Complex upgrades demand advanced expertise
Partial upgrades to existing automation systems can be difficult, requiring close cooperation between the system integrator and plant personnel.
When it comes to upgrading automation systems, some of the most difficult projects are partial upgrades where some components must be replaced while others must be left in place, often for budgetary reasons. For many of these projects, extended downtime is not an option, increasing the degree of difficulty. Water and wastewater plants often are particularly susceptible to these problems because of aging control systems, limited budgets, and requirements for continuous uptime (see Figure 1).
Projects involving partial upgrades require a close partnership between the end user and the system integrator throughout the project, from design to startup. Inevitably, issues with existing hardware and software, and the integration between old and new, are found after the contract is signed. Only a true partnering arrangement, where both parties are committed to each other for the long term, can allow each of these issues to be addressed with little or no impact on the project cost, schedule, and performance.
The two water/wastewater projects described in this article fit that description. Each was completed successfully through a partnership between a municipality and Tesco Controls Inc., a system integrator specializing in the water/wastewater industry.
Project 1: Replacing, converting, and upgrading
A ground-water treatment plant was running two different Wonderware InTouch (v. 9.5) supervisory control and data acquisition (SCADA) applications on obsolete Microsoft Windows XP computers. Each was communicating to in-plant Square D SyMax programmable logic controllers (PLCs) over a legacy serial SyNet communication protocol and media. Several remote SyMax PLCs also were connected to the SCADA system over a serial radio link.
The municipality’s ultimate goal was to replace all legacy PLCs at both in-plant and remote sites, but the project was budgeted for a phased approach, with only three PLCs initially slated for replacement. In the first phase, one in-plant PLC and two remote PLCs would be replaced with a hot-standby Schneider Modicon M580 PLC and Schneider Modicon M340 PLCs, respectively. The remaining plant and remote PLCs would be replaced in future phases. However, the municipality needed to keep the other existing in-plant and remote SyMax PLCs communicating and operating during the upgrade process (see Figure 2).
The second goal was to upgrade the SCADA software and hardware to Wonderware InTouch for System Platform 2017, running on a virtualized infrastructure. This entailed migrating existing InTouch screens communicating to the nonupgraded plant and remote PLCs to the System Platform application, while developing new screens following updated end user standards.
The main challenges of this project included:
- Migrating a critical process in an operational water treatment plant
- Minimizing downtime to keep the plant online and producing water
- Maintaining visibility and alarming at the SCADA system through the transition
- Minimizing the amount of plant staff needed to run the plant manually during cutovers
- Performing cutovers within 8-hour staff availability windows
- Performing a phased integration where only part of the plant would be upgraded
- Maintaining the legacy serial radio network communicating to remote sites
- Performing the migration with incomplete documentation of the existing control system, including missing details of the existing PLC software and panel wiring.
These challenges required Tesco to:
- Determine the best approach for a legacy migration from Square D SyMax PLCs to new Schneider M580 and M340 PLCs
- Reverse-engineer the existing SyMax PLC code to be reprogrammed in Schneider Unity software for the new Schneider PLCs
- Port over legacy components until a future phase of the project
- Upgrade the SCADA system hardware and software.
Replacing PLCs and converting protocols. Since the existing in-plant SyMax PLCs had to remain online, Tesco used a Niobrara R&D Modbus serial-to-Ethernet bridge module to bridge the existing SyNet network to the new Modbus TCP network as seamlessly as possible. This is shown in the upper part of the partial upgrade system architecture diagram in Figure 2. Bridging the new and old networks with the serial-to-Ethernet bridge module allowed the existing SyMax PLCs to establish peer-to-peer communication with the new M580 PLC while maintaining communications with the SCADA system.
To facilitate the roadmap for the future project phases, Tesco coordinated with the municipality to install an additional serial-to-Ethernet bridge module at each upgraded remote site to convert the serial radio communication protocol to Modbus TCP, which was required by the upgraded remote PLCs. This was critical to keeping costs down for the current project until the district could install a new radio system in future phases. This serial-to-Ethernet bridge solution successfully maintained a high standard of reliability for the current communications infrastructure.
SCADA upgrade. Since the plant could not be taken offline, the cutover process for the SCADA upgrade was planned carefully and coordinated between the contractor and the operations group, with the end user’s project manager taking a central role in synchronizing the different elements of the upgrade. Strong communication between these teams was paramount to the success of this project. The cutover was workshopped over several months with all involved parties into a three-part process.
