Siemens SIMATIC NET TeleControl SINAUT ST7, Системное руководство

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Properties of the SINAUT components
1.10 SINAUT ST7sc SCADA Connect software
SINAUT ST7 station control system
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System Manual, 09/2016, C79000-G8976-C178-10
1.10.1 The special properties of SINAUT ST7sc
Acquisition of the process data
The SINAUT station acquires the process data when it changes and transfers it via the WAN
to SINAUT ST7sc. There the received SINAUT messages are decoded and stored in the
ST7sc tag management according to the configuration. Via the OPC server interface "Data
Access" an OPC client can read this received data from the ST7sc tag management. This is
either synchronous or (recommended) asynchronous, in other words the OPC server
interface only transfers the data when there have been changes in the ST7sc tag
management.
In the opposite direction, the OPC client can write data that should be sent to a station (e.g.
commands, setpoints, parameters) to the ST7sc tag management via the OPC server
interface. These are converted to SINAUT data messages and sent via the WAN to the
SINAUT station specified in the configuration.
The item buffering procedure
On special feature of SINAUT systems is the property that process data is backed up to
prevent loss. If, for example, the connection from the station to the control center fails, the
station saves all the data changes detected during the failure locally with a time stamp. This
means that connection failures of several hours or even days can be bridged without loss of
data. So that this data stored in the stations later arrives reliably at the OPC client, ST7sc
has the item buffering procedure that helps to avoid loss of data on the way to the OPC
client:
● when the OPC "Data Access" interface, that represents a process image, is updated by
the SINAUT stations faster than the client can read it;
● when the OPC client is not available for a brief or longer period or when the OPC
communications path fails.
While ST7sc normally only creates one "memory cell" per item in which the latest status or
value of the item is kept ready, when the item buffering procedure is selected a buffer is
created per item in which all changes to the item involved are saved in order with a time
stamp. These changes are stored until the individual changes can be transferred to the OPC
client.
The item buffering procedure requires an HMI application tat can process time-stamped data
even if the time stamp is already several days old, e.g. after a longer connection failure.