U.S. patent application number 15/233426 was filed with the patent office on 2016-12-01 for methods, devices and systems which determine a parameter value of an object or an environment from a voltage reading associated with a common mode signal of a balanced circuit.
The applicant listed for this patent is Millar Inc.. Invention is credited to Huntly D. Millar, Robert L. Pauly, Richard T. Thornton.
Application Number | 20160349291 15/233426 |
Document ID | / |
Family ID | 48875204 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160349291 |
Kind Code |
A1 |
Millar; Huntly D. ; et
al. |
December 1, 2016 |
Methods, Devices And Systems Which Determine A Parameter Value Of
An Object Or An Environment From A Voltage Reading Associated With
A Common Mode Signal Of A Balanced Circuit
Abstract
A method for determining a value of a parameter of an object or
an environment includes positioning a device having a balanced
circuit in or on an object or within a particular environment,
wherein the balanced circuit comprises elements which are
operationally sensitive to changes in a parameter of the object or
the environment. The method further includes measuring a common
mode signal of the balanced circuit and determining, from the
common mode signal, a value of the parameter. An exemplary
implementation of the method includes determining temperature using
a resistive sensor having a Wheatstone bridge circuit with two
variable resistors and two fixed resistors. Embodiments of systems
and devices configured to employ such methods are provided,
particularly medical probes, electronic signal monitoring devices,
and systems employing such devices.
Inventors: |
Millar; Huntly D.; (US)
; Thornton; Richard T.; (Bacliff, TX) ; Pauly;
Robert L.; (Friendswood, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Millar Inc. |
Houston |
TX |
US |
|
|
Family ID: |
48875204 |
Appl. No.: |
15/233426 |
Filed: |
August 10, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13551811 |
Jul 18, 2012 |
9429479 |
|
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15233426 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 17/10 20130101;
A61B 5/11 20130101; G01K 7/20 20130101; A61B 2562/0271 20130101;
G01L 9/065 20130101; A61B 5/1073 20130101; A61B 5/14539 20130101;
A61B 2562/0247 20130101; A61B 5/14542 20130101; G01L 1/2262
20130101; A61B 2562/029 20130101; G01L 1/2281 20130101; G01L 9/045
20130101; G01K 13/002 20130101 |
International
Class: |
G01R 17/10 20060101
G01R017/10; A61B 5/145 20060101 A61B005/145; A61B 5/107 20060101
A61B005/107; A61B 5/11 20060101 A61B005/11 |
Claims
1. A method for determining values of parameters of an object or an
environment, wherein the method comprises: positioning a device in
or on an object or within a particular environment, wherein the
device comprises a balanced circuit, and wherein the balanced
circuit comprises elements which are operationally sensitive to
changes in a first parameter of the object or the environment;
measuring a common mode voltage derived from the balanced circuit
which correlates to a common mode signal of the balanced circuit;
determining, from the measured common mode voltage, a value of the
first parameter; measuring a differential voltage between signal
output nodes of the balanced circuit; and determining, from the
differential voltage, a value of a second parameter of the object
or environment which is different from the first parameter, wherein
at least one of the steps of measuring the differential voltage and
determining the value of the second parameter is performed
substantially simultaneously with at least one of the step of
measuring the common mode voltage and determining the value of the
first parameter.
2. The method of claim 1, wherein the first and second parameters
are selected from a group consisting of temperature, pressure,
volume, velocity, pH, oxygen concentration and humidity.
3. The method of claim 1, wherein the balanced circuit is a
half-bridge Wheatstone bridge circuit.
4. The method of claim 3, wherein half-bridge Wheatstone bridge
circuit comprises two variable resistors respectively comprising
opposing sides of the Wheatstone bridge circuit.
5. The method of claim 1, wherein the device is a medical
probe.
6. A system, comprising: a device having a balanced circuit; an
electronic signal monitoring unit configured for electrical
communication with the device to measure electrical parameters of
the balanced circuit; circuitry for coupling to the balanced
circuit, wherein the circuitry, when coupled to the balanced
circuit, is configured to: generate a common mode voltage which
correlates to a common mode signal of the balanced circuit; and
generate a differential voltage of the balanced circuit, wherein
the electronic signal monitoring unit comprises means for measuring
the differential voltage and the common mode voltage; and a storage
medium comprising program instructions which are executable by a
processor for respectively determining, from the common mode
voltage and the differential voltage, different parameters of an
environment in which the device is arranged.
7. The system of claim 6, wherein the different parameters are
selected from a group consisting of temperature, pressure, volume,
velocity, pH, oxygen concentration and humidity.
8. The system of claim 6, wherein one of the different parameters
is temperature, and wherein the device is absent a temperature
sensor distinct from the balanced circuit.
9. The system of claim 6, wherein the circuitry is disposed between
the device and the electronic signal monitoring unit.
10. The system of claim 6, wherein the circuitry is disposed within
the device.
11. The system of claim 6, wherein the circuitry is disposed within
the electronic signal monitoring unit.
12. The system of claim 6, wherein the device is a medical
probe.
13. The system of claim 6, wherein the balanced circuit is a
half-bridge Wheatstone bridge circuit.
14. A device, comprising: a Wheatstone bridge circuit having two
fixed resistors and two variable resistors; compensation circuitry
coupled to the Wheatstone bridge circuit which is configured to
compensate for variations of a resistive coefficient of a
conductive material comprising the Wheatstone bridge circuit due to
ambient temperature changes of the conductive material; and common
mode signal circuitry coupled to the Wheatstone bridge circuit
which generates a voltage correlating to a common mode signal of
the Wheatstone bridge circuit.
15. The device of claim 14, wherein the compensation circuitry
comprises one or more fixed resistors in parallel with at least one
of the two variable resistors of the Wheatstone bridge circuit.
16. The device of claim 14, wherein the device is a medical
probe.
17. The device of claim 16, wherein the common mode signal
circuitry is disposed within an electrical connector of the medical
probe.
18. The device of claim 16, wherein the common mode signal
circuitry is disposed within a tip of the medical probe.
19. The device of claim 16, wherein the medical probe is a
catheter.
20. The device of claim 14, further comprising reference voltage
circuitry for generating a biased reference voltage relative to an
excitation voltage applied to the Wheatstone bridge circuit.
