All The World's A Puzzle: Real World Feedback and Control Systems: The Puzzle of Feedback and Control on a Daily Basis

So feedback and control is a science of gathering, interpreting and acting on information.

So how does this apply to everyday life?

There a loads of examples all around us that incorporate feedback and control methods.

1.) Smoke Detectors

Because they are so commonplace, it is easy to overlook smoke detectors as feedback and control mechanisms. Smoke detectors work by having a beam of light directed across its inside radius. When smoke rises and encounters the smoke detector, this beam is interrupted (sensing mechanism). When the light cannot be detected, the alarm is activated (actuation). The control computations for a smoke detector a very basic. Is the light interrupted? Yes or no. The smallest amount of smoke can set them off, which is why they are both a fire safety and fire prevention device: they can sense the fire before it is big enough to cause any substantial damage.

Despite their simplicity, these little alarms do have their setbacks. Anyone who has ever burned something by accident can tell you that smoke detectors, though advertised as fire prevention, can not distinguish between smoke caused by a fire and smoke caused by ruined Christmas dinner or a candle. Sometimes, when their batteries are running low, they beep for a different reason altogether, and can cause their owners a lot of frustrations. I learned that the hard way this past weekend.

(technical help provided by http://chemistry.about.com/cs/howthingswork/a/aa071401a.htm

2.) Thermostat

The older version of the thermostat operated using a bimetallic strip. I believe some rooms in my house still use this old design. As the temperature around the thermostat changes, the two metals in the strip expand and contract at different rates. This causes the strip to bend (the way depending on the temperature). The bend it was tells the old thermostat that the house is getting too cold and it's time to heat things up (sensing mechanism). The thermostat then turns the heat on (sometimes full throttle) until the bimetallic strip returns to its original state (actuation) and then it shuts off. Once again, the control calculation is very simple and can be broken down into a yes or no question for simplicity. Modern thermostat's can sense the temperature in the room using a digital thermometer and then compare that temperature with the input temperature. If it is too cold the it will warm the house until the appropriate temperature is achieved. The one flaw I see in this design is the preference of the owner. Maybe he or she does not want the house at a constant temperature when they are not home. Maybe they can not afford that. A timer run thermostat seems like a more environmentally and economically safe choice.

3.) Automatic Doors

We have all encountered these at the grocery store. You step on the black tarp (sensing mechanism) and the door slides open (actuation). However, the control computation's for this device are slightly more complex than those of the previous two. For example, the doors do not open if a cat or bird happens to stand on the mats. The sensor has been programmed to measure the applied force on the mats and then compare it to the weight of the average human, or a set weight like fifty pounds. Anything below that will not activate the doors. For the most part, these kinds of entrance ways have always seemed well designed and functional. However, there is the risk of injury if the sensor fails. From personal experience, my mother once witnessed a man mistake the wrong door for the automatic one. He was ok, but had he been walking faster or been holding scalding hot coffee in his hands, things may not have ended as well. If a store experiences a power outage, will people be trapped inside? There are too many situational problems to consider for this product. While they are helpful, I would not deem them 'ideal'.

4.) Fish Tank Heater

This device will always have a special place in my heart, as it keep my little friends alive through the long Maine winters. A fish tank heater, like a thermostat, measures the temperature of the surrounding water (sensing mechanism) and compares it to a set temperature (my tank is set currently for 80F). If the water is too cold, then it will automatically turn on until the temperature in the tank is equal to the set temperature (actuation). The calculation, while similar to the thermostat, is much more complex, as an error of a few degrees can result in some very dead fish. The extended length of the heater allows it to get a more accurate reading by exposing more of its surface area to the water. I have had one for two years now and so far no complaints. I have, however, heard the horror stories of heaters malfunctioning due to water damage and becoming so hot that the fish are boiled alive. Despite my heater's intense insulation and shatter proof casing, I always worry just a little bit and check it for signs of damage whenever I clean it.