Part one of the cutover involved all equipment out of service, so that the running process would not be interrupted. This also allowed the integration team to check its cutover plan against the reality of challenges that could develop in the field, such as wiring not being landed where indicated on as-built project drawings, and wiring not connected to field assets outside of the panels being modified. It was a necessary safeguard that allowed the team to test the approach. The success of this part of the cutover familiarized the team with the reality of the field conditions.
Part two of the cutover involved equipment in service but in a standby state. If a piece of equipment was in use and encountered unexpected downtime, the cutover standby equipment could be brought into immediate use. At this juncture, communication between the old SyNet network and the new Modbus TCP network became necessary because of the requirement of peer-to-peer communication between legacy and new PLCs. Additionally, the new SCADA system was communicating with the new in-plant PLC and tested against all field inputs and outputs.
Part three of the cutover involved the remaining in-service and live equipment. With parts one and two successfully completed, the project teams were familiar with and confident in the cutover approach. Operations first changed the plant over to use redundant equipment, made ready in part two of the cutover, where applicable. The system being cutover was divided into two trains (Train 1 and Train 2), only one of which was in service at a given time. This allowed the team to place one train in service, then cut over the train not in use. The newly upgraded train was then placed in service, and the remaining train was cut over, completing the SCADA upgrade.
The new Wonderware System Platform 2017 software was installed on an HP Server PC running Microsoft/Hyper-V Failover High-Availability Clusters with off-premises cluster redundancy connected by a wide area network (WAN). All the Wonderware System Platform virtual machines (VMs) were hosted within this cluster.
The SCADA system now includes an operator interface that allows monitoring and control of plant and remote assets with reporting, trending, alarm generation, event recording, and other features. All of these features are delivered to desktop through Microsoft Remote Desktop Services.
Project 1 results. The purpose of this project was to upgrade plant operations by improving PLC maintainability and SCADA robustness, while keeping the existing plant operations intact. The former SCADA system relied on long-outdated technology. Additionally, the old computers were equipped with SyNet proprietary daughter cards that plugged directly into the SyNet network via the Windows XP computer motherboard.
Through this project, these outdated and unsupported physical-world liabilities were replaced with a new, virtualized SCADA system, subject to backups of all virtual machines as simple data that can be copied off to a storage device. This significantly improved the end user’s disaster recovery capability. The obsolete Windows XP computers were replaced with Microsoft Hyper-V cluster-based Microsoft 2016 Datacenter Edition virtual images.
With a SCADA system that is modern and up-to-date, the end user can stop worrying about where to procure the parts to support a generation of obsolete operating systems and control software. There is an expected future cost savings in operator and maintenance outlays as the new architecture alleviates the end user’s focus from maintaining their tools to producing and delivering high quality water to their consumers.
Project 2: PLC consolidation and SCADA software upgrade
In this municipal wastewater treatment plant, a SCADA system using Rockwell Automation FactoryTalk View SE (v. 7.0) communicated with more than 15 Allen-Bradley PLC-5s used for process control. Several other PLCs, primarily Allen-Bradley MicroLogix models, were used for additional control. The SCADA system communicated to a ControlLogix gateway via EtherNet/IP, and this gateway converted the protocol to DH+ to communicate with the PLC-5 network.
The end user wanted to combine all of these existing PLCs into three hot-standby pairs of Allen-Bradley ControlLogix PLCs, each operating remote input/output (RIO) devices that communicated over the plant’s fiberoptic EtherNet/IP network.
As each of the remaining PLCs was converted to become RIO, the associated process control logic needed to be migrated to one of the three ControlLogix masters. Also required was a SCADA update to FactoryTalk View SE (v. 8.1) and the removal of the existing ControlLogix gateway, which was no longer needed because the DH+ network was eliminated with the retirement of the PLC-5s.
The main challenges of this project included:
- Consolidating existing PLC peer-to-peer communications into three new ControlLogix master PLCs
- Maintaining active communications on both the EtherNet/IP and the DH+ networks during the migration
- Maintaining setpoints and statistical data when updating each PLC
- Reusing existing analog signal line filters from PLC to equipment
- Automating the SCADA database conversion from PLC-5 tags to ControlLogix tags
- Reusing the existing PLC-5 16-bit structure to the greatest extent possible while properly migrating it into ControlLogix syntax and 32-bit structure
- Keeping downtime to a maximum of six hours for any process area, which required short cutover windows to maintain plant operations
- Assisting the end user with contingency plan development for manual plant operations during PLC cutovers.
