Detroit Water and Sewerage Deploys HART Technology to Improve Customer Satisfaction
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SOLUTION
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RESULTS
- Complaints about low water pressure have been virtually eliminated since a majority of these complaints have been attributed to faulty regulating valves operated by our wholesale customers.
- Safety has also been improved since the need to enter the OSHA regulated confined space of the underground metering facilities for troubleshooting purposes has been greatly reduced or eliminated..
- Metering data obtained from the HART-instrument is communicated and stored in digital form, eliminating paper-based recordings.
- A digital packet radio network, which functions like a wireless intranet, is used to “carbon copy” all metering data to redundant data historians and to SCADA PCs that DWSD provided to each customer.
- The need for having redundant metering systems has been eliminated since the same metering data reported from our HART-based instruments to the RTU, is “carbon copied” every five minutes directly from the on-site RTU to DWSD as well as to our wholesale customers within a few seconds – we provided a SCADA PC to each wholesale customer. This has already contributed to improved customer satisfaction.
“HART has served us so well by utilizing all of our existing plant assets.”
By Dennis L. Green, P.E.
Head Water Systems Engineer
Detroit Water and Sewerage Department (DWSD)
The Detroit Water & Sewerage Department (DWSD) is the third largest water and wastewater utility in the United States. DWSD provides services to nearly 1 million Detroit residents and, on a wholesale basis, to over 3 million suburbanites living in the surrounding areas.
To determine water consumption at the point-of-sale, we had installed metering systems. Our point-of-sale metering systems included a variety of traditional instruments such as mechanical meters, venturis, orifice systems, magnetic flowmeters and chart recorders. Likewise, our wholesale customers had installed their own point of purchase metering systems, acting in parallel, to make their own measurements. Very often, the redundant metering systems would register different volumes, which led to billing disputes.
The solution was modernizing and unifying the point of sale metering system and transmitting the data in real-time to DWSD and every wholesale customer. An essential and critical part of the multi-million dollar modernization project was implementing an automatic meter reading/supervisory control and data acquisition (AMR/SCADA) system that relies on the HART global standard to deliver consistent, reliable data on system performance.
The innovative application of HART technology enabled us to use existing analog instrumentation and skills set of our technicians while providing us the benefits of a state-of-the-art digital and paperless metering system.
Today, the HART standard based digital metering system has not only improved the reliability of our water metering operations but has also provided our customers with greater satisfaction by virtually eliminating billing disputes caused by metering problems. As a bonus, our new HART based smart instruments also provide additional flexibility to make on-line configuration changes including calibration, perform calculations and support real-time remote diagnostics.
DWSD Services
With an operating budget of over $350 million, DWSDs’ services extend well beyond the Detroit city limits to an 8-county area of more than 1,000 square miles including approximately 43% of Michigan’s population. DWSD, which is a branch of the City of Detroit government, employs about 3,200 persons and has the fifth lowest combined water and sewerage rates per month amongst the 20 most populated cities in the United States. DWSD operates five water treatment plants pumping an average of 655 million gallons of clean drinking water each day, peaking at 1.5 billion gallons per day.
DWSD serves about 90 wholesale customers representing about 137 suburban communities via nearly 300 underground metering facilities. Figure 1 illustrates one such underground metering facility. These metering facilities typically include flow and pressure measuring instruments, valves and actuators to monitor and control the flow of water to the wholesale customer.
Akin to custody transfer stations, these metering systems, which include approximately 750 smart instruments, provide valuable inputs to detect and compute water usage, and hence billable sale to each wholesale customer. Since the metering systems are critical for billing purposes, we often refer to the meters as our point-of-sale “cash registers”.
Figure 1. Typical underground metering facility
Need For a New Metering System
Prior to implementation of the AMR/SCADA project, the metering facilities included a variety of traditional instruments such as mechanical meters, venturis, orifice systems, differential pressure transmitters, sonic meters, magnetic flowmeters and chart recorders. The existing metering facilities used no electronics with the mechanical meters, and all other instruments used chart recorders and mechanical pulse totalizers.
Thus, recording of all metering data was paper-based and collected manually bi-monthly or weekly by human meter readers. Various instrumentation companies including Smar, Endress+Hauser, and ABB manufactured these instruments.
By the mid-1990s, however, many of our wholesale customers had concerns over their water consumption data. They elected to install their own point-of-purchase “cash registers” to collect more frequent readings and validate their DWSD water bills. The point-of-purchase “cash registers” included redundant metering systems measuring the same water flow and pressure as DWSD recorded on our paper chart recorders. Quite often, the two metering systems disagreed over the water consumption data.
Moreover, the resolution of the chart records was insufficient to prove one party’s assertions over the other, the simple odometer-type totalizers provided no profiles of the consumption data between visits by our meter readers, and all humans make occasional mistakes when recording data. The disagreements over a mutually acceptable set of measurements resulted in billing disputes, customer dissatisfaction and loss of thousands of dollars in revenues.