Description
[0001] This application is a continuation of pending U.S. patent
application Ser. No. 13/551,811, filed on Jul. 18, 2012 and
entitled "METHODS, DEVICES AND SYSTEMS WHICH DETERMINE A PARAMETER
VALUE OF AN OBJECT OR AN ENVIRONMENT FROM A VOLTAGE READING
ASSOCIATED WITH A COMMON MODE SIGNAL OF A BALANCED CIRCUIT" the
entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention generally relates to methods, devices and
systems for determining parameter values of objects and
environments and, more specifically, to methods, devices and
systems which utilize a voltage reading associated with a common
mode signal of a balanced circuit to determine a value of a
parameter of an object or an environment.
[0004] 2. Description of the Related Art
[0005] The following descriptions and examples are not admitted to
be prior art by virtue of their inclusion within this section.
[0006] Many sensors employ balanced circuits for determining
information. In particular, a balanced circuit may be configured
such that information of interest for a sensor may be determined
from a differential voltage between the output nodes of the
balanced circuit. More specifically, each line of a balanced
circuit may be configured with elements which are operationally
sensitive to changes in a parameter of an object or an environment
in which the balanced circuit is disposed and each of the elements
may be configured to alter the voltage along its respective line in
an opposing manner. In general, it is the objective of such
balanced circuits to have signal lines of matched impedances such
that noise and interference induced in each of the lines does not
substantially affect the accuracy of the differential voltage
measurement attributed to the information of interest. In
particular, having matched impedances on each signal line allows
noise and interference signals to be canceled for a differential
voltage measurement. On the contrary, any inequality in the noise
and/or interference induced in each line will result in such
signals not being fully cancelled.
[0007] In order to ensure the accuracy of a differential voltage
measurement, a common mode voltage between the signal output nodes
of the balanced circuit is often monitored. In particular, a common
mode voltage of a presumably balanced circuit is monitored relative
to a target voltage or relative to the differential gain of the
circuit, the latter scenario of which is referred to as a
common-mode rejection ratio. The term "common mode voltage" refers
to the voltage at a given location that appears equally and in
phase from each signal conductor to a common reference.
Alternatively stated, the term "common mode voltage" refers to the
instantaneous algebraic average of two signals within a balanced
circuit with both signals referenced to a common reference.
Although both differential mode and common mode signals are
analyzed when using a balanced circuit, they are generally
referenced as "wanted signals" and "unwanted signals,"
respectively. In particular, differential mode signal measurements
relate directly to determining the value of a parameter being
measured by a sensor and, thus, are considered "wanted." In
contrast, common mode signal measurements reflect the portions of
the signals which do not contribute to determining the information
of interest for a sensor and, thus, are considered "unwanted." In
other words, common mode signal measurements are only monitored in
conventional practices for determining whether to accept or throw
out differential mode signal measurements relating to a variable
parameter.
SUMMARY OF THE INVENTION
[0008] The following description of various embodiments of methods,
devices and systems is not to be construed in any way as limiting
the subject matter of the appended claims.
[0009] Embodiments of a method for determining a value of a
parameter of an object or an environment includes positioning a
device having a balanced circuit in or on an object or within a
particular environment, wherein the balanced circuit comprises
elements which are operationally sensitive to changes in a
parameter of the object or the environment. In addition, the method
includes measuring a voltage derived from the balanced circuit
which correlates to a common mode signal of the balanced circuit
and determining, from the measured voltage, a value of the
parameter.
[0010] Embodiments of a method for determining temperature using a
resistive sensor having a Wheatstone bridge circuit with at least
two variable resistors includes positioning the resistive sensor
such that the at least two variable resistors of the Wheatstone
bridge circuit are arranged in an environment in which temperature
is to be determined. The method further includes measuring, while
the two variable resistors are arranged in the environment, a
temperature detection voltage between a first voltage derived from
the Wheatstone bridge circuit which is proportional to a summed
voltage of signal output nodes of the Wheatstone bridge circuit and
a second voltage which is proportional to a reference voltage for
the Wheatstone bridge circuit. Moreover, the method includes
determining, from the temperature detection voltage, a temperature
of the environment.
[0011] Embodiments of devices include a Wheatstone bridge circuit
with at least two variable resistors and common mode circuitry
coupled to the Wheatstone bridge circuit which generates a voltage
correlating to a common mode signal of the Wheatstone bridge
circuit. The devices further include compensation circuitry coupled
to the Wheatstone bridge circuit which is configured to compensate
for variations of a resistive coefficient of a conductive material
comprising the Wheatstone bridge circuit due to ambient temperature
changes of the conductive material.
[0012] Embodiments of electronic signal monitoring devices for
monitoring and processing signals received from a balanced circuit
of a medical probe include a first means for receiving output
signals from the balanced circuit. In addition, the electronic
signal monitoring devices include a second means for determining
from one or more of the received output signals a voltage which
correlates to a common mode signal of the balanced circuit.
Moreover, the electronic signal monitoring device includes program
instructions which are executable by a processor for determining,
from the voltage, a temperature of an environment in which a tip of
the medical probe is arranged.
[0013] Embodiments of systems include a device having a balanced
circuit and further an electronic signal monitoring device
configured for electrical communication with the device to measure
electrical parameters of the balanced circuit. Moreover, the
systems include circuitry for coupling to the balanced circuit that
is configured to generate a first voltage which correlates to a
common mode voltage of the balanced circuit. The electronic signal
monitoring device includes a means for measuring the common mode
voltage. The systems further include a storage medium with program
instructions which are executable by a processor for determining,
from the common mode voltage, a value of a parameter of an
environment in which the device is arranged.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Other objects and advantages of the invention will become
apparent upon reading the following detailed description and upon
reference to the accompanying drawings in which:
[0015] FIG. 1 is a flowchart of a method for determining a value of
a parameter of an object or an environment;
[0016] FIG. 2 is a flowchart of a method for determining
temperature of an environment using a resistive sensor;
[0017] FIG. 3 is a schematic diagram of an exemplary circuit which
may be utilized in the method outlined in FIG. 2;
[0018] FIG. 4 is a schematic diagram of another exemplary circuit
which may be utilized in the method outlined in FIG. 2;
[0019] FIG. 5 is a schematic diagram of yet another exemplary
circuit which may be utilized in the method outlined in FIG. 2;
and
[0020] FIG. 6 is a schematic diagram of a medical probe system for
determining temperature of an environment in which a medical probe
is arranged.
