U.S. patent number RE34,070 [Application Number 07/534,732] was granted by the patent office on 1992-09-22 for method and system for transferring calibration data between calibrated measurement instruments.
This patent grant is currently assigned to Troxler Electronic Laboratories, Inc.. Invention is credited to Ali Regimand.
United States Patent |
RE34,070 |
Regimand |
September 22, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Method and system for transferring calibration data between
calibrated measurement instruments
Abstract
The present invention provides a method and system which is
useful on instruments requiring experimentally determined
calibration curves by which calibration data can be transferred to
a plurality of field gauges, thereby avoiding the necessity of
individually calibrating each gauge each time calibration is
necessary. The field gauges are initially cross related to a master
gauge. At a later time when a new calibration is necessary, the
master gauge is calibrated using carefully prepared samples of a
test material. Using the experimentally derived calibration curves
with the cross relation data provides calibration data for the
field gauges.
Inventors: |
Regimand; Ali (Research
Triangle Park, NC) |
Assignee: |
Troxler Electronic Laboratories,
Inc. (Research Triangle Park, NC)
|
Family
ID: |
26920235 |
Appl.
No.: |
07/534,732 |
Filed: |
June 7, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
226137 |
Jul 29, 1988 |
04864842 |
Sep 12, 1989 |
|
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Current U.S.
Class: |
73/1.88;
250/252.1; 702/91 |
Current CPC
Class: |
G01D
18/008 (20130101); G01N 23/025 (20130101) |
Current International
Class: |
G01D
18/00 (20060101); G01N 23/02 (20060101); G01D
018/00 () |
Field of
Search: |
;73/1R
;364/571.01,571.04,571.07,571.05,571.06,571.08
;250/390.04,390.05,252.1R,390.01,390.06,390.03,252.1A |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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353118 |
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Jul 1991 |
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EP |
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2264674 |
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Jan 1975 |
|
DE |
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160378 |
|
Jun 1983 |
|
DD |
|
135842 |
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Jul 1985 |
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JP |
|
240118 |
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Sep 1969 |
|
SU |
|
1008684 |
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Mar 1983 |
|
SU |
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1093985 |
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May 1984 |
|
SU |
|
2072349 |
|
Sep 1981 |
|
GB |
|
Other References
Troxler Electronic Laboratories, Inc., Brochure on the Troxler 3241
Asphalt Content Gauge, published by Jul. 1988, 2 pages. .
Troxler Electronic Laboratories, Inc., Operations Manual for 3241-B
Asphalt Content Gauge, 1985, pp. 20-22. .
Illinois Department of Transportation Specification, Jan. 1987, pp.
5-6..
|
Primary Examiner: Noland; Tom
Attorney, Agent or Firm: Bell, Seltzer, Park &
Gibson
Claims
That which I claim is:
1. A test method for use with measurement instruments of the type
which obtain measurement data from a sample and which utilize
experimentally determined calibration curves to convert the
measurement data into measurement readings, said test method being
characterized by facilitating the calibration and use of a number
of field instruments, and comprising the steps of
providing a master measurement instrument;
providing at least one field measurement instrument;
establishing a cross relationship between the measurement data
detected by the master instrument and the measurement data detected
by the field instrument;
.Iadd.obtaining a background measurement by the master instrument;
.Iaddend.
establishing master calibration data for a particular material by
testing samples using the master instrument;
creating adjusted calibration data, specific for a particular field
instrument, by adjusting the master calibration data based upon the
previously established cross relationship between the master
instrument and that particular field instrument .Iadd.and the
previously obtained master instrument background
measurement.Iaddend.;
.Iadd.obtaining a background measurement by the field instrument;
.Iaddend.and
using the adjusted calibration data in the field instrument
.Iadd.and the background measurement obtained by the field
instrument .Iaddend.to convert measurement data obtained by the
field instrument into measurement readings.
2. The method according to claim 1, wherein the step of creating
adjusted calibration data comprises storing the cross relationship
between the master instrument and the field instrument in the field
instrument, transferring the calibration data of the master
instrument to the field instrument, and applying the stored cross
relationship to the master calibration data to create adjusted
calibration data in the field instrument for use in converting the
measurement data obtained by the field instrument into measurement
readings.
