Error Diagnosis IM 308-B
99
05/01 AWB2700-1384GB
9
Solution
X
Operate PLC without battery. Acknowledge delay is not stored.
X
Operate IM 308B without acknowledge delay and monitor in
cycles
X
Program measures for the acknowledge delay in the OBs
h
In an installation a PLC start-up problem occured when the
installation was switched off via the main switch. The PLC did
not restart because an acknowledge delay occured that is
programmed by the master interface module IM 308B. This
acknowledge delay is important in order to avoid a certain state
in the installation when a slave fails when no cyclic monitoring
of the IM 308B has been programmed.
The start-up problems above did not occur when the installation
was manually started and when the PLC power supply was
switched on and off.
The acknowledge delay during start-up was caused by the
following reason:
When the installation is switched off, the general power supply
is initially interrupted which also supplies the DP slaves. One
second later, the power supply of the PLC is interrupted. That
means, before the PLC is switched off, there is enough time for a
station failure to be noted and an acknowledge delay to be sent
to the CPU. Because this message is not acknowledged, the error
is still present at start-up. Therefore the PLC does not start and
must be manually started.
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