Note: Descriptions are shown in the official language in which they were submitted.
CA 02506158 2009-09-30
METHOD FOR ERROR DETECTION AND FLOW DIRECTION
DETERMINATION IN A MEASURING METER
Background of Invention
Field of the Invention
100011 The invention relates generally to measuring meters. More specifically,
the
invention relates to flow direction and error detection protocols of a data
recorder
for a measuring meter.
Background Art
100021 Meters that measure usage of a material based on flow are widely used
to
keep track of the consumption of an end user. For example, utility companies
that
supply water to their customers typically charge for their product based on
usage.
Usage of water is typically measured by a meter that is installed for each
individual customer on their respective water supply line. A utility company
employee periodically (usually once a month) manually collects the reading
from
the meter. These readings are usually cumulative, so the amount of usage for
the
present period is calculated by subtracting the reading from the previous
period.
Once the usage is calculated, the customer is billed for that amount of water
used
during that period.
[00031 Manually reading water usage meters is labor intensive, time consuming
expensive, and subject to human error especially for residential customers
because
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each meter monitors relatively little water usage as compared with larger,
commercial customers, As a result, electronic meters have been used to allow
for
quicker, more efficient, and more accurate cnllection of water usage data. The
electronic meters measure water usage by monitoring the water flow through a
conventional, mechanical fluid meter, The usage readings are stored
electronically
and then transmitted via radio signals to a local transmitter/receiver
operated by
the utility.
(00041 However, electronic meters require a power sozurce. Typically, such a
meter relies on a battery for power. The battery must be replaced manually,
which
is another time consuming and expensive process. Additionally, if the battery
fails, the utility may be unable to determine the correct water usage at the
meter
and comcquently under.bill the customer,
Summary of Invention
(00051 In some aspects, the invention relates to a method for correcting data
signal
errors in a meter, comprising: receiving ordered data signals from the meter;
analyzing the sequence of the ordered data signals to detect a missing signal;
and
compensating for the missing data signal by adding a predetermined value to a
sequence counter.
100061 In other aspects, the invention relates to a method for correcting data
signal
errors in a meter, comprising: receiving ordered data signals from the meter;
analyzing the sequence of the ordered data signals to detect a missing signal;
and
compensating for the missing data signal by adjusting a variable that
indicates the
last valid direction of the meter,
100071 In other aspects, the invention relates to a method for detecting
errors in a
meter, comprising: step for receiving a sequence of data signals of the meter;
step
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for analyzing the sequence of data signals to detect a missing data signal;
and step
for compensating for a missing data signal,
[00081 Other aspects and advantages of the invention will be apparent from the
following description and the appended claims,
Brief Description of Drawings
[0009] It should be noted that Identical features in different drawings arc
shown
with the same refcrr nce numeral.
[0010] Figure 1 shows a diagram of an electronic water meter monitoring system
in accordance with one embodiment of the present invention.
[0011) Figure 2 shows a cut-away diagram of a selfpowercd water meter in
accordance with one embodiment of the present invention.
[0012] Figure 3 shows i view of the display of an electronic data recorder in
accordance with one embodiment of the present invention.
[0013] Figure 4 shows a block diagram of the ASIC circuitry of the electronic
data
recorder in accordance with one embodiment of the present invention.
[0014] Figure 5a shows a perspective view of two Wiegand Wire sensors with a
four-Pole magnet In accordance with one embodiment of the pre.wnt invention.
[0015) Figure 5b shows an overhead view of two Wiegand Wire sensors with a
four-pole magnet in accordance with one embodiment of the present invention.
[00161 Figure 6a shows a perspective view of two Wiegand Wire sensors with a
four-pole magnet in accordance with an alternative embodiment of the present
invention.
[00171 Figure 6b shows a side view of two Wiegand Wire sensors with a four-
pole
magnet in accordance with an alternative embodiment of the present invention.
