Real-World Feedback Control Systems

Everyday we encounter several feedback-control systems and just to name a few....

1. Thermostat
Probably the simplest and most popular feedback control systems, a thermostat senses the current temperature of a room (sensor mechanism), compares the input to the set or desired temperature (which acts as the control aspect/mechanism), and then either turns the heater "on" or "off" to raise/lower the temperature of the room until it is at or above the "set" temperature (actuation). This system has stood the test of time as it automatically adjusts as needed and maintains a relatively constant temperature.

 Issues:  The heater is either on full power or off completely, regardless if the room temp. falls a little or a lot below the goal. (As the environmentalist in me speaks out) What a waste of energy! An alternative design would be to use a power proportional to the difference between the desired temp. and current temp, i.e. 20% of power capabilities if 10 degree difference.

2. Oven (and Microwave)
Similar to the thermostat, the temperature inside the oven is measured (sensing), compared to the set temperature indicated on the dial (control), and then the heat is turned on until the temperature reaches the set point (actuation).

Issues: Again, the heat is either turned on or off completely. Since there is no "in-between" power, the temperature fluctuates and can be off (slightly or considerably) -- and coming from a baking enthusiast, that is not fun for a cake or pie. Baking time vary from oven to another, and this is not efficient (particularly if you have to re-make your cake because it did not bake right). A proportional setting for the power is also recommended.

3. Alarm Clock

Moving away from the technological examples and towards human-body systems, I highlight the alarm clock. There are two parts really. The first begins with you setting a time the night before (control) and once the current time matches the set time (sensing), it sets off a computed sound (actuation). The second part begins with you hearing the Beep-Beep sound from your alarm clock, and you react immediately (hence, bang-bang systems). Most people wake up, but you also might just hit the "Snooze" button. 

Issues: It doesn't always work. It's an open-loop control system and cannot regulate if you wake up, how quickly, if you have heard it or not, etc. Some alarm clocks try to compensate for the issue by having a mid-step: one app forces you to get up and take a picture of the door (of course, it checks to see if it matches the previously save image of that door) and one tech-savvy clock that actually jumps off your table and forces you to catch it in order to turn off the noise. Still, you have the seeming impossible problem of waking the people who sleep through their alarms... Maybe a small shock to the finger?

4. Elevator
In such a system (and returning to bigger technological developments), each floor represents a value (1, 2, 3, 4,....). and depending on the difference (sensing) in cable spins or altitude between the current floor and the desired floor input value (control), it either spins in (raise) or spins out (lower) to achieve the indicated value (actuation).

Issues: Fairly straightforward and successful. However, an engineer most likely has to deal with a lot of fine tuning to eliminate bumps or skips, creating a smooth movement with the weight of the elevator.

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