One would think that because the Fieldbus Foundation defines so many other parameters in its standards that the time for the Compel Data message used for the Publish/Subscribe messages on which control in the field is based would also be standardized. Not so. This sometimes makes it difficult for designers to properly estimate the macrocycle requirements, which is unfortunate since in many cases the bandwidth of the Fieldbus system is now the design constraint.
The following are what I have been told are the times for the Compel Data message in various hosts:
• Emerson DeltaV – 30 milliseconds
• ABB – 35 milliseconds
• National Instruments – 30 milliseconds
• Honeywell Experion 15-17 milliseconds
If you have information on the Compel Data time for any other DCS host systems (Yokogawa, Ovation, GE, Invensys, Siemens, Yamatake/Azbil, etc) please reply with comments to this post so other readers can learn this information as well. Thank you for your assistance in expanding the knowledge of our community.
More news about this week's (June 21-23) ISA Communications Division Symposium on Thursday June 23.
