U.S. patent application number 12/163413 was filed with the patent office on 2009-06-04 for method for discriminating between operating conditions in medical pump.
This patent application is currently assigned to Abbott Laboratories. Invention is credited to Chad E. Bouton, Clark E. Fortney, Steven R. Nelson, Dale M. Radcliff.
Application Number | 20090144025 12/163413 |
Document ID | / |
Family ID | 32600889 |
Filed Date | 2009-06-04 |
United States Patent
Application |
20090144025 |
Kind Code |
A1 |
Bouton; Chad E. ; et
al. |
June 4, 2009 |
METHOD FOR DISCRIMINATING BETWEEN OPERATING CONDITIONS IN MEDICAL
PUMP
Abstract
A method is disclosed for determining the operating condition of
a medical pump based on data derived from a pressure sensor and a
position sensor. The pressure sensor generates pressure data by
sensing the force on the pumping element. The position sensor
generates position data by tracking the pumping cycle and
determining the position of the pumping element. The pump pressure
data and pump position data are processed and the calculated
results compared with a pre-determined threshold value to determine
the operating condition of the pump. The three main types of
operating conditions of concern are the following: normal
condition, where liquid is present and no leaks exist in pumping
chamber; leak condition, where liquid is present but a leak exists
in the pumping chamber; and air stroke condition, where the chamber
contains some air.
Inventors: |
Bouton; Chad E.; (Delaware,
OH) ; Radcliff; Dale M.; (Dublin, OH) ;
Nelson; Steven R.; (Grove City, OH) ; Fortney; Clark
E.; (Gahanna, OH) |
Correspondence
Address: |
JACKSON & CO., LLP
6114 LA SALLE AVENUE, #507
OAKLAND
CA
94611-2802
US
|
Assignee: |
Abbott Laboratories
Abbott Park
IL
|
Family ID: |
32600889 |
Appl. No.: |
12/163413 |
Filed: |
June 27, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11503471 |
Aug 11, 2006 |
7452190 |
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12163413 |
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10624667 |
Jul 22, 2003 |
7104763 |
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11503471 |
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60418914 |
Oct 16, 2002 |
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60418986 |
Oct 16, 2002 |
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Current U.S.
Class: |
702/182 |
Current CPC
Class: |
A61M 2205/332 20130101;
A61M 2205/15 20130101; A61M 5/365 20130101; A61M 2205/3331
20130101; A61M 5/14224 20130101; A61M 2205/12 20130101 |
Class at
Publication: |
702/182 |
International
Class: |
G06F 15/00 20060101
G06F015/00 |
Claims
1. A method for determining operating conditions in a medical pump
having a cassette with a pumping chamber, comprising: monitoring
the pump cycle with a position sensor; starting a testing timer for
a pre-determined test time at a specified portion of the pump
cycle; closing the pumping chamber to flow during at least a
portion of the specified portion of the pump cycle; acquiring a
plurality of pressure reference values during a first portion of
test time from a single pressure sensor; calculating and storing a
pressure anchor value by averaging the reference values; setting a
first prior integration term of zero; acquiring a pressure data
value from the pressure sensor; calculating and storing a new
integration term by subtracting the anchor value from the data
value to obtain a resultant, multiplying the resultant by a
weighting value to obtain a product, and adding the product to the
prior integration term; repeating the steps of acquiring the
pressure data value and calculating and storing the new integration
term until the pre-determined test time has expired; and comparing
the new integration term with a pre-determined threshold value to
determine the operating condition of the pump.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 11/503,471 filed Aug. 11, 2006, which is a
divisional application of U.S. patent application Ser. No.
10/624,667 filed Jul. 22, 2003 and issued as U.S. Pat. No.
7,104,763 on Sep. 12, 2006, which claims the benefit of U.S.
provisional application No. 60/418,914 filed Oct. 16, 2002 and U.S.
provisional application No. 60/418,986 filed Oct. 16, 2002, the
disclosures of each of which are incorporated by reference for all
purposes.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method of determining the
operating condition of a medical pump. More particularly, this
invention relates to a method of determining fluid status in
positive displacement fluid pumping devices for the delivery of
fluids to a patient.
