U.S. patent application number 10/961450 was filed with the patent office on 2005-04-21 for method and circuit for detecting a change in inductance.
This patent application is currently assigned to DELPHI TECHNOLOGIES, INC.. Invention is credited to Cyran, Curtis P., Disser, Robert J..
Application Number | 20050083046 10/961450 |
Document ID | / |
Family ID | 33098415 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050083046 |
Kind Code |
A1 |
Cyran, Curtis P. ; et
al. |
April 21, 2005 |
METHOD AND CIRCUIT FOR DETECTING A CHANGE IN INDUCTANCE
Abstract
A method and circuit for detecting a change in inductance of a
variable inductance element. An oscillating signal has a frequency
that varies with inductance of the element. An intermediate voltage
is produced at a level that varies according to frequency of the
oscillating signal. The intermediate voltage is scaled to produce
an output voltage.
Inventors: |
Cyran, Curtis P.; (Dayton,
OH) ; Disser, Robert J.; (Dayton, OH) |
Correspondence
Address: |
MICHAEL SMITH*
DELPHI TECHNOLOGIES, INC.
P.O. Box 5052
Mail Code: 480-410-202
Troy
MI
48007-5052
US
|
Assignee: |
DELPHI TECHNOLOGIES, INC.
|
Family ID: |
33098415 |
Appl. No.: |
10/961450 |
Filed: |
October 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10961450 |
Oct 8, 2004 |
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10615570 |
Jul 8, 2003 |
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6803773 |
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Current U.S.
Class: |
324/209 |
Current CPC
Class: |
G01D 5/243 20130101;
G01R 27/2611 20130101 |
Class at
Publication: |
324/209 |
International
Class: |
G01B 007/24 |
Claims
1. A method for detecting changes in inductance of a variable
inductance element comprising the steps of: a) producing an
oscillating square wave signal having a frequency that varies in
proportion to variations in inductance of the variable inductance
element; b) inputting the oscillating square wave signal to a
phase-locked loop circuit and producing an intermediate analog
voltage that varies in proportion to variations in frequency of the
oscillating square wave signal of step a); c) scaling the
intermediate analog voltage of step b) to produce an output analog
voltage; and d) detecting changes in inductance of the variable
inductance element based upon changes in the output analog voltage
of step c).
2. The method of claim 1, wherein the variable inductance element
comprises an inductive sensor.
3. The method of claim 2 where the inductive sensor includes at
least one coil located adjacent a magnetostrictive object.
4. (canceled)
5. The method of claim 1, wherein step d) includes inputting the
output analog voltage to an analog to digital converter.
6. (canceled)
7. The method of claim 1, wherein step a) involves connecting the
variable inductance element in a feedback path of an oscillator
circuit.
8. The method of claim 1 wherein the scaling of step c) involves
offsetting and amplifying the intermediate analog voltage.
9. A circuit for producing a voltage level substantially
proportional to inductance of a variable inductance element, the
circuit comprising: an oscillator stage having a feedback path and
the variable inductance element connected therein and producing an
oscillating signal having a frequency that varies with inductance
of the variable inductance element; a conversion stage comprising a
phase-locked loop circuit operatively connected to receive the
oscillating signal and producing an intermediate analog voltage
that varies in proportion to variations in the frequency of the
oscillating signal; and an amplification stage operatively
connected to receive the intermediate analog voltage and operating
to offset and amplify the intermediate analog voltage to produce an
output analog voltage with a voltage level proportional to
inductance of the variable inductance element.
10. (canceled)
11. (canceled)
12. The circuit of claim 9 wherein the amplification stage includes
an adjustable offset control component.
13. The circuit of claim 12 wherein the adjustable offset control
component comprises a potentiometer.
14. The circuit of claim 12 wherein the adjustable offset control
component comprises an automated control component.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to inductive
sensors, and more particularly to a method for detecting a change
in the inductance of an inductive sensor.
BACKGROUND OF THE INVENTION
[0002] Conventional inductive sensors may use an inductive coil
positioned relative to a magnetostrictive object such that magnetic
flux lines induced by an alternating electric current in the coil
pass through the object in a direction substantially parallel to
the strain direction. The inductance of the coil is measured over
time. A change in permeability of the object due to a change in
strain of the object is detected or determined from a change in the
measured inductance over time.
[0003] What is needed is an improved method for accurately
detecting a change in the inductance of such inductive sensors as
well as other variable inductance elements.
