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Motion sensor controlled vending machines

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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

Duty Cycle and Control Logic

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.
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. [2]


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. 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.[3] [4]


False Activation Prevention


Emission Reductions

A decrease in energy consumption translates to a reduction in carbon dioxide emissions from the burning of fossil fuels. The specific reduction in greenhouse gas emissions is dependent on the energy supply mix that provides power to the organization.


Below is a breakdown of the energy supply mix in Ontario from 2005:

Nuclear 51%

Renewable 23%

Natural Gas 7%

Coal 19%


The EPA released U.S. data that relates energy production of various sources to the resulting carbon dioxide emissions. The U.S. data was analyzed to determine the average carbon dioxide emissions released by each energy source and then compared to Ontario's energy supply mix. The result is approximately 0.222 tons of carbon dioxide is emitted in Ontario for each megawatt of energy produced.



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