[0003] Modern medical care often involves the use of medical pump
devices to deliver fluids and/or fluid medicine to patients.
Medical pumps permit the controlled delivery of fluids to a
patient, and such pumps have largely replaced gravity flow systems,
primarily due to the pump's much greater accuracy in delivery rates
and dosages, and due to the possibility for flexible yet controlled
delivery schedules. Of the modern medical pumps, those
incorporating a diaphragm or pump cassette are often preferred
because they provide a more accurate controlled rate and volume
than do other types of pumps.
[0004] A typical positive displacement pump system includes a pump
device driver and a disposable cassette. The disposable cassette,
which is adapted to be used only for a single patient and for one
fluid delivery cycle, is typically a small plastic unit having an
inlet and an outlet respectively connected through flexible tubing
to the fluid supply container and to the patient receiving the
fluid. The cassette includes a pumping chamber, with the flow of
fluid through the chamber being controlled by a plunger or piston
activated in a controlled manner by the device driver.
[0005] For example, the cassette chamber may have one wall formed
by a flexible diaphragm which is reciprocated by the plunger and
the driver to cause fluid to flow. The pump driver device includes
the plunger or piston for controlling the flow of fluid into and
out of the pumping chamber in the cassette, and it also includes
control mechanisms to assure that the fluid is delivered to the
patient at a pre-set rate, in a pre-determined manner, and only for
a particular pre-selected time or total dosage.
[0006] The fluid enters the cassette through an inlet and is forced
through an outlet under pressure. The fluid is delivered to the
outlet when the pump plunger forces the membrane into the pumping
chamber to displace the fluid. During the intake stroke the pump
plunger draws back, the membrane covering the pumping chamber pulls
back from its prior fully displaced configuration, and the fluid is
then drawn through the open inlet and into the pumping chamber. In
a pumping stroke, the pump plunger forces the membrane back into
the pumping chamber to force the fluid contained therein through
the outlet. Thus, the fluid flows from the cassette in a series of
spaced-apart pulses rather than in a continuous flow.
[0007] One of the requirements for a medical pump is that it is
able to detect when it is operating under certain abnormal
situations and to alert the user to these problems. Specifically,
the pump should detect when flow of fluid is blocked, there is no
fluid in the line, there is no cassette in the pump, if the pump
has primed correctly, and if the valves in the pump are sealing
properly.
[0008] Previous pumps that could supply all this information used
at least two sensors associated with the pump chamber or tubes to
provide input to the control system. The use of multiple sensors
requires more physical space on the pump and potentially results in
a higher unit manufacturing cost.
[0009] It is therefore a principal object of this invention to
provide methods of using single pressure sensor to discriminate
between operating conditions in a medical pump.
[0010] These and other objects will be apparent to those skilled in
the art.
SUMMARY OF THE INVENTION
[0011] A method is disclosed for determining the operating
condition of a medical pump based on data derived from a pressure
sensor and a position sensor. The pressure sensor generates
pressure data is by sensing the force on the pumping element. The
position sensor generates position data by tracking the pumping
cycle and determining the position of the pumping element. The pump
pressure data and pump position data are processed. The processed
data is compared with a pre-determined threshold value to determine
the operating condition of the pump. The three main types of
operating conditions of concern are the following: normal
condition, where liquid is present and no leaks exist in pumping
chamber; leak condition, where liquid is present but a leak exists
in the pumping chamber; and air stroke condition, where the chamber
contains some air.
DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a graph showing data from a pump cycle
illustrating normal, leak and air stroke conditions;
[0013] FIG. 2 is an enlarged view of the graph of FIG. 1, taken
along line 2-2, showing data from a pump cycle illustrating normal,
leak and air stroke conditions;
[0014] FIG. 3 is a graph showing data from a pump cycle
illustrating normal stroke conditions with various back-pressure
levels;
[0015] FIG. 4 is a flow chart illustrating one embodiment of
determining the operating condition of a medical pump according to
the present invention;
[0016] FIG. 5 is a flow chart illustrating another embodiment of
determining the operating condition of a medical pump according to
the present invention;
[0017] FIG. 6 is a flow chart illustrating another embodiment of
determining the operating condition of a medical pump according to
the present invention; and
[0018] FIG. 7 is a schematic diagram of the cassette pump,
illustrating the functional components of the pump and the
cassette.
DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION
[0019] The present invention will be described as it applies to its
preferred embodiment. It is not intended that the present invention
be limited to the preferred embodiment. It is intended that the
invention cover all modifications and alternatives that may be
included within the scope of the invention as defined by the claims
that follow.
[0020] It will be understood by one of ordinary skill in the art
that the term medical pump as used herein includes but is not
limited to enteral pumps, parenteral infusion pumps, ambulatory
pumps, or any positive displacement fluid pumping device for the
delivery of fluids to a patient.
[0021] FIG. 7 is a schematic diagram illustrating the functional
components of a medical pump 10, which is used in connection with a
disposable cassette 12 for delivering a fluid to a patient. The
medical pump 10 and cassette 12 are shown with several components
for implementing the present invention. Those of ordinary skill in
the art will appreciate that the pump 10 and cassette 12 include
many more components than those shown in FIG. 7. However, it is not
necessary that all these components be shown in order to disclose
an illustrative embodiment for practicing the present
invention.
[0022] Details of pump 10 and cassette 12 that are not discussed
below can be determined by reference to commonly assigned and
co-pending non-provisional application entitled MEANS FOR USING
SINGLE FORCE SENSOR TO SUPPLY ALL NECESSARY INFORMATION FOR
DETERMINATION OF STATUS OF MEDICAL PUMP, which claims priority from
provisional applications U.S. Ser. No. 60/418,986 and 60/418,914,
the disclosure and drawings of which are hereby specifically
incorporated herein by reference in its entirety. This disclosure
describes in detail means of using a single pressure sensor and a
single position sensor to supply all necessary information to
determine the status of a medical pump. The disclosures and
drawings of the provisional applications U.S. Ser. No. 60/418,986
and 60/418,914 are also specifically incorporated herein by
reference in their entirety. Commonly assigned and co-pending
non-provisional application U.S. Ser. No. 29/166,389 entitled PUMP
CASSETTE discloses the particular cassette 12 described below. Pump
cassettes and cassette pumps in general are well known in the art
of medical fluid delivery, as evidenced by commonly assigned U.S.
Pat. Nos. 4,818,186; 4,842,584; and 5,000,664, the entire
disclosure and drawings of which are hereby specifically
incorporated herein by reference.
[0023] Cassette 12 includes a housing 14 on which is disposed an
inlet port 16 for accepting the fluid flowing from an IV bag or
other fluid container (not shown). Similarly, fluid lines (not
shown) couple an outlet port 18 on housing 14 to the body of a
patient.
[0024] A pumping chamber 20 is connected in fluid flow
communication between the inlet port 16 and the outlet port 18. The
pumping chamber 20 operates to meter fluid through the cassette
12.
[0025] An inlet valve 22 resides between inlet port 16 and the
pumping chamber 20. Inlet valve 22 operates to physically open and
close the fluid communication between inlet port 16 and pumping
chamber 20.
[0026] Similarly, an outlet valve 24 resides between the pumping
chamber 20 and outlet port 18. Outlet valve 24 operates to
physically open and close the fluid communication between pumping
chamber 20 and outlet port 18. The pumping chamber 20, inlet valve
22, and outlet valve 24 are all operatively associated with the
pump 10 to control the flow of fluid through the cassette 12.
[0027] A processing unit 26 with a testing timer 27 is included in
pump 10 and performs various operations described in greater detail
below. A display/input device 28 communicates with the processing
unit 26 and allows the user to receive output from processing unit
26 and/or input into the processing unit 26. Those of ordinary
skill in the art will appreciate that display/input device 28 may
be provided as a separate display device and a separate input
device.