3. The method according to claim 1, wherein the step of creating
adjusted calibration data comprises applying the previously
established cross relationship between the master instrument and
the field instrument to the master calibration data to create the
adjusted calibration data, transferring the thus created adjusted
calibration data to the field instrument, and storing the adjusted
calibration data in the field instrument for use in converting the
measurement data obtained by the field instrument into measurement
readings.
4. The method according to claim 1, wherein the step of
establishing a cross relationship between the master instrument and
the field instrument comprises obtaining measurement data for a
plurality of samples using the master instrument, obtaining
measurement data for the same plurality of samples using the field
instrument, and defining a relationship between the measurement
data obtained by the field instrument and the measurement data
obtained by the master instrument; and wherein said step of
creating adjusted calibration data comprises applying the thus
defined relationship to the master calibration data to thereby
derive the adjusted calibration data for the field instrument.
5. A test method for use with nuclear gauges of the type which
measure the neutron moderating characteristics of a sample by
detecting thermal neutron counts, and through the use of
calibration constants for a particular type of material, provide a
measurement of the amount of a hydrogenous substance in a sample of
the material, said test method being characterized by facilitating
the calibration and use of a number of field gauges, and comprising
the steps of
providing a master neutron gauge;
providing at least one field neutron gauge;
establishing a cross relationship between the thermal neutron
counts detected by the master gauge and those detected by the field
gauge;
.Iadd.obtaining a background measurement by the master gauge;
.Iaddend.
establishing master calibration constants for a particular material
using the master gauge;
creating adjusted calibration constants, specific for a particular
field gauge by adjusting the master calibration constants based
upon the previously established cross relationship between the
master gauge and that particular field gauge .Iadd.and the
previously obtained master gauge background
measurement.Iaddend.;
.Iadd.obtaining a background measurement by the field gauge;
.Iaddend.and
using the adjusted calibration constants in the field gauge
.Iadd.and the background measurement obtained by the field gauge
.Iaddend.to obtain measurements of the amount of the hydrogenous
substance in a sample of the material.
6. The method according to claim 5, wherein the step creating
adjusted calibration constants comprises storing the cross
relationship between the master gauge and the field gauge in the
field gauge, transferring the calibration constants of the master
gauge to the field gauge, and applying the stored cross
relationship to the master calibration constants to create adjusted
calibration constants in the field gauge for use in obtaining
measurements of the amount of said hydrogenous substance in a
sample of material.
7. The method according to claim 5, wherein the step of creating
adjusted calibration constants comprises applying the previously
established cross relationship between the master gauge and the
field gauge to the master calibration constants to create the
adjusted calibration constants, transferring the thus created
adjusted calibration constants to the field gauge, and storing the
adjusted calibration constants in the field gauge for use in
obtaining measurements of the amount of said hydrogenous substance
in a sample of material.
8. The method according to claim 5, wherein the step of
establishing a cross relationship between the master gauge and the
field gauge comprises obtaining measurements of a plurality of
samples by the master gauge, obtaining measurements of the same
plurality of samples by the field gauge, and defining a
relationship between the measurements obtained by the field gauge
and those obtained by the master gauge; and wherein said step of
creating adjusted calibration constants comprises applying the thus
defined relationship to the master calibration constants generated
on the master gauge to thereby derive the adjusted calibration
constants for the field gauge.
9. The method according to claim 5, wherein said step of
establishing a cross relationship includes the step of establishing
an initial background measurement by each of the master gauge and
field gauge .[.and further wherein said step of establishing
calibration constants includes obtaining a subsequent background
measurement by the master gauge and said step of creating adjusted
calibration constants also includes obtaining a subsequent
background measurement by the field gauge.]..
