Update and bump: The whitepaper, DCS Controller Loading Reduction for Sequence Logic - A Boiler Control Project Case Study, is now available.

Original post:

Let's close this week with a post about sequence control loading improvements in boiler operations. I managed to get my hands on a draft of a whitepaper from Emerson's Shawn Zadeh who is a Process Automation Engineer on the Process Systems and Solutions team.

For one particular boiler control project, Shawn and a colleague observed that the DeltaV controller processor Free Time statistic was very good on the two controllers being used. With everything being mostly the same on the project vs. other projects with respect to motor control modules (CMs), control loop CMs, and discrete input CMs; the only striking exception was the way they chose to complete sequences.

Sequential tasks are often handled using IEC 848 sequential function charts (SFCs). In the whitepaper, Shawn notes there have been previous project tradeoffs in SFC implementations with controller scan rates and controller free time. The logic can be intensive when following the ISA-88 (S88) model with phase modules running SFCs that are often used in equipment modules. Shawn describes the upside to SFCs that are easy to understand because they clearly and simply represent the steps of the process. SFCs also work well for high-level programming of control sequences. They are familiar to many people, because SFC is one of the languages specified in IEC 61131-3, and they are used frequently in programming PLCs. And SFCs are self-documenting and easy to troubleshoot and debug.

For those not familiar with SFCs, it consists of a series of steps linked by transitions. A step is essentially a state of the system, and can be active or inactive (idle); the initial step is always active at start-up. Some steps have actions associated with them (open a valve, close a gate, etc.) that will be performed only if the step is active. A transition is enabled when the step preceding it is active and the logical condition(s) for the transition are satisfied. When a transition is enabled the step preceding it becomes idle and the one following it becomes active.

What Shawn and team did was to develop a technique for programming DeltaV systems for boiler control that replaces SFCs with function blocks to align with standard boiler control conventions, but had the unanticipated effect of using a very low amount of controller processing time as well. Function blocks, defined by IEC 61499, cover a broad range of applications. They are used traditionally for continuous control, but work quite well for discrete control. Function blocks are easy to use, help reduce training requirements, allow reuse of programming elements, and can reduce processor loading compared to SFCs.

For the sequence control strategy, the control module was broken into two main sections: the Sequence Control Initiation area and the Control Sequence Operation and Shutdown area. They wanted to delineate where the sequence setpoint is determined and where the sequence actions and confirmations are in order to facilitate troubleshooting. Shawn shared that the combination of the two areas that can handle failure detection (through the use of interlock and permissive functions), using a standard interface, and the connection between the two areas and the sequence logic contained in a top-down format that's easy to read is unique.

Using this approach, the project controllers could perform complete unit operation control (i.e. sequence and continuous control) at a 200ms scan rate, which can satisfy nearly all non-SIS process and manufacturing control requirements. Operational runtime has proven this approach to be a robust method for the sequencing requirements found in these types of boiler project. Shawn sees reuse of this approach on modules that require fast scan times on multiple units/independent sequences running on a single controller.

I'll update the post once the whitepaper is finalized and available on the www.EmersonProcess.com website. DCS Controller Loading Reduction for Sequence Logic - A Boiler Control Project Case Study.

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Posting will be lighter this week than normal. I'm in Atlanta for the ISA Marketing and Sales Summit. I'll be speaking with automation supplier sales and marketing folks on my favorite topic, social media. The talk is titled, Social Media--Should We, Should We Not, or Should We Just Ignore the Whole Thing.

The talk will be live-streamed, beginning at 8:30am EDT/12:30UTC on Thursday, September 2.

If you are a sales or marketing person, or want to know how we think, feel free to join us.

There is also an active Twitter conversation happening for the event with the #ISAms twitter hashtag. By following Twitter searches of this hashtag, you can connect with folks at the event and follow the happenings, even if you're not present.

Like last year, our Emerson Exchange coming later this month will use the hashtag #EMRex to help connect Twitter conversations around the event.

Update: Here's the presentation uploaded to SlideShare:

The recorded video is available on the ISA Marketing and Sales Summit site. My portion begins at the 37 minute mark.

A week ago, I highlighted a whitepaper sharing some of the advantages in top-mounting DP flow transmitters in steam applications. The whitepaper's author, Emily Vinella, pointed me to a presentation, What Do You Know About Wireless DP Flow?, which will be given by Emerson's Kyle Nelson and Nathan Stokes at the upcoming Emerson Exchange.

Kyle and Nathan point out that DP [differential pressure] flow measurement continues to be the most often used type of flow measurement, is well understood, and that the measurements are inherently accurate, repeatable, and have quick response times. Smart transmitters dynamically compensate in real-time based on pressure, temperature, density, and flow rate.

Wireless DP flow devices, base on the IEC 62591 WirelessHART standard, open up areas of the plant that may not have been measured because of distance, difficulty, or expense to install wired devices. Four wireless DP flow measurement options are available including integrated wireless on a single variable DP flowmeter, single variable transmitter with a wireless THUM adaptor, separate transmitters with integral wireless to achieve multivariable compensation, and multivariable transmitters with wireless THUM adaptors. The best option is a function of what is currently installed in the facility.

