Pumps & Systems, October 2007
Growing infrastructures are creating more complex problems for municipalities than ever before, forcing them to search for a diverse range of system solutions to issues involving energy savings, maintenance savings and total life cycle cost analysis.
Higher technology suppliers have embraced these diverse challenges and responded with large, costly solutions that are highly customized for each application. These solutions sometimes focus on producing PLC-based remote terminal units (RTUs) and SCADA systems (or the like) to address even the simplest issues.
Though this would appear to be a logical step up from relay logic, it is an illogical step in addressing the practical needs of pump station operators today. These operators really need a controller characterized by high flexibility, easy setup, and input and output configurations similar to SCADA.
The next generation of technology for operating pump stations, characterized by this type of compact, preprogrammed unit with many value-added functions, can be a powerful, yet economical, solution. It actually began a few years ago, when an earlier generation microprocessor-based level control was introduced as more of a standalone device that controls the starting and stopping of pumps with the aid of a submersible pressure transducer. That control works within a network to provide a telemetry solution at a local level with its major emphasis as a level controller.
To develop the next generation controller, certain controls and monitoring suppliers gathered research from users of that earlier control, combined with studies of other industry needs. They discovered that pump operators need:
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A plug and play controller with the programmability and flexibility to handle the most difficult applications.
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A smart and dynamic user interface to indicate all critical information on an easy-to-use graphical display with internationally recognized symbols.
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A user friendly and simple programming menu with configurable parameters to set the necessary items to optimize the pump station.
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Proper built-in noise immunity to ensure accurate and consistent information.
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Ability to acquire data and trending information.
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Interfaceable to a software tool for remote programming and program backup.
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Built-in communication protocols to allow for remote station surveillance utilizing a wireless technology interface.
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The controller must achieve a life cycle cost that translates into real savings for the operator.
Life Cycle Costs
The life cycle cost analysis (LCC) of next generation pump controller technology focuses on maintaining energy savings and pump reliability. Different pump alternation schemes are built into these units to allow for the traditional and classic successive alternation of pumps that all pump duplex controls include.
These include a built-in asymmetrical alternation scheme that allows the operator to operate one pump for a programmed number of starts before the second pump starts. For example, the ratio can be 9-to-1, allowing the first pump to start 9 times and the second to start once. This keeps the second pump fresh and "closer to new."
Another feature is built-in flow capacity and flow tracking, which can trend the pump station inflow to sense an abnormal flow and adjust start and stop times accordingly. The basis for these flow trackings is to prevent costly overflows. The ability to stagger and vary discharge flows, as well as set and operate during off-peak hours, results in energy bill reductions.
Built-in DI-amplifiers allow a conductive seal sensor probe to interface directly into the controller and eliminate the need for external seal leak relays to be installed in the control system. Motor thermal inputs, pump current monitoring, PT100 sensor inputs, run indicators and a complete low and high level float backup are integrated into the newest units.
These units perform built-in checks, such as the "heartbeat check" of the submersible pressure transducer that is the life line of the system, providing the 4-mA to 20-mA current signal that correlates with the pump station water level utilized with the controller.
Certain units incorporate a mixer control algorithm into the software that automatically operates a submersible mixer in a pumping station to reduce any sedimentation buildup. This ensures a smooth pump startup, reducing the chances of a pump blockage upon startup.
The newest controllers store up to 4,280 events, such as alarms with date and time stamps. This data is typically used for planning maintenance and determining any upgrades required in the future. The logged information can include energy usage and rain accumulations, both for which digital inputs are provided. This can help with analyzing the effects of an abnormal rain fall on the pumping network. The logged values can be displayed in tabular or graphical form.
Accompanying software connects serially to these new units to retrieve the required data and log up to eight different parameters at different intervals, allowing the output to be customized and different aspects of the pump station to be monitored.
Life cycle costs must be tailored to fit the application and type of equipment. Next generation pump station controller technology significantly reduces operator support costs and efficiency losses.
A correlation exists between an impeller's loss of efficiency and additional energy costs. All pump impellers wear greatly depending on the impeller type and discharge pressure. Assuming the average inflow to the pumping station is generally the same over time, the pumps will run longer to compensate the loss of performance due to impeller wear. Next generation pump controllers alert the pump operators of efficiency fall off due to this phenomenon.
Comparison to PLCs
PLC-based systems are sometimes preferred over the more traditional relay type control systems usually found within the municipal industry. However, the costs to install, program and maintain a PLC-based system can be far greater than a new "off the shelf" pump controller with these built-in features.
Onsite changes are virtually impossible with a PLC type of system, which often requires trained specialists to be called into duty. In most cases, the station is programmed with unique code (even if identical to another station design). Next generation control package technology is far more user friendly and cost effective.
Summary
The next generation of pump station controllers are used in pumping networks to provide optimal functionality in a compact size controller.
Suppliers have obtained the lowest life cycle cost integrated into the functionality of the controller by incorporating and meshing energy savings, optimal programmability, logic functionality to customize pump station designs and groundbreaking features into one superior solution.
In the future, look for the next evolution of this technology to be able to monitor and program all of these capabilities through a web-based COMLI or MODBUS protocol.