Acquiring Leading Edge Technology to Improve Customer Satisfaction
DWSD decided it must modernize and unify the point-of-sale metering system and improve customer satisfaction. Our goal was to eliminate dispute-causing devices such as chart recorders and mechanical totalizers and replace them with a digital and paperless metering system specifically to:
1) Improve dependability, accuracy and confidence in the metering data by recording meter readings every 5 minutes – Objectives were ending the practice of our wholesale customers installing their own redundant metering equipment that often disagreed with DWSD’s, leading to billing disputes. Failure of any single component of the system must not disrupt system performance, any recording of data, or any calibration work of the meter technicians – excepting the one failed meter register.
2) Preserve metering data integrity – Data consistency must be maintained throughout the system. The same consumption data must be concurrently provided to DWSD as well as each wholesale customer. In addition, there must be opportunities to recover data when failures occur.
3) Archive 10-years of meter data in redundant historian systems for efficient storage and retrieval, engineering analysis and process improvement.
4) Provide an intuitive, easy-to-use, user interface to assist our staff in the setup and calibration of the meters while automatically documenting the data for certification of our “cash register” - the billing meter. Minimal reliance on paperwork to share information throughout the system by storing the calibration reports in the database of the AMR/SCADA historian.
5) Reduce operating costs of the Meter Operations Division by standardizing on the equipment used and by controlling software revisions.
To get the maximum out of the investment in the meters, they are usually sized for predicted future consumption that may or may not develop. By using peak hourly consumption data, rather than maximum meter capacity, a more equitable rate formula can be established based on peak consumption. In addition, the range of the instruments can be set based on actual peak demands to improve the accuracy of the instruments as the technicians have a basis for making their range adjustments as consumption increases or declines over the years.
DWSD is owned and operated by The City of Detroit and has had to resist frequent regionalization attempts by some of its suburban customers. Being a rate funded utility and having to defend those rates annually, the project risk and overall installed costs were of paramount importance to our management. Any proposed solution incorporating the latest and greatest technology had to address risks and costs satisfactorily and, in addition, had to address the risk of failure. hat is, a backup plan had to be developed and approved by our management in case the proposed solution did not function as planned.
Demand Based Rate Model
In addition to the above described project objectives, Stephen Gorden, former director of DWSD, had expressed a desire to use the modernization project for restoring DWSD’s traditional position as an industry leader. His vision was to introduce a demand based water usage rate model in the water utility industry. More specifically, he wanted a system that would support the development of a demand based rate model, similar to the model(s) used by the electric utility industry, where there is an infrastructure charge based on peak load and a consumption charge for total usage. This requirement implied that the new metering system was capable of performing and preserving multiple reads every hour to identify the peak hourly demand.
Developing a New AMR/SCADA System by Leveraging HART Technology
Before launching the project to modernize the point-of-sale metering system, we had recognized the ability to calibrate instruments remotely and on-line as an important function to improve reliability and confidence of metering data. By 1996, we were well underway to implement an instrument upgrade project to incorporate the HART standard into many of our existing 4-20mA instruments. The HART based smart instruments would facilitate calibration and at the same time preserve our investment.
During 1996-97, DWSD developed and implemented a pilot-scale version of the AMR/SCADA system to modernize the point-of-sale metering system. The pilot project was expanded (1999-2002) to a $10 million major infrastructure upgrade. Figure 2 illustrates a schematic diagram of DWSD’s AMR/SCADA system. The AMR/SCADA system utilizes a packet radio network of personal computers, programmable logic controllers (PLCs), and remote terminal units (RTUs). The system relies on the power of HART communication to deliver consistent, reliable data on system performance.
Figure 2. Schematic of DWSD’s AMR/SCADA system
The decision to adopt the HART standard for integrating our meters was relatively simple since we already had in-house experience. Perhaps, more importantly, HART was evaluated to be the only stable and reliable technology available at the time which would enable us to integrate a vast array of diverse field devices and technologies including mechanical, venturi, orifice, magnetic and sonic meters into a single digitally networked system.
Other field device technologies such as FOUNDATION™ fieldbus and Profibus-DP were still evolving, costly, and radically different and incompatible with our existing smart instrumentation. Use of these other technologies would have substantially increased the project risk and the total installed costs.
HART technology was an ideal fit for our requirements since it delivered the benefits of an all digital system at a minimized incremental investment for the modernization project. Most of our existing instrumentation was HART-capable, which enabled us to use the existing wiring. The project easily gained management approval mainly due to our ability to default back to the existing analog-chart-recorder system in case of difficulties.
Maintaining the Look and Feel of Mechanical Meters to Ease Transition
At the start of the pilot project, our technicians and customers indicated a strong preference for mechanical meter-type totalizers at each metering site. To improve their comfort level with the electronic instruments, we configured the LCD displays of the HART-based smart instruments to indicate the current value of the measured variable, e.g., flow rate and/or totalized flow, which provided an emulation of the odometer-like registers of the mechanical meters. Figure 3 illustrates one such HART-based smart instrument (manufactured by SMAR International) indicating measured flow rate. The LCD alternates displaying the flow rate and totalized flow (not shown).