[0028] A memory 30 communicates with the processing unit 26 and
stores code and data necessary for the processing unit 26 to
calculate and output the operating conditions of pump 10. More
specifically, the memory 30 stores an algorithm code 32 formed in
accordance with the present invention for processing data to
determine the operating condition of the pump 10.
[0029] An electric motor 34 is controlled by processing unit 26 is
energized by a power supply (not shown) to serve as a prime mover
for rotatably driving a shaft 36.
[0030] A pumping element 38 is operatively associated with the
shaft 36. When energized, the pumping element 38 reciprocates back
and forth to periodically down-stroke, causing pumping element 38
to press on pumping chamber 20, driving fluid through cassette 12.
On an up-stroke, pumping element 38 releases pressure from pumping
chamber 20 and thereby drawing fluid from inlet port 16 into
pumping chamber 20.
[0031] An inlet control element 40 is operatively associated with
the shaft 36. When energized, inlet control element 40 reciprocates
back and forth to periodically down-stroke, causing inlet control
element 40 to press on inlet valve 22, closing pumping chamber 20
to fluid influx. On an up-stroke, inlet control element 40 releases
pressure from inlet valve 22 and thereby allows the flow of fluid
from inlet port 16 into pumping chamber 20.
[0032] An outlet control element 42 is operatively associated with
the shaft 36. When energized, outlet control element 42
reciprocates back and forth to periodically down-stroke, causing
outlet control element 42 to press on outlet valve 24, closing
pumping chamber 20 to fluid efflux. On an up-stroke, outlet control
element 42 releases pressure from outlet valve 24 and thereby
allows the flow of fluid from pumping chamber 20 to outlet port 18.
Thus the open or closed state of pumping chamber 20 is controlled
by the positioning and movement of inlet and outlet control
elements 40 and 42.
[0033] A pressure sensor 44 is operatively associated with the
pumping element 38. The pressure sensor 44 senses the force on
pumping element 38 and generates a pressure signal based on this
force. The pressure sensor 44 communicates with the processing unit
26, sending the pressure signal to the processing unit 26 for use
in determining operating conditions of pump 10.
[0034] One of ordinary skill in the art will appreciate that the
pressure sensor 44 may be a force transducer or any other device
that can operatively sense the pressure brought to bear on the
pumping chamber 20 by pumping element 38.
[0035] A position sensor 46 tracks the pumping cycle of pump 10 by
determining the position of the pumping element 38. The position
sensor 46 can be operatively associated with the shaft 36, a cam or
camshaft 76 attached to the shaft 36, or the pumping element 38
itself. The position sensor 46 generates a position signal by
directly or indirectly detecting the position of the pumping
element 38. For instance, in one embodiment the position sensor 46
is a Hall Effect sensor having a magnet (not shown) in relational
contact with shaft 36. The rotational position of shaft 36 can be
monitored to indirectly detecting the position of the pumping
element 38. The position sensor 46 communicates with the processing
unit 26, sending the position signal to the processing unit 26 for
use in determining operating conditions of pump 10. One of ordinary
skill in the art will appreciate that the position sensor 46 as
used herein includes but is not limited to mechanical indicators
such as pivoting dial indicators, electronic switches, Hall Effect
sensors, and optical based position detectors.
[0036] In operation, at the beginning of a pumping cycle, outlet
control element 42 operates to close outlet valve 24 so that there
is no fluid communication between pumping chamber 20 and outlet
port 18. Inlet valve 22 is opened to permit pumping chamber 20 to
be in fluid communication with inlet port 16. In the next phase of
the pumping cycle, inlet control element 40 operates to close inlet
valve 22, thereby closing fluid communication between inlet port 16
and pumping chamber 20. Outlet valve 24 continues to remain closed.
