This simulator models a photoelectric smoke detector's sensing chamber — mounting base, light labyrinth, infrared emitter, off-axis photodiode receiver, aerosol volume, signal-processing board and alarm indicator — as a first-order chamber-fill process feeding an optical decision-and-qualification-timer model. Adjust smoke concentration, ventilation, contamination and threshold settings, and watch how the receiver signal develops toward a latched alarm.
• Equipment laboratory tab: a real-time 3D cutaway workbench of the mounting base, light labyrinth, infrared emitter, off-axis photodiode, aerosol in the chamber, signal-processing board and alarm indicator, with Home view, Focus selected part, Show full enclosure / Exploded view toggle, Auto rotate, Expand and Hide/show labels camera controls, a clickable numbered component list with callouts, live stats, a 'What is happening?' sequence narrative, switch-state tokens and a readings table, plus an experiment control desk with Pause/Advance 0.1 s/Advance 1 s stepping, a playback-speed selector (real time, 10× slow motion, 10× faster, 1 minute per second), Start trial/Stop equipment/Acknowledge/Reset alarm memory actions, and controls for incoming aerosol concentration (0-100 normalized units), chamber exchange time constant (1-20 s), contamination offset (0-30 signal units), optical decision threshold (10-60 signal units), and the continuous qualification time (0.5-5 s). • Curves & measurements tab: a primary-measurements chart (chamber aerosol, receiver signal and decision threshold together), a response/sequence chart (qualification timer vs. latched alarm state), the model equations, and snapshot measurement readouts. • Experiments tab: guided experiments (clean air, smoke entry, restricted exchange, contamination) each with an expected outcome, a Run model checks button that runs the built-in verification suite against independent fresh models, and a timestamped event log with a Prepare trial report export. • Learn & assess tab: lesson content on admitting aerosol, scattering the beam, qualifying the signal and distinguishing contamination from an alarm, a knowledge-check quiz with reset, and a scope/references note linking to an external addressable photoelectric smoke detector product page.
This is a photoelectric (light-scattering) detector: an infrared emitter illuminates the chamber, but its beam does not point directly at the receiver. Instead, particles entering through the light labyrinth scatter some of that infrared light toward an off-axis photodiode, which is why more smoke means more scattered light reaching the receiver rather than a beam being blocked. Chamber aerosol concentration follows a first-order fill process, dC/dt = (Cin − C)/τ, where the exchange time constant τ (set by the chamber exchange time control) governs how quickly the chamber's internal concentration catches up to whatever concentration is arriving from outside — a larger time constant means the same incoming smoke level takes longer to show up as chamber concentration.
The receiver's modeled signal S adds a contamination offset to that chamber concentration (S = C + contamination), representing dust or aging buildup that raises the baseline signal without necessarily indicating smoke. The processing board compares S against the decision threshold and only latches an alarm once S stays at or above threshold continuously for the full qualification interval — a momentary spike is not enough. Once latched, the alarm indicator stays lit even if the chamber later clears, since acknowledging or clearing smoke does not itself erase alarm memory; that requires an explicit Reset alarm memory action.
Watch the primary-measurements chart to see chamber aerosol rise with the lag set by the exchange time constant, the receiver signal track that chamber value plus contamination, and the decision threshold as a fixed reference line — alarm latching only happens once the signal crosses and stays above that line for the full qualification time shown on the second chart. A contamination offset alone (with no smoke) can raise the baseline signal and prompt a maintenance indication without crossing the roughly 25-unit alarm threshold used in the guided contamination experiment, illustrating why dust buildup is tracked as a separate condition from an actual alarm.
The Run model checks button exercises independent, freshly-built chamber and threshold models — separate from your current trial — to confirm the fill-and-qualification logic behaves consistently, not just for your current control settings. All optical units here are normalized values for teaching purposes; this is not a smoke-obscuration calibration, a detector listing/certification test, or a manufacturer-specific spacing or sensitivity specification, and particle trajectories and light paths are illustrative rather than a physically simulated optical model.
It models a photoelectric (light-scattering) smoke detector chamber as a first-order aerosol fill process feeding an optical signal that must cross a decision threshold and stay there for a qualification time before the alarm latches. It uses normalized, generic educational parameters rather than a specific listed device's certified spacing or sensitivity.
This is an off-axis, light-scattering design: the emitter and receiver are angled so the receiver only sees light scattered by smoke particles, not the direct emitter beam. More smoke scatters more light toward the receiver, which is how the detector senses aerosol without a beam-blocking (obscuration) geometry.
No. Once the signal has stayed above threshold for the full qualification time, the alarm indicator latches and stays lit even after the chamber clears. Acknowledging an alarm only records operator awareness; restoring the detector requires the explicit Reset alarm memory action.
The Run model checks button runs the shared checks.js verification suite against independent, freshly built chamber-fill and threshold-qualification models — separate from your live trial — confirming the underlying detection logic behaves consistently across settings.