Siemens SIMATICS PCS7 brochure Operating modes

© Siemens AG 2011

Operating modes

The communication mode between the control center and outstation (RTU) depends on the support provided by the tele- control protocol, the configuration of the telecontrol commu- nication, and the type of WAN.

The SINAUT ST 7 telecontrol protocol supports the following operating modes:

•Polling

-Control of data exchange by the TIM module of the con- trol center

-The TIM of the control center calls the outstations and node stations one after the other

-Stations with modified data (since the last transmission) send this when called

-Stations without modified data only acknowledge the call

-Transmission of control center data for the stations in between the calls

-Data exchange using internode communication between the stations is possible via the polling TIM of the control center

•Polling with time slot procedure

-Operating mode for a radio network with division of the radio frequency between several providers

-Typically 6 s/min (time slot) for each provider for data exchange

-Data exchange during the time slot is carried out as described under "Polling"

-Following the data exchange, the frequency swaps to the next provider

-Data exchange using internode communication between the stations is possible via the polling TIM of the control center

-Control of the polling TIM by DCF77 or GPS radio-con- trolled clock for exact observation of the time slot

•Multi-master polling with time slot procedure

-Operating mode for communication between outsta- tions and more than one control center via dedicated line or radio network

-Each control center is assigned one or more time slots per minute for polling

-Separate data buffer for each control center in the sta- tions (including node stations)

-Data exchange using internode communication between the stations is possible via the polling TIM of the active control center

-Redundant internode communication is possible; upon failure of the preferred control center, internode commu- nication is carried out via the TIM of the alternative con- trol center

-Each TIM of the control centers involved must be con- trolled by means of a DCF77 or GPS radio-controlled clock for exact observation of the time slot

•Spontaneous mode in dial-up networks

-Data from outstations and node stations can be assigned priorities for transmission in the dial-up network: normal, high, alarm

-Immediate establishment of a dial-up connection for data with alarm priority or high priority; priority trans- mission of alarm frames

-Intermediate storage of data with normal priority; trans- mission during the next dial-up connection with the part- ner in the original chronological order (FIFO principle)

-Transmitted data from the control center always has high priority

-Data exchange possible between the stations with direct internode communication

•Spontaneous mode in the TCP/IP-based WAN

-Establishment of a permanent S7 connection between two TIMs or between TIM and control center

-Exchange of SINAUT ST7-specific data packets via this

S7 connection using S7 communication functions with application of the TCP/IP transport protocol

-If the data transmission costs are related to the data quantity, processing is carried out with priority as with spontaneous mode for dial-up networks: immediate transmission of data with high priority and alarm priority (latter with priority); collection of data with normal prior- ity and transmission in larger blocks

-If the data quantity is not cost-relevant, all data is trans- mitted immediately to the respective partner, i.e. with- out intermediate storage. Message frames with alarm priority then have priority.

SINAUT ST7 telecontrol protocol 19