[0021] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof are shown by
way of example in the drawings and will herein be described in
detail. It should be understood, however, that the drawings and
detailed description thereto are not intended to limit the
invention to the particular form disclosed, but on the contrary,
the intention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the present
invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Turning to the drawings, a flowchart of a method for
determining a value of a parameter of an object or an environment
is shown in FIG. 1. A specific application of such a method
utilizing a resistive sensor for determining temperature of an
environment is outlined in a flowchart depicted in FIG. 2. FIGS.
3-5 depict schematic diagrams of exemplary circuits which may be
utilized in the method outlined in FIG. 2. FIG. 6 illustrates an
exemplary system configured to perform the method outlined in FIG.
2. In particular, FIG. 6 illustrates a schematic diagram of a
medical probe system for determining temperature of an environment
in which a medical probe is arranged. Although FIGS. 3-5 are
specifically directed to methods and circuits involving a resistive
sensor with a Wheatstone bridge circuit having two variable
resistors and two fixed resistors and FIG. 6 is specific to systems
and devices involving medical probes, the methods, systems and
devices encompassed by the disclosure provided herein are not so
restricted. Furthermore, although FIGS. 2-6 are described for
determining temperature of an object or environment, the methods,
systems and devices provided herein are not so limited.
[0023] Rather, as encompassed by the flowchart of FIG. 1, the
methods, systems and devices considered herein may involve any
device having a balanced circuit which includes elements which are
operationally sensitive to changes in a parameter of an object or
an environment. The device may be any tool, mechanism or physical
means which can accommodate the balanced circuit and which can be
placed in proximity to, on, or within an object or environment of
interest. The balanced circuit may be of any configuration having
any type of operationally sensitive elements known in the art.
Thus, the methods, systems and devices described herein are not
limited to use of resistive sensors. Furthermore, the methods,
systems and devices considered herein may be used to determine any
measurable parameter of interest which relates to operationally
sensitive elements of a balanced circuit and, moreover, may be used
on or within any object or environment in which a device having the
balanced circuit can access. As such, the methods, systems and
devices considered herein are not restricted to determining a
temperature of an object or an environment, much less an
environment in which a medical probe is arranged. It is noted that
applications and devices alternative to those disclosed in
reference to FIGS. 2-6 are provided throughout this disclosure, but
the citation of such should not be construed to limit the scope of
the methods, systems and devices which may encompass the method
outlined in FIG. 1.
[0024] Turning to FIG. 1, the flowchart includes block 10 for
positioning a device having a balanced circuit in or on an object
or within a particular environment, wherein the balanced circuit
comprises elements which are operationally sensitive to changes in
a parameter of the object or the environment. As set forth in
detail below in reference to FIGS. 2-6, an example of an applicable
balanced circuit for the device is a silicon strain gauge, such as
a Wheatstone bridge circuit, having at least one gauge configured
to increase in resistance with a change in pressure and at least
one other gauge configured to decrease in resistance with the
change in pressure. The balanced circuits encompassed by the
methods, systems and devices disclosed herein, however, are not
restricted to being operationally sensitive to pressure nor are
they restricted to being silicon strain gauges. In particular,
other types of parameter sensitive elements and/or balanced
circuits may be used, including but not limited to those which may
be sensitive to changes in acceleration, tension, force,
temperature, volume, velocity, pH, oxygen concentration or
humidity.
[0025] Similar to the balanced circuit, the device employing the
balanced circuit and the object and/or environment in which the
device is placed may vary. As noted above, the device may be any
tool, mechanism or physical means which can accommodate the
balanced circuit and which can be placed in proximity, on, or
within an object or environment of interest. Furthermore, the
object or environment of interest may be any object or environment
having a variable parameter that is desired to be measured. As an
example, FIGS. 2-6 describe methods, device and systems in which
temperature is the variable parameter desired for measurement and
FIG. 6 discusses an exemplary implementation of a medical probe
system for measuring temperature of a bodily fluid, a body part or
a body cavity. As noted above, however, the methods, devices and
systems encompassed by the disclosure herein are not limited to the
description of FIGS. 2-6. As such, the methods, devices and systems
described herein may be configured to measure variable parameters
other than temperature, such as but not limited to pressure,
acceleration, tension, force, volume, velocity, pH, oxygen
concentration or humidity. Further, the methods described herein
may be implemented in devices and systems other than for use with
medical probes. For example, an electrocardiogram system could be
configured to implement the methods described herein.
[0026] Turning back to FIG. 1, the method outlined therein
includes, as denoted in blocks 12 and 14, measuring a voltage
derived from the balanced circuit which correlates to a common mode
signal of the balanced circuit and further determining, from the
measured voltage, a value of the parameter. Applications of such
steps in the method outlined in FIG. 2 are respectively denoted in
blocks 22 and 24. In particular, the method outlined in FIG. 2
includes block 20 for positioning a resistive sensor (e.g., a
piezoresistive sensor) such that at least two variable resistors of
a Wheatstone bridge circuit of the sensor are arranged in an
environment in which temperature is to be measured. Thereafter,
block 22 includes measuring a temperature detection voltage while
the two variable resistors are arranged in the environment and,
then at block 24, a temperature of the environment is determined
from the measured temperature detection voltage.
[0027] It is noted that when a Wheatstone bridge circuit includes
more than two variable resistors, two or more (and possibly all) of
the variable resistors may be arranged in the environment in which
temperature is to be measured and, thus, the process of measuring
the temperature detection voltage may be when two or more (and
possibly all) of the variable resistors are arranged in the
environment.
[0028] As denoted in block 22, the temperature detection voltage is
measured between a first voltage derived from the Wheatstone bridge
circuit which is proportional to a summed voltage of signal output
nodes of the Wheatstone bridge circuit and a second voltage which
is proportional to a reference voltage for the Wheatstone bridge
circuit. The operation of such steps may be better understood when
described in relation to the exemplary circuits depicted in FIGS.
