23-Ind-B5 Ergonomics · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — Dec. 2015 — 98-Ind-B5 Ergonomics. Three-hour, open-book exam (all notes, books and any non-communicating calculator permitted); the paper requires 4 of its 5 questions (Part A mandatory, any two of Part B's Questions 2–4, and Part C mandatory) — all five are solved below for completeness.
Reference texts: Sanders & McCormick, Human Factors in Engineering and Design (7th ed.) — controls/displays, anthropometry, workplace and computer-workstation design; Waters, Putz-Anderson & Garg, NIOSH Applications Manual for the Revised NIOSH Lifting Equation (1994) — the RWL/LI formula and multiplier tables reproduced on the exam's own pages 6–7.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The panel below replaces the all-analogue original with a mixed digital/graphical human-machine interface, grouped by function into five zones so the operator's search pattern matches the process rather than an arbitrary layout.
Digital numeric displays for temperature, pressure and density. The -5°C thickening point is a precise threshold, not a trend to eyeball, so temperature is read as an exact digital number rather than a needle position; pressure and density readouts follow the same logic wherever the operator must confirm a specific value against a setpoint. Digital numeric displays are the correct choice whenever the task is "read an exact quantity," per standard control/display design guidance — an analogue dial forces the operator to interpolate between graduations, which is unnecessary risk on a food-safety-relevant setpoint.
Graphical/analogue mimic display for vat fill level. Volume, by contrast, is a "how full, how is it trending" judgement, which is exactly what a vertical bar mimic display is for: the bar rises and falls the same way the physical vat does (pictorial compatibility), so the operator reads it at a glance without consulting a number, and can perceive rate-of-change (filling fast vs. slow) far more naturally than from a sequence of digits.
Rotary control with a hard detent at 20 rpm for the mixer arm. A rotary knob follows the population stereotype that clockwise increases speed, and the physical detent lets the operator find the standard 20 rpm setting by feel, without watching the display — freeing visual attention for the temperature/density readouts during the critical thickening phase.
Spatially mapped inflow/outflow levers. The inflow and outflow controls are placed on the side of the panel that matches the real inlet/outlet piping and pulled/pushed in the direction that matches the resulting flow (movement compatibility) — this is the single most common source of "wrong valve" errors in process panels when violated, and is trivial to get right at the design stage.
A single "ready to package" indicator, not a raw density number. Because the packaging window (soft/fluid enough for the 3 cm nozzle, not liquid, not frozen) is narrow and time-pressured, forcing the operator to interpret a raw density percentage under pressure invites error; a threshold-triggered green light collapses that judgement into a go/no-go cue the operator can act on instantly, with the numeric gauge still available underneath for anyone who wants the detail.
A guarded, centrally reachable emergency stop. Mechanical mixing with a rotating arm needs a stop the operator can reach without searching, recessed/guarded so it cannot be triggered by an incidental knock.
Operating this panel exercises the full human information-processing chain, from raw sensing through to motor response:
Sensation. The visual system is the dominant channel — reading the digital numerics, the bar mimic, the rotary knob's pointer position and the ready-light colour. An audible alarm (e.g., on a temperature excursion) would add the auditory channel as a parallel, attention-capturing route that does not compete for the eyes already occupied elsewhere on the panel.
Perception and pattern recognition. The operator does not read the mimic bar as "62% of 40 cm"; they perceive it directly as "vat filling normally" by pattern, and likewise recognise the knob sitting in its detent as "running at spec" without reading the number — this is what makes graphical/analogue coding faster than digits for trend judgements.
Attention. Selective attention scans the five zones in a learned sequence (temperature and density first during the critical thickening/packaging transition, flow and mixing arm as background checks); divided attention is required in the window where temperature is approaching -5°C at the same time as density must be watched for the packaging threshold — exactly the transition the ready-light indicator is designed to offload.
Working memory. The operator holds the current setpoint and recent trend ("still 1.5 degrees to go, cooling normally") while attending to other zones; this is a limited resource, which is precisely why the design pushes trend information into a mimic display and threshold information into a status light rather than requiring the operator to remember and mentally compare raw numbers.
Decision-making. The operator compares each reading against a known target (is temperature at -5°C yet? is density in the packaging window?) and decides whether to adjust a control or wait — a recognition-primed decision for a trained operator rather than a from-scratch calculation.
Response selection and motor execution. Once a decision is made, the operator selects and operates the corresponding control (turn the speed knob, open the outflow valve); control-display compatibility and adequately sized targets (the detented knob, the guarded E-stop) reduce both the time and the error rate of this final motor step, consistent with Fitts's Law governing movement time to a target of a given size and distance.
