7.5 Example: PLC and Network Monitoring
In automation systems the correct working of the I/O
controller (PLC) and network is of highest priority. The
PROFINET interface is designed so that it can monitor the
system for the availability of the I/O controller and the
network.
The typical faults that the PROFINET interface can detect
are:
•
Power loss (I/O controller or network
components).
•
Cable faults (broken cable).
•
Malfunction of networks components (partly).
•
I/O controller program stopped execution.
The Danfoss FC series frequency converters have two
separate functions to monitor and indicate communi-
cations faults:
•
Warning 34, activated by the fieldbus interface to
indicate a fault on the fieldbus.
•
Alarm 17, activated by the frequency converter if
the frequency converter has not received a
control word for a user specified time.
The PROFINET Interface suppresses the warning 34 for the
first 60 s after power-up, this is to allow the I/O controller
to establish communication to the PROFINET interface and
to avoid any sporadic faults while the network
infrastructure is settling.
For monitoring communication from controllers (and the
fieldbus interface) the frequency converter has a function
that monitors the reception of I/O data to the control
word. The monitor feature has a timer that can be set to a
value from 0.5 s up to 6000 s (1.6 Hours). At power-up the
timer is disabled until it receives a valid control word
(CTW).
When the timer is armed, the timer must be retriggered
within the time set in
parameter 8-03 Control Timeout Time
.
Retriggering is done by receiving a new control word. If no
control word is received within this time, the frequency
converter issues alarm 17, and execute one or more
commands:
•
Set the motor into a well-defined state (for
example, stop, trip).
•
Set digital outputs into a well-defined state (for
example, on, off, no change).
By this, the frequency converter reacts in a known way, if
communication faults occur.
Application Examples
PROFINET
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