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CTMA: Engineering and Applied Technology

CTMA · Work through your exam, one topic at a time.

All guide sections

Engineering and Applied Technology

Engineering and Applied Technology tests the physical fundamentals a technology manager is expected to reason with: measurement and tolerances, material and component behavior, basic mechanical and electrical calculations, reliability and maintenance, automation, and safety compliance.

Core rules

  • Tolerance stack-up: worst case adds tolerances arithmetically; statistical (RSS) combines them as the square root of the sum of squares. Worst case is conservative and is used where function is safety-critical.
  • Clearance range = (minimum bore − maximum shaft) to (maximum bore − minimum shaft).
  • Reliability: series systems multiply their reliabilities; redundancy raises availability. Availability = MTBF ÷ (MTBF + MTTR).
  • Ohm's law V = IR; power P = VI = I²R. Watch units - mA versus A, kW versus W.
  • Maintenance: preventive (time-based), predictive (condition-based, e.g., vibration, thermography), reactive (run-to-failure). Predictive suits expensive assets whose failure is intolerable.
  • Hierarchy of controls: elimination → substitution → engineering controls (guards, interlocks) → administrative (lockout/tagout, procedures) → PPE last.
  • GD&T controls form, orientation, location, and profile, describing function more precisely than symmetric plus/minus dimensions.

Worked example

A bore is 20.10 ± 0.04 mm; a shaft is 20.00 ± 0.03 mm.

  • Bore range: 20.06 to 20.14. Shaft range: 19.97 to 20.03.
  • Minimum clearance = 20.06 − 20.03 = 0.03 mm. Maximum clearance = 20.14 − 19.97 = 0.17 mm. The fit is always clearance, never interference. If design requires at least 0.05 mm for lubrication, worst case fails; shifting the shaft to 19.98 ± 0.03 caps the maximum shaft at 20.01 and restores the 0.05 mm minimum - which is why the reasoning must start from worst case, not the nominal.

Traps

  • Using RSS when the stem asks for worst case, or the reverse.
  • Treating MTBF as a wear-out life; for constant-failure-rate items it is the exponential mean, not a guaranteed service life.
  • Mixing mm and inch, or mA and A, inside one calculation.
  • Choosing PPE as the primary control when elimination or guarding is feasible.
  • Assuming redundant paths multiply reliability the way series elements do.