Trace a feedback pathway

Supplied materials

• All measurements and observations below are supplied classroom examples. They are not data from actual learners or a claim about a particular real site.
• Paper or a browser document for a labeled drawing, table or explanation.
• Worked problem inputs: A model rises above reference, activates cooling, then reduces cooling as the reading returns. Trace the loop.
• Assessment case 1: A sensor detects rising temperature, a controller changes an output and temperature then falls. What is warranted? Which inference or prediction is best supported?
• Assessment case 2: Which scientific label fits the specifically described step or feature? Supplied case: Information compared with reference range.
• Assessment case 3: Which scientific label fits the specifically described step or feature? Supplied case: Modeled cooling mechanism activates.
• Assessment case 4: Which scientific label fits the specifically described step or feature? Supplied case: New reading reduces further action.
• Assessment case 5: Which scientific label fits the specifically described step or feature? Supplied case: Receptor detects a change.
• Assessment case 6: After correction, the measured variable approaches its set range and the controller reduces output. What follows? Which inference or prediction is best supported?

Learn the idea

Negative feedback opposes a deviation from a regulated range. It does not mean a harmful response. A simplified loop includes sensor, control, effector and response.

Sensor means detects the regulated change. Controller means compares information with reference. Effector means performs a corrective action. Feedback means result influences later control.

For the supplied mechanism problem, A model rises above reference, activates cooling, then reduces cooling as the reading returns. Trace the loop. Detection informs control, an effector produces cooling, and the new reading feeds back. Because the response opposes the original deviation, this is negative feedback in the stated model.

1. Read the supplied problem and mark the structures, processes or quantities named: A model rises above reference, activates cooling, then reduces cooling as the reading returns. Trace the loop.
2. Draw the relevant boundary, pathway or comparison and label it using the scientific ideas above.
3. Write a causal explanation or calculation, showing how each observation supports the result.
4. Compare your reasoning with the worked solution; name a condition that would change or limit the inference.

Check your reasoning

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Take it further

New feedback case: reading falls below reference, a controller activates warming, and warming stops as the reading returns. Expected: corrective action opposes the initial decrease, so this is negative feedback despite using warming rather than cooling.

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