10. A test method for measuring the asphalt content of an
asphalt-aggregate paving mix with the use of nuclear gauges of the
type which measure the neutron moderating characteristics of a
sample of the asphalt-aggregate mix and obtain thermal neutron
counts which represent, through the use of calibration constants, a
measurement of the asphalt content of a sample of the
asphalt-aggregate mix, said method characterized by facilitating
the calibration and use of a number of field gauges and comprising
the steps of
providing a master neutron gauge;
providing at least one field neutron gauge;
.Iadd.establishing initial background measurements by the master
gauge and by the at least one field gauge; .Iaddend.
establishing a cross relationship between the thermal neutron
counts detected by the master gauge and those detected by the field
gauge when measuring the asphalt content of a sample;
.Iadd.obtaining a subsequent background measurement by the master
gauge for use in comparison against the initial master gauge
background measurement to adjust for changes in counts since
establishment of said cross relationship; .Iaddend.
establishing master calibration constants for a particular variety
of asphalt-aggregate paving mix using the master gauge;
generating adjusted calibration constants for the particular
variety of asphalt-aggregate paving mix which are specific for a
particular field gauge by adjusting the master calibration
constants based upon the previously established cross relationship
between the master gauge and that particular field gauge .Iadd.and
the previously established initial master gauge background
measurement.Iaddend.;
.Iadd.obtaining a subsequent background measurement by the field
gauge; .Iaddend.and
using the adjusted calibration constants in the field gauge
.Iadd.and the initial and subsequent background measurement
obtained by the field gauge .Iaddend.to obtain measurements of the
asphalt content of the particular variety of asphalt-aggregate
paving mix.
11. The method according to claim 10, wherein the step of
generating adjusted calibration constants comprises storing the
cross relationship between the master gauge and the field gauge in
the field gauge, transferring the calibration constants of the
master gauge to the field gauge, applying the stored cross
relationship to the master calibration constants to create adjusted
calibration constants in the field gauge, and storing the thus
created adjusted calibration constants in the field gauge for use
in obtaining measurements of the asphalt content of a sample of the
asphalt-aggregate paving mix.
12. The method according to claim 10, wherein the step of
generating adjusted calibration constants comprises applying the
previously established cross relationship between the master gauge
and the field gauge to the master calibration constants to generate
the adjusted calibration constants, transferring the thus generated
adjusted calibration constants to the field gauge, and storing the
adjusted calibration constants in the field gauge for use in
obtaining measurements of the asphalt content in an
asphalt-aggregate paving mix.
13. The method according to claim 10, wherein the step of
establishing master calibration constants for a particular variety
of asphalt-aggregate paving mix comprises using the master gauge to
obtain thermal neutron counts for a plurality of samples of the
paving mix having known asphalt contents.
14. A test method for measuring the asphalt content of an
asphalt-aggregate paving mix with the use of nuclear gauges of the
type which measure the neutron moderating characteristics of a
sample of the asphalt-aggregate paving mix by detecting thermal
neutron counts, wherein the gauges are calibrated through the use
of calibration constants for a particular variety of
asphalt-aggregate paving mix and the gauges provide a measurement
indicative of the asphalt content in a sample of the particular
variety of paving mix, said method being characterized by
facilitating the calibration and simultaneous use of a number of
field gauges, and comprising the steps of
providing a .[.lab based.]. master neutron gauge;
providing at least one field neutron gauge;
establishing a cross relationship between the thermal neutron
counts detected by a master gauge and those detected by the field
.Iadd.gauge .Iaddend.by obtaining a background thermal neutron
count by the master gauge and thermal neutron counts of a plurality
of samples of different compositions by the master gauge, also
obtaining a background thermal neutron count by the field gauge and
thermal neutron counts of the same plurality of samples, and
defining the cross relationship between the thermal neutron counts
obtained by the master gauge and those obtained by the field
gauge;
storing the thus established cross relationship in the field
gauge;
establishing master calibration constants for a particular variety
of the asphalt-aggregate mix by using the master gauge to obtain
thermal neutron counts for samples of known asphalt content;
establishing a master background measurement on the master
gauge;
transferring the master calibration constants and the master
background measurement to the field gauge;
generating adjusted calibration constants for the particular
variety of asphalt-aggregate paving mix which are specific for the
particular field gauge by adjusting the master calibration
constants based upon the cross relationship which is stored in the
field gauge, and
using the adjusted calibration constants in the field gauge to
obtain measurements of the asphalt content of the particular
asphalt-aggregate paving mix.
