Faucet Sensing Technologies:Active Infrared Sensing
Electronic, sensor-activated faucets seem like a technological miracle: Place your hand under the spout, and water starts flowing...like magic. But their inner workings rely on technologies that have been around for decades, cleverly adapted to a faucet spout. Improved sanitation is the most obvious benefit of touch-free fittings. Because these faucets have no handles, there is no means of spreading dirt or harmful bacteria from one user to the next. Touch-free operation also makes the faucets accessible to virtually anyone, regardless of age or physical ability. Another plus is water conservation. Sensor-activated faucets eliminate wasted water flow by discharging only what the user needs. Depending on local codes, water flow rates for lavatories vary from a maximum of 2.2 gallons per minute (gpm) to 1.5 gpm for the new EPA WaterSense standard, with many public restrooms using just 0.5 gpm. Although all automatic faucets generally have the same function, there are two main sensing technologies used in sensor faucets to activate water flow: active infrared (AIR) and capacitance sensing. Both technologies are presence sensors, not motion sensors. Because there seems to be an aura of mystery surrounding these sensing technologies, this paper will explain both and provide a better understanding of application usage.
Sensing technologies
Active Infrared Sensing
The predominant sensing technology used in touch-free plumbing devices is AIR. AIR detects the presence of objects by actively emitting infrared light and waiting for this light to come back to it. To achieve the task of emitting and receiving, AIR sensors employ two key components: an emitter (transmitter) light emitting diode (LED), which emits a beam of infrared light, and a receiver (photodiode) that looks for the reflection of the emitted light. When the emitted infrared light is reflected from a user’s hand, an electronic signal is sent to open the solenoid and allows water to flow. When the receiver no longer “sees” reflection of the light, the control electronics then send yet another electrical pulse to the solenoid, this time, instructing the solenoid to close. For example, as the user’s hands enter the beam’s path, the light is reflected back into a sensor receiver that activates water flow. When hands move away from the sensor, the loss of reflected light signals water flow to stop. The LEDs are aimed so that only objects under the faucet will reflect the infrared light back toward the receiver. A more distant object may reflect some of the infrared light, but the light signal will not reach the sensor at the proper angle or intensity and will not be strong enough to be considered a valid target if it even reaches the receiver.
These components are housed within the sensor module that is located in the faucet spout, in a separate sink hole to the side of the faucet spout, or in a special compartment up next to the water outlet. Inherently, this provides easy installation and serviceability. Further, infrared sensors save water by ensuring that water is delivered “on demand,” only when a valid target, such as a user’s hands, are present. While historically AIR has faced some environmental challenges with highly reflective surfaces, such as stainless steel and un-reflective surfaces (black colors and wool fabrics, in particular), many of these issues have been effectively addressed. Whether it is improved receivers (photodiodes), special lenses to direct and focus the infrared light, and/or sensor algorithms to better interpret the returned light.