3-5 as set forth below. In general, however, the processes outlined
in blocks 12, 14, 22 and 24 of FIGS. 1 and 2 are directed to
measuring a common mode signal of a balanced circuit and using the
common mode signal to determine a value of a parameter of an object
or an environment. This is contrast to conventional techniques of
monitoring common mode signals against predetermined thresholds to
simply accept or reject a differential mode signal measurement.
[0029] In addition to steps 12 and 14, the method of FIG. 1 may, in
some embodiments, include measuring a differential mode voltage of
the balanced circuit as denoted in block 16 and further determining
from the differential mode voltage a value of another distinct
parameter of the object or environment in which at least part of
the balanced circuit is arranged as denoted in block 18.
Applications of such steps in the embodiment of FIG. 2 are outlined
in blocks 26 and 28, specifically measuring a differential voltage
between signal output nodes of the Wheatstone bridge circuit and
determining from the differential voltage measurement a pressure of
the environment. As with the description of the processes outlined
in blocks 12, 14, 22 and 24, the operation of the processes
outlined in blocks 16, 18, 26 and 28 may be better understood when
described in relation to the exemplary circuits depicted in FIGS.
3-5 as set forth below. As noted above, the processes outlined in
blocks 12, 14, 22 and 24 of FIGS. 1 and 2 are directed to using a
common mode signal to determine a value of a parameter of an object
or an environment. Combining such a technique with measuring a
differential mode signal to determine a value of another parameter
of an object or environment as outlined in blocks 16, 18, 26 and 28
advantageously increases the functionality of balanced circuit
sensors for determining more information of interest. In some
cases, combining the techniques may allow fewer sensors to be used
for an evaluation of an object or an environment. For example, the
method discussed in reference to FIG. 2 may obviate a need for a
temperature sensor distinct from the resistive sensor in a
system.
[0030] The dotted lines between some of the blocks in FIG. 1 denote
that the operations outlined in blocks 16 and 18 may be conducted
prior to, subsequent to, or at substantially the same time as the
operations outlined in blocks 12 and 14. Likewise, the dotted lines
between the some of the blocks in FIG. 2 denote that the operations
outlined in blocks 26 and 28 may be conducted prior to, subsequent
to, or at substantially the same time as the operations outlined in
blocks 22 and 24. In some cases, it may be advantageous (i.e., time
effective) for the processes outlined in blocks 14 and 18 to be
performed simultaneously. Likewise, it may be desirable (i.e., time
effective) for the processes outlined in blocks 24 and 28 to be
performed simultaneously in some embodiments. In any case, the
dotted lines around blocks 16, 18, 26 and 28 in FIGS. 1 and 2
denote the processes outlined therein are optional. In particular,
it is noted that the methods, devices and systems described herein
may be performed to determine a value of a single parameter of an
object or environment and do not need to include measuring a
differential mode voltage of the balanced circuit or determining a
parameter value therefrom. To this end, it is noted that although a
resistive sensor (e.g., a piezoresistive sensor) may include
elements which are operationally sensitive to changes in
environmental pressure as described above, the sensor need not be
used to measure pressure in an environment. The resistive sensor
could be simply used to measure temperature of that environment.
Alternatively, the resistive sensor could be used to measure both
pressure and temperature of the environment as described above.
[0031] As noted above, the circuits depicted in FIGS. 3-5 are
examples of which may be employed for the method outlined in FIG.
2. Other circuits employing additional, fewer and/or different
elements, however, may be employed to effect the operations
outlined in FIG. 2. For example, although a Wheatstone bridge
having two variable resistors and two fixed resistors (commonly
referred to as a half-bridge circuit) is specifically described in
reference to FIGS. 3-5, silicon strain gauges having four variable
resistors (commonly referred to as full-bridge circuits) may be
alternatively used. Furthermore, different summation circuitry may
be employed for the temperature detection circuitry described in
reference to FIGS. 3-5. Moreover, different reference voltage
circuitry other than what is disclosed in reference to FIGS. 4-5
may be used. In some cases, the summation operations described in
reference to FIGS. 3-5 may be partially or wholly done via software
(i.e., via processor-executable program instructions) instead of
partially or wholly via circuitry. In other words, the temperature
detection circuitry described in reference to FIGS. 3-5 may, in
some cases, be partially or wholly substituted by software having
program instructions for performing such computational operations.
A particularly suitable application of such is to have
computational program instructions disposed on or accessible by an
electronic monitoring system which is in electrical communication
with the device comprising the balanced circuit as described in
more detail below in reference to FIG. 6.
[0032] Turning to FIG. 3, circuit 30 is shown having Wheatstone
bridge 32 coupled between power supply 34 and reference 36.
Reference 36 may be ground or any node of circuit 30 common to
Wheatstone bridge 32. The specifications of power supply 34 may
generally depend on the application in which the circuit is
employed and, thus, may vary widely among systems. An exemplary
specification for power supply 34 when circuit 30 is applied within
a medical probe system, for example, may be a maximum of 5 volts,
but specifications of larger and smaller voltages may be employed.
In some cases, circuit 30 may include potentiometer 38 for
adjusting the level of the power transmitted to Wheatstone bridge
32 as shown in FIG. 3, but such an element is optional. It is noted
that the dotted line to which numeral 32 refers to in FIG. 3 is
used to schematically indicate which elements of circuit 30 makeup
Wheatstone bridge 32. The dotted line to which numeral 32 refers is
not part of the circuit nor does it indicate that Wheatstone bridge
32 is an optional element in circuit 30.