15. A test method for measuring the asphalt content of an
asphalt-aggregate paving mix with the use of nuclear gauges of the
type which measure the neutron moderating characteristics of a
sample of the asphalt-aggregate paving mix by detecting thermal
neutron counts, wherein the gauges are calibrated through the use
of calibration constants for a particular variety of
asphalt-aggregate paving mix and the gauges provide a measurement
indicative of the asphalt content in a sample of the particular
variety of paving mix, said method being characterized by
facilitating the calibration and simultaneous use of a number of
field gauges, and comprising the steps of
providing a .[.lab based.]. master neutron gauge;
providing at least one field neutron gauge;
establishing a cross relationship between the thermal neutron
counts detected by a master gauge and those detected by the field
.Iadd.gauge .Iaddend.by obtaining a background thermal neutron
count using the master gauge and thermal neutron counts of a
plurality of samples of different compositions by the master gauge,
also obtaining a background thermal neutron count using the field
gauge and thermal neutron counts of the same plurality of samples
using the field gauge, and defining the cross relationship between
the measurements obtained by the master gauge and those obtained by
the field gauge;
storing the thus established cross relationship;
establishing master calibration constants for a particular variety
of the asphalt-aggregate mix by using the master gauge to obtain
thermal neutron counts for samples of known asphalt content;
establishing a master background measurement on the master
gauge;
generating adjusted calibration constants for the particular
variety of asphalt-aggregate paving mix which are specific for the
particular field gauge by adjusting the master calibration
constants based upon the cross relationship;
transferring the adjusted calibration constants to the field gauge;
and
using the adjusted calibration constants in the field gauge to
obtain measurements of the asphalt content of the particular
asphalt-aggregate paving mix.
16. A test system for measurement instruments of the type which
obtain measurement data from a sample and which utilize
experimentally determined calibration curves to convert the
measurement data into measurement readings, said test system being
characterized by facilitating the calibration and use of a number
of field instruments, and comprising
a master measurement instrument;
at least one field measurement instrument;
means for storing a derived cross relationship between the
measurement data detected by the master instrument and the
measurement data detected by the field instrument;
means for storing master calibration data derived from .[.tests.].
.Iadd.measurements .Iaddend.with the master measurement instrument
on a particular material;
means for applying the stored cross relationship to the stored
master calibration data to create adjusted calibration data;
and
means in the particular field instrument for using the adjusted
calibration data in the field instrument .Iadd.and a background
measurement made by the field instrument .Iaddend.to convert
measurement data obtained by the field instrument into measurement
readings.
17. The system according to claim 16, wherein the means for using
the adjusted calibration data also includes means for storing the
cross relationship between the master instrument and the field
instrument and for receiving the recorded master calibration data
and for receiving the adjusted calibration data.
18. The system according to claim 16, wherein the means for storing
and using the adjusted calibration constants also includes means
for receiving the adjusted calibration data.
19. The system according to claim 16, further including
means for recording measurement data by the master instrument for a
plurality of samples;
means for recording measurement data by the field instrument for
the same plurality of samples; and
means for deriving a cross relationship between the measurement
data obtained by the master instrument and the measurement data
obtained by the field instrument.
20. A test system for nuclear gauges of the type which measure the
neutron moderating characteristics of a sample, and through the use
of calibration constants determined for each particular material a
gauge may provide a measurement of the amount of a hydrogenous
constituent in a sample of the material, wherein the calibration of
a plurality of field gauges is facilitated by the system
comprising
a master neutron gauge;
at least one field neutron gauge;
means for storing a derived cross relationship between a field
gauge and a master gauge defining the variance between the thermal
neutron counts detected by the master gauge those detected by the
field gauge .[.between the gauges.]. for a sample;
means for storing .[.derived.]. master calibration constants
.Iadd.derived from measurements with the master gauge .Iaddend.for
a particular material;
means for applying the stored cross relationship to the stored
master calibration constants to create adjusted calibration
constants; and
means in the particular field gauge for .[.storing and.]. using
.Iadd.the thus created .Iaddend.adjusted calibration constants
.Iadd.and a background measurement made by the field gauge
.Iaddend.to measure the amount of a hydrogenous constituent in a
sample of the particular material.
