2.4 Quality and traceability
2.4.1 Archive system Definition
Historical values and value patterns are stored in process value archives for documentation purposes. In addition to process values, WinCC also archives messages in the message archive and user data in the user archive. This data (such as alarms and trends) is stored in the inte- grated Microsoft SQL Server runtime databases "Alarms" and "Trends", which you can access directly in many ways (see "Unlimited plant configuration").
The memory requirement is minimal due to powerful, loss- less compression functions. Historical data is necessary to compile essential operational and technical information about the plant:
● What exactly happened in the process? ● When was the specified temperature reached? ● Why was the quality of batch A higher than batch B? Archive size and segmentation made to order
Figure 58 Configuring the short-term archive Process values or messages are stored in a short-term archive, the size of which can be configured by the user. The maximum archiving period can be specified as required by the application at hand, for example, one month, one year, or until a maximum volume of data is reached. Each individual archive can also be segmented.
The following example applies analogously to process value archives: You configure a 100-MB message archive for one week's messages. This message archive consists of 5 indi- vidual segments of 20 MB each for one work day's mes- sages. When the end of the first work day or the individual segment has been reached, the system continues archiving in the second segment. When the end of the week or the message archive has been reached, the first segment is deleted, and the system continues archiving in this segment. In order to ensure seamless, continuous documentation of the process, messages are placed in a backup archive, either locally, on a network drive, or on a long-term archive server, each time the end of a message archive is reached. If necessary, the backup archive can be read out and ana- lyzed with WinCC instruments at any time. The swap out ensures that no data is lost even during long-term archiving.
Process visualization with SIMATIC WinCC 2.4 Quality and traceability Storing messages in the archive
All messages with the "Message is archived" option are placed in the message archive, where additional comments can be added (see "Message system").
All values of a process tag that is assigned to a process value archive are stored internally in archive tags on a continuous basis:
● An analog archive tag stores numerical process values, such Fill level.
● A binary archive tag stores binary process values, such as Motor On/Off.
● A compression tag , for example, stores the average value of the last 60 process values each minute. ● A process-driven tag stores raw data, such as a meas-
urement series of process values.
In order to acquire a measurement series comprising many measurement points or quickly changing process values, a message frame of raw data is transferred from the automa- tion system to WinCC and archived in a process-driven tag. Example: Time stamp, data type, one or more process values of one or more process tags, upper and lower limits for acquisition and archiving. Because the message frame can have varying structures (for example, it is also used by S5/S7 functions), a special standardization DLL breaks down the message frame into individual process values. In the WinCC basic system, up to 512 archive tags can be configured. PowerPacks allow an expansion in the final structure of up to 120,000 archive tags in the central archive server (see WinCC/Central Archive Server option).
Timing
Messages are archived on so-called message events (for example, "Incoming message" or "Message acknowl- edged"). Process values are archived cyclically or on an event-driven basis, depending on the archiving method:
Archiving Parameters Meaning Continuous cyclic: control of the process value Archiving cycle = integer multiple of the acquisi- tion cycle
Cycle in which the process value is stored in the process value archive.
Cycle in which the process value is read from the AS. Continuous selective: control of the process value within an event- driven period Start event Stop event Archiving cycle
Starts the process-value archiving cycle, for example, when the sun shines. Ends the process-value archiving cycle, for example, when it rains or the sun no longer shines.
Cycle in which the process value is to be stored in the process-value archive. Acyclic:
control of critical events
Event The process value is archived when the event occurs, for example, when a given tem- perature is exceeded. Acyclic:
status changes
Value
change The process value is archived each time a change occurs.
An event occurs whenever a connected tag or ANSI C script has a value of "1" or "TRUE". With binary archive tags, you can also indicate the signal change, upon which the process value is archived, for example from 0 to 1. With analog archive tags, you can influence the archiving in the following additional ways:
● Hysteresis for cyclic archiving, absolute or as a percent- age. A process value is archived whenever its value changes by at least a certain percentage (for example, 10%).
● Lower and upper limit: A process value is only archived if it lies between a given lower and upper limit.
● In the case of cyclic archiving from all process values that were read out from the process tag during the pe- riod between acquisition and archiving, an processing function calculates a specified value. This can be the average value, the cumulative value, the minimum or maximum value, the most recent value, or a value calcu- lated by means of a function. This processed value is then archived instead of the acquired process values. Reducing data volume by compression: Example: Every minute, a processing function calculates the average value, for example, of the 60 process values that were processed at a rate of one per second. These calculated values are archived continuously in a separate compression archive, internally in a compression tag. You choose whether the archived process values should be deleted, copied to the compression archive, or moved following compression. Data output
Archived data can be output in runtime:
● Process values in WinCC OnlineTrendControl and WinCC OnlineTableControl (see "User-friendly display of tables and trends")
● Statistical evaluation of process values in WinCC RulerControl
● Process values in F(x) representation in WinCC FunctionTrendControl
● As hard-copy archive logs (see "Reporting and logging system")
● Messages in the message window (see "User-friendly message view")
Special features of the process value archive
● The "Tag Logging Fast" short-term archive stores proc- ess values whose archiving cycle is less than or equal to a definable threshold (for example, <= 1 minute). You can also archive process-driven tags (raw data) and acyclically acquired process values here. The process values are first compressed and stored in a binary file. When a specific file size is reached, they are then trans- ferred to the short-term archive.
● The "Tag Logging Slow" short-term archive stores proc- ess values whose acquisition cycle exceeds a threshold of 1 minute, for example. The process values are written directly to the short-term archive without first being com- pressed.
● You can also store process value archives in the main memory. The advantage of this is that process values can be written to and read very quickly. Disadvantage: Process values archived in the main memory are deleted as soon as runtime is over and are not saved to a backup archive.
2.4 Quality and traceability Process visualization with SIMATIC WinCC ● The Archive Wizard creates preconfigured process-value
archives and compression archives.
● All settings and parameters can be specified not only for one archive tag, but also as default settings for the type as a whole, for example, binary archive tags. Each newly added binary archive tag will then be configured with the default parameters.
● To avoid archive spikes and distribute the archiving load evenly, archiving timing within the archiving cycle can be adjusted on a case-by-case basis.
Special features of the message archive
Configuration data and runtime data are stored for each message:
● Message status
● Time stamp, time difference with respect to "Incoming" status
● Name of PC, application, and user
● Message class, message type, message priority ● Configured message text and colors
● Loop-in alarm
Therefore, if you do subsequently modify the configuration data, the archived message data remains unchanged. Because the entire message context was archived along with the message itself, archived messages are always displayed in their original format, for example, with the archived message type and color.
Special features of the archive system
● You activate the file signature to prevent subsequent changes from being made in a swapped backup archive. ● A configured alternative path for the backup archive is
used if a backup medium is occupied or unavailable (for example, due to a power failure). In this case, system messages are issued accordingly, if configured. ● To access the data of an already swapped backup ar-
chive in runtime, connect the backup archive to the pro- ject, for example, in the Archive System Editor, online in the WinCC controls, or automatically in runtime via VBScript, or by placing the backup archive in the direc- tory "<Project>\CommonArchiving". The archived values are inserted in a configured table and trend in runtime according to your time stamp.
● All swapped WinCC archives can be accessed via the WinCC/DataMonitor and WinCC/ConnectivityPack. ● The WinCC/ConnectivityPack option gives you direct
access to archived process values and messages through interfaces such as WinCC OLE-DB Provider. ● The WinCC/ODK (Open Development Kit) option pro-
vides additional access options.