I hope the live blog posts from last week’s Emerson Exchange conference in Texas gave you a flavor for some of the happenings. In one of the posts, 7 Ways Fieldbus Improves Operator Confidence and Performance, I received a great comment back from Emerson’s Jonas Berge and wanted to share it in today’s post:
The real-time status provided by fieldbus enables process problems to be distinguished from device problems, thereby minimizing nuisance shutdowns of the control loop on sensor failure.
Transmitters are digital, controllers are digital, and positioners are digital. I personally believe it doesn’t make sense to run analog signals between them. Fieldbus does not rely on 4-20 mA which means totally digital closed loop that is and time-synchronized from end to end, from sensor to actuator. Eliminating 4-20 mA I/O cards and their associated scan delays and jitter improves control response time which in turn results in tighter control, particularly compared to remote I/O with additional network and link delays.
Doing away with 4-20 mA also does away with multiple D/A and A/D conversions. This leads to higher resolution and accuracy. Errors due to current calibration differences between transmitter output and DCS input are also done away with. This is particularly important in flow and level applications such as tank gauging. The “on-scale” errors associated with 4-20 mA signals are eliminated too.
Fieldbus gets rid of the process variable value skew that sometimes results from mismatched 4-20 mA range settings between transmitters and the control system. Measurement values are also transmitted over the full sensor limit, not limited to a narrow 4-20 mA portion.
Diagnostics not only detect outright failures, but predictive diagnostics can be used to prevent problems by reporting when ambient conditions are exceeded etc. – in real time.
Diagnostics is not just for transmitters and control valves, but also the other half of the instrumentation: discrete devices like intelligent two-wire fieldbus on/off valves and electric actuators / motor operated valves (MOV) using fieldbus also provide diagnostics. NAMUR NE107-compliant device alarm rationalization notify the right person without alarm flooding.
More devices can be added to the existing bus without laying homerun cable or using more I/O cards
These operation & maintenance benefits as well as project benefits are covered in the FF brochure.
Jonas also shared some of his experiences from Emerson Exchange in posts in the Emerson Exchange 365 community. In his post, AMS Suite / Asset Reliability Roadmap, he highlights some of the enhancements presented. Jonas also provided a thoughtful comment to the recap of the presentation, Why are there missing measurements? He notes, “…this presentation really embodies what Peter Zornio called “pervasive sensing” at the opening of the Exchange.”