31/03/05 - Article - New diagnosis functions on AS-Interface
Automation can be so incredibly easy. The new diagnosis functions on AS-Interface are handled as easily as the system itself. Master of the new generation detect duplicate addresses at once, slaves monitor themselves and the AS-i Analyser by Bihl+Wiedemann provides a complete "fintness check" for the whole system at the push of a button.
Easy installation, simple
usability, high cost-effectiveness, absolute compatibility both within the own
system and with other fieldbusses: The list comprising the most important
reasons for using AS-Interface on the primary level has been very substantial
so far. Now a new argument even extends this list: an extensive package filled
up with diagnosis functions which almost do not require any expertise.
It is
a matter of fact: the best errors are those which do not even occur. AS-i
offers these kind of errors. For example: an unshielded conductor cannot be
shielded incorrectly and where no bus termination is necessary, also none can
be forgotten.
Being a market leader for the primary automation level
AS-Interface constitutes the basis for applications which become always more
complex. Therefore the speed for locating a fault becomes very important. The
AS-Interface technology which offers an extremely low margin of error, sets the
standard, not for the first time. This is in accordance with the AS-i
philosophy: Always a step ahead!
No matter if they are
used as pure controllers or as Gateways respectively Links to other bus
systems: The AS-i Master in Stainless Steel open up real new possibilities in
the field of on-site-diagnosis.
Many users of automation systems know from
their own - often painful - experience how hard it previously turned out to be
to recognise the assignment of one address to two slaves. This problem has
found an end now. Bihl+Wiedemann`s new Master identifies this case and transfer
the error message to the higher PC in order to enable this PC to react
accordingly at once.
For the very first time a Master also contains an earth
fault detector, which so far has only been sold as an additional stand-alone
component. The big advantage of the earth fault detector`s integration: it has
the "direct line" to the controller which can process its signal immediately
and actuate the appropriate procedure via the subordinate fieldbus: such as an
alarm, an immediate stop of the application, a systematic shutdown of the
application or an instant transition to the offline-phase.
Another
additional early-warning-system is the integrated noise detector which
continually checks the analog signal on the bus line. If the noise in the pause
time of the signal exceeds a certain level, an error message will be sent
automatically. In that manner emerging problems can be covered in a state in
which telegram repetitions do not occur yet. Critical situations can thus be
analysed more easily, such as disturbances that are cyclically linked to the
course of a process.
The fourth administrator integrated inside the new
Master is the overvoltage detector. It recognises severe common mode
oscillations on the AS Interface line, which sometimes disturb externally
connected sensors. Due to the highly fluctuating potential this only happens in
extreme cases where other systems would fail completely. But if it really
happens this particular error will not be identified by means different from
the overvoltage detector.
By the way: not only the Masters pave the way to
the AS-i technology as a self-monotoring system. Nowadays the Slaves of AS-i
specifiaction 3.0 have become more than pure "command receivers". The new
profiles permit the transfer of arbitrary amounts of serial data. In this
manner the new profiles offer many additional options for parameterization and
diagnosis.
On the one hand it provides the
user with a complete "fitness check" for the whole system at the push of a
button, on the other hand it reveals the "sanctum" of the system:
Bihl+Wiedemann offers with the new Analyser an all-purpose diagnosis tool for
the AS-Interface.
The "listener" on the network registers and checks all
message traffic. The analyser Integrated into the network as a passive
component and supplied by the network is interoperable like every AS-i device.
This means: it can also be used in a network with products from different
manufacturers.
The standard mode is especially made for users which only
have basic knowledge in AS-i. In this operation mode the messages are analysed
mostly in a statistical manner by the Analyser. The analyser displays the
results on the notebook which is connected to it for the duration of the check
via the RS232 interface. A complete documentation of the system can be printed
out. And this documentation serves for example as basic information for a
application`s extension or as evidence for the system`s functional efficiency
at the moment of handover. In other words: this document can be of great
advantage in many cases.
A special benefit of
the Analyser is its huge velocity. It only needs an average duration of a
test-run to fulfil its task. The tab "overview" already displays an excellent
overview of the system`s "state of health" after a few minutes: the green bar
stands for "slave is communicating normally (including permitted message
repetitions)", yellow means "this slave should be checked" und red indicates "a
major fault, the slave must be checked". Selecting the standard function "Data"
this tab displays the current I/O data of all slaves. This is also refreshed
once a second. Thus the entire periphery data is available for the check of an
application; it does not have to be extracted from the PLC (the host). The tab
"Configuration" allows to store the current network configuration: a function
which especially simplifies the application`s documentation.
After switching
to "Advanced Statistics" the monitor displays the number of repeated messages
for each slave as well as the number of Master calls to each slave. Both are
continually read from the network, totalled and transmitted to the PC each
second. The results of this procedure can be used either to check of the
long-term stability of a network or to control the success of
corrections.
The expert mode leads the user deeply into the system`s
inwards. The Analyser stores all telegrams entirely or selected parts of them
only. So the expert gets the perfect information basis to analyse the data
"offline" on a notebook thereafter.
There are some criteria to select the
data: the moment of the storage`s start is determined by "Trace Trigger", for
example before or after particular events like erroneous telegrams. In order to
extend the regarded period and to allow long-term analysis, additional
contentwise and temporally restrictions can be made by filters. So the
recording process can be reduced to single slaves, specific master calls or
slave answers.
The analyser can record up to 256,000 telegrams (called
frames as well), an amount of data that can be used for analysis of both the
AS-i network and the application.
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Article as PDF file |
The article appeared in shortened version in the AS i Magazin, issue 1, volume 2, p. 10