Next, pumping element 38 begins a down-stroke movement which
presses pumping element 38 against pumping chamber 20, causing
pumping chamber 20 to compress, thereby increasing the pressure
within pumping chamber 20. Pressure sensor 44 reads and transmits
this pressure data to processing unit 26. Under normal conditions
pumping chamber 20 is compressed sufficiently and a desired
pressure profile is generated. At a given position of shaft 36 or
point in the pumping cycle, the outlet control element 42 operates
to open outlet valve 24 so that fluid flows from pumping chamber 20
to outlet port 18. The pump cycle then repeats.
[0037] The processing unit 26 retrieves the operating condition
algorithm 32 from memory 30 and applies it to the pressure and
position data received from this pump cycle. The pump pressure data
and pump position data are processed. The processed data is
compared with a pre-determined threshold value to determine the
operating condition of the pump. The three main types of operating
conditions of concern are the following: normal condition, where
liquid is present and no leaks exist in pumping chamber; leak
condition, where liquid is present but a leak exists in the pumping
chamber 20 (including at the inlet valve 22 or outlet valve 24);
and air stroke condition, where the chamber contains some air. Once
the operating condition is determined, the processing unit 26
outputs the operating condition display 28 and/or uses the
determined operating condition to adjust operation of the pump
10.
[0038] One of ordinary skill in the art will understand that the
threshold values for any of the algorithms disclosed herein are
predetermined empirically from experimental data, and will vary
from pump model to pump model.
[0039] Referring to FIG. 1, the position sensor 46 is used to
trigger a capture event where pressure sensor 44 data is captured
for processing and operating condition discrimination. FIG. 1 shows
time plots of the pressure and position signals taken with a
prototype unit in the laboratory. The position signals are digital
in nature and take on values near 3 or 0 V. The remaining analog
signals that rise and fall more gradually are the signals that
represent the pressure sensor 44 measurements. There is one
pressure sensor 44 in the system and the four analog signals shown
represent four different example operating conditions that have
been superimposed onto the same plot. Each will be used to explain
the operation of the signal processing algorithms to be
disclosed.
[0040] When large amounts of data under various experimental
conditions were collected, certain observations were made
immediately. As shown in the example set of data shown in FIG. 1,
the initial time region between -0.4 s and 0 s did not seem to
offer opportunities for signal discrimination. Furthermore, other
regions beyond 0.2 s also did not seem to offer signal differences
that corresponded with the operating conditions of interest.
Specifically, in these regions of non-interest, the back-pressure
and other elements in the system seemed to dominate the pressure
signal characteristics. In a region of interest, marked by line
2-2, the system is indeed operating with the pumping chamber 20
closed such that the pressure sensor 44 is detecting a building
pressure during the pumping stroke. This allows unique conditions
under which it may be possible to discriminate between normal,
leaky, and air-filled pumping conditions.
[0041] Referring to FIGS. 1 and 2, the data for the region of
interest marked by line 2-2 of FIG. 1 is shown with greater detail.
Pump cycle data was collected in the laboratory by subjecting a
prototype pump to a wide variety of operating and environmental
conditions to analyze the region of interest more closely. To
develop effective and robust algorithms, it was important to
analyze time shifting, bias shifts or offsets, and other variations
that could occur. The four digital position signals are numbered as
A and the four pressure signals are numbered B-E. The example
pressure signals B-E correspond to the three previously mentioned
operating condition types (Normal, Leak, and Air Stroke), and in
addition a back-pressure in the system may be present. The numbered
cases in the figure are as follows:
[0042] B: Normal type, no back-pressure;
[0043] C: Normal type, relatively high back-pressure present;
[0044] D: Leak type, low back-pressure; and
[0045] E: Air Stroke, low back-pressure.
[0046] Those of ordinary skill in the art will recognize that the
magnitude, timing, and shape of the pressure signals may vary
somewhat depending on the source or location of the leak(s), amount
of air, or amount of back-pressure. For example, there are at least
two more cases or combinations not shown in FIG. 2. These cases are
leak type with high back-pressure and air stroke with high
back-pressure.