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[001.81 Figure 6c shows an overhead view of two Wieland Wire sensors with a
four-pole magnet in accordance with an alternative embodiment of the present
invention,
100191 Figure 7 shows a signal generated by a Wiegand Wire sensor during a
transition from a N polar section of a magnet to a S polar section of a magnet
and
a signal generated during a transition from a S polar section of a magnet to a
N
polar section of a magnet in accordance with one embodiment of the present
invention.
(0020] Figure 8 shows a graph of the outputs of Sensor A and Sensor B in
relation
to the. amount of angular rotation of the magnet in accordance with one
embodiment of the present invention.
(00211 Figure 9 shows a. graph of the separation of the outputs of Sensor A
and
Sensor B into four separate channcls in accordance with one embodiment of the
present invention,
[00221 Figure 10 shows a graph of the state of Sensor A and Sensor B when the
magnet is turning counter-clockwise that is obtained from the four channel
outputs
of the sensors in accordance with one embodiment of the present invention.
(0023] Figure 11 shows a graph of the State of Sensor A and Sensor B when the
magnet is turning clockwise that is obtained from the four channel outputs of
the
sensors in accordance with one embodiment of the present invention.
[00241 Figure 12 shows a graph of the state of Sensor A and Sensor B when the
magnet is turning counter-clockwise and reverses to turning clockwise that is
obtained from the four channel outputs of the sensors in accordance with one
embodiment of the present invention.
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[0025] Figure 13 shows a block diagram of the components used for processing
the
data gencratad by the sensors in accordance with one embodiment of the present
invention.
10026] Figure 14a shows A chart of corresponding Sensor inputs, Signal
detection
outputs, and Flow direction inputs in accordance with one embodiment of the
present invention.
[0027[ Figure 14b shows a chart that indicates the binary addresses of an
occurring
signal in accordance with one embodiment of the present invention,
[0028] Figure 15a shows a chart that indicates the sequence of binary address
values when the meter flow is running forward in accordance with one
embodiment of the present invention.
[0029] Figure 1 Sb shows a chart that indicates the .sequence of binary
address
values when the metcx flow is running in reverse in accordance with one
embodiment of the present invention.
[0030] Flqure 16a shows a chart that indicates the SUBADD value when the meter
is running forward in accordance with one embodiment of the presort invention.
100311 Figure 16b shows a chart that indicates the SUBADD value when the meter
is running in reverse in accordance with one embodiment of the present
invention.
100321 Figurc l7a shows a chart that indicates the SUBADD values for a missing
signal when the motor flaw is running forward in accordance with one
embodiment of the present invention,
[0033] Figure 17b shows a chart that indicates the SUBADD values for a missing
signal when the meter flow, is running in reverse in accordance with one
embodiment of the present invention.
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(00341 Figure i R shows a chart that indicates the states of Sensor A and
Sensor B
with a missed signal and no change in flow direction in accordance with one
embodiment of the present invention.
(0035) Figure 19 shows a chart that indicates the states of Sensor A and
Sensor B
with a missed signal and a change in flow direction in accordance with one
embodiment of the present invention.
(0036) Figure 20 shows a flow chart that summarizes the operations related to
processing signal information in accordance with one embodiment of the present
invention,
Detailed Description
(0037) A me&suring;meier with an error detection and flaw direction
determination
protocol has ben developed. The measuring meter measures and records
volumetric usage of a material as it passes through the meter. The meter could
be
used in utility applications to measure water, gas or electricity usage.
Additionally, such meters are commonly used in industrial applications to
measure
the flowrates of various components. In this section, a self-powered water
meter
in a utility application will be used to describe various embodiments of the
present
invention. However, it should he understood that the invention as described,
can
be applied to many different types of measuring meters in a wide variety of
applications.
(0038) Figure 1 shows a diagram of an electronic water motor monitoring system
in accordance with one embodiment of the present invention. The system 10
includes an electronic water meter 12a or 12b for an individual customer. The
meter is typically located at a point on the customer's individual supply line
between the customer and utility's main supply line. A meter interface unit
(MIU)
14a or 14b is connected to the respective meter 1291 or 12b. The MU 1491 or
14b
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is an electronic device that collects meter usage data from an electronic
register on
Its respective meter and transmits the data to a local transmitter/receiver
16a or
16b via radio signals. In alternative emhodiments, other external, devices
could be
used such as a laptop computer, a data logger, or other suitahlc device known
in
the art, Two alternative embodiments of the electronic water meters are shown.
