25/03/05 - Information - Innovation Step 2 of the AS-Interface Analyser: New functions and new possibilities




Innovation Step 2 of the AS-Interface Analyser:

New functions and new possibilities

The user appreciates AS-Interface's features such as simplicity, insensibility for disturbances, the robust construction with many options such as tree structure, self-configuration etc. "Almost always" a network once constructed, runs for many years from the beginning without any problem. It can be expanded and adopts a back-up slave automatically e.g. after a mechanical damage. This is all guaranteed by the Master's clever network management.

However, sometimes "almost always" is not sufficient in the user's opinion: In case of an error – even if it makes up much less than 1 percent of the application – the user wants to isolate the cause quickly. In a "normal" case, he occasionally would like to obtain more detailed information. He wants to look over the shoulder of the Master's automatic to learn how stable his net runs and is eager to examine the net more exactly than the system was actually designed to. And the user often wishes to document the state of a network.

In these cases the tool AS-Interface Analyser is the best choice. Bihl+Wiedemann now offers the Innovation Step 2 of the Analyser which absorbed additional requirements from practical experience. This article is about the Analyser's new features. The details already known are described in (1).		  
Figure 1: The "traffic-lights representation" constitutes the central statement of the Analyser.

AS-Interface Analyser:

The functions

  • In the Statistics Mode the entire telegram traffic within the net is statistically analysed. The central view is the traffic-light representation (green-yellow-red, figure 1) which evaluates each slave's ability to communicate and so it gives the user an impression of the function of the examined network.
  • In this manner you can also check the success of modifications and measures for improvement of the network.
  • The protocol of of a network's actual state (see figure 3) is created by these results and can be used e.g. as an acceptance report including configuration, error rate, type of error.
  • In the Data Mode the Analyser displays the topical I/O values of the slaves.
  • In the Trace Mode the Analyser stores the entire telegram traffic and provides it for its examination on a notebook. In this way the course of the communication can be verified in greatest detail applying triggers and filters if required.



Innovation Step 2:

What is new?

  • The definition and determination of "Consecutive Errors" establishes a basis for a network's evaluation made as rationally as possible.
  • The Analyser's LED traffic lights allow checking the network without the help of an attached notebook.
  • Default-settings and offline-processing of the protocols are possible.
  • Topical analog I/O signals and condition of the safety slaves are displayed.
  • The Function of the safety monitor is represented in the "Trace Mode".
  • The Optimized operator guidance permits less experienced users to expand to the "Expert Mode".
  

1 New functions

The Analyser is still the "listener on the AS-Interface network". It supervises and evaluates the entire telegram traffic without intervening. The results are analyzed and displayed on a notebook or a PC (s. box "The Functions").
The version 2.0 of the Analyser brings a whole set of new possibilities in addition to many improvements in detail (s. box "What is new ?").

Figure 2: The functions of the new operation modes: The new functions are highlighted in terms of color.




1.1 Online Statistics and Consecutive Error

The Online Statistics, e.g. the logging of the actuate condition of the facility (Figure 1 and 3), are still the most important points.


Figure 3: Printing the protocol an entire documentation of the actual state of a facility is possible. It comprises the "Overview (traffic lights"), the configuration, the "Advanced statistics", and the "Consecutive errors". It can be manually supplemented by detailed data regarding the facility (e.g. types of devices etc.). The figure shows the summary of the protocol's first page.

The "Consecutive Error" has been newly introduced. It describes for each slave how often a telegram had to be consecutively repeated before getting a valid response telegram. The "Consecutive Error" is another interpretation of the "Online Statistics" which allows a very detailed evaluation of repetitions accepted by many systems (Figure 4, details see below).


Figure 4: The new feature "Consecutive Error" evaluates the telegram repetitions graphically and numerically. The distribution on 6 classes can be visualized with the mouse pointer: Slave 10 has failed completely 3 times.

1.2 Offline Statistics and LED Traffic Lights


The "Offline Statistics" has been largely improved. Now default-settings for the protocols can be forced, statistics and protocols can be stored and be added offline afterwards.
As hitherto the Analyser can be operated as a data collector (for a long period eventually) without being attached to the notebook. In this mode the LEDs serves as "Summation Traffic-Lights" for the network. Therefore, the user can already percept without the notebook if fundamental disturbances on the network has registered while swiching the Analyser on.


1.3 Analog Data and Safety Data


Now both the digital I/O and the analog data are displayed in the "Data mode". The Analyser composes the data triple of the transmission of analog values to a complete value just like a master does.
For all 2 channel Safety at Work slaves the momentary states "released" or "free" are indicated (Figure 5).
Figure 5: The momentary state of the safety slaves is displayed in the "Data Mode" as well.


1.4 Trace Mode and Safety Monitor

The operator guidance of the trace mode has been made more user friendly. So even users less experienced are able to apply this mode.
Another new feature is the interpretation of a trace in the manner of a safety monitor. The user is able to watch in which moments the safety slaves demanded the switch off of the network and in which moments the slaves were released again (Figure 6). Switch-off-situations can be precisely analyzed in combination with filter and trigger settings. The switch off command of the safety monitor can be used as a trigger impulse.