In the presentation, Kyle and Nathan review installation examples for each option. I'll pick the first one, integrated wireless on a single variable DP flowmeter highlight the shared examples. A silicone manufacturer needed to measure 365degF saturated steam flow. These measurements had to be installed in physically challenging to reach locations and wide ambient range conditions, down to -20degF. Other flow measurement technologies had been tried without success. Their solution was to top-mount the wireless DP flowmeters and eliminate $40K of wiring, $15K heat tracing, and $2K impulse lines. By adding these measurements they improved ongoing energy management, reduced operating and maintenance costs, and increased overall safe operations.

A second application was on a steel roll cooling system for a steel manufacturer. They needed better cooling management to accommodate heavier and wider material. Due to a difficult installation location, the cooling system had been manually managed. As larger material was introduced into the manufacturing processes, the defect rate began to increase. The solution was to install four wireless Annubar Flowmeters to allow the water cooling spray to be finally tuned to reduce the defect rate. In addition to the quality improvements, unplanned downtime was reduced, and maintenance costs were lowered from reduced grease system and bearing failures.

Kyle and Nathan describe other applications including diesel and kerosene production measurement, wellhead steam injection, and energy management measurement for environmental reporting. Each had unique challenges that led to the selection of one of the four wireless options.

If you'll be at the Emerson Exchange and have opportunities to add flow measurement to improve your process or address regulatory requirements, make sure to stop by one of Kyle and Nathan's two workshops.

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Emerson's Gordon Lawther, an automation system modernization specialist, will be presenting at this year's Emerson Exchange. His presentation, Total Installed and Commissioned Cost Savings using Electronic Marshalling in Brownfield Modernization Projects pretty much sums up its focus.

Gordon cites a recent ARC Advisory Group study that estimates $53 billion USD in installed control systems that have been in operation for more than 20 years. If you consider the technology changes in your personal life in the last twenty years, you'll appreciate the advancements in system capabilities.

Gordon and the modernization team performed an analysis for a specialty chemical process manufacturer seeking to replace a 20+ year old system. The objective of the analysis was to consider the total installed and commissioned cost including the control system equipment, front-end engineering design, electrical and instrumentation (E&I) design engineering, control system configuration, training, installation, cutover and commissioning, startup, freight, taxes, and contingency.

The analysis considered replacing the I/O with low-density I/O (8 channels/card), high-density I/O (32 channels/card), and electronically marshalled I/O. The plant staff wanted to reuse as much of the existing cabinets as possible, and reuse some of the existing wire marshalling infrastructure. The plant had two rack rooms 300 feet apart. The cutover would occur during a plant turnaround so the analysis did not have to consider a hot cutover case.

Gordon enumerates some assumptions. Some of these included:

• Cabinets have commonly used dimensions with a 19" rail
• Power and networking connections are included in the estimations
• DeltaV controllers and I/O won't be mounted in existing marshalling or field termination cabinets
• Existing wiring does not have enough slack to reach DeltaV controller I/O locations
• Electronically marshalled I/O can be oriented to accommodate existing wiring in the same cabinet
• No new field wiring or instrumentation is included in the scope

For each case, the team performed a project task analysis. This analysis looked at the work associated with the new controllers and the associated wire marshalling. For the base case with low-density I/O, the work steps associated with the new controller included I/O lists & controller sizing, cabinet layout, power & grounding for controller and I/O cards, and I/O wiring schematics. The marshalling tasks included cabinet layout, terminations / interposing relay design, wiring schematics, and home run cables between the two rack rooms.

For the case with electronic marshalling, the steps eliminated for the new controllers were I/O card power and grounding, I/O wiring schematics, and home run cables. Steps were added to the marshalling tasks including the CHARM I/O card assembly, power and grounding for the individual CHARMs, and network layout.

Through this project task analysis, the electronic marshalling case estimated 63% lower installation costs, and 38% lower E&I design costs. The cost of the control system hardware was higher for the electronic marshalling case. Overall total installed and commissioned cost was 26% lower for the electronic marshalling case. With the high-density I/O case, the cost differential was reduced to 8%. Gordon notes the electronic marshalling case also provided single channel integrity, redundancy down to the individual I/O channel, design and installation flexibility, and the ability to bind each I/O channel to any controller up to 4 controllers per CHARM I/O card.

Gordon sums up his findings that the electronic marshalling approach reduces DCS cabinet design and complexity of the drawings, reduces wiring terminations and multi-core home run cables, reduces rack room footprint with the amount depending on whether the CHARMS are located in the rack room or out in the field junction boxes with a network connection back to the rack room.

If you're among the ARC Advisory Group's $53B club and at the Emerson Exchange, you may want to attend one of Gordon's two workshops. His presentation is loaded with visual builds to better convey the alternatives in this analysis.

MP3 | iTunes