PLC consolidation. Tesco leveraged Rockwell Automation conversion products and tools to migrate both the Allen-Bradley hardware and Rockwell Software (see Figure 3). Designing with the hardware retrofit kit allowed Tesco to maintain the original PLC-5 I/O terminations, and to couple these terminations with harnesses to the new ControlLogix hardware.
Using the software conversion tool enabled Tesco to substantially maintain the existing PLC-5 coding style in ControlLogix, but with some code revisions required per Rockwell Automation recommendations:
- Analog scaling had to be confirmed for every point, as I/O card handling changed significantly between PLC generations. PLC-5 systems used specific block transfer reads and writes (BTRs and BTWs) to access the data, while ControlLogix systems presented the data through the I/O tree, but often required additional moves or scaling instructions to be applied to replicate the original program.
- Communication and message blocks between PLC-5s used DH+, and these blocks between PLC-5s and ControlLogix, used an EtherNet/IP to DH+ gateway. Every instance required particular attention to accommodate the new architecture.
- Proportional-integral-derivative (PID) control had slight differences between PLC generations, particularly with regard to input and output scaling. The migration was performed by maintaining existing registers and SCADA tags for compatibility with the original logic and SCADA systems, but converting the values as necessary for appropriate operation with the ControlLogix PID block and structure.
- PLC-5 timers had different time scales than ControlLogix, which use milliseconds exclusively. Therefore, the new ControlLogix code and SCADA application needed to be configured to accommodate the time scales.
To minimize downtime, a hot onsite cutover was required. Tesco performed the migration of code following these steps in sequence, for each original PLC:
- Upload the live existing PLC-5 program to get current setpoint values.
- Convert the uploaded PLC-5 program to ControlLogix using the conversion tool.
- Download the resultant ControlLogix program to an intermediate ControlLogix PLC.
- Use the conversion tool to handle current setpoint values and transfer them into the intermediate PLC.
- Transfer the resultant program from the intermediate ControlLogix PLC to the proper master ControlLogix PLC, ensuring there are no conflicts.
SCADA upgrade. Tesco leveraged tools to convert existing PLC-5 tags and replicate them to ControlLogix tags. To speed this process and eliminate any errors arising from manual conversion, Tesco developed a software tool to automate tag conversion. Taking one process area at a time, a new tag set was uploaded to the existing SCADA system for testing.
Project 2 results. Through good documentation practices, appropriate contingency plans, and a thorough understanding of the plant’s operational characteristics and the end user’s goals, Tesco was able to perform a relatively seamless hot cutover of the PLCs. Tesco was able to cutover one PLC per day, with approximately 20 minutes spent for the physical hot cutover, and the remainder of the day was used for testing and verification.
Greenfield automation projects can be designed upfront with a great deal of certainty. The same is true to a lesser extent with rip-and-replace projects where the entire automation system is upgraded, sometimes with significant outage time, often only leaving the field wiring and instrumentation in place.
This is not the case with projects requiring incremental, partial upgrades to an automation system and demanding minimal-outage cutovers. These types of projects invariably have unforeseen issues arising throughout the execution stage, long after the contract has been signed.
Inexperienced system integrators may underestimate the full scope and complexity of these types of projects. This can lead to numerous change orders and delay requests as issues arise during project execution.
End users with complex upgrade projects should instead seek an experienced and informed system integrator with a history of developing and maintaining long term relationships with their clients. This will allow these types of projects to be executed on time and at budget, while meeting or exceeding all performance requirements.
Stephen Goldsworth is the systems engineering group manager at Tesco Controls Inc. He leads the team responsible for performing end user system assessments and designing efficient, user-friendly automation systems. He has a thorough understanding of unique processes and a broad perspective on many technologies and systems used in process automation.
Raju Nair is PLC programming manager at Tesco. He establishes the technical process requirements for the company’s projects and performance teams. He has coordinated multiple complex projects for water/wastewater and renewable energy, including one of the largest EPA clean-ups in the U.S. He possesses a solid understanding of PLC programming best practices, and has led the company in the standardization and templating of PLC coding.
Jonathon Shores, a member of Tesco’s Systems Engineering Group, applies more than two decades of experience as a SCADA developer and systems analyst to design and implement practical, user-friendly systems for water/wastewater agencies. His experience includes designing process control interfaces, system communication topologies, and databases. He also has developed database mining techniques.
This article appears in the Applied Automation supplement for Control Engineering and Plant Engineering.
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