The first embodiment includes a meter 12a and MIU 14a that are located
underground or a "pit" unit, the other embodiment includes a meter 12b and
MIU 14b that are located above ground. Two alternative types of
transmitter/receivers 16a and 16h are also shown. The first
transmitter/receiver
16a is mounted in a vehicle while the othcr transmitter/receiver is a handheld
unit
16b. An additional type of transmitter/receiver may be permanently mounted at
a
location central. to multiple meters and MIUs. Each of these
transmitter/receivers
allows utility persofinel- to receive usage data without manually reading each
individual meter. Instead, when each transmittedruxiver 16a and 16b is within
range of a MIU 14a or 14b, the data from the meter is transmittal to the
transmitter/receWer that in turn Iran emits it to the computer system of the
utility
18_ The computer system 18 then calculates the usage of each customer based on
the data. Appropriate billing for each customer is then generated by the
utility.
100391 The electronic water meters of the system are self-powered by an
internal
"Wiegand Wire". The Wiegand Wire is a device that generates electrical signals
when it is exposed to a magnetic field with changing flux polarity, The wire
may
also be used to induce voltage across a coil located near the wire. The
polarity of
the magnetic field is changed by relying on the kinetic energy of the fluid
moving
through the meter. In some embodiments, the fluid turns an internal water
wheel
that in turn rotates an attached shaft as it moves through the meter. Multiple
magnets are arranged on a circular disc that is attached to the rotating
shaft. As
the circular disc rotates along with the shaft, the movement of the magnets
induces
alternating fields of magnetic flux within the Wiegand Wire that is located in
close
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proximity to the disc. The signals generated by the wire due to the changes in
the
magnetic flux are used to power the electronic circuits that monitor the
meter. The
rate, volume, and direction of fluid flow through the meter may also he
determined
by analyzing the number and rate of signals generated by the wire.
(0040) Figure 2 shows a cut-away diagram of a self-powered electronic water
meter 20 in accordance with one embodiment of the present invention. In this
embodiment, the electronic water meter 20 is connected to a water supply line
at
the meter's inflow connector 22. Water flows from the supply line through the
connector 22 into the meter body 26 and out through the outflow connector 24
to
the customer. As the water flows through the meter body 26, It forces an
internal
flow wheel 28 to rotate. The rotating flow wheel 28 In turn rotates a circular
magnetic disc 30 that is- connected to the flow wheel 28 by h shaft (not
shown),
The disc 30 In this embodiment is shown with four separate magnetic zones
(labeled "N" and "S" for the polar orientation of each zone) that make up a
four-
pole magnet. In other embodiments, different configurations of magnets could
he
used.
100411 As the magnetic disc 30 rotates, it changes the magnetic flux polarity
for
the Wiegand Wire sensor 32 that is located adjacent to the disc 30. As
described
previously, the changes In polarity induce signah that are generated by the
sensor
32. These signals represent data concerning the water flow through the meter
20
and also provide power to the electronic circuits of the meter. Specifically,
the
stream of signals corresponds to the rate and direction of the water flow
through
the meter. The flow race of the water through the meter 20 is calibrated to
the rate
of rotation of the flaw wheel 28, the magnetic disc 30, aed the signal stream
generated by the sensor 32. In Figure 2, only one Wiegand Wire sensor 32 is
shown in use with the meter 20. It should be understood that multiple sensors
could be used in a meter for alternative embodiments of the present invention.
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100421 The data is processed and stored in an. electronic data recorder 34
that is
attached to the meter 20. The recorder 34 contains an ASIC (Application
Specific
Integrated Circuit) chip that processes the data, In some embodiments, nan-
volatile memory, which serves to store the data, is located within the ASIC.
