Limit Switches and other switch types may readily list their travel ratings. Product datasheets may also be referenced for further detailed specifications since these may not be readily listed.
Pretravel otherwise known as Travel is the distance the switch actuator (such as a button or lever) is required to move in order for the contacts to change state, such as from OFF to ON. For multiple throw switches, this may apply to the changing of throws.
Differential Travel is the actuator travel distance between the switch’s closed contact state to the open (released) contact state, otherwise known as the mechanical hysteresis from the ON to OFF position. For multiple throw switches, this may apply to the changing of throws. As an example, if a switch has multiple actuators or buttons, the differential travel may refer to the variation in distances each actuator needs to travel in order to activate its respective set of contacts.
Overtravel is the additional distance the actuator can be pressed or moved beyond the point where the electrical contacts have already closed or altered their state, providing a margin for continued physical movement without affecting the electrical state. Too much overtravel or continued actuation force beyond the overtravel limit can reduce a switch’s life. All switches can tolerate a certain amount of overtravel, and some are provided with a special mechanism that allows a very long overtravel without damage.
Basic ON/OFF Switch Travel Diagram
- Some actuators ON resting position may be more similar or same to the actuators OFF position
- Differential Travel is somewhere between the ON (Pre)travel state and Overtravel state
- Differential travel never applies to momentary switches, only latching switches