Siemens SIMATICS PCS7 brochure Telecontrol protocols, General/elementary telecontrol functions

© Siemens AG 2011

Telecontrol protocols

General/elementary telecontrol functions

Telecontrol systems use special protocols to implement data transmission between the control center and the outstations (RTUs) at the process level for the automation functions on site. These telecontrol protocols manage the secure and error- free data transmission over the WAN even with a low band- width and poor transmission quality.

In addition to short transmission times for the information, this task requires effective protection of the frames against:

•Undetected bit errors

•Undetected frame errors resulting from synchronization errors

•Undetected loss of information

•Frame falsification

•Segregation or fault in related information

This particularly applies to event-controlled frames over trans- mission channels with a limited bandwidth and uncertain noise response.

Since irregular bit sequences are compiled for data transmis- sion, no limitation in codes must exist.

Time tagging

When linking RTUs by means of SINAUT ST7, DNP3,

IEC 870-5-101 or IEC 870-5-104 telecontrol protocol, the raw data in the outstations is provided with a time tag and trans- mitted to the PCS 7 TeleControl OS (server/single station) acting as control center. Adaptation, further processing, and archiving are carried out here. This procedure is appropriate for the event-based principle of operation of the telecontrol protocol as well as the subsequent chronological processing of data previously buffered in the outstation.

Clock synchronization

The PCS 7 TeleControl OS is the clock master for the RTUs connected by means of SINAUT ST7, DNP3, IEC 870-5-101 or IEC 870-5-104, and regularly synchronizes their date and time via the telecontrol connection. Switching over between sum- mertime and wintertime is also considered during the syn- chronization.

Data buffering

The SINAUT ST7, DNP3, IEC 870-5-101 and IEC 870-5-104 telecontrol protocols support reliable on-site intermediate buffering of the data including time tag, e.g. if a communi- cation path is faulty or a station has failed. In addition, inter- mediate buffering of data can also be an effective means for reducing connection costs in the dial-up network.

A data update for all participating communication partners is performed automatically following debugging or restarting of the failed station. Important events are not lost, and the integrity of the control center archive is assured.

14General/elementary telecontrol functions