In
this example, the memory is non-volatile which is memory that will not lose
its
stored data when power Is removed. Examples of non-volatile memory include:
core memory; ROM; EPROM; flash memory; bubble memory; battery-backed
CMOS-RAM; etc. In this example, the non-volatile memory is a ferro-electric
RAM ("FeRAM"). This type of memory is typically used in mobile applications.
It is alga m.ay be used in applications that are very demanding in tcTms of
minimizing power usage while maximizing performance. In still other
embodiments, non-volatile logic or other non-volatile structures could be
used.
Figure 3 shows a view df the display of the top of the electronic data
recorder 34.
The recorder 34 has, a cover 36 (shown in the open position) that protects the
display 38 from dirt, debris, etc, The display 38 itself is an LCD (Liquid
Crystal
Display) that shows data. In the present embodiment, nine digits may be shown
by the LCD. Jn alternative embodiments, other types and numbers of display
schemes could be used. The display is power by bank of solar cells 40 that are
exposed to sunlight when the cover 36 is opened. The display is convenient to
use
in case a manual reading of the meter is necessary due to failure of an MIU or
other system component
100431 figure 4 shows a. block diagram of the ASIC circuitry of the electronic
data
recorder. In this embodiment, two Wiegnnd Wire sensors 32 are used to supply
two separate data streams to the ASIC 41. Each censor 32 produces a separate
positive ("+") and a negative ("-") data stream. Other connections to the ASIC
include a power supply (EXT POWER) that is external to the ASIC and a ground
(GND) connection. In this embodiment, the two Wiegand Wire sensors 32
generate the external power supply. Other connections for the ASIC include: an
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enable signal (ENABLE); a data signal (DATA); a clock signal (CLOCK); a
read/write signal (R/W); a output signal (PULSE OUTPUT); and a signal
direction
signal (PULSE DIRECTION). F.ach of these signals connections passes through a
host interface (not shown) to rest of the data recorder.
[0044] Figures 5a and 5b show views of one embodiment of a four-pole magnet
with two Wiegand Wire. sensors 42. The magnet 44 is a circular-shaped disc
with
a surface divided into four Section. The sections represent the two polarities
of
the magnet, either North ('N") or South ("S"). The surface of each magnet 44
has two alternating N sections and two alternating S sections. The two sensors
are
labeled Sensor A 46 and Sensor B 48. In this example, the senora 46 and 48 are
placed apart at a 135 angle. Each sensor has a positive terminal 50 and 54
and a.
negative terminal-52 and 56. Each sensor terminal 90, 52, 54, and 56 has an
attached lead 5? that in turn may be connected to a monitor such as an
oscilloscope to determine the value the sensor output.
[0045] Figures 6a, 6b, and 6c show an alternative configuration of a four-pole
magnet With two Wiegand Wire sensors 59. In this embodiment, the magnet 58 is
cylindrical-shaped. The magnet 58 has two sensors 60 and 62 located parallel
to
the length of the cylinder. The sensors are labeled Sensor A 60 and Senior B
62
and are placed apart at a 1350 angle. Each sensor has a positive terminal and
a
negative terminal that is connected to an external monitor with leads 64. The
cylindrical surface of the magnet 58 is divided into upper and lower segments
which each have four sections of alternating polarity for a total eight
magnetized
polarity zones. The values of the sensor outputs in this embodiment 59 will be
the
same as the disc-shaped magnet embodiment 42 shown in Figures 5a and 5b.
(0046) Referring back to Figure 5b, if the magnet 44 rotates in a counter-
clockwise
direction. the N polar section under Sensor A 46 will transition to Sensor B
48. As
the N polar section of the magnet 44 transitions to the following S polar
section, a
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positive signal Is generated as shown in Figure 7 ("N -- S"). The magnet 44
will
rotate approximately 45 between a positive signal of Sensor A 46 and a
positive
signal of Sensnr B 48_ As the magnet 44 continues to rotate counter clockwise,
the S polar section will transition to the other N polar section. This
transition ("S
--> N") will generate a negative signal as shown in Figure 7. Once again, the
magnet 44 will rotate approximately 450 between a negative signal of. Censor A
46
and a negative signal of Sensor B 48. Figure 8 shows a graph of the outputs
of.
