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Micro switch terminology: force, travel & contact states
Understand operating force, pre-travel, overtravel, movement differential, operating point and contact arrangement before comparing micro switch drawings.
Read the drawing consistently.
Definitions explain how to discuss a mechanism. Use the complete part number's controlled drawing for actual positions, limits and test conditions.
- Operating force (OF)
- The actuator force needed to change the contact state. Compare values at the specified actuation point: a lever and a direct plunger can require different forces.
- Releasing force (RF)
- The actuator force at which the mechanism returns to its normal contact state as the applied load is reduced.
- Pre-travel (PT)
- Actuator movement between the free position and the operating position. Use the drawing datum and direction shown for the exact actuator.
- Overtravel (OT)
- Actuator movement available beyond the operating position. The assembly must remain within the specified travel limit.
- Movement differential (MD)
- The movement between the operating point and the release point. Allow for this difference in the sensing mechanism.
- Total travel (TT)
- The complete actuator movement from the free position to the specified total-travel position. It includes pre-travel and overtravel.
- Free position (FP)
- The actuator position with no external operating force applied, measured from the drawing reference.
- Operating position (OP)
- The actuator position where the contacts change to the operated state. Include mounting and assembly tolerances in the evaluation.
- Releasing position (RP)
- The position where the contacts return to their normal state while the actuator is being released.
- Total-travel position (TTP)
- The actuator position at the specified end of travel. Check how the mechanism limits motion before using it as an assembly stop.
- Normally open / normally closed (NO / NC)
- Contact states refer to the unoperated condition. Verify COM, NO and NC against the exact terminal diagram; do not infer the pinout from a similar housing.
- SPDT / DPDT
- Single-pole double-throw and double-pole double-throw describe contact arrangements. Circuit configuration alone does not establish electrical rating or approval.
- Electrical life / mechanical life
- Electrical endurance is specified under a defined load and test condition. Mechanical endurance describes operation under its stated test conditions. They are not interchangeable service-life promises.
- Rated load / sensing load
- A power-switching rating is not proof of reliable switching at a tiny sensing current. Identify voltage, current, inrush and load type for contact selection.
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