A group of 50 industry experts from water supply, wastewater and storm water backgrounds developed a new report, “...
Simple, low-power network architecture with menu-driven central control can revolutionize filtering operations
Imagine that you are in the final stages of constructing a
ten-filter water treatment plant. Start-up for the filter control system alone
requires the contractor to coordinate with representatives from the valve
supplier, actuator supplier, instrument supplier, filter console supplier, the
electrician and the integrator to put together a system that is supposed to
work as one complete unit.
Now imagine the additional complications of a controls
upgrade project where older, existing equipment must be integrated with a new
In the water treatment industry, these headache-inducing
scenarios are the norm. However, this is expected to change with the
introduction of the industry's first complete, turnkey automation system for
Although the basic components of any filtering system
include the filter console, the communications link, the actuators and the
instrumentation, it is the turnkey integration of these components into a
pre-packaged, pre-engineered and even pre-programmed system that merits its
classification as a major step forward.
Combined with the use of pneumatically-operated actuators,
this "total solution" can reduce installation costs by 30-40%, ensure
reliability, reduce maintenance and increase safety. Furthermore, a
single-source system ensures a single point of responsibility for installation
A solution whose time has come
As all water treatment officials and engineers know, the
Safe Drinking Water Act mandates strict control of turbidity within levels that
can be achieved only through exacting control of filter operations. As a result,
new facilities must incorporate state-of-the-art equipment and many older
plants must undergo controls upgrading. But the complicated process often
leaves plant managers searching for an easy place to begin.
"On a typical filter control project, the control
system designer has to start from scratch," said Patrick Moorman, an
instrumentation and control specialist of nearly 30 years with Black &
Veatch Corporation, a engineering, consulting and construction company
providing water and wastewater services for clients around the world. "You
have to buy this piece from one vendor and another piece from another; then
have a contractor put it all together. Then, hopefully, find a system
integrator that can program the software, troubleshoot it and make it all work."
In response to this challenge, vendors have each offered
their own, increasingly sophisticated elements; the control console, the
networking, the sensors, the actuators and the valves. Yet, any piecemeal
approach to upgrading can result in increased complexity and heightened
"As a result of the necessary control, there's a lot of
electrical instrumentation within the filter pipe gallery," noted Willard
Jordan of Electrical Expertise which specializes in engineering the
instrumentation and SCADA system design for water and wastewater treatment
plants. "But all this extra wiring creates its own problems. You have a
myriad of boxes and conduit and wires that looks like a bowl of spaghetti. I've
had installations where we've had to go back and replace wire-trays and conduit
where they actually just rotted off the wall after several years of operation.
That's real time consuming because you can only do it one filter at a
Some solutions have focused solely on the collection of data
from the sensors as a means of simplifying the process. While these higher
level fieldbuses provide improved performance, they do so at a much higher
"There's been newer data-highway systems around for a
while now," said Jordan, "but they usually are high-dollar,
proprietary protocol like Allen Bradley or Honeywell."
In the face of diminishing federal, state and local
revenues, most water treatment facilities enjoy little leeway in expanding
their installation costs. If anything, decreased expense and complexity is
sought at all levels; especially at the control console.
"With some of the older systems, all of the data
signals from the sensors would come up to this large instrument control panel
on the top of the filter gallery, and then go through a series of relay
switches to handle the signals for opening and closing all the valves,"
said Patrick Moseley, a senior engineer who heads up the electrical SCADA
department for Chiang, Patel & Yerby Inc., which offers planning, design
and construction management services for environmental projects including
waterworks and wastewater systems. "It can get quite complicated," he
Ultimately, the price paid for attacking the problem of
improved data access and control in a hodgepodge fashion comes in the form of
diluted responsibility. Nothing is more frustrating for a plant engineer than
having vendors dodge culpability when a problem arises.
