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The typical duty cycle of
the motion sensor controlled vending machine revolves around whether people are around the machine or not. Usually power is cut off to the machine within 15 minutes of a person’s presence in front of it. Most devices are designed to shut off for approximately 2 hours and then turn back on activate a compressor cycle in order to maintain an optimal interior temperature. When a person walks up to it, the machine lights, electrical components and compressor are activated in order to provide service for the person. <br />
In order to prevent high-head-pressure restarts on the compressor, general control logic ensures that it is allowed to run a complete cooling cycle before shut down and a sensor ensures that the machine does not shut down before the cycle is complete. <ref> E Source Companies LLC (2009), ''Vending Machine Energy Savings'', http://www.mge.com/business/saving/madison/pa_50.html </ref>
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 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. <br />
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. The pyroelectric sensor is connected to an energized relay, which acts as a "switch," completing the load circuit. As this warmer, or more energized object, moves along the lens of the sensor, the relay becomes de-energized, the contacts of the relay become operational, activating the detection switch of the control panel. Similarly, if an object colder than the background wall is presented into the field of view of the sensor, the difference in infrared energy will still cause the relay to be de-energized, activating the detection switch.