The present system is a proprietary DCS of the Foxboro I/A series brand. The particular DCS uses non-redundant controllers which have been responsible for spurious shutdowns. In reviewing options for upgrading the DCS and improving its performance, we've considered the following:

1.Upgrading the non-redundant controllers to redundant 'hot-spares' controllers.

2. Upgrading the proprietary DCS to a Foundation Field Bus system.

I would appreciate any information on the 2nd option: upgrading from a classical proprietary control system to a foundation fieldbus system, and the consequent challenges and benefits. Specifically, I would like real life success/failure data and gains/losses with respect to: cost, system down-time, operational efficiency and maintainability.

Thank you very much.

 

If the invalid shutdowns are being caused by controller failures, making them redundant might help, but the cause of failure still needs to be assessed and remediated. If I/O or power supply issues are causing the problem, then redundant controllers or control upgrade may not help. Most control upgrade projects will require a safety, regulatory or cost justification. Are the controllers really the root cause? Often, inadequate or improperly maintained instrumentation can cause similar problems. The control logic could also be an issue...

 

The major "hassle" of upgrading the system to FF is that you also need to change your devices to FF and the wiring may need to be modified as well. However, you may want to get away from analog signal transmission anyway.

Whenever centralized controllers are used you need redundancy to get availability. This applies universally, regardless if analog or bus devices are used. However, using FF you could decentralize control to the field devices getting - eliminating the need for redundancy. But, completely decentralizing control to the field has other challenges. If you contact me on the address below we (SMAR) can advise you in more detail. For starters we have a white paper that addresses the pros and cons of control in the field.

To learn more about fieldbus migration, take a look at chapter 5 of the yellow book "Fieldbuses for Process Control: Engineering, Operation, and Maintenance" buy online:
http://www.isa.org/fieldbuses

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus and Ethernet at your own pace: www.isa.org/fieldbuses
Learn OPC and automation software at your own pace: www.isa.org/autosoftware

 

Since you are planning to replace or at least upgrade the "I/O" portion of your control system this is certainly the right time to consider migrating to FF. HOWEVER, moving to FF requires that you also change out your field instruments as well. If you are NOT prepared to do so at this time, then the field is open as far as which DCS product you use. (They are all proprietary to at least some extent once you get "inside" the controller.)

Most manufacturers make conversion kits to go from one manufacturer to another though if you change manufacturers you will also have to migrate all your control and applications.

FF is the way of the future so I would encourage you to post again to the list or myself (iverhappen-at-member.isa.org) if you would like more information on what is required to make this migration. My initial guess is that your most economic option is your option 1.

Ian Verhappen

 

1) Spurious tripping shall be avoided in case trip the system/plant due malfunctionning single controller by changing Redundant controller.

2)Upgradation of conventional DCS to FF system, following shall be stricly considered :
a)Replace/upgrade all field instruments from conventional to FF devices
b) Existing DCS processor may not able to handle FF devices if required need to be upgraded.
c)Conventional I/O modules to be replaced by Fieldbus Interface Module with suitable power supply etc.