Figure 3. HART-based smart instrument indicating flow rate (PV measured in m3/hr)
Unlocking the Power of HART To Reap Big Dividends
Most HART-based smart devices are capable of performing multiple functions in a single instrument. Previously, we required multiple electrical devices for detecting the rate of flow, outputting a proportional signal, integrating the proportional rate signal into a volume, and totalizing the volume.
Thus, by combining functions we were able to eliminate these old devices, as we selected HART-based differential pressure transmitters that are capable of performing on-board, flow totalization and self-monitoring for diagnostics. In addition, the HART data communications protocol provides the values to the PLC/RTUs in binary bit streams that virtually eliminate signal transfer errors.
As a result of HART technology, we were able to distribute the totalization function to a lower, HART-enabled smart device level, instead of the traditional PLC/RTU device. This resulted in reducing the load on the PLC/RTU, as well as eliminating the potential loss of data in case of a power loss. A schematic diagram of an advanced metering system based on HART technology is illustrated in Figure 4.
Figure 4.Schematic of a Venturi/Orifice meter based on HART technology
The flow totalization data is actually retained in the memory of each HART-enabled smart instrument even when there is a loss of power. As a matter of fact, our system survived the massive power failure of August 14, 2003 that occurred in the Northeastern part of the United States with little or no loss data. This was an unrehearsed critical test since it occurred during our peak-revenue summer months.
As an additional benefit, by executing the totalization function at the HART device level, we were able to obtain much more accurate totalization data. The HART device integrates totalization data sampled far more frequently than the PLC/RTU. As a result, the totalization values are more accurate.
The sampling frequency of the microprocessor based instrument approaches the Nyquist criteria for integrating the fluctuations of the water flowing through venturis and orifices that can reach to audio frequencies. The best of the communications protocols for instrumentation are substantially slower resulting in random sampling errors that although small relative to instantaneous flow, accumulate in the totalized flow far beyond acceptable limits.
With the need to read instantaneous flow for range switching combined with the necessity of totalizing flow in the instrument, this project would have been far more costly without the HART ability to read multiple functions in a single smart instrument. By shifting the calculations to the smart instruments, we freed the PLC/RTU to perform other tasks, such as device monitoring for all HART devices located at the underground metering facilities, and storing 31 days of metering data collected at 5-minute intervals.
We were also able to maintain greater accuracy of metering data throughout our water-distribution system, largely due to HART’s ability to preserve the full accuracy of the measuring element in a digital format. The improved accuracy has directly resulted in increased revenues, since our old mechanical meter based cash registers often erred in favor of our wholesale customers.
The need for having redundant metering systems has been eliminated since the same metering data reported from our HART-based instruments to the RTU, is “carbon copied” every five minutes directly from the on-site RTU to DWSD as well as to our wholesale customers within a few seconds – we provided a SCADA PC to each wholesale customer. This has already contributed to improved customer satisfaction.
Our wholesale customers can access metering data received from their respective meters directly rather than receiving it through our headquarters. This assures our wholesale customers that DWSD is not adjusting or manipulating their metering data.
HART enables the master device such as the PLC/RTU to automatically query each smart instrument to detect the types and brands of HART-based instruments on the network. Instrument data such as their brand type and serial numbers are collected each day for a permanent record of each instrument. HART enables the detection and documentation of instrument changes that invalidate calibration.
Metering data received from failed instruments is not logged or used in any billing computation. Previously, a failed analog instrument sometimes produced bogus signals thereby corrupting the meter readings.
HART-enabled remote monitoring, calibration, and validation of metering systems have contributed to improved safety and greater customer satisfaction. Our technicians can now perform these tasks on any HART-based smart device in the comfort of their office. For example, pause and resume signals can be sent remotely to these instruments for series connected meters for range switching. With improved diagnostics, our technicians can quickly detect and repair failures in our water distribution system.
Complaints about low water pressure have been virtually eliminated since a majority of these complaints have been attributed to faulty regulating valves operated by our wholesale customers. Our system now monitors these valves and reports any problems directly to the customers.
Safety has also been improved since the need to enter the OSHA regulated confined space of the underground metering facilities for troubleshooting purposes has been greatly reduced or eliminated. Previously, there have been fatal accidents in these underground metering facilities.
Metering data obtained from the HART-instrument is communicated and stored in digital form, eliminating paper-based recordings. A digital packet radio network, which functions like a wireless intranet, is used to “carbon copy” all metering data to redundant data historians and to SCADA PCs that DWSD provided to each customer.
The DWSD meter technicians use radio linked laptop computers for configuration and direct entry of calibration data, eliminating paper and copying errors. By analyzing the real-time and historical data collected, we have improved efficiency by revising operating procedures.
HART has served us so well by utilizing all of our existing plant assets. Other fieldbus technologies have matured considerably since 1996, when DWSD began piloting our system. Nevertheless, we would still use HART, even if the project were starting today. Other newer fieldbus technologies would have cost us at least twice as much, since we would have had to discard a majority of our existing instruments.
Looking ahead, DWSD is developing another SCADA system for controlling our treated water transmission system and wastewater collection system, which includes new sewer meters. Since many instruments included in the SCADA system are also HART-capable, we would like to tie them in into our water metering AMR/SCADA system.