21. The system according to claim 20, wherein the means for storing
and using the adjusted calibration constants also includes means
for storing the cross relationship between the measurements by the
master gauge and those by the field gauge and for receiving the
recorded master calibration constants and for deriving the adjusted
calibration constants.
22. The system according to claim 20, wherein the means for storing
and using the adjusted calibration constants also includes means
for receiving the adjusted calibration constants.
23. The system according to claim 20, further including
means for recording thermal neutron counts by the master gauge for
a plurality of samples;
means for recording thermal neutron counts by the field gauge for
the same plurality of samples;
means for deriving a cross relationship between the thermal neutron
counts detected by the master gauge and those detected by the field
gauge.
24. A test system for nuclear gauges of the type which measure the
neutron moderating characteristics of a sample of an
asphalt-aggregate paving mix, and through the use of calibration
constants determined for each particular asphalt-aggregate paving
mix a gauge may provide a measurement of the asphalt content of a
sample of the asphalt-aggregate paving mix, wherein the calibration
of a plurality of field gauges is facilitated by the system
comprising
a master neutron gauge;
at least one field neutron gauge;
means for recording derived master calibration constants for a
particular asphalt-aggregate paving mix;
means in the particular field gauge for storing a cross
relationship between the thermal neutron counts detected by the
master gauge and those detected by the field gauge;
means in the particular field gauge for receiving the recorded
master calibration constants and for applying the stored cross
relationship to the master calibration constants to create adjusted
calibration constants; and
means in the particular field gauge for using the thus-derived
adjusted calibration constants to measure the asphalt content in a
sample of the particular asphalt-aggregate paving mix.
25. A test system for nuclear gauges of the type which measure the
neutron moderating characteristics of a sample of an
asphalt-aggregate paving mix, and through the use of calibration
constants determined for each particular variety of
asphalt-aggregate paving mix a gauge may provide a measurement of
the asphalt content of a sample of the asphalt-aggregate paving
mix, wherein the calibration of a plurality of field gauges is
facilitated by the system comprising
a master neutron gauge;
at least one field neutron gauge;
means for storing a derived cross relationship between the thermal
neutron counts detected by the master gauge and those
.Iadd.detected .Iaddend.by .[.each.]. .Iadd.a .Iaddend.field gauge
.Iadd.based upon measurements of samples by the master gauge and
the field gauge.Iaddend.;
means for storing derived master calibration constants for a
particular asphalt-aggregate paving mix .Iadd.based upon
measurements by the master gauge of samples of the particular
asphalt-aggregate paving mix.Iaddend.;
means for applying the stored cross relationship to the stored
master calibration constants to create adjusted calibration
constants; and
means in the particular field gauge for receiving, storing and
using adjusted calibration constants .Iadd.and a background
measurement made by the field gauge .Iaddend.to measure the asphalt
content in a sample of the particular asphalt-aggregate paving mix.
.Iadd.
26. A test method for use with nuclear gauges of the type which
measure the neutron moderating characteristics of a sample by
detecting thermal neutron counts, and through the use of
calibration constants for a particular type of material, provide a
measurement of the amount of a hydrogenous substance in a sample of
the material, said test method being characterized by facilitating
the calibration and use of a number of field gauges, and comprising
the steps of
providing a master neutron gauge;
providing at least one field neutron gauge;
establishing a cross relationship between the thermal neutron
counts detected by the master gauge and those detected by a
particular field gauge;
storing in the particular field gauge the thus established cross
relationship between the master gauge and the particular field
gauge;
establishing master calibration constants for a particular material
using the master gauge;
transferring the thus established master calibration constants for
the particular material to the field gauge;
applying the cross relationship stored in the field gauge to the
thus transferred master calibration constants to create adjusted
calibration constants in the field gauge specific for the
particular field gauge; and
using the adjusted calibration constants in the field gauge to
obtain measurements of the amount of the hydrogenous substance in a
sample of the material. .Iaddend. .Iadd.
