On channels on which non-continuous polling is used, use the fields within the Communication Statistics Updates section of the Scan Parameters tab to specify when the communications statistics are updated for the channel.
Non-continuous polling applies to PSTN channels.
It also applies to Direct channels, if one or more of the following situations apply:
- During eavesdropping (when a new system runs in parallel to an existing system—see Using Eavesdropping to Test a New Server’s Configuration)
- Any protocols that rely on exceptional reporting rather than ‘conventional’ scanning. The driver-specific documentation indicates if non-continuous polling is used by a particular protocol.
Where none of the above situations apply to a Direct channel, ClearSCADA ignores the settings in the Communication Statistics Updates section of the Form and updates communications statistics at the end of each System Scan (see Scanning Process).
The Communication Statistics Updates section of the tab contains these fields:
Unless your system has a large number of channels and/or outstations, there should be no need to change these Communication Statistics Updates properties from their defaults. Increasing the Interval, and setting the Offset for multiple channels, can result in reduced CPU load on the ClearSCADA server.
- Interval—Use to specify the frequency at which a channel’s communications statistics are updated. Enter the frequency in the OPC Time Format, for example, 1M for one minute. You can enter the value directly in the field, or use the Interval Window (accessed via the field’s browse button) to specify the required frequency.
- Offset—Use to specify the offset, from midnight, for the first communications statistics update. Thereafter, the statistics are updated at the frequency specified in the Interval field, above.
Enter the offset in the OPC Time Format, for example 30S for a 30-second offset. You can enter the value directly in the field, or use the Interval Window (accessed via the field’s browse button) to specify the required offset.
Example:
The Update Rate for a channel has these settings:
Interval = 1M
Offset = 30S
If the time is currently 00:00:00, the next Communications Statistics update will occur at 00:00:30, followed by another update at 00:01:30, then another update at 00:02:30, and so on, at 1-minute intervals offset to 30-seconds past each minute.
Whenever a Direct channel’s communications statistics are updated as per the settings specified in the Communication Statistics Updates fields, the communications statistics for one of the outstations on that channel are also updated. When the next Interval elapses, the channel’s communications statistics are updated again, along with the communications statistics for the next outstation on the channel. This approach enables each of the outstation’s statistics to be updated in turn, without causing excessive loading on the server and clients. (With PSTN outstations, communication statistics are updated at the end of each call.)
You can view the statistics of an individual channel or outstation via that item’s Status display (see Status Displays in the ClearSCADA Guide to ViewX and WebX Clients). To view the statistics of more than one channel or outstation, display the Channel Scanning Statistics List, or the Outstation Comms. Statistics List, respectively. (For more information on Lists, see the ClearSCADA Guide to Lists.)