Figure 6: Evaluation of a trace like in a Safety monitor. It shows first the code sequence (in hexadecimal) of the two Safety Slaves with the addresses 1 and 2 and then the changes between "free" and "release" for both Slaves within the trace.

1.5 Trace Mode: Offline Working


Now a trace can be stored in the Analyser's file format ("normal format") or it can be exported to Excel so that the data can be also processed without Analyser. The user can subsequently apply view filters and saftey monitors to files stored in the normal format.


2 The benefits of the Analyser


In our opinion there are four key aspects for the use of the Analyser:

Error or Repetition?


Nobody would interprete the call back "Pardon?" in an interpersonal communication (which is only accustically disturbed) as an error as long as the repetition is clearly articulated and the "Pardon?" does not have to be repeated too many times. The most important aspect: the sender's "Yes" is not received as a "No" by the receiver.
The same applies to every bus system: firstly the message to be transmitted must reach the addressee – the Master (more precisely: the user program) and the slave respectively – correctly: the "Yes" must not become a "No". Secondly the message must arrive on time: the repetition must not lead to a reduction of the data's "availability".
As opposed to the interpersonal communication the "Pardon?" (repetition of a message) is already indicated as a transmission error. And exactly this fact is misleading: A certain amount of repetitions is not only acceptable but it is planned with AS-Interface according to the specification because the two mentioned requirements are fulfilled:
  • Highly effective downlocks prevent that incorrect data (in respect of content) attain to the adressee and are processed there.
  • One single repetition takes only 150 µs because of the brevity of the AS-i telegrams and this value is normally negligible
In praxis, therefore, it is important to distinguish between repetitions and real errors and to evaluate them reasonably. The Analyser relentlessly detects every repetition, even those which do not threaten the function of a network. The user receives a protocol which describes the deviations of his network from the (assumed) ideal network and which points to potential risks. But he has to accept certain repetitions for economical reasons. The traffic lights representation helps the user to decide how many repetitions are acceptable for a standard application. In special cases he can decide himself by means of consecuitve errors.
  1. Bihl+Wiedemann provides the user with the new Analyser, the new Master with advanced diagnostics (2) and the AS-i Tuner. So in case of an error the user is able to identify virtually all disturbances on AS-Interface networks with the help of these tools.
    In the "Statistics Mode" the Analyser offers statistical short- and long-term checks. The traffic-lights represent the evaluation of a standard application's slaves. The data mode shows the topical digital and analog I/O data and the "Trace Mode" makes all telegrams available either entirely or in a filtered form.
    The Master with advanced diagnostics indicates errors formerly hard to be recognized such as duplicate addresses, noise on the AS-Interface signal, and severe common mode oscillations on the AS-Interface line in extreme environments.
    Finally the Tuner enables detecting and eliminating the disturbances caused by the impedance.
  2. The Analyser can create a protocol of the actual state for every new or modified network. This protocol documents the structure and the function.
    Since the Analyser can detect repetitions before they lead to disturbances, the protocol can be a basis for anticipatory maintenance.
  3. Networks working trouble-free can be taken to a special stability test by the Analyser if the user regards it as useful. Thinkable cases: applications whose stop would cause extra high expenses or Safety at Work networks which are less resistant in respect of repetitions due to time constraints.
    The Analyser namely draws an unvarnished picture of the network. In contrast to all Masters (except for special developments for laboratory use) which always suspend the first repetition, the Analyser indicates the first repetition. So you can learn easily how stable a network runs and whether this network could cause trouble if being slightly modified. Or whether a network shows repetitions which can be tolerated because they supposably hardly make for problems (s. box "Error or Repetition?").
    The traffic lights representation of the "Online Statistics" is sufficient for standard applications. It warns if a slave shows more than 1 % repetitions within 1 second (yellow) or it reports an error if the number of repetitions rises up to more than 5 % or if a slave temporary fails completely (red).
    The new feature "Consecutive Error" offers an even more detailed analysis. By classifying the repetitions into different classes, the consecutive error provides a measure for the probability of a "Config-Error". If a valid telegram is sent always after the first repetition already, the risk is low. A high risk is caused if often 5 or 6 telegrams are necessary before a valid telegram appears.

    Therefore, this inspection of a network (with traffic lights representation or consecutive error) is especially recommended for using a Bus Termination also. Since many Masters do not show repetitions, the stability of a 100 m network cannot be achieved with the AS-i Bus Termination eventually. This should be checked.
  4. With the Analyser's data you can partly examine the application controlled by the network. The most important example for this: switch-off situations with Safety-at-Work applications. Here a trace can be analyzed with the help of the function "Safety Monitor" and each change of the application's state before being switched off can be reconstructed by the trigger. Furthermore every 150 µs the "Trace Mode" provides the application with data which allow the user to scan single segments of the application systematically. These examples do not only refer to errors on AS-Interface but directly to the application's optimization.
 



Article as PDF file

Literature
(1) Madelung, O.W.: Der "Lauscher" im Netz. (Ein Analyser für AS-Interface), Computer & Automation, issue 2/2003
(2) Madelung, O.W.: Problem Doppeladressierung geknackt. SPS Magazin, issue 12, decembre 2003, p. 77-79

The article appeared in the SPS-Magazin, issue 5 + 6, May 2005, p. 32 - 34

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