[0033] As shown in FIG. 3, Wheatstone bridge 32 may include two
variable resistors 40 and 42 and two fixed resistors 44. In some
embodiments, variable resistors 40 and 42 may be configured to be
operationally sensitive to changes in pressure in an environment in
which they are arranged. In particular, one of variable resistors
40 and 42 may be configured to increase in resistance with a change
in environmental pressure and the other variable resistor may be
configured to decrease in resistance with the change in
environmental pressure. An example of a Wheatstone bridge having
such characteristics is one which has variable resistors 40 and 42
made of a semiconductive material and, thus, the Wheatstone bridge
serves as a piezoresistive sensor. In any case, ensuing to a design
of varying resistance with changes in environmental pressure, a
differential mode voltage of Wheatstone bridge 32 (i.e., a
differential voltage between signal output nodes 46 and 48) may be
measured and then used to determine (i.e., quantitate) the pressure
of the environment in which the variable resistors are arranged as
noted in FIG. 3. Such process steps are denoted in blocks 26 and 28
of FIG. 2. In alternative embodiments, variable resistors 40 and 42
may be configured to be operationally sensitive to changes in a
parameter other than pressure, such as but not limited to
temperature, humidity, force, tension, volume, velocity, pH, oxygen
concentration and acceleration. In such cases, the differential
mode measurement will accordingly be used to quantitate the noted
parameter.
[0034] As further shown in FIG. 3, circuit 30 may optionally
include compensation circuitry 49 coupled to Wheatstone bridge 32.
In general, compensation circuitry 49 is configured to compensate
for variations of a resistive coefficient of a conductive material
comprising the Wheatstone bridge circuit, specifically variable
resistors 40 and 42, due to ambient temperature changes of the
conductive material. For example, in embodiments in which variable
resistors 40 and 42 are made of a semiconductive material,
compensation circuitry 49 may be configured to compensate for
variations of a piezoresistive coefficient of the semiconductive
material due to ambient temperature changes of the semiconductive
material. There are a wide variety of manners known in the art in
which to compensate for temperature changes and, thus, compensation
circuitry 49 is depicted very generally in FIG. 3 so as to not
limit the scope to which it may be. An example of compensation
circuitry which may be used is one or more fixed resistors in
parallel with at least one of variable resistors 40 and 42 of
Wheatstone bridge 32. It is noted that the compensation circuitry
is not limited to when Wheatstone bridge 32 includes two variable
resistors and, more specifically, may be employed when Wheatstone
bridge 32 includes any plurality of variable resistors.
[0035] In any case, with the inclusion compensation circuitry 49 in
circuit 30, the accuracy of the differential mode measurement of
Wheatstone bridge 32 in relation to a parameter of interest may be
improved. In particular, compensation circuitry 49 may aid in
counteracting changes in pressure sensitivity of a conductive
material comprising Wheatstone bridge 32 due to temperature changes
such that resistance changes of variable resistors 40 and 42 are
maintained substantially uniform with pressure changes regardless
of the ambient temperature. Although compensation circuitry may be
beneficial in some cases, it is not required for the methods,
devices and systems described herein. In particular, a balanced
circuit may be void of such compensation circuitry if the effects
on pressure sensitivity are not large enough to warrant significant
inaccuracy of a differential mode measurement from the circuit.
[0036] In any case, circuit 30 may include temperature detection
circuitry 50 coupled to Wheatstone bridge 32 as shown in FIG. 3.
Similar to the dotted line encompassing the elements of Wheatstone
bridge 32, the dotted line to which numeral 50 refers to in FIG. 3
is used to schematically indicate which elements of circuit 30
makeup temperature detection circuitry 50. The dotted line to which
numeral 50 refers is not part of the circuit nor does it indicate
that temperature detection circuitry 50 is an optional element in
circuit 30. FIG. 3 depicts temperature detection circuitry 50
including two signal lines coupled to Wheatstone bridge 32. As one
skilled in the art would be aware, the signal lines are effectively
coupled to signal output nodes 46 and 48 of Wheatstone bridge 32.
Direct coupling to the signal output nodes is not shown in FIG. 3
to simplify the depiction of temperature detection circuitry
50.
[0037] As shown in FIG. 3, the signal lines of temperature
detection circuitry 50 include fixed resistors 52 and 54,
respectively, and are joined to form a closed loop. Such a design,
in effect, produces a measurable voltage at node 56 which is
proportional to a summed voltage of signal output nodes 46 and 48
of Wheatstone bridge 32. Alternatively stated, a measurable voltage
is generated at node 56 which is proportional to a summation of the
voltages at the output nodes of Wheatstone bridge 32. In yet other
words, the design produces a measurable voltage at node 56 which
correlates to a common mode signal of Wheatstone bridge 32. As used
herein, the term "common mode signal" refers to the average value
of signals at the positive and negative output nodes of a
differential circuit. A quantitative measure of a common mode
signal is referred to as common mode voltage, which as noted above
refers to the voltage at a given location that appears equally and
in phase from each signal conductor to a common reference.
Alternatively stated, the term "common mode voltage" refers to the
instantaneous algebraic average of two signals within a balanced
circuit with both signals referenced to a common reference.
[0038] Depending on the resistances of resistors 52 and 54, the
voltage measured between nodes 56 and 58 may be the common mode
voltage of Wheatstone bridge 32 or may be of greater or lesser
proportion thereto. In particular, when the resistances of
resistors 52 and 54 are substantially equal, the voltage measured
between nodes 56 and 58 is the common mode voltage of Wheatstone
bridge 32. In some cases, however, it may be advantageous to
produce a voltage which is larger or smaller than the common mode
voltage of Wheatstone bridge 32 and, thus, in some cases, resistors
52 and 54 may have different resistances. For example, it may be
desirable to produce a voltage which is larger than the common mode
voltage of Wheatstone bridge 32 such that a voltage reading between
nodes 56 and 58 may be amplified. In particular, an amplified
voltage measurement between nodes 56 and 58 may aid in ascertaining
a temperature of the object or environment in which at least
variable resistors 40 and 42 of Wheatstone bridge 32 are disposed.
Regardless of whether the voltage measured between nodes 56 and 58
is the common mode voltage of Wheatstone bridge 32 or is of greater
or lesser proportion thereto, the measured voltage may be
referenced as correlating to a common mode signal of Wheatstone
bridge 32 since the measured voltage is in relationship with the
average value of signals at the signal output nodes of Wheatstone
bridge. As used herein, the term "proportional" means corresponding
in value by a set ratio, wherein the ratio is a non-negative number
(whole or fractional) that is less than, equal, or greater than 1.
As such, the term "proportional" is inclusive to values which are
the same as well as those which are non-negative multiples of each
other.
