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New non-contact IR sensors detect occupancy without movement
Room occupancy detectors that switch off or turn down the heating and lighting in a room when it is not in use can have a huge impact on the operating costs of buildings and are becoming increasingly popular. They suffer from one major drawback however.
Most existing pyroelectric sensors detect motion, and if the occupants of a room sit still they may find that the lights are switched off. This issue is encountered in most offices and homes, but is a particular challenge in hospitals, as patients are by certain definition, immobile.
Omron’s MEMS occupancy sensor
A new non-contact MEMS sensor launched by Omron Electronic Components addresses this issue fully. By monitoring the heat that the occupants emit rather than their movement, it can reliably detect the presence of humans in an area.
The ultra-sensitive sensor is an outstanding alternative to pyroelectric sensors or PIR detectors in home automation, building automation, healthcare, security and industrial applications. It is so sensitive that, if required, it can even detect where in a room the occupants are – valuable not only for security applications but also for hospitals, as it allows staff to tell if a patient has left his or her bed without the need for an intrusive video camera.
The new Omron D6T is based on an exceptionally sensitive infrared temperature sensor that makes full use of the company’s proprietary MEMS sensing technology. Most human presence sensors rely on movement, but this device is able to detect occupancy by sensing body heat and provides a more reliable basis for switching off lighting, air conditioning and other services when the space is empty.
As these sensors are able to monitor the temperature of a room, they can also be used to control the level of heating and air conditioning systems and maintain optimal room temperature levels without wasting energy.
Unusual changes in temperature can also be used in other ways, for example to detect line stoppages, identify hot spots before a fire breaks out or in clinical applications to check whether a patient has left the bed.
Area temperature measurement
MEMS sensors like Omron’s new D6T measure temperature across the whole field of view, contrasting with conventional thermal sensors, which are restricted to measurements at a single point. Configured as an array (1×8 and 4×4 arrays are currently available), the sensor can assign temperature information to a specific cell, adding a positional dimension to its presence and temperature data.
The result is higher accuracy, lower crosstalk and a wider field of view. Using multiple sensors in a room multiplies these benefits: a quad 4×4 array sensor module can be used to obtain higher resolution or broader coverage, for example identifying a person’s location within 1m across a 16m2 area.
The technology behind these new thermal sensors combines a MEMS micro-mirror structure for efficient IR radiation detection with a high- performance silicon lens to focus the infrared rays onto its thermopiles. Proprietary application-specific integrated circuits then make the necessary computations and convert sensor signals into digital I2C outputs.
All components were developed in-house and are fabricated in the company’s own MEMS facilities. The result is high ±1.50C accuracy with excellent noise immunity (measured as noise equivalent temperature difference) of less than 0.14 0C.
With the cutting edge MEMS technology that is utilised in these sensors, the company is aiming to contribute towards creating new advanced energy-saving household appliances as well as home and building energy management systems and a wide variety of factory automation applications. For more product details please visit:
