Safety Limit Switch Topic: Pretravel

FAQ No. FAQ02292

Question

What is pretravel (PT)?

Answer

Refer to the following table of terms for operating characteristics.

Operating Status

Classification Term Abbreviation Unit Definition
Force Operating
Force OF N, Nm The force needed to be applied to the Actuator to move from the free position to the operating position.
Direct
Opening
Force DOF
(See note 2.) N, Nm The force needed to be applied to the Actuator to move from the operating position to the direct opening position.
Total
Travel
Force TTF N, Nm The force needed to be applied to the Actuator to move from the free position to the total travel position.
Travel Pretravel PT mm, ° The travel distance or angle from the free position to the travel position of the Actuator.
Direct
Opening
Travel DOT
(See note 2.) mm, ° The travel distance or angle from the free position to the direct opening position of the Actuator.
Total
Travel TT mm, ° The travel distance or angle of the Actuator from the free position to the total travel position.
Position Free
Position FP mm, ° The Actuator position when no external force is applied.
Operating
Position OP
(See note 1.) mm, ° The position where the moving contact starts to open or close when an external force is applied to the Actuator.
Direct Opening Position DOP
(See note 1.) mm, °
The Actuator position when the moving contacts are directly open when an external force is applied to the Actuator.
Total
Travel
Position TTP mm, ° The Actuator position when the Actuator has reached the stopper.

Note 1: For slow-operating safety switches, the operating position (OP) and return position (RP) are almost identical.

Note 2: The DOF, DOT, and DOP values were specified to ensure that the direct opening mechanism (forcibly opened contacts) functions correctly.

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