A motion trace shows how the mechanism moves, not merely when the contacts change state. Travel, velocity, overtravel and rebound can reveal damper, latch, linkage and lubrication problems that a simple timing result misses.

Learning objectives

Identify key points on a motion curve, use the manufacturer’s reference window and combine motion with timing and coil-current evidence.

Core engineering principles

Total travel is a geometric quantity

It reflects mechanism stroke and sensor setup. Incorrect transducer mounting can create a plausible but false result.

Velocity must be measured in the specified zone

Average speed over the entire stroke can hide the contact-region velocity that controls interruption and closing energy.

Overtravel and rebound show energy control

The mechanism can move beyond final rest and return. Excessive values may indicate damper, buffer or linkage problems; too little can also signal restricted movement.

Contact bounce differs from mechanism rebound

Electrical bounce is repeated contact making or separation, while mechanical rebound is movement of the linkage. The analyser channels must distinguish them.

Baseline comparison is powerful

Trends from the same breaker, sensor method, voltage and temperature are often more diagnostic than generic thresholds.

Engineering application method

  1. Step 1: Mount the transducer according to the breaker-specific fixture and direction.
  2. Step 2: Zero and scale travel before operation.
  3. Step 3: Record travel, contacts, coil current and command voltage together.
  4. Step 4: Calculate velocity only over the specified segment.
  5. Step 5: Compare with manufacturer limits and historical baseline.

Practical example

A breaker can meet opening time but show reduced contact-region velocity and excessive rebound. This pattern can point to damper or lubrication degradation before a timing failure appears.

Common mistakes

  • Mounting the sensor on an unvalidated linkage point.
  • Using full-stroke average velocity.
  • Confusing bounce with rebound.
  • Comparing traces recorded with different scales.
  • Adjusting travel to improve one number without checking contact wipe.

Design and review checklist

  • Is the transducer mounting repeatable?
  • Where is velocity calculated?
  • Are overtravel and rebound within limits?
  • Do electrical and mechanical channels agree?
  • Is a baseline trace available?

Standards basis and official sources

Engineering note: Verify the contracted standard edition, amendments, manufacturer evidence and project-specific studies before applying these principles to a supplied assembly.

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