[0039] As shown in FIG. 3, a voltage reading between nodes 56 and
58 may relate to temperature, particularly when Wheatstone bridge
32 includes resistive elements as described above. In view thereof,
the voltage reading between nodes 56 and 58 is sometimes referred
to herein as "a temperature detection voltage." In other
embodiments, the voltage reading between nodes 56 and 58 may relate
to a different variable parameter of an object or environment,
depending on the sensitivity of resistors 40 and 42 to different
parameters. In any case, the voltage reading between nodes 56 and
58 is used to determine a value of a parameter of interest for an
object or environment. More specifically, a computational
correlation between a parameter and voltage readings between nodes
56 and 58 of circuit 30 may be predetermined and the correlation
may be used to determine the value of the parameter from a given
voltage reading. In some cases, the computational correlation may
be a polynomial equation having a voltage reading between nodes 56
and 58 of circuit 30 as a variable. Accordingly, the process
outlined in block 24 of FIG. 2 may include computing temperature of
the environment from a polynomial equation having the temperature
detection voltage as a variable. In some cases, the polynomial
equation may be a first degree polynomial equation (i.e., a linear
equation), but polynomial equations of larger degrees are
possible.
[0040] As noted above, the circuits depicted in FIGS. 4 and 5 offer
additional examples which may be employed for the method outlined
in FIG. 2. The circuits of FIGS. 4 and 5 are similar to circuit 30
depicted in FIG. 3 in that they include Wheatstone bridge 32 and
optional potentiometer 38 coupled between power supply 34 and
reference 36 and further include optional compensation circuitry
49. The specifics of such elements discussed above with respect to
FIG. 3 may be applied to the circuits depicted in FIGS. 4 and 5 and
are not reiterated for the sake of brevity. As set forth in more
detail below, the circuits of FIGS. 4 and 5 differ from circuit 30
depicted in FIG. 3 by the inclusion of different temperature
detection circuitry as well as reference voltage circuitry
configured to generate a biased reference voltage relative to an
excitation voltage applied to Wheatstone bridge 32. The disclosure
of the different temperature detection circuitry in FIGS. 4 and 5
emphasizes that the voltage derived from Wheatstone bridge 32 may
be of any proportion to a summed voltage of signal output nodes of
the Wheatstone bridge. Furthermore, as set forth in more detail
below, the inclusion of reference voltage circuitry in the circuits
of FIGS. 4 and 5 discloses that the "second voltage" specified in
block 22 of FIG. 2 may, in some embodiments, be in reference to
power supply 34 rather than just in reference to reference 36 as
depicted in FIG. 3. As such, it is noted that the phrase "reference
voltage for the Wheatstone bridge" denoted in block 22 of FIG. 2
can refer to either the excitation source or a common reference of
a Wheatstone bridge.
[0041] As shown in FIG. 4, circuit 60 includes temperature
detection circuitry 62 as well as resistors 70 and 72 between power
supply 34 and reference 36. In general, resistors 70 and 72 makeup
exemplary reference voltage circuitry which is configured to
generate a biased reference voltage at node 74 relative to an
excitation voltage applied to Wheatstone bridge 32. In other words,
resistors 70 and 72 bias reference 36 to power supply 34 such that
the voltage to which the output voltage from temperature detection
circuitry 62 is referenced may be set to a predetermined value
relative to power supply 34. An example of a bias is half of power
supply 34, but resistors 70 and 72 may be configured to generate
other proportions of power supply 34. It is noted that resistors 70
and 72 are merely an example of reference voltage circuitry which
may be used to bias reference 36 to power supply 34. Any biasing
techniques known to those skilled in art may be used in circuit 60
and, thus, the methods, devices and system described herein are not
necessarily limited to the embodiment depicted in FIG. 4.
[0042] Temperature detection circuitry 62 of FIG. 4 differs from
temperature detection circuitry 50 of FIG. 3 by the inclusion of
buffers 64 and 66 as well as potentiometer 68 instead of resistors
52 and 54. Buffers 64 and 66 may be generally configured to ensure
that the voltage reading between potentiometer 68 and node 74 does
not have a loading effect on the differential mode measurement
between signal output nodes 46 and 48 of Wheatstone bridge 32.
Potentiometer 68 may be configured to match an incoming signal at a
particular reference temperature to that of the biased signal at
node 74 such that voltage output for that temperature would be zero
volts. Such a design may aid in simplifying the determination of
temperature from a given temperature detection voltage. As with the
reference voltage circuitry of resistors 70 and 72, the use of
buffers 64 and 66 is merely an example of circuitry which may be
used to ensure that a loading effect is not imposed on Wheatstone
bridge 32 Likewise, the use of potentiometer 68 with biasing
circuitry is merely an example in which to null out a voltage
reading for a particular temperature. Other techniques known to
those skilled in art may be used in circuit 60 and, thus, the
methods, devices and system described herein are not necessarily
limited to the embodiment depicted in FIG. 4.
[0043] As shown in FIG. 5, circuit 80 differs from circuit 60
depicted in FIG. 4 by inclusion of temperature detection circuitry
82 as well as buffer 76 from node 74. Circuit 80 includes resistors
70 and 72 as is included in circuit 60 of FIG. 4. In addition,
temperature detection circuitry 82 includes buffers 64 and 66 as
well as potentiometer 68 as is included in temperature detection
circuitry 62 of FIG. 4. The specifics of such elements discussed
above with respect to FIG. 4 may be applied to circuit 80 depicted
in FIG. 5 and are not reiterated for the sake of brevity.
[0044] As shown in FIG. 5, temperature detection circuitry 82
includes amplifier 84 and amplifier calibrator controls 86. In
general, amplifier 84 adjusts voltage output from potentiometer 68
based on the presets in amplifier calibrator controls 86. Such
circuitry allows for bi-directional voltage output depending on the
null output voltage adjustment of potentiometer 68. Buffer 76
offers impedance isolation from power supply 34 and reference 36 to
improve the temperature detection voltage reading from circuit 80
relative to circuits 30 and 60 of FIGS. 3 and 4. It is noted that
use of buffer 76, amplifier 84, and amplifier calibrator controls
86 are merely examples of circuitry which may be used to offer
impedance isolation and amplify signals. Other techniques known to
those skilled in art may be used in circuit 80 and, thus, the
methods, devices and system described herein are not necessarily
limited to the embodiment depicted in FIG. 5.