27. A test method for measuring the asphalt content of an
asphalt-aggregate paving mix with the use of nuclear gauges of the
type which measure the neutron moderating characteristics of a
sample of the asphalt-aggregate paving mix and obtain thermal
neutron counts which represent, through the use of calibration
constants, a measurement of the asphalt content of a sample of the
asphalt-aggregate paving mix, said test method being characterized
by facilitating the calibration and use of a number of field
gauges, and comprising the steps of
providing a master neutron gauge;
providing at least one field neutron gauge;
establishing a cross relationship between the thermal neutron
counts detected by the master gauge and those detected by a
particular field gauge when measuring the asphalt content of a
sample;
storing in the particular field gauge, the thus established cross
relationship between the master gauge and the particular field
gauge;
establishing master calibration constants for a particular
asphalt-aggregate paving mix using the master gauge;
transferring the thus established master calibration constants for
the particular paving mix to the field gauge;
applying the cross relationship stored in the field gauge to the
thus transferred master calibration constants to create adjusted
calibration constants in the field gauge specific for the
particular field gauge;
storing the adjusted calibration constants in the field gauge;
and
using the adjusted calibration constants in the field gauge to
obtain measurements of the asphalt content in a sample of the
particular asphalt-aggregate paving mix. .Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to measurement instruments requiring
experimentally determined calibration curves, where minor
variations in instrument characteristics necessitate individual
calibration, and more particularly relates to a method and system
which facilitates the calibration of such instruments.
BACKGROUND OF THE INVENTION
Many types of measurement instruments rely upon experimentally
determined calibration curves to convert the raw data which is read
by the instrument into an accurate measurement reading. Typically,
the calibration curve is derived by taking measurement readings
with the instrument on several samples whose composition has been
determined analytically, and then constructing a calibration curve
which relates the experimentally determined measurement readings to
the analytically determined composition values. Because of minor
variations from one measurement instrument to another, a
calibration curve is unique for a particular instrument, and it is
therefore necessary for each measurement instrument to be
calibrated individually. The present invention provides a method
and system which greatly facilitates the calibration procedure.
This invention is described herein in terms of the calibration of a
neutron gauge designed for measuring the asphalt content of
bituminous paving mixes. This invention can, however, be embodied
in many different forms and can be used with other types and
designs of instruments which employ experimentally derived
calibration curves.
Lowery, et al. U.S. Pat. No. 3,492,475 discloses a portable nuclear
gauge which utilizes a fast neutron source and a thermal neutron
detector for determining the composition of a bulk material, such
as a bituminous paving mix, placed in a sample pan. This type of
gauge relies upon the neutron moderating characteristics of
hydrogen atoms present in the composition for determining, for
example, the amount of asphalt in a paving mix or the amount of
moisture in a building material. For these determinations it is
known that the amount of asphalt or the amount of moisture can be
related to the hydrogen content of the material, and the hydrogen
content of the material can be determined by subjecting the sample
to radiation from a fast neutron source and detecting neutrons
which have been slowed or thermalized as a result of interaction
with the hydrogen nuclei present in the sample. The number of
thermalized neutrons detected (counted) over a period of time is
utilized in determining the hydrogen content of the sample.
In operating the gauge, it is first necessary to establish a
standard count for calibration purposes. This is accomplished using
a standard sample having a known hydrogen content, for example, a
block of polyethylene. Then calibration curves are produced for the
particular material being tested, by using carefully prepared
samples having a known content of the hydrogen-containing material
of interest (e.g. asphalt or moisture). After the calibration
curves have been produced, unknown test samples can be placed in
the gauge and counts are taken. By reference to the calibration
curve, the corresponding content of the hydrogen-containing
material for that count can be read.
