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Thinking in Diagrams

Chapter 8: Sense, Compare, Correct

Drafted for Aryeh's edit.

For chapter 8: Sense, Compare, Correct

Timing

Section titled “Timing”
  • Reading the chapter: about 11 minutes, its 1,687 words of prose at 150 words a minute. Not counted in those minutes: 6 figures, 1 pair, 2 understanding checks, the reading exercise and the exercises.
  • A session: 45 minutes, the exercises set for it. (estimate)
  • Afterwards: 55 minutes, the exercises set for then. (estimate)

Common misreadings

Section titled “Common misreadings”
  • An external driver wired into the gap. In the bad diagram, outdoor temperature’s signal ends at the temperature gap; the lab’s check reports it, naming the signal. In the understanding check about a hearing aid, the gap between the loudness set and the loudness read is this choice, as a signal from the hot day to degrees above 37 °C is in the reading’s third question.
  • The measured value taken for the controlled variable. In the understanding check about a fridge, the temperature of the food on the back shelf is the wrong choice for the measured value: the thermostat reads the air by the door. In FC 01’s brief, the carbon dioxide in the air and the meter’s reading are two variables.
  • A part that acts drawn in place of a quantity. In the reading’s second question, nerve cells and sweat glands are things; the variables are temperature sensed by nerve cells and sweating, as the thermostat’s corrective action is boiler output, not the boiler.
  • The brain’s regulatory center looked for among the variables. To an engineer it is a controller, here the signal from the gap to the corrective action; in the reading’s first question, the measured value and the target are the wrong choices for it.
  • A target drawn as something the loop changes. In the reading’s third question, a second target is a wrong choice for what a run adds; in FC 03, the new tree halfway across is the kayaker’s choice, and no signal ends at the target.

Exercises to set

Section titled “Exercises to set”

The session goes from one control loop, through a stock and an external driver, to a published loop of body temperature; a late correction, control with accumulation and the case come afterwards.

For a session

Afterwards

Sources

Section titled “Sources”
  • Chapter 8, Sense, Compare, Correct: its bad diagram, understanding checks, reading and exercises, and the lab’s checks on them.
  • OpenStax, Anatomy and Physiology 2e, section 1.6, “Homeostasis” (LibreTexts), Figure 1.10b, the figure the reading redraws.