[0045] As set forth above, the methods, systems and devices
considered herein may be used to determine any measurable parameter
of interest which relates to the operationally sensitive elements
of a balanced circuit and, moreover, may be used on or within any
object or environment in which a device having the balanced circuit
can access. As merely an example of a system which may be
configured to perform the methods described herein, FIG. 6 depicts
a schematic diagram of medical probe system 90 having a device
which includes circuitry by which to measure a voltage derived from
a balanced circuit arranged within medical probe 92 which
correlates to a common mode signal of the balanced circuit. In
addition, medical probe system 90 includes processor executable
program instructions 102 for determining from the measured voltage
a temperature of an environment in which a tip of medical probe 92
is arranged. As described in more detail below, an alternative
configuration to medical probe system 90 is to incorporate the
computational operations of temperature detection circuitry 96
and/or the reference voltage circuitry described below into program
instructions 102, thus negating the inclusion of either or both of
such circuitry within the system.
[0046] In any case, the medical probe systems described in
reference to FIG. 6 (including variations to the depiction in FIG.
6) may be used for any application using a medical probe in which
temperature of bodily fluids, cavities or tissue may be of interest
and/or temperature of fluids administered into a body via a
catheter may be of interest. Examples of applications include but
are not limited to the drainage or administration of fluids into a
body, measuring/monitoring arterial or vein blood pressure,
measuring/monitoring pressure of body cavities, and thermodilution
techniques. It is noted that medical probe system 90 is merely an
example of a system which may be configured to perform the methods
described herein. Other medical probe systems including devices and
features additional or alternative to those described in reference
to FIG. 6 may be suitable as well. In addition, a variety of other
types of systems in any field may be configured to perform the
methods described herein, particularly any of which involve
differential signal processing.
[0047] In general, medical probe 92 of medical probe system 90 may
include any type of medical probe, i.e., medical probe 92 may be a
medical probe of any size, material, type, purpose, etc. and may be
a single or multiple tipped medical probe. The term "medical
probe," as used herein, refers to a long, slender instrument for
exploring wounds, body cavities, or body passages. Thus, the term
"medical probe" encompasses catheters as well as devices including
no lumen. In general, the term "catheter" as used herein is
inclusive to catheters having an open lumen (i.e., having an
unblocked lumen) as well as catheters having a closed lumen (i.e.,
a lumen having an obstruction such that the catheter cannot be used
for the passage of fluid). As common to all medical probes, medical
probe 92 includes at least one tip 93 which is used to access a
particular bodily fluid, body part or body region. Specific to the
medical probes considered herein, tip 93 includes at least a
portion of a balanced circuit, particularly elements of a balanced
circuit which are operationally sensitive to a parameter of a
bodily fluid, a body part or a body region. The balanced circuit
may be of any type or configuration.
[0048] An example of a balanced circuit which may be suitable for a
medical probe is a Wheatstone bridge with two variable resistors
and two fixed resistors. Alternatively, a Wheatstone bridge having
four variable resistors may be used. In yet other embodiments,
another type of balanced circuit may be employed. In any case, the
entire balanced circuit may be disposed within tip 93 in some
embodiments. In other cases, however, less than the entire balanced
circuit may be disposed within tip 93 and, in some embodiments,
only the operationally sensitive elements of the balanced circuit
may be disposed within tip 93. In particular, in some case, it may
be desirable to minimize the size of tip 93 as well as the areal
space of the medical probe tubing and, thus, it may be beneficial
to include only a portion of a balanced circuit therein. In any of
such cases, the remaining portion of the balanced circuit may be
disposed in electrical connector 94 of medical probe 92 and/or or
within the tubing of the medical probe.
[0049] As shown by operational connection 97 in FIG. 6, electrical
connector 94 and electronic signal monitoring device 95 may be
jointly configured for electrical communication with each other. In
particular, electronic signal monitoring device 95 is configured to
measure electrical parameters of the balanced circuit disposed
within medical probe 92 and, thus, electrical connector 94 includes
a means for sending output signals of the balanced circuit therein
and electronic signal monitoring device 95 includes a means for
receiving such output signals. In some embodiments, each of
electrical connector 94 and electronic signal monitoring device 95
may include an electrical port configured for securely and
operatively coupling with an electrical connector of the other
(i.e., hard-wired input/output terminals). In such cases, the
coupling may be direct or may be through intermediary means. In yet
other embodiments, electrical connector 94 and electronic signal
monitoring device 95 may additionally or alternatively include
transmitters to transmit signals wirelessly. In any case,
electronic signal monitoring device 95 may be configured to process
data received from the balanced circuit disposed within medical
probe 92, as described in more detail below with respect to means
98 and 99. In some embodiments, electronic signal monitoring device
95 may, be configured to supply power and ground to the balanced
circuit within medical probe 92 as well as any other circuitry
disposed therein. As such, electronic signal monitoring device 95
may, in some cases, include an excitation voltage terminal for
supplying an excitation voltage to the balanced circuit disposed
within medical probe 92 and also a reference common voltage
terminal for supplying a reference common voltage for the balanced
circuit.
[0050] As described above in reference to FIGS. 2-5, the methods,
devices and systems described herein may utilize a resistive sensor
(i.e., a balanced circuit having resistive elements) and, thus, in
some embodiments, medical probe 92 may include a resistive sensor.
In such cases, medical probe 92 may optionally include compensation
circuitry coupled to the balanced circuit disposed therein. In
general, as described above in reference to FIG. 3, the
compensation circuitry is configured to compensate for variations
of a resistive coefficient of a conductive material comprising the
balanced circuit due to ambient temperature changes of the
conductive material. As further described above, although
compensation circuitry may be beneficial in some cases, it is not
required for the methods, devices and systems described herein and,
thus, medical probe 92 may be void of compensation circuitry in
some embodiments. In any case, medical probe 92 may, in some cases,
include reference voltage circuitry for generating a biased
reference voltage relative to an excitation voltage applied to the
balanced circuit disposed therein. In addition or alternatively,
electronic signal monitoring device 95 and/or a device between
medical probe 92 and electronic signal monitoring device 95 may
include such circuitry. Examples of such circuitry are described in
reference to FIGS. 4 and 5, but the scope of such is not so
limited. In yet other embodiments, the computational operations of
such reference voltage circuitry may be incorporated into program
instructions 102, thus negating the inclusion of such circuitry
within medical probe 92 and/or electronic signal monitoring device
95. In yet other embodiments, medical probe system 90 may be void
of means to change values of a reference voltage.
