DWSD SCADA system via HART
Detroit Water and Sewerage Deploys
HART Technology to Improve Customer Satisfaction
2003 PROJECT OBJECTIVES
Redundant metering systems would register different
volumes, which led to billing disputes.
Modernize and unifying the point of sale metering system
and transmit the data in real-time to DWSD and every wholesale customer.
Use existing analog instrumentation and the skill set
of our technicians while providing us the benefits of
a state-of-the-art digital and paperless metering system.
Distribute the totalization function to a lower,
HART-enabled smart device level, instead of the
traditional PLC/RTU device.
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.
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
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
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
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. That 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
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
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.