SAS Snap Action Safety Pull Switch
Slack/Broken Cable Design
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The Thermo Scientific Ramsey Snap Action Switch (S.A.S.) was specifically designed to function as Slack/Broken Cable type Pull Cord but without the false trips associated with the effects of weather conditions such as temperature variations affecting the cables, ice, snow, wind and vibration.
How it works
Pre-tensioned springs are installed at the extremity each side of the pull cord cable run. Cable tension is kept equal on both sides.
In normal operation, should an emergency present itself, the cable is pulled in any direction and the pull cord switch’s arm rotates clockwise or counter-clockwise thus activating the micro switches in order to alarm. If the cable breaks or becomes slack, the opposing pre-tensioned spring pulls the
arm in that direction. The contact behavior for a cable that has broken is the same as pulling the cable.
Cable lengths are kept equal on opposite sides of the Pull Cord switch. This is particularly suitable to installations prone to wide temperature changes minimizing nuisance trips or stops associated with coef cient of expansion characteristics of actuation cables.
The snap action design uses a two step function. The switch arm must be pulled to a locked position. As a second step, an internal linkage then permits the spring loaded cam to fully rotate ensuring that both micro switches are activated together. This ensures that partial arm rotation due to temperature changes; snow, ice or wind effects on the cable cannot activate one micro switch and not the other.