SUMMARY OF THE INVENTION
[0004] In a first aspect, a method for detecting changes in
inductance of a variable inductance element involves the steps of:
a) producing an oscillating signal having a frequency that varies
in proportion to variations in inductance of the variable
inductance element; b) producing an intermediate analog voltage
that varies in proportion to variations in frequency of the
oscillating signal of step a); c) scaling the intermediate analog
voltage of step b) to produce an output analog voltage; and d)
detecting changes in inductance of the variable inductance element
based upon changes in the output analog voltage of step c).
[0005] In another aspect, a method is provided to convert a known
range of inductance change of a variable inductance element between
a first inductance and a second inductance into a desired range of
analog voltage change between a first voltage level and a second
voltage level. The method involves the steps of: a) establishing an
oscillator circuit incorporating the variable inductance element so
as to produce an oscillating signal having a frequency that varies
with inductance of the variable inductance element, the oscillating
signal produced with a first frequency when the variable inductance
element has the first inductance and produced with a second
frequency when the variable inductance element has the second
inductance; b) establishing a circuit to convert the frequency of
the oscillating signal to an intermediate analog voltage, the
intermediate analog voltage produced at a first intermediate level
when the oscillating signal has the first frequency and produced at
a second intermediate level when the oscillating signal has the
second frequency; and c) establishing a circuit to scale the
intermediate analog voltage so as to produce an output voltage
within the desired range, the output voltage produced at the first
voltage level when the intermediate analog voltage is at the first
intermediate level and produced at the second voltage level when
the intermediate analog voltage is at the second intermediate
level.
[0006] In a further aspect, a circuit for producing a voltage level
substantially proportional to inductance of a variable inductance
element includes an oscillator stage having the variable inductance
element connected therein and producing an oscillating signal
having a frequency that varies with inductance of the variable
inductance element. A conversion stage is operatively connected to
receive the oscillating signal and produces an intermediate analog
voltage that varies in proportion to variations in the frequency of
the oscillating signal. An amplification stage is operatively
connected to receive the intermediate analog voltage and operates
to offset and amplify the analog voltage to produce an output
analog voltage with a voltage level proportional to inductance of
the variable inductance element.
[0007] The foregoing methods and circuit provide a practical,
effective and relatively inexpensive way to detect changes in
inductance of a variable inductive element.
SUMMARY OF THE DRAWINGS
[0008] FIG. 1 is a flow chart of one method;
[0009] FIG. 2 is a schematic of one circuit in accordance with the
method;
[0010] FIG. 3 is a detailed schematic of one implementation of the
circuit of FIG. 3; and
[0011] FIG. 4 is a schematic of one alternative for producing an
offset voltage.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0012] A flow chart 10 illustrating one embodiment of a method is
shown in FIG. 1 and a corresponding circuit 100 is shown in FIG. 2.
First, assume the case of any variable inductance element. In one
example the element is an inductive sensor, which in one form is a
coil located adjacent a magnetostrictive object. However, other
variable inductance elements are contemplated. A range of change in
inductance of the variable inductance element, such as between a
first inductance L1 and a second inductance L2, is known or
otherwise identified at step 12. For example, in many inductive
sensor applications the anticipated range of change in inductance
of the inductive sensor will be known. A target range of
corresponding voltage change, such as between a first voltage level
VO1 and a second voltage level VO2, is known or otherwise
identified in step 14. For example, in a digital system a standard
range of identifiable voltage change might be between VO1=0 volts
and VO2=5 volts. In another example the target voltage range might
be VO1=0.5 volts to VO2=4.5 volts.
[0013] At step 16 an oscillator circuit 102 (FIG. 2) is established
and the variable inductance element incorporated therein such that
the oscillator circuit produces an oscillating signal having a
frequency that varies with inductance of the variable inductance
element. The oscillating signal 104 is produced with a first
frequency f1 when the variable inductance element has the first
inductance L1 and is produced with a second frequency when the
variable inductance element has the second inductance L2. At step
18 a circuit 106 is established to convert the frequency of the
oscillating signal 104 to an intermediate analog voltage VI. The
intermediate analog voltage VI is produced at a first intermediate
level VI1, which in one example is a non-zero level, when the
oscillating signal 104 has the first frequency f1 and is produced
at a second intermediate level VI2, which may also be a non-zero
level, when the oscillating signal 104 has the second frequency f2.