Sensor A and Sensor B in relation to the amount of angular rotation of the
magnet.
As the magnet rotates 1901, a total of four signals will have been generated:
one
positive and one negative for each of the two sensors. After the magnet has
completed a full revolution of 364 , a total of eight signals will have been
generated: two positive and two negative for each of the two sensors.
100471 In order to better determine how the magnet is moving, the outputs of
Sensor A and Sensor B may be broken up Into four separate channels. Each
sensor is divided into a positive and a negative output (i.e., A+, A-, B+, and
B-).
Figure 9 shows a graph of the separation of the outputs of Sensor A and Sensor
B
into four separate channels in comparison with the original signals. Sl lining
the
signals is done with an electronic circuit that divides the signals into
positive and
negative channels. The negative signaLs arc then rectified or changed into
positive
signals in their respective channel.
[00481 Once the signals of Sensor A and Sensor B arc broken tip into four
channels, these channels may be converted into a state indicator for each
sensor as
shown in Figure 10, The state of each sensor is indicated by an output (i, e.,
either
HIGH or LOW), with the state being HIGH after a positive signal and LOW after
a negative signal. The state of both sensors may be indicated by the value of
a two
bit binary value (i.e., either "I" or "0") with 1 corresponding to HIGH and 0
corresponding to LOW. In the two digit number that indicates the state of both
11
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sensors, the first or most significant digit represents the state of Sensor A
while the
second or least significant digit represents the state of Sensor B.
(0049] . As shown the Figure 10, the A bit value is leading while the 13 bit
value is
trailing when the magnet is rotating in a counter-clockwise direction.
However,
Figure 11 shows a set of corresponding values when the magnet is turning in a
clockwise direction. In this example, the B bit value is leading while the A
bit
value is trailing. The specific sequence of the binary state indicators are
unique
for the specific direction of flow through the m.ctcr. In this example, the
states
shown in Figure 10 are indicative of forward flow through the meter and the
states
shown in Figure 11 are indicative of a reversal of flow direction through the
meter.
Figure 12 shows an example of a cet of values where the direction of flow is
reversed from counter-clockwise to clockwise after an initial rotation of 1800
by
the magnet.
(0050] Figure 13 shows it block diagram 66 of the components used for
processing
the data generated by the sensors. In order to determine the direction of flow
of
the meter and the presence of a missing signal, data must be collected from
the
occurring signal and the previous signal. The calculation of the direction of
flow
is dependent on data from the occurring signal ("N') that is provided by the
four
sensor outputs 68 and the data from the previous signal ("N-1") that is stored
in
the status register memory 72. In this example, the status register memory 72
is a
ferro-electric random access memory ("FeRAM'). This type of, memory is
typically used in mobile applications. The data of the N-1 signal is stored in
the
memory at a previous address that is indicated by a 2-bit binary value ("PAO
and
PA 1 "). The data of the N signal Is stored at a new address ("NA") that is
Indicated
by a 2-bit binary value shown as shown in Figure 14b. A 1-bit binary value
that
indicates the last valid direction ("LVD") of the meter flow is also stored in
the
status register memory 72. The LVD is calculated with the data of the N-1
signal
according to the sequence of state indicators.
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[00511 Data is received from the four channels of the sensor outputs 68 and
input
into the binary encoder as flow direction inputs as shown in Figure 14a. When
the
meter flow is running forward, the repeating gequencc of binary address values
is
shown in Figure 15a. When the meter is running in reverse, the repeating
sequence of binary address values is shown in Figure 15b.
[0052] It is possible for a sensor to miss a signal or simply generate a
signal with
insufficient energy to be detected by the ASIC. An error in the form of a
missing
data hit is detected by calculating a temporary 2-hit binary variable called
"SUBADD", SUBADI) is calculated by subtracting the value of PA from NA. In
this embodiment, subtraction is accomplished by two's complement addition.
This is a technique that simulates subtraction for binary numbers by adding a
negative binary number (i.e., 4 + (-2) instead of 4 - 2). The negative binary
number is generated taking the one's complement of the number to be subtracted
(i.e., the subtrahend), and adding one to its value to obtain the two's
complement
of the number. The one's complement is simply the inverted value of the number
where all "0"s arc changed to "1"s and all "1"s are changed to "0"s. Once the
two's complement is obtained it is added back into the number to be subtracted
from (i.e., the minuend) to obtain SUBADD.
[00531 As shown in Figure 16a, when the meter flow is continually running
forward. the SUBADD value Is always "0l". Figure 16b shows that when the
meter flow is running in reverse, the SUBADD value is always "11". When the
SUBADD value is "00", there is no change in the values of NA and PA. This
indicates the receipt of two consecutive signals on the same input. This is an
illegal signal which is ignored by the system. However, if a signal from one
of
the sensors is missed for any reason, the SUBADD value is always "10". Figure
17a shows the calculation of the SUBADT) values for a missing signal when the
meter flow is running forward. Figure 17b shows the calculation of the SUBADD
values for a missing signal when the meter flow Is running in reverse.
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100541 Once a missed signal is detected, measures to compensate for the error
are
taken by the system. In the example shown in Figure 18, a signal is missed on
Channel A- without a change in the direction of meter flow. As mentioned
previously, the LVD (last valid direction) bit is a 1=bit binary value that
indicates
the direction the magnet rotated during the previous signal. In this example,
an
LVD value of "1" indicates a forward or up flow and an LVD value of "0"
indicates a reverse or down flow. The "action" indicates the action to be
taken
with various counters. An action of "+n" means that n will be added to a
counter
called REG UP that counts up while an action of "-n" means that n will be
added
to a counter called REG DN that counts down. Each counter will be incremented
once for each signal received. The REG DN value will be subtracted from REG
UP to determine the value of the net counter called NET.
[00551 In Figure 18, six, signals are detected before the seventh signal is
missed in
the A. channel. The. next detected signal comes from the 8- channel and causes
the state to change from 11 to 10 (A state, B state). At this point, the state
change
appears (incorrectly) to the system as a change in flow direction. The LVD
changes in value from 1 to 0 because of the supposed change of flow direction.
The next signal is received from the A+ channel. However, the present state is
10
with its most significant bit value set to 1, so it cannot change. This
results in the
current state having the same value as the previous state. The indication of a
current state and a previous state having the same value is an alternative way
of
detecting a missed signal. When thin halpens, the system will realize a signal
has
been missed and compensate. Since the LVD has a value of 0 and the system
realizes that every time a signal is missed the flow direction appears to
change, the
system compensates by adding 4 to the REG UP counter and changes the LVD
value back to 1. If the LVI) bad a value of 1 after the signal had been
missed, the
system would compensate by adding 4 to the RECT UP counter and changes the
LVD value back to 0.
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[0056] In the example shown in Figure 19, a signal is missed on Channel A-
with a
change in the direction of meter flow. When a change in flow direction nears,
the angle the magnet travels after the last signal may vary considerably. A
signal
on the A+ channel that is followed by a change in direction should
theoretically
yield a signal on the A- channel. The same basic algorithm described
previously
for detecting and compensating for a missing signal without a change in
direction
will also work for detecting and commpensating for a missing signal with a
change
in direction Specifically, the system will compensate for the missed signal by
adding 4 to the REG DN counter. However, since there was a true change of
direction the LVD value will not be changed. Figure 29 ,howl a flow chart that
summarizes there operations related to processing signal information.
100571 Advantages ofthe present invention include the ability to determine
flow
direction and detect missing or improper signal sequences in sensor output
regardless of the cause of the error. Another advantage of the system includes
the
ability of the system to compensate for an error in signal detection in both
instances of a change in flow direction and no change In flow direction.
[0058] While the invention has been described with respect to a limited number
of
embodiments, those skilled in the art, having benefit of this disclosure.,
will
appreciate that other cmbndimentr can be devised which do not depart from the
scope of the invention as disclosed here. Accordingly, the scope of the
invention
should be limited only by the attached claims.
sl1s~-~.x
