Rope pull switch RPS

Task of rope pull switches

In contrast to switches with EMERGENCY STOP pushbuttons, rope pull switches have a significantly larger triggering range, as actuation is possible over the entire length of the rope and is not limited to the small area within immediate reach of the switch. Rope pull switches are used wherever extensive danger areas need to be secured.
The advantage of rope pull switches is that plant or machine areas can be shut down immediately from any point in the work area in the event of danger - without the need to install individual EMERGENCY STOP devices at short intervals.

Function and technology of rope pull switches

EN 60947-5-5 - 6 (requirements for EMERGENCY STOP pushbuttons and rope pull switches) defines precise guidelines for the functionality of rope pull switches. For example, the reset of the latching device (EMERGENCY STOP button) must be carried out either by turning a key, turning the pushbutton in the specified direction or by a pulling movement. Rope pull switches are usually activated by pulling on a plastic-coated steel cable.

In addition, EUCHNER's rope pull switches have an EMERGENCY STOP latching switch on the housing that fulfills the same function. When activated, the safety contacts are actuated and a stop signal is generated, which switches the machine off immediately. Similarly, a break or unhooking of the rope must activate an EMERGENCY STOP signal. This means that a defect in the safety system is detected immediately and the safety function is warranted at all times.
For this function, the rope pull switches have a center position and two switch-off positions. During normal machine mode, the switch is in the center position. If the rope is pulled or breaks, the switch changes to one of the switch-off positions and stops the machine. The EUCHNER rope pull switches are also equipped with a window to display the rope position.

Installation and rope attachment

Attachment

According to EN ISO 13850, EMERGENCY STOP devices must be arranged in such a way that they can be easily reached and safely actuated by people at risk. When using wire ropes - as with rope pull switches - visibility can be improved by means of marking flags.

For a proper and safety-compliant version of the pull-wire system, a tensioner spring must be provided on the counter bearing. This enables direction-independent activation at any point along the cable route.

Rope attachment

EUCHNER offers a wide range of accessories for mounting; assembly of the rope pull switches. The pull wire is clamped between the RPS and the counter spring and supported using eyebolts. The support points are set at regular intervals within a few meters.

Changes in direction of the steel rope can be realized using rope pulley blocks. Changes of direction up to a maximum of 90° are possible. The advantage of rope pulley blocks is that the frictional forces between the steel cable and the reversal points are kept to a minimum.

The RPS..SC variants are equipped with a quick-release head that enables the rope to be installed quickly. In addition, the rope tension can be readjusted directly on the quick-release head.

Mounted RPS system:

Rope length and temperature dependency

In applications with rope pull switches, the temperature dependency of the entire system must be taken into account in order to avoid unintentional activation due to temperature-related rope elongation or shrinkage. For this purpose, the possible cable length is determined and the trigger point is regularly readjusted.

The following diagram illustrates the relationship between rope length and temperature fluctuation. Ideally, mounting; assembly should take place at an ambient temperature of 20°C.