Dispelling Myths About Ultrasonic Occupancy Sensors

By Craig DiLouie, Lighting Controls Association

Published December 2006

Occupancy sensors can be specified in a broad range of indoor and outdoor applications for 1) energy savings (by reducing the amount of time the lighting system is operating), 2) security purposes (by indicating that an area is occupied), and 3) minimizing light pollution (by reducing use of outdoor lighting).

Generally, occupancy sensors provide higher energy savings when the space is either 1) intermittently occupied—left unoccupied for two or more hours per day, and 2) spaces where the lights are typically left on when the space is unoccupied. Ideal applications include offices, classrooms, copy rooms, restrooms, storage areas, conference rooms, warehouses, break rooms, corridors, filing areas and other spaces. Because prevailing energy codes require automatic shutoff, occupancy sensors have become a standard feature in new construction and remain a proven strategy for retrofits.

Occupancy sensors detect the presence or absence of people using one or a combination of several methods. The most popular methods are passive infrared (PIR) and ultrasonic. Most occupancy sensor manufacturers offer both PIR and ultrasonic sensors. Dual-technology sensors use both methods. Each method has advantages and disadvantages that make it more suitable for some applications than others.

This special report from the Lighting Controls Association addresses certain marketing and sales claims made in the industry about ultrasonic sensors by at least one manufacturer that are false.

Ultrasonic Sensors

Ultrasonic occupancy sensors utilize the Doppler principle to detect occupancy through emitting an ultrasonic high-frequency signal (typically 32-40 kHz) throughout a space, sense the frequency of the reflected signal, and interpret change in frequency as motion in the space. This technology has been used for more than 25 years in commercial lighting and security devices, and has proven to be the most effective method for detecting small body movements.

Figure 1. Ultrasonic sensors. Courtesy: Watt Stopper/Legrand

Ultrasonic occupancy sensors, with its distinctive advantages and limitations, can be more appropriate for some applications than PIR sensors, and vice versa. Neither technology is superior except in the context of an individual application need related to cost, sensitivity, line of sight, field of view, etc. This is why most manufacturers offer both types of sensors, because some applications call for PIR and some call for ultrasonic. A growing number of products combine these technologies into a more robust sensor (dual-technology sensor) that offers high sensitivity but minimizes the chance of false-on or false-off switching.

See Table 1 for a comparison of PIR and ultrasonic sensors. Also click here to see Figure 3, a diagram that illustrates the decision-making process of selecting PIR versus ultrasonic (opens in pop-up window; close window to return to article).

Table 1. Comparison of PIR and ultrasonic sensors.

Figure 2. Decision diagram offering guidance for selection of PIR versus ultrasonic occupancy sensors. Courtesy: Watt Stopper/Legrand

Dispelling Myths about Ultrasonic Sensors

FDA certification: There have been claims in the industry that the U.S. Food & Drug Administration (FDA) certifies occupancy sensors. The FDA does not examine, test or certify sensors based on any type of sensing technology.

ADA certification requirement: There have been claims that the Americans with Disabilities Act (ADA) requires third-party certification for occupancy sensors. This is also false. What ADA does require is that hand-operated controls must meet specific parameters regarding the amount of effort or pressure needed to activate them. The ADA also has created rules regarding mounting heights and obstructions as part of dealing with issues of access for the disabled. The required mounting height for wall-switch controls, for example, is 36-48 in. off the floor.

Hearing aids: There have been claims that ultrasonic sensors interfere with the operation of hearing aids. National Electrical Manufacturers Association (NEMA) member companies report less than five incidents per year of any type of hearing aid interaction; the possibility for interaction is remote, according to manufacturers. Hearing aid manufacturers also report that customer support calls about hearing aid interference with ultrasonic sensors are very limited. Ultrasonic sensors that operate at 32 kHz and above do not interfere with hearing aids.

There has been a claim that hearing aids detect the emission of ultrasonic sensors and stress the hearing aid device’s battery, causing it to fail prematurely. Another claim is that when the hearing aid detects the emission of ultrasonic sensors, it triggers the automatic gain control feature of the aid, lowering its detection so that sounds in the normal audible range are not easily heard.

Independent research by NEMA has demonstrated that these claims are not true for modern hearing aids.

The NEMA-sponsored study, conducted by David F. Henry, PhD and Barak Dar, “Effects of Ultrasonic Sensors on Hearing Aids” (February 2006), concluded:

“After assessing 23 hearing aids representing the digital products of all major hearing aid manufacturers, just two hearing instruments were severely affected by ultrasonic occupancy sensor devices. One device, the ImpaCt DSR675 manufactured by AVR Sonovation, has not been in production for over four years. Newer hearing instruments from this manufacturer have exhibited no interference when exposed to the ultrasonic occupancy sensor signals. The second device, the Bravo, manufactured by Widex, is still in production. However, the manufacturer reports that they have developed a modification that can be made to the instrument that greatly reduces the susceptibility of the instrument to ultrasonic occupancy sensor signals.”

When interaction occurs, it is typically the result of a hearing aid that has fallen into disrepair or has drifted out of its spec, as determined by NEMA findings which have been re inforced by independent testing. Hearing aids should be periodically re-calibrated to within specifications to avoid interference problems. A hearing aid that exhibits interference problems should be returned to the patient’s audiologist or clinician for adjustment. In all cases, the problem can be resolved quickly and easily.

Ultrasonic operation, however, may result in minor noise in the hearing aid, although this does not affect hearing aid performance. Henry and Dar add: “Several [hearing aid] instruments from other manufacturers emit minor noises when exposed to the ultrasonic occupancy sensor devices, but not to the extent of rendering them inoperable, or affecting their performance.” The potential for minor noise is typical of electrical devices of which ultrasonic sensors is a minor contributor. For example, cell phones, microwave ovens, electric motors and many other electrical devices can generate audible noise in hearing aids.

Health hazard: There have been claims that ultrasonic sensors present a health hazard. This is false; ultrasonic transmission poses no known health hazard. A small speaker in an ultrasonic sensor, usually 8-10 mm in diameter (about the same size as an I-Pod ear bud) is used to emit the ultrasonic tone. These small speakers are sufficient for the occupancy sensor’s use, and are incapable of generating any significant volume, according to manufacturers. The frequency and decibel levels used with ultrasonic sensors fall well within the safety guidelines of the U.S. Food & Drug Administration, the World Health Organization, and various governments of industrialized nations around the world.

When installed properly, ultrasonic sensors are completely safe and are highly effective at controlling lights and saving energy, according to members of NEMA and the Lighting Controls Association.

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