A more recent model of this gauge has been produced by applicant's
assignee embodying the principles of the Lowery patent and sold as
the "Model 3241 Asphalt Content Gauge" by Troxler Electronic
Laboratories, Inc. This gauge includes a microprocessor to
facilitate calibration and computation of the sample asphalt
content. Calibration can be made by taking gauge counts on two or
more samples of known asphalt content. The microprocessor then
constructs a calibration equation from these data points, and the
gauge provides a direct readout of the percent asphalt, thus
eliminating the necessity of calculations and reference to external
calibration tables.
In order to obtain the most accurate measurements, the gauge must
be calibrated each time the composition of the material is changed.
This is because the number of counts recorded is only
representative of the hydrogen atoms present in the sample. There
is an assumption made when using a thermal neutron gauge that the
differences in hydrogen count from sample to sample are because of
changes in the amount of the substance of interest, such as
moisture or asphalt content, and that all other factors are
maintained substantially constant. The calibration is done when it
is clear that the "other factors" are not going to be constant.
Such changes may occur, for example, when using a new aggregate in
the paving mix or a new source or grade of asphalt. A new aggregate
may have a different average moisture content or a different
intrinsic hydrogen content. In the case of asphalt, different
sources of asphalt may have a different concentration of hydrogen.
At a time when there is such a change, the gauge must be calibrated
using carefully prepared samples of known concentrations of the
hydrogen-containing material of interest.
As discussed above, the calibration procedure involves taking
hydrogen counts with the gauge using several samples of known
composition, and establishing a correlation, (e.g. an equation or a
calibration curve) which can be used to obtain a percent asphalt
reading from the hydrogen counts obtained from a test sample of
unknown composition. The calibration procedure itself is not unduly
complex, and is practical with a single gauge or where a relatively
few gauges are involved. However, where a number of field gauges
are used, as is frequently the case in many operations, the
necessity of manually calibrating all the gauges becomes quite
burdensome and time consuming. The gauges generally need to be
taken out of the field and sent to a lab where samples of the new
aggregate can be carefully mixed and tested to get a proper
calibration. This involves the inconvenience of the loss of use of
the gauges during the time they are being calibrated, and also the
inconvenience of having to transport the gauges back and forth from
the lab.
With the foregoing in mind, it is an object of the present
invention to overcome the problems and disadvantages of the prior
practices discussed above and to provide an improved system for
calibrating gauges in a simpler and more time efficient manner
without having to transport the gauges back to the lab.
SUMMARY OF THE INVENTION
The invention achieves the foregoing and other objects by providing
an efficient system by which calibration data can be transferred to
a plurality of field gauges, thereby avoiding the necessity of
individually calibrating each gauge. The calibration data required
by the gauges is obtained by a master gauge typically kept at the
lab. This calibration data is easily transferred to the respective
field gauges so that the field gauges are permitted to stay in the
field.
The process essentially comprises providing a master instrument
(e.g. a neutron gauge), and at least one field instrument (e.g. a
neutron gauge). Since each instrument has different measurement
characteristics, a cross relationship is established between the
readings obtained from the master instrument when measuring a
particular material and those detected by the field instrument when
measuring the same material.
When a calibration is necessary, due to the use of a new material
source for example, the conventional manual calibration procedure
is carried out in the lab on the master gauge and master
calibration constants are established for the particular material.
Adjusted calibration constants, specific for a particular field
gauge, are created by adjusting the master calibration constants
based upon the previously established cross relationship between
the master gauge and the particular field gauge. The adjusted
calibration constants are used in the field gauge to obtain
measurements on the new material.
In accordance with one embodiment of the invention, the field
gauges are specially equipped with means for storing the previously
derived cross relationship between the master gauge and the field
gauge, and means is provided in the field gauge for directly
receiving master calibration constants obtained from the master
gauge. The gauge is also equipped with means for applying the
stored cross relationship to the newly obtained master calibration
constants to create adjusted calibration constants specific for the
particular field gauge. Thus whenever a calibration is necessary,
such as when a new variation of asphalt is used, the master