[0051] In any case, medical probe system 90 may, in some
embodiments, include temperature detection circuitry 96 as
illustrated in FIG. 6. In general, temperature detection circuitry
96 is configured to generate a voltage which is proportional to a
summed voltage of signal output nodes of the balanced circuit
disposed within medical probe 92 (i.e., a voltage which is
proportional to a summation of the voltages at the signal output
nodes of the balanced circuit). Examples of circuitry are described
in reference to FIGS. 3-5, but temperature detection circuitry 96
is not necessarily so limited. As denoted by the dotted lines
extending from temperature detection circuitry 96 in FIG. 6,
temperature detection circuitry 96 may be disposed within medical
probe 92, electronic signal monitoring device 95, and/or between
medical probe 92 and electronic signal monitoring device 95 (i.e.,
within an intermediary means between the devices). In cases in
which temperature detection circuitry 96 is disposed within medical
probe 92, temperature detection circuitry 96 may be disposed within
tip 93 and/or electrical connector 94. As described above, an
alternative configuration to medical probe system 90 is to
incorporate the computational operations of temperature detection
circuitry 96 into program instructions 102, thus negating the
inclusion of such circuitry within the system.
[0052] As shown in FIG. 6, electronic signal monitoring device 95
may, in some cases, include means 98 for determining a voltage
between the voltage generated by temperature detection circuitry 96
(or comparable program instructions) and another voltage which is
proportional to the common reference voltage or the excitation
voltage supplied to the medical probe. The voltage determined by
means 98 is referred to herein as a temperature detection voltage
since it is used to determine the temperature of the environment in
which tip 93 is arranged, particularly by program instructions 102
in medical probe system 90. In particular, FIG. 6 shows medical
probe system 90 with storage medium 100 including program
instructions 102 coupled to electronic signal monitoring device 95
via input therefrom. In general, program instructions 102 are
executable by processor 104 for generating output 106 and, more
specifically, for determining, from the temperature detection
voltage measured by means 98, a temperature of an environment in
which tip 93 of medical probe 92 is arranged. Such a process may
include any of the particularities described in reference to block
24 of FIG. 2 and are not reiterated for the sake of brevity. In
some embodiments, electronic signal monitoring device 95 and
storage medium 100 may be one of the same and, thus, in some cases,
electronic signal monitoring device 95 may include program
instructions 102. In other cases, storage medium 100 may be a
device distinct from electronic signal monitoring device 95.
[0053] In general, the term "storage medium," as used herein, may
refer to any electronic medium configured to hold one or more set
of program instructions, such as but not limited to a read-only
memory, a random access memory, a magnetic or optical disk, or
magnetic tape. The term "program instructions" may generally refer
to commands within a program which are configured to perform a
particular function, such as receiving input, recording receipts of
signals, and processing signals. Program instructions may be
implemented in any of various ways, including procedure-based
techniques, component-based techniques, and/or object-oriented
techniques, among others. For example, the program instructions may
be implemented using ActiveX controls, C++ objects, JavaBeans,
Microsoft Foundation Classes ("MFC"), or other technologies or
methodologies, as desired. Program instructions implementing the
processes described herein may be transmitted over on a carrier
medium such as a wire, cable, or wireless transmission link.
[0054] As shown in FIG. 6, electronic signal monitoring device 95
may, in some embodiments, include means 99 for measuring a
differential mode voltage of the balanced circuit dispose within
medical probe 92, particularly via signals transmitted from
electrical connector 94 of medical probe 92. In such cases, program
instructions 102 may be further executable by processor 104 for
determining, from the differential voltage, a pressure of the
environment in which tip 93 is arranged. As such, medical probe
system 90 may be used in such embodiments to determine temperature
and/or pressure of the environment in which tip 93 is arranged. As
described in detail above, a benefit of the methods, devices and
systems described herein is that a balanced circuit may be used to
monitor two variable parameters of an object or an environment.
Hence, fewer sensors may be used for an evaluation of an object or
an environment. As such, medical probe 92 may, in some embodiments,
be absent a temperature sensor distinct from the temperature
detection means dually provided by the balanced circuit disposed
therein and temperature detection circuitry 96. Alternatively
stated for cases in which medical probe 92 includes a resistive
Wheatstone bridge and compensation circuitry, medical probe 92 may
be absent a temperature sensor distinct from the resistive sensor
made up by the Wheatstone bridge, the compensation circuitry and
temperature detection circuitry 96. Such scenarios may be
particularly advantageous when available space at tip 93 is
limited. In any case, electronic signal monitoring device 95 may be
configured to utilize means 98 and 99 at the same time or in
succession.
[0055] It will be appreciated to those skilled in the art having
the benefit of this disclosure that this invention is believed to
provide methods, devices and systems which utilize a voltage
reading associated with a common mode signal of a balanced circuit
to determine a value of a parameter of an object or an environment.
Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. For example, although the
description of methods, devices and systems provided herein are
specific to Wheatstone bridge circuits including resistive elements
for determining temperature of an environment, the methods, devices
and systems provided herein may be constructed with a variety of
balanced circuits having any type of operationally sensitive
elements for determining any type of variable parameter of an
object or environment. Accordingly, this description is to be
construed as illustrative only and is for the purpose of teaching
those skilled in the art the general manner of carrying out the
invention. It is to be understood that the forms of the invention
shown and described herein are to be taken as the presently
preferred embodiments. Elements and materials may be substituted
for those illustrated and described herein, parts and processes may
be reversed, and certain features of the invention may be utilized
independently, all as would be apparent to one skilled in the art
after having the benefit of this description of the invention.
Changes may be made in the elements described herein without
departing from the spirit and scope of the invention as described
in the following claims.
* * * * *