At step 20 an amplification circuit 108 is established to offset
and amplify the intermediate analog voltage VI so as to produce an
output voltage VO at the first voltage level VO1 when the
intermediate analog voltage VI is at the first intermediate level
VI1 and to produce an output voltage VO at the second voltage level
VO2 when the intermediate analog voltage VI is at the second
intermediate level VI2. A detection unit 110, such a processor, can
then be used to examine the voltage of the output signal VO to
identify and track changes in inductance of the variable inductance
element.
[0014] Accordingly, the basic method of detecting changes in
inductance of a variable inductance element involves producing an
oscillating signal 104 having a frequency that varies in proportion
to variations in inductance of the variable inductance element;
producing an intermediate analog voltage VI that varies in
proportion to variations in frequency of the oscillating signal
104; scaling the intermediate analog voltage VI to produce an
output analog voltage VO; and detecting changes in inductance of
the variable inductance element based upon changes in the output
analog voltage VO. In one implementation the scaling step involves
both amplifying and offsetting the intermediate analog voltage.
[0015] Referring now to FIG. 3, a more detailed schematic of one
embodiment of the circuit of FIG. 2 is provided. The illustrated
oscillator circuit or stage 102 is set up around comparator 120 and
is formed as an RL oscillator with a variable inductance element,
in the form of inductive sensor S1, connected in the feedback stage
or path of the oscillator. Resistor R3 is also connected in the
feedback stage. The oscillator output frequency is proportional to
the time constant produced by the feedback stage. As the inductance
of sensor S1 varies, the time constant changes and therefore the
frequency of oscillating signal 104 varies. The circuit component
values are selected to produce oscillating signal 104 varying
between frequencies f1 and f2 when the inductance of sensor S1
varies between inductances L1 and L2. Resistors R4 and R5 are also
provided in the oscillator circuit. Transistors Q1 and Q2 are 5
provided in the output path of the oscillator to provide increased
current capacity in the output oscillating signal 104. The
illustrated conversion circuit or stage 106 is set up as a
phase-locked loop (PLL) circuit using a PLL integrated circuit (IC)
122 (such as the 74HC4046A). Resistor R6 is connected between an
inhibit input of the IC 122 and ground to maintain that input low.
Resistors R7 and R8, in combination with capacitor C1, are selected
to set the frequency range of a voltage controlled oscillator (VCO)
within IC 122. The intermediate voltage VI is produced by providing
the output of a phase comparator internal of IC 122 to an RC filter
combination provided by resistor R9 and resistor R10 and capacitor
C2. Preferably the output voltage VI is produced between voltage
level VI1 and VI2 that falls within a linear operating range of the
PLL circuit. For example, VI1 may be around 2 volts and VI2 may be
around 4 volts. The illustrated amplification circuit or stage 108
utilizes an operational amplifier 124 (such as the MC33202), with
VI forming one input of the op-amp through resistor R 1I and with
an offset voltage level VOFFSET forming the other input to the
op-amp through resistor R14. The offset voltage is set up by a
potentiometer using resistor R16. Resistor and capacitor pairs R12,
C4 and R13, C5 are provided for proper op-amp stability and
operation. An RC filter formed by resistor R15 and capacitor C3 is
provided at the output side of the op-amp to provide increased
stability of the voltage output VO. The illustrated detection unit
110 is provided by a micro-controller 126, with the signal VO being
applied to an A/D input of the microcontroller to facilitate
digital processing and analysis of the output signal VO.
[0016] Referring to FIG. 4, in place of the potentiometer set up on
resistor R16, an alternative embodiment of amplification circuit or
stage 108 could utilize a PWM output channel of the microntroller
126 to set the offset voltage VOFFSET through the RC filter created
by resistor R17 and capacitor C6. In such a case the
microcontroller 126 could be programmed to automatically set the
offset voltage.
[0017] The foregoing description has been presented for purposes of
illustration. It is not intended to be exhaustive or to limit the
invention to the precise forms or procedures disclosed, and
obviously many modifications and variations are possible in light
of the above teaching. For example, while specific embodiments of
oscillator circuit or stage 102, conversion circuit or stage 106,
amplification or scaling circuit or stage 108 and detection unit
110 are shown and described with reference to FIG. 3, it is
recognized that in each case other circuit configurations could be
used. It is intended that the scope of the invention be defined by
the claims appended hereto.
* * * * *