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Motion Sensor Controlled Vending Machines

Introduction


Vending machines operate 24 hours per day, seven days a week using large amounts of energy throughout those hours of operation. In addition to consuming 2,500 to 4,400 kilowatt-hours (kWh) of energy per year, they add to cooling loads in the spaces they occupy. At average electricity costs of about US$0.08/kWh, annual operating costs can range from $200 to $350.

New, efficient vending machines are available that can greatly reduce operating costs through the use of motion sensors. These sensors allow the machines to function only when a person is present in front of the sensor. The compressors run only enough to maintain a suitable temperature throughout the workday, but the lights and other components remain off in order to minimize overall energy consumption. [1]

The Technology

Passive Infrared Sensors

Most vending machine sensors use a type of technology known as passive infrared sensors (PIR), which unlike optical sensors that use an LED transmitted and infrared receiver, emits nothing. Rather than radiating, the PIR responds to infrared energy being emitted by any nearby objects. Any object with a temperature above zero degrees Celsius emits infrared energy, through black-body radiation. Invisible to the human eye, the magnitude of this radiation varies with temperature - which is exactly what makes the PIR function the way it does.

Although invisible to the human eye, the magnitude of infrared energy can be quantified by a pyroelectric sensor. This sensor is placed behind an infrared-transparent cover, so that it may monitor objects with varying infrared energy. Similarly to the way an electric charge is created when visible light strikes a solar cell, these sensors generate a small charge when subjected to infrared energy. As an object with a more intense infrared energy, such as a person, is detected by the sensor, it overlaps a section on the chip that had previously been subjected to some much cooler object, such as a wall in the background. [2] [3]




  1. E Source Companies LLC (2009), Vending Machine Energy Savings, http://www.mge.com/business/saving/madison/pa_50.html
  2. Machine Design (2008), Sensor Sense: Passive Infrared Motion Sensors,http://machinedesign.com/article/sensor-sense-passive-infrared-motion-sensors-0710
  3. Wikipedia, Passive Infrared Sensor,http://en.wikipedia.org/wiki/Passive_infrared_sensor#PIR-based_motion_detector
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