[0047] Data for many other condition combinations were collected
and analyzed, and the region of interest (shown in FIG. 1 at line
2-2 and in FIG. 2) remained the most viable one. In particular,
data captured prior to a next rising edge G of the position sensor
46 proved to be an effective data set. This is due to the widely
varying and uncorrelated effects that the back-pressure in the
system that occurs after this rising edge G has on the pressure
signal. Therefore the specific region of interest (at line 2-2)
occurs between the second falling edge F of the position sensor 46
that occurs in the complete pump cycle and a time point before the
next rising edge G of this position signal.
[0048] A number of algorithms were considered and tested prior to
the development of the final preferred set. Among these included a
simple threshold method and a method in which the falling edge of
the pressure signal was analyzed (falling edge method).
[0049] The simple threshold method involved comparing the pressure
signal against a predetermined threshold. However, varying signal
offsets in the system reduced the performance of this method,
making this method ineffective in discriminating between the
operating conditions.
[0050] Referring to FIG. 3, in the falling edge method, the time
derivative (or slope) of the data falling within the region of
interest (at line 2-2 in FIG. 1) was calculated and compared to a
negative threshold. With this approach a falling edge, usually
typifying a normal stroke, would result in a time derivative
calculation that would exceed the negative threshold. Air strokes
and certain leak conditions often did not contain this falling edge
characteristic and would not exceed the set threshold. However, a
normal stroke with a significant back-pressure often did not have
this falling edge. This can be seen in FIG. 3, where some normal
type strokes do have the falling edges when the back-pressure
levels are low and some do not when the back-pressure is high. This
condition therefore made the falling edge method ineffective in
discriminating between the operating conditions.
[0051] Other approaches and variations in the same general spirit
were considered, but only the preferred approaches below will be
described in detail in this disclosure. Three main embodiments of
the preferred algorithms were developed and are listed as
follows:
[0052] Class 1: Delayed Threshold Algorithm;
[0053] Class 2: Weighted Integration Algorithm; and
[0054] Class 3: Integrated Split Derivative Algorithm.
[0055] There are a variety of possible variations on each class of
algorithm. These variations include varying the technique of
weighting, disabling the weighting, position of anchor, and
sequence order in which data is analyzed. The Class 1 delayed
threshold algorithm is the preferred embodiment. However, the other
algorithms to be described can perform equally as well under
certain conditions. Therefore, all algorithms are equally important
and will be discussed in equivalent detail.
[0056] Referring to FIG. 4, the overall operation of the Class 1
algorithm 110 is shown in flowchart form. The Class 1 algorithm 110
begins at start block 112. A decision block 114 monitors the pump
cycle through position signal A to determine when a region of
interest is occurring. In this example, the region of interest is
specified as starting when the second falling edge F of the
position signal A is detected in each new pump cycle. When the
second falling edge F is detected at decision block 114, the Class
1 algorithm 110 proceeds to block 116. Block 116 starts the testing
timer 27 for a pre-determined test time Td. Then a block 118
acquires a plurality of pressure reference values at some
pre-determined sampling rate during a first portion of test time,
and once the first Na pressure reference values have been acquired
a pressure anchor value is calculated and stored by averaging these
pressure reference values. This anchor is stored and will be used
in later calculations.
[0057] Anchoring is a technique used in this and the other
algorithms as a process that removes the overall offset variation
observed in the pressure signal from one pump cycle to the next and
between each physical pump unit. This process involves averaging a
number of the initial data points in the data set of interest and
subtracting this averaged valued from all subsequent data points in
the set.
[0058] A block 120 acquires a pressure data value and then
calculates and stores a resultant value by subtracting the anchor
value from the data value. A buffer is created and maintained for
storing the last Nb resultant value samples (or data points). This
buffer may be a circular buffer to improved processing efficiency.
