Biological systems from an engineer's point of view.

Reeves GT, Fraser SE - PLoS Biol. (2009)

Related In: Results  -  Collection

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pbio-1000021-g002: Examples of Control Loops(A) Schematic of a simple control loop. The process output is monitored by a sensor, and the value of this output signal is passed to a device called a controller. The controller calculates the difference between the output signal and the set point (the desired value of the output), and responds accordingly, often by physically manipulating an input parameter, such as a control valve.(B) Schematic of cruise control. The car is the process, and the car's speed is the output. A speedometer sensor within the car tells the cruise control the car's speed. The actuator on the cruise control then responds by opening or closing the throttle, allowing air intake into the engine.
Mentions: The engineering and applied mathematics subfield of “control theory” refers to the use of feedback loops to ensure that system outputs, such as product purity, are maintained at set values (see general control loop in Figure 2A). Cruise control (now standard on most cars) is an everyday example of a feedback control system. When at the desired speed, the driver implements the set point by pushing the “set” button. Thereafter, the controller calculates the difference between the current speed and the set point, and opens or closes the throttle accordingly (Figure 2B). In reality, the controller uses not only the current difference (proportional control), but also the time history of the difference (integral control) and how fast that difference is changing (derivative control) to decide how strongly to respond. As each of the control strategies has inherent advantages and disadvantages, rarely do engineers implement only one control strategy at a time; most often controllers are of the PI (combining proportional and integral) or PID (combining all three) type.

View Article: PubMed Central - PubMed

Affiliation: Biological Imaging Center, Beckman Institute, Division of Biology, California Institute of Technology, Pasadena, California, USA.

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