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Decision Lab · D6 · Sensor evidence, priorities and reset permission

A safety latch changes what the controller may do

Read the stated sequence as a set of permissions. A normal temperature error does not authorize bypassing an active protective state.

Original case · Suggested 18 minutes · Edition 2026-10-12.1

By the end of this workshop

  • Choose a method that respects the supplied conditions.
  • Explain how a changed condition affects the decision.
  • Identify a physical or procedural cross-check and an applicability limit.
  • Record the assumption you would verify next time.

Start with the complete model

Givens and assumptions

  • Original training sequence: normal cooling modulates when room temperature exceeds 75°F.
  • A coil temperature at or below 35°F, or a coil-sensor fault, latches the protective state.
  • Latched state commands supply fan OFF, outdoor-air damper CLOSED, heating valve 100% and cooling valve 0%.
  • Release requires a healthy coil sensor, coil temperature above 42°F and an operator reset. All three conditions are required.
  • Current room temperature 82°F; coil temperature 34°F; sensor healthy. The protective state is active.
Study calculator, scratch notepad and whiteboard

Supports +, −, *, /, ^, parentheses, sqrt, abs, log (base 10), ln, sin, cos, tan, pi and e. Confirm units independently.

Scratch text and drawings stay in this tab and clear when you leave or reload. Save important reasoning in a response or reflection below before leaving.

Scratch whiteboard

Sketch a control volume or air path with a mouse, pen or touch. Ink stays in this page session and clears on reload. Use the response and reflection fields as a keyboard alternative. Sign in before starting and save a reflection to retain your reasoning.

1 · Choose the method

Which command set follows the supplied active protective state at room 82°F and coil 34°F?

Choose one response

2 · Change the condition

Predict before you inspect the calculation.

The coil reaches 45°F with a healthy sensor, but no operator reset has occurred.

  • The same original latch-release rule requires a healthy coil sensor, coil above 42°F and an operator reset. Coil is now 45°F, sensor healthy, reset absent; room remains 82°F.

Check the first decision to open the changed-condition response.

Personal notes are not automatically graded. Workshops are linked learning experiments, separate from timed diagnostics and mocks. They do not predict a pass or award instructional hours.

Reference navigation drill

Search concept: controls, sensors, actuators, integral action

Explain the distinction between setpoint reset, integral reset and manual latch release.

Use an authorized reference. A search term does not guarantee that a current examination reference contains every relationship used in this teaching case.

Where this model stops

Original illustrative sequence only. Real protective actions and reset requirements depend on the approved design and equipment instructions. Do not adopt this command set as a general design rule.

The PE Mechanical: HVAC and Refrigeration examination uses the NCEES PE Mechanical Reference Handbook. These source links provide study context; they are not additional exam-day references.

Found an unclear condition or calculation? Include workshop latched-control-sequence and the step in your comment.

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