A decision block 122 shows just such a circular buffer, and repeats
the steps of acquiring the pressure data value and calculating and
storing the resultant value until the pre-determined test time Td
has expired. Thus, as each new pressure data value is acquired the
buffer is updated, until the pre-determined value of time Td has
elapsed. If time Td has elapsed, then the data acquisition is
complete and the final processing occurs.
[0059] During the final processing, a block 124 calculates a test
value by averaging the resultant values, and compares this test
value with a pre-determined threshold value to determine the
operating condition of the pump. Thus, in the last step, the
algorithm 110 averages the Nb data points in the storage buffer and
compares this averaged value to a set of predetermined thresholds
to determine the operating condition of the pump (i.e. normal,
leak, or air stroke).
[0060] Referring to FIG. 5, the overall operation of the Class 2
weighted integration algorithm 130 is shown in flowchart form. This
algorithm begins the same way as the Class 1 algorithm 130 begins,
but the difference of operation lies in the update buffer and final
steps.
[0061] The Class 2 algorithm 130 begins at start block 132. A
decision block 134 monitors the pump cycle through position signal
A to determine when a region of interest is occurring. In this
example, the region of interest is specified as starting when the
second falling edge F of the position signal A is detected in each
new pump cycle. When the second falling edge F is detected at
decision block 134, the Class 2 algorithm 130 proceeds to block
136. Block 136 starts the testing timer 27 for a pre-determined
test time Td. Then a block 138 acquires a plurality of pressure
reference values at some pre-determined sampling rate during a
first portion of test time, and once the first Na pressure
reference values have been acquired a pressure anchor value is
calculated and stored by averaging these pressure reference values.
This anchor is stored and will be used in later calculations.
[0062] A block 140 makes the core calculations of algorithm 130
during the buffer update to calculate an integration term. The
following equation describes the integration term used in block
140: I.sub.k-I.sub.k-1+(d.sub.k-A)W(t).
[0063] Where I.sub.k represents the integration term, I.sub.k-1
represents the prior integration term, d.sub.k represents the newly
acquired pressure data value, A represents the anchor value, and
W(t) represents the weighting value which is a function of the time
(or position) at which the new pressure data value was acquired.
The function W(t) can be linear, polynomial, or any other function
of time to allow the emphasis and de-emphasis of various regions in
the data set.
[0064] The block 140 sets a first prior integration term I.sub.k-1
of zero when the algorithm first begins during each new pump cycle.
The block 140 acquires a pressure data value d.sub.k and then
calculates and stores a new integration term I.sub.k by subtracting
the anchor value A from the data value d.sub.k to obtain a
resultant, multiplying the resultant by a weighting value W(t) to
obtain a product, and adding the product to the prior integration
term I.sub.k-1.
[0065] A decision block 142 repeats the steps of acquiring the
pressure data value d.sub.k and calculating and storing the new
integration term I.sub.k until the pre-determined test time Td has
expired. Thus, as each new pressure data value d.sub.k is acquired
the new integration term I.sub.k is updated, until the
pre-determined value of time Td has elapsed. If time Td has
elapsed, then the data acquisition is complete and the final
processing occurs.
[0066] During the final processing, a block 144 compares the
integration term I.sub.k with a pre-determined threshold value to
determine the operating condition of the pump (i.e. normal, leak,
or air stroke).
[0067] Referring to FIG. 6, the overall operation of the Class 3
integrated split derivative algorithm 150 is shown in flowchart
form. The Class 3 algorithm 150 begins the same way Class 2 130
begins, but no anchor calculation is used, and the update buffer
and final steps differ.
[0068] The Class 3 algorithm 150 begins at start block 152. A
decision block 154 monitors the pump cycle through position signal
A to determine when a region of interest is occurring. In this
example, the region of interest is specified as starting when the
second falling edge F of the position signal A is detected in each
new pump cycle. When the second falling edge F is detected at
decision block 154, the Class 3 algorithm 150 proceeds to block
156. Block 156 starts the testing timer 27 for a pre-determined
test time Td.
