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Safety switches NP/GP/TP
General Information
Safety switches are safety-related machine control components
in accordance with EN 954-1 and BGI 575. They are designed to
safely interrupt the safety circuit or to prevent operation until any
danger to the user has been eliminated.
Since safety switches prevent the operation of a system under
certain conditions (generally for as long as the safety guard
remains open), they are also described as interlocking devices.
Interlocking devices are available with or without a guard-locking
device.
According to EN 1088, electromechanical switches with no guard-
locking device must be designed so that they positively switch off
hazardous movement when safety guards are opened. They also
prevent machines from being restarted when the safety guard is
open. EUCHNER safety switches NP, GP are examples of an
interlocking device without a guard-locking device.
In order to ensure that the process is not interrupted by
unintentional opening of the safety guard, safety switches with
electromechanical guard-locking devices are frequently used for
process protection.
A guard-locking device can be used for personal protection, if the
locking magnet is controlled by a standstill monitor and the safety
switch has a fail-safe system for monitoring the solenoid.
With the aid of the interlocking monitoring system, EUCHNER safety
switch TP meets all the necessary conditions for use for personal
protection.
Safety switches NP, GP and TP have been designed so that the
same actuators can be used for both types of switch. For the
design engineer, this offers the advantage of simplicity: If safety
switches with and without a guard-locking device are used, only
the drilling pattern for the switch needs to be modified. The
actuator assembly remains the same. For different applications
where hinged and sliding doors are used, EUCHNER offers straight
or bent actuators. Actuators with rubber bushings facilitate flexi-
ble fastening or bedding of the actuator. Where there is a slight
misalignment of the door, the actuator aligns itself to the switch
actuator opening.
When inserted, spring bearing actuators (so-called hinged
actuators) fit almost friction-free. They are suitable for small hinged
doors with a minimum radius of 100 mm.
In this context, the actuator with overtravel is a particularly
interesting example. When the door is closed, this allows a certain
amount of “play”. In the closed state, the door can move slightly
in the direction of the actuator. With protective doors this is
particularly useful if they have a rubber buffer as a stop. An actuator
with overtravel prevents unintentional stopping of the machine
when the door or actuator (in the case of the NP, GP switch)
springs back.
In practice, a misalignment of the protective doors may be noticed
when in operation. If preventative action is not taken, the actuator
may be driven against the actuator head and damage it when the
door is being closed.
To protect the actuation head, EUCHNER offers a metal funnel for
safety switches NP, GP and TP (see page 42). The use of this
extra component increases the depth of actuator travel and an
overtravel actuatdor does not relieve the system operator from
the responsibility of maintaining the protective door alignment at
regular intervals.
In order to prevent tampering, actuators must be positively
connected to the protective door. It should not be possible to
break the connection with simple tools. All EUCHNER actuators
are supplied with safety screws.
The safety screws and both the straight and bent actuator, are
made of stainless steel. This material property is particularly
necessary for the food and chemical industries where the safety
switch requirements are higher. With their highly resistant housing
material (PA6, a glass-fiber reinforced thermoplastic) and the high
degree of protection IP 67 for safety switches NP, GP and TP,
they can be used in the toughest environmental conditions.
The actuation head in safety switches NP, GP and TP can easily
be changed to any 90° position for the approach direction.
Removing the 4 actuation head screws, the opening for the
actuation head can be rotated to the required approach direction.
If the actuation head is permanent in order to prevent tampering,
it can be secured to the housing with safety screws (see chapter
on accessories).
If an adapter (see page 43) has been installed between the housing
and the actuation head, safety switches NP can be tripped from
the top by actuators with increased overtravel. The unused actuator
opening can be sealed with the cap supplied.
With modern wiring concepts there is a trend towards plug-in
connections. A switch with plug-connectors can be easily replaced
during servicing work. EUCHNER offers safety switches NP and
TP with 6-pole and 11-pole plug connectors. In addition to the
relevant mating connectors, connectors with fixed cables are also
offered as accessories. Safety switches with M12 plug connector
are available on request.