5 System monitoring
Positioner DC 6-06 23
5.2.1 Stop request
A stop request is present when 3802 SystemStopRequest = 1. This means that either an
externally selected stop signal is active or a fatal system error has occurred (
10.7
Emergency shutdown errors).
An external stop signal is selected by 2810 SwitchStopRequest (
5.2.1.1 External stop
request by a digital input) or 2809 AnaStopRequest (
5.2.1.2 External stop request by an
analogue input). Both signals are of equal value in the program flow: If one of the two
values is present, then the stop request 3802 SystemStopRequest is active, if both values are
inactive, then 3802 SystemStopRequest is also deactivated unless a fatal error is present.
5.2.1.1 External stop request by a digital input
A digital stop request is indicated by 2810 SwitchStopRequest = 1. The assignment of
a certain digital input to this function is described in detail in
6.1.1 Assignment of
digital inputs.
This stop request can be executed as high-active or low-active by the software. High-
active means that the stop request is only active when the signal = 1. Low-active
means that the stop request is activated when the signal = 0. The desired signal type
is defined with 4811 DigStopOpenOrClose.
4811 DigStopOpenOrClose = 0 Stop request is only active when the switch is
closed
4811 DigStopOpenOrClose = 1 Stop request is only active when the switch is
open
Parameter 4810 DigStopImplsOrSwitch can als
o be used to select whether the stop
will only last for as long as the request itself is active, or whether a one-off switch
impulse is sufficient to activate the stop. In the latter case the stop request is only
terminated when the system is stopped.
4810 DigStopImplsOrSwitch = 0 Stop request is only active when stop
command is present
4810 DigStopImplsOrSwitch = 1 A one-off switch impulse keeps the stop
request active until the system stops
Digital inputs are not monitored for errors and must
not be used for safety-related functions as defined by
classification societies
The use of a monitored analogue input instead of a digital
input for the external stop request is therefore possible.
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