In the case of a change, the telecontrol substation detects the process data and transfers it over the relevant WAN to SINAUT ST7sc. The received SINAUT messages are decoded here and stored in the ST7sc variable list as configured. An OPC client can read these received data from the ST7sc variable list via the OPC server interface "Data Access". This is performed either synchronously or asynchronously.

In the reverse direction, the OPC client can write data that is to be sent to a station (e.g. commands, set points, parameters) to the ST7sc variable list via the OPC server interface. These are converted to SINAUT data frames and sent via the WAN to the telecontrol substation specified by means of configuration.

A special feature of the telecontrol system is that process data are protected against loss. If the connection from the substation to the control room fails, for example, the local substation will save all the data changes that occur during the downtime complete with time stamps. This ensures that connection downtimes of several hours or even several days can be bridged without loss of data. So that the data saved in the substations will also arrive at the OPC client safely later, ST7sc contains the "item buffering" procedure, which helps to avoid data loss on the way to the OPC client:

• When the OPC "data access" interface that represents a process image is updated by the substations faster than the client can read it;
• When the OPC client is not available for a shorter or longer time or when the OPC communication path fails.

ST7sc normally only creates one "memory cell" per item in which the last status or value of the item is retained, but when the item buffering procedure is selected, one buffer is created per item in which all changes to the affected item are saved consecutively complete with time stamps. Saving is performed until the individual changes can be transferred to the OPC client.

The item buffering procedure requires an HMI application that can process time-stamped data even when the time stamp is several days old, e.g. following a long connection failure.

System configuration with SINAUT ST7sc

Redundant application

SINAUT ST7sc supports connection to a redundant client system. Two ST7sc systems must be used in this case. The data received from the stations are transferred by them in parallel and mutually independently to both clients and data are received from the clients that must be sent to the substations.

The redundancy mechanisms are located in this case on the client side:

• The client ensures that the data transferred in parallel is evaluated and compared correctly;
• The client transfers data to be sent to the substation once only to one of the two ST7sc, so that transmission is not duplicated.

Configuration

The ST7sc is configured using the ST7sc Config tool that is included in the scope of supply of the ST7sc software CD.

The documentation for the ST7sc and the Config tool is also located on this CD.