FEATURE SENSORS & SENSING SYSTEMS


SENSING A NEED for Coronavirus


infection checking I


t is well know that one of the most obvious signs of infection is a raised


body temperature. Being able to detect this quickly will not only protect others but could also warn the individual, who may not know that have been infected. Of course there are many simple ways to measure human body temperature but a preferred solution is to capture the information quickly and automatically, transparently to the individual being checked, and without contact.


NON-CONTACT SENSING Accurate non-contact thermal infrared temperature sensors could provide a way forward. Such sensors bring the advantages of continuous non-contact temperature measurement to a variety of applications, particularly accurate occupancy and proximity sensing – which has traditionally been carried out using pyroelectric or passive infrared (PIR) sensors. Both types of sensors are capable of


detecting the slightest temperature change in the field of view. However, whereas PIR sensors respond to temperature changes, effectively detecting the movement of a body or other warm object that contrasts with the cooler background, Omron’s D6T sensors monitor temperature continuously and so can detect a stationary presence. As an example, the D6T sensors,


which are optimised for body- temperature monitoring, can be added to an access-control system in order to automatically check the temperature of a visitor on arrival. They feature a silicon lens and MEMS thermopile to detect far-infrared radiation emitted from the surface of the face or body. A signal-processing ASIC integrated in the same package converts the sensor output to a digital temperature reading and ensures a high signal to noise ratio (SNR). The result is a compact device


26 SEPTEMBER 2020 | DESIGN SOLUTIONS


that is well suited to embedded applications and relieves key signal- processing workloads from the system host processor.


TAKING BODY TEMPERATURE MEASUREMENTS The typical accuracy of D6T sensors, as supplied, is ±1.5˚C. To use these devices in a precision body temperature monitoring context, such as coronavirus infection checking, additional custom calibration is recommended for increased accuracy. An effective way to calibrate the


sensor is to start by setting both the upper target temp (y0) and the lower target temp (y1) to cover a suitable range. For an access-control system, designed to assess the surface temperature of a human face, a typical range could be from about 32˚C to 38˚C. To calculate a correction factor and


thus ensure accurate temperature measurement with D6T sensors, a calibration source such as a blackbody furnace can be used. The source is set first to the lower limit temperature (let’s call it y0) and measured with the D6T. We recommend recording, for instance,


ten measurements to get an average sensor output reading (x0), making sure first to allow about 15 minutes for the system to stabilise after powering on. The source is then set to the upper maximum temperature (y1), and the average of a second set of sensor readings (x1) taken in the same way as before. Using the reference source


settings and recorded temperature measurements, the calibrated target object temperature, y, for any given sensor output reading, x, can be calculated using this formula:


With the COVID-19


pandemic at the forefront of people’s minds, David Pearson, technical director


at Anglia Components, looks into why non-contact


temperature sensing is such an important technology


Being able to quickly detect raised body temperatures could protect others while warning the individual who may not realise they have been infected


Thanks to the integrated signal-


processing ASIC, D6T sensors output the digital temperature value via an I2


C


interface that the host system can read directly. The sensor comes mounted on a PCB with terminations provided, allowing easy electrical connection.


ACCESS CONTROL AND MORE Anglia can supply the full range of Omron D6T sensors – from single-pixel to 32x32 resolution – to address the gamut of non-contact temperature- sensing applications. This could now include COVID-health monitoring as well as traditional uses. Samples and evaluation tools are


available free of charge to registered account customers within EZYsample.


Anglia Components www.anglia-live.com


/ DESIGNSOLUTIONS


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