Timestamp Handling

The IEC60870-5 protocol supports data updates through three types of transmission:

non-timestamped

timestmaped

double transmission

Plant SCADA requires a timestamp to be pushed into the I/O server and the rest of the SCADA system for every data update. Where a protocol has not provided a timestamp, a Plant SCADA driver will typically create a timestamp based on the time the data was received.

A special case exists in the IEC870IP driver, where two input tag address options are available:

• "S" prefix addresses are only updated by protocol messages with a timestamp:

  • SD<IOA>

  • SI<IOA>

  • SL<IOA>

  • SF<IOA>

  • SQD<IOA>

• "Non-S" type tags use a driver manufactured timestamp by default:

  • D<IOA>

  • I<IOA>

  • L<IOA>

  • F<IOA>

  • QD<IOA>

For data archiving and event analysis, Plant SCADA offers event trend and timestamped alarm recording options with millisecond accuracy. To avoid superfluous or missing updates due to out of sequence timestamps during startup, active device transitions, or double transmissions, the IEC870IP driver exposes "S" prefix addresses which are only ever updated by protocol messages with a timestamp.

These tags remain #BAD quality at startup until a message with a timestamp arrives. Messages with a value change but no timestamp will not be pushed to Plant SCADA for these tags.

Double transmission is a IEC60870-5 feature where an RTU will place a high priority value update in its transmit queue as soon as possible after an event. The device will also place a second lower priority message with the same value and also a timestamp.

To capture and action the first high priority data change, a "non-S" tag can be displayed on a page or non-timestamped alarm. Using the "S" prefix tags allows Plant SCADA to archive only the timestamped messages for analysis.

In summary:

• When configuring event trends, timestamped digital or timestamped analog alarms, an "S" prefix tag address should be used.

• When configuring display pages and non-timestmaped alarms, the "non-S" tags should be used.

  Note: You need to carefully consider the tag address you use for timestamped alarms and event trends, as the use of a "non-S" tag may cause a delay in the delivery of information to an operator.

The ManufactureTimestamp parameter

The Citect.ini parameter Data Interrogation Parameters allows one of two options to be selected when configuring "non-S" type tags. The default is to push a driver manufactured timestamp to the I/O server each time for consistency. The alternative option is for the driver to update a tag with a protocol timestamp if one is available. Be aware that this may cause a value displayed on a page to flicker or step backward at times.