"Typically, the mechanical guys install the valves and
actuators, the electrical guys wire it up, and the instrumentation guys apply
the instruments and control panel," said Moseley. "But when a problem
crops up with the filter, you have all these subcontractors and the general
contractor pointing fingers at each other."
The demand for unified systems and single point responsibility
has already been demonstrated by the recent popularity of a product that
includes the underdrain, media and control system. Yet this does little good
for those water treatment plants that already have a satisfactory filter bed,
or those that require an entirely new data acquisition and control system.
Completely upending the old way of assembling filter control
systems from scratch, Filter Magic designed and engineered a water and
wastewater filter control system that utilizes a menu driven operational
control console and a two-wire data and control bus to simplify and guarantee
backwashes that comply with federal turbidity levels.
The system is configured around what Filter Magic calls the
"Loop," which consists of four elements: the central console, the
communications link, the actuators and the instrumentation.
While these elements, individually, comprise the basic
components of any filtering system, it is the turnkey integration of these
components at very low voltage, the intuitive human machine interface, the
complete automation and the simplicity with which this feat is accomplished,
that merits its classification as a major step forward.
Engineers created menu-driven software and graphics of the
filter, recognizing that not every operator is sufficiently trained to perform
a backwash operation. The detailed graphic changes with each command to
demonstrate that the command entered per the menu was successfully completed.
Each filter has its own PLC, completely sidestepping the
need for a slow, crash-prone PC. Limit switches on all valves act as
permissives to also prove the commands were completed, while acting as
safeguards against performing an improper command that could put the filter in
In keeping with its promise of automation, the console
includes a completely hands-off control sequence that derives input from
sensors to determine when and how the backwash process should take place.
Yet, this system also offers three other levels of control
that allow increasing operator input to the point of total manual control. The
menu directs the operator to perform the exact sequence of backwash operations.
Still, a plant operator has some latitude to configure
parameters, such as filter basin water levels, air scour time and low/high
backwash durations. On the other hand, safeguards built into the code prevent
unwarranted deviations from the process sequence so that the clear well cannot
be accidentally contaminated. Redundant power supplies automatically switch in
the event of failure, and a battery-powered UPS keeps the entire system powered
for a minimum of ten minutes. Even then, all programming is permanently stored
in the non-volatile memory.
The communication link
Engineers opted for the proven, open architecture AS-i
network. Supported by over 100 vendors worldwide, it operates at a low level of
automation. This two-wire, 24 VDC bus carries both the network communications
signal and the power needed for the peripheral devices by way of a redundant
(in case of a line break) ring topology. The AS-i interface is ideally suited
to the needs of devices, such as sensors and actuators, where low connection
cost per node is critical and simplicity is paramount.
Jordan explained the arrangement from his perspective as an
electrical engineer in the field.
"The Loop wires carry the control signal, which is
multiplexed at a proprietary frequency. The DC power flows on the same two
wires. At each sensor or actuator you have a potted electronic device--with its
own addressæthat acts as the interface. These fit into a standard NEMA
4/4X screw-covered junction box. The device accepts the signal coming in and
converts it to a contact closure to open and close the valve. If you need valve
status, it takes the same contact closure status and converts it into a signal
to go back to the console."
In the case of pre-existing protocols at any given facility,
both the console and the AS-i network can be designed with gateways to
communicate with other options, such as plant SCADA, Allen-Bradley, Modicon,
GE, Siemens, Profibus, Modbus, RS232C, 422, 485, Modbus+, Device Net or
The Loop encompasses control of all the necessary valves: influent,
effluent, backwash, airwash, filter-to-waste valve and drain valve.
The manufacturer supplies the actuators, which are
pneumatically operated and capitalize on a simple "rotary vane"
design utilizing only one moving part. This design ensures accurate,
incremental control and eliminates hysteresis. Each actuator is assigned a
default setting in the event a power grid goes out. The actuator holds its
respective valve in the open or closed position until power is restored, thus
preventing the flooding of filter galleries and protecting treated water.
