Turnkey Automation Available To Water Works Industry

Aug. 6, 2003
Simple, low-power network architecture with menu-driven central control can revolutionize filtering operations

About the author: David Rizzo, D.P.M. has written more than two dozen engineering articles regarding all aspects of water production including metering, treatment, recycling, irrigation and its use in power plants. For further information, phone 214/343-0025.

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 control system.

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 filtering operations.

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 and support.

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 vulnerability.

"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 time."

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 cost.

"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 added.

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.

Loop concept

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.

The console

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 operational jeopardy.

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 Ethernet TCP/IP.

Valve actuation

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 electric actuators.

"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 instrumentation

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 reliable feedback.

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 installation.

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.

Turnkey solutions

What appears to be a total solution stands to revolutionize the entire water treatment industry as more engineering professionals recognize its value.

"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 console.

"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, they're history."

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 system."

Ultimately, the appeal for Filter Magic turnkey filtering systems rests with the fact that they stem, by definition, from a single source.

"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 works."

All signs seem to indicate the future of water treatment will revolve around the concept of turnkey automation.

About the Author

David Rizzo

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