temperature of your forehead's temporal artery using an infrared scanner. These devices offer accurate measurements quickly and are appropriate for infants and children. Similarly, tympanic or digital ear thermometers use infrared sensors to measure the temperature of thermal radiation from the ear canal.
As discussed earlier, non-contact thermometers differ when it comes to medical and industrial applications. However, the principle of working remains the same, which is infrared sensing. All objects with mass emit some amount of energy in the form of heat. An infrared (IR) thermometer detects the infrared radiations emanating from the object as well as the surroundings and determines the surface temperature of the object.
These temperature measurement devices are typically available in the form of body IR thermometers, industrial IR thermometers, and thermal imaging cameras.
Body Infrared (IR) Thermometer
A body IR thermometer enables accurate non-contact temperature measurement and is suitable for medical use, such as screening human surface temperature. The device reads the temperature in less than a second with accuracy, usually between ±0.4°C (± 0.7°F), or ± 0.3°C (0.5°F). However, for accurate results, the device must be as close as possible to the body surface.
Besides, body temperature measurements are accurate if taken in ambient conditions. These devices often include features such as setting minimum and maximum thresholds, color-changing display, and audible alarms. Body IR thermometers usually cost about $75 to $125 apiece.
Industrial Infrared (IR) Thermometer
The purpose of an industrial IR thermometer is to measure surface temperatures of industrial applications. As such, these devices have an extensive temperature range, typically from -50°C to over 1000°C. The wide measurement range also means that there is a slight trade-off in measurement accuracy. These thermometers have an error factor in the range of ±2°C (4°F) or ± 2% of reading. However, this range is more than satisfactory for most industrial applications.
Compared to medical IR thermometers that require close measurement distance, these devices are dependent on the field of view. For example, a 60:1 field of view means you can keep a distance of 60 inches from the object and measure the temperature of a 1-inch spot. You'll get an Industrial IR thermometer for around $150. However, note that this device is not suitable for body temperature measurement.
Thermal Imaging Camera
A thermal imaging camera is a sophisticated device capable of providing accurate temperature measurements with an error factor usually within ±0.5°C (±0.8°F). The device comes with zooming capabilities and can also include built-in analysis software.
Thermal imagers also have an extensive temperature range that varies from -20°C up to 650°C. These devices are also suitable when it comes to scanning individuals or groups of people. But, compared to other temperature measurement devices, thermal imaging cameras are more costly. While a low-resolution camera costs about $150, a high-end device can go up to $20,000.
Thermal imaging cameras from OMEGA are available in the $4000-$5000 range and are suitable for most industrial applications as well as human temperature measurement.
Non-contact Screening Vs. Clinical Diagnostics
It is crucial to understand that surface temperature measurement through IR thermometers is simply a method to screen an individual or group. It is not a substitute for the accuracy and reliability of a clinical diagnosis since the surface temperature is more susceptible to changes in the surroundings.
Non-contact screening, however, is useful in cases where there is a need to maintain distance from the person to prevent possible infection, as in the case of COVID-19. As such, non-contact thermometers can serve as a first step towards isolating possible individuals with a fever and carry out a clinical diagnosis for confirmation.
Key Considerations for Human Temperature Screening
Although modern thermometers have become more accurate, these devices can also generate false positives if you take the measurements in unfavorable conditions.
Take body temperature measurements in an ambient temperature environment for better accuracy. Similarly, a sudden draft of cold or hot air can give misleading results.
For non-contact body temperature measurements using forehead thermometers, make sure that there is no obstruction between the device and the body as well as the distance between the two is as close as possible.
If you are bringing the device to a warmer or cooler location, make sure to allow the device at least 20 minutes to adjust to the temperature of its surroundings. Remember that IR thermometers cannot see through a glass, liquids, and transparent surfaces.