[0069] A block 158 makes the core calculations of algorithm 150
during the buffer update to calculate a figure of merit. The
following equation describes the figure of merit calculation used
in block 158: FOM.sub.k=FOM.sub.K-1+(d.sub.k-d.sub.k-q)W(t)
[0070] Where FOM.sub.k represents the figure of merit, FOM.sub.K-1
represents the prior figure of merit, d.sub.k represents the newly
acquired pressure data value, d.sub.k-q represents any other
pressure data value in the set, and W(t) represents the weighting
value which is a function of the time (or position) at which the
new pressure data value was acquired. The function W(t) can be a
linear, polynomial, or any other function of time to allow the
emphasis and de-emphasis of various regions in the data set.
[0071] The block 158 sets a first prior figure of merit FOM.sub.K-1
of zero when the algorithm 150 first begins during each new pump
cycle. The block 158 acquires the prior pressure data value
d.sub.k-q and the new pressure data value d.sub.k, where the prior
pressure data value d.sub.k-q is any data value other than the new
pressure data value. The block 158 calculates and stores a new
figure of merit FOM.sub.k by subtracting the prior pressure data
value d.sub.k-q from the new pressure data value d.sub.k to obtain
a resultant, multiplying the resultant by the weighting value W(t)
to obtain a product, and adding the product to the prior figure of
merit FOM.sub.K-1.
[0072] A decision block 160 repeats the steps of acquiring the new
pressure data value d.sub.k and calculating and storing the new
figure of merit FOM.sub.k until the pre-determined test time Td has
expired. Thus, as each new pressure data value d.sub.k is acquired
the new figure of merit FOM.sub.k is updated, until the
pre-determined value of time Td has elapsed. If time Td has
elapsed, then the data acquisition is complete and the final
processing occurs.
[0073] During the final processing, a block 162 compares the figure
of merit FOM.sub.k to pre-determined thresholds to determine the
operating condition of the pump (i.e. normal, leak, or air stroke).
For example, in one embodiment one threshold is set at 450 so that
if the Figure of Merit is above 450, the pump interprets this as a
normal fluid stroke; below 450, as an air stroke.
[0074] Several variations on each class of algorithms are possible
which can enhance performance. These variations include varying the
trigger event, technique of weighting, disabling the weighting,
position of anchor, and the sequence order in which data is
analyzed.
[0075] While the trigger event in the preferred embodiment is the
second falling edge F of the position sensor, the trigger event can
be changed to reduce system variation sensitivity as needed. The
trigger event may be, for example, the second rising edge G in the
pump cycle shown in FIG. 1. Setting rising edge G as the trigger
event may reduce delay between the trigger event and data
collection in the Class 1 algorithm 110, for example. This is
important due to the fact that the Class 1 algorithm 110 will
perform more satisfactorily if the pressure signal data collected
correlate to a certain desired pump position. Since there is no
pump element position or speed sensing available, the timer and
predicted speed is used to estimate the current position.
Shortening the delay between the trigger event and key data
collection will reduce the accumulating effects of speed variations
in the pumping motor and estimated position error, therefore
increasing the probability that the collected data corresponds to
the desired and anticipated position.
[0076] Another variation involves the smoothing of the data set. It
is possible to acquire all data of interest before algorithm
calculations begin. In this case, the data can be smoothed prior to
core calculations. This is effective when the pressure signal
contains undesirable noise.
[0077] The anchor location is another variable that can be changed
to enhance system performance. In Class 1 algorithm 110 and Class 2
algorithm 130 embodiments the anchor is calculated by using the
first Na data points. Depending on the curvature and nature of the
data set, it may be advantageous to calculate this anchor by using
the data points at some other location within the data set. This
may accentuate a certain feature near the new anchor location and
increase the discrimination level of the algorithm.
[0078] Whereas the invention has been shown and described in
connection with the embodiments thereof, it will be understood that
many modifications, substitutions, and additions may be made which
are within the intended broad scope of the following claims. From
the foregoing, it can be seen that the present invention
accomplishes at least all of the stated objectives.
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