Capable of carrying up to eight amps at 24 VDC, the AS-i
wire loop supplies sufficient power to open and close the solenoid on each
pneumatically operated actuator. The system also works with plants that rely on
"You do not have to switch over to pneumatic
actuators," said Fred Underwood, developer of the system. "In plants
that already have electric actuators, the address on the network bus will point
to a transformer that converts our 24 volts to the 125 volts on an electric
actuator. In such cases, the actual 480 VAC required to power the
actuator/valve movement is usually already wired into the pipe gallery."
The Loop includes the high-quality sensors required for metering
any water filtering application: level transmitter, head loss transmitter,
turbidmeter and an effluent flow transmitter. Each sensor is sized, selected
and calibrated for optimum performance within the prescribed application.
All instruments return data back to the console via the AS-i
bus. Incoming data is checked by the receiver for possible faults by comparing
the parity bit and several other independent values to ensure accurate and
In keeping with its self-positioning as being pre-packaged,
the Filter Magic Loop comes pre-engineered specifically for each filtering
plant. At the factory, each component is addressed and configured with the AS-i
communications network and the console, then tagged appropriately for ease of
After factory testing, the entire system is shipped as a
kit, including wiring harnesses. On-site operator training follows installation
with documentation including operation and maintenance manuals.
What appears to be a total solution stands to revolutionize
the entire water treatment industry as more engineering professionals recognize
"The real advantage of the system is that they provide
a pre-packaged, pre-engineered scheme and even developed pre-programmed software,"
said Moorman. "The possible best niche for Filter Magic is a retrofit job
because a lot of the legwork--the design and fabrication--is already thought
out; so there are some efficiencies there. The bottom line is they should be
able to deliver it a little more competitively."
As an example, the elimination of redundant wiring turns out
to be a strong suit of such turnkey systems. Specifically, the AS-i bus reduces
the size of cabinets and cable ducts while eliminating terminating resistors
and excessive connectors, bridges, terminal housings and distributing clamps.
This translates into less installation time and reduced maintenance. According
to the AS-i technical forum, typical cost savings range from 15-40% compared
with traditional cabling methods.
"This system has eliminated all the extra enclosures,
conduit and wiring," reiterated Jordan. "Now you only need to run
one-inch conduit with a couple of number 12 wires to as many as six filters and
you're in business. This eliminates about 90% of the previous wiring."
These efficiencies also manifest themselves at the control
"We are now able to eliminate all of those relays and
switches up at the control panel," said Moseley. "Because they are
supplying you with a panel that is already pre-programmed and field tested,
Filter Magic definitely simplifies the wiring and programming. When it arrives
on the job site, it's ready to go."
Equally important, low voltage architectures help improve
safety conditions for plant workers.
"If you go with a pneumatic actuating system, the
advantage is that you eliminate the 480 power voltage and also the 125 volt
control voltage," said Underwood. "There is a tremendous safety issue
there. Everybody is concerned about flooding and subsequent short circuits. At
the very least, once you get one of these electric actuators filled with water,
Wave of the future
Water treatment operators are already eagerly incorporating
turnkey solutions, such as the underdrain. This trend promises to accelerate with
the offering of a complete filtering instrumentation and control system.
"One of our clients asked us to consider this
route," said Moorman. "We looked at it and agreed that it is a viable
scheme. We then proceeded with the design, based on use of the Filter Magic
Ultimately, the appeal for Filter Magic turnkey filtering
systems rests with the fact that they stem, by definition, from a single
"Filter Magic represents a combination of
technologies--some that have been around the industry for a while--but this is
probably one of the first times that key components, like the console, have
allowed all of these technologies to be brought together," noted Moseley.
"You have the valves, the actuators, the instrumentation, the bus highway,
the control, all wrapped up as a single product. What's nice is that underneath
it all, there is a single point of responsibility to ensure the filter system
All signs seem to indicate the future of water treatment
will revolve around the concept of turnkey automation.