Function Description - Weber PL751A Operation Manual

Operating Manual

2. Function description

Software version: PL751A – V3
The EN81 specifies protection against unintended movement of the lift car in case the doors are
open. In order to fulfil this specification, the PL 751A circuit board has been developed. It can
take on the following monitoring functions:
 Monitoring of type-tested braking elements which are used on lift systems for the
prevention of unintended movement of the lift car in case of open doors, e.g. contact-
monitored brakes or valves or speed restrictors with locking devices.
 Monitoring of the main contactor
 For control units with a setting for approaching and adjusting with open doors, a two-
channel safety switch is often used to bridge the open door and locking switch. Any
unintentional movement is therefore recognised by the PL 751A when the lift car leaves
the door zone with open doors and with the main contactor dropped out.
In case of error, the safety relay K79 on the PL 751A is dropped and the safety circuit opened.
As a result, the lift is shut down. The voltage fail-safe re-start lock prevents unintentional
recommissioning of the system.
Because the main contactors and valve coils are connected at the end of the safety circuit, these
contactors and valves drop out. The current flow to the motor and brakes, or the oil flow from
the cylinder to the hydraulic unit, are interrupted.
The lift stops independently of the individual drop-out time of the braking elements used. This
function is independent of the control unit computer.
The door zone area is normally set to the limits laid down in EN81, however this can be reduced
at any time if required by the system conditions.
It is to be observed that the lift car comes to a standstill within the permissible area after leaving
the flush position of the stop. Should it not stop in time, then the door zone is to be reduced until
the required area complies in all cases.
After an error has been recognised, only an authorised person may re-activate the lift. Switching
off and switching on the main switch, or loss and return of the power supply will not lead to a
reset of the PL 751A. For recommissioning of the lift, actuation of the reset button on the PL
751A is necessary. Additionally, a separate reset button can be connected. This reset button
may only be accessible to qualified persons. A reset signal is also generated via the travel button
of the inspection run equipment.
The correct function of the K79 safety relay is monitored internally via a forcibly actuated NC
contact. After each run, the relay is dropped once and the function of the relay contact and the
safety circuit tap are checked. Should the subsequent input "B2" not be de-energised after
opening the contact K79 in the safety circuit, then the error is stored and activation of the relay
prevented.
The output G1 "OK / Test" is connected to the lift control unit and normally conducts +24V. It is
briefly switched off during the test phase, and in case of an error it is permanently switched off.
The lift control unit interprets a duration of more than two seconds as an error and shuts down
the lift.
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PL 751A
Version 2.0
Weber Lifttechnik GmbH
© Weber Lifttechnik GmbH