AS-Interface Analyser
Valuation of Errors
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Subject to reasonable modifications due to technical advances.
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23.
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2006
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6
Valuation of Errors
With the analyser a very effective instrument for the examination of the data traffic
on the AS-Interface line is made available. It indicates each telegram repetition as
an "Error". However, it is the user of the analyser who has to interpret the practical
meaning of such an "error".
AS-Interface was developed as an industrial communication system with an
unshielded cable and therefore, it is used extremely successfully. Single telegram
repetitions are taken into account thereby. They appear if the safety routines de-
tect an incorrect code in a telegram. That forces immediately a first repetition of
the telegram which leads to a delay of approx. 150 µs. If also this repetition
remains unsuccessful also the master attempts two communicate another two
times with this slave during the two following cycles. The analyser registers this as
a "consecutive error. Only if a slave exhibits a consecutive error of the class 6 (a
total of 6 repetitions in 3 cycles in a row), the master takes the slave out of com-
munication automatically and report a "Configuration Error" (the slave is automa-
tically taken up to communication again at the moment it works correct again -
compare AS-Interface specification).
The user of the analysers must know that these repetitions, called "errors", only
interfere with the network level. So the superior control or an actuator obtains no
wrong values. Exactly the safety routines mentioned prevent this.
The new function "Consecutive Error" supplies an important assistance for this in-
terpretation additionally. It shows how frequently successive repetitions took place
in order to receive a valid slave response. Thus, it shows how close a slave was
to log-off from communication. This is to be regarded as a critical case.
6.1
Uncritical Networks
If a net is considered to be "uncritical" in the sense that a short disturbance (e.g.
even a temporary malfunction of a slave) does not threaten the application becau-
se the application does not stop, this state can be tolerated in many cases. One of
these uncritical situations is e.g.: single yellow slaves or even red slaves appear
(beside many green slaves) for hours in a net which is, nevertheless, not "notice-
able" in a different way.
Using AS-Interface single telegram repetitions are (nearly) a normal
subject. The "green" area is defined according to this knowledge
(fig. 3b). Therefore, the detailed results of an analysers in the
"advanced statistics" or in the trace mode must not lead to the
unreasonable demand that each AS-Interface net must run abso-
lutely free of telegram repetitions. In fact the results give indications
concerning the quality and insensitivity to interference of the respec-
tive net. They should be interpreted according to the application and
to the particular situation.
Summary of Contents for as-interface ANALYSER 3RK1 904-3AB01
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