neers offering interactive technical support capabilities that can
be drawn upon for the duration of the relationship.
When choosing between a DCS- or PLC-based automation
system, municipal water and wastewater system operators
should look beyond the initial capital expense and weigh a
variety of factors. But before doing so, it is beneficial to first
take a step back and develop an automation master plan. This
plan should be based on a strategic vision for the organization’s long-term needs and an understanding of how automation technology can address those needs today and well
into the future. Increasingly, forward-thinking municipalities
are developing an integrated automation master plan that lays
the foundation for strategically unifying operations throughout the entire service area in a phased approach, over a period
of time — 5, 10 or even 15 years. This enables organizations
to expand and take advantage of new technologies as circumstances dictate.
As operational, regulatory, environmental and economic
issues facing the water and wastewater industry continue to
evolve, one thing remains unchanged: the need for municipalities and regional authorities to do more with less. Deploying
DCS technologies can help organizations effectively address
these challenges, enabling them to be good stewards of the
public assets entrusted to them not only today but well into
the future. WW
About the Author: Doug Johnson is director of business development for Emerson Automation Solutions Power & Water. He holds a B.S. in electrical engineering
(magna cum laude) from West Virginia University and an MBA from the University
of Pittsburgh’s Katz Graduate School of Business. Johnson is a member of the Water
Environment Federation and American Water Works Association.
Circle No. 245 on Reader Service Card
MAINTENANCE AND UPGRADES
Installing systems with components sourced from different suppliers can also increase time and expenses related to
maintenance. DCS technology is typically easier and more
cost-effective to maintain, while also offering integrated diagnostics capabilities, which provide comprehensive, system-wide information that can signal problems before they result
in costly equipment or process failures.
Another point of differentiation concerns the system’s
database. Because PLC systems often require multiple databases, adding points in conjunction with a plant expansion,
or changing points to reflect new equipment or processes,
requires careful management to ensure there are no conflicts. These concerns are eliminated with a DCS, which uses
a single, common database. Upgrades are also typically more
straightforward, as DCS suppliers are expected to ensure forward compatibility of their hardware and software throughout the life of the system. As PLC-based systems are upgraded, the task of ensuring that future releases of one element
of the system are compatible with the remainder of the system can become burdensome. Systems integrators may also
be unaware of compatibility issues between PLCs and HMI
software as those components evolve over time.
LONG-TERM SERVICE AND SUPPORT
Perhaps the most-important consideration for selecting
an automation system is something that is often overlooked
during the procurement process: long-term service and support. A vendor should be an integral part of the end user’s team
of trusted advisors. While PLC systems integrators can provide
a certain level of tech support, they may have to rely on the
manufacturer for extensive troubleshooting. Conversely, DCS
suppliers typically employ and train a network of qualified engi-
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It should be noted that the above
comparisons do not apply to single stage
(non-VTP) submersible pumps (see
Fig. 3) where the motor is located above
the impeller and casing. Such motors are
not restricted by small well casing sizes
and can often compete in efficiency with
aboveground motors. WW
1. Budris, Allan R. “Special Vibration Considerations
for Vertical Turbine Pumps,” Water World, December
2. Budris, Allan R. “Back to Basics, How to Improve Vertical Turbine Pump Reliability Through Optimum Bearing Selection,” Water World, December 2013.
3. Peerless Pump Company. “Submersible Motor
Pumps vs. Line-shaft Turbines for Deep-Well Service,” Technical Information Bulletin, Number Nineteen, 2006.
4. Franklin Aid. “Line Shafts vs. Submersibles: Some
Big Advantages for the Sub,” Franklin Electric, February 2017.
About the Author: Allan R. Budris, P.E., is an independent consulting engineer who specializes in training,
failure analysis, troubleshooting, reliability, efficiency
audits and litigation support on pumps and pumping
systems. With offices in Washington, N.J., he can be
contacted via e-mail at email@example.com.
Circle No. 246 on Reader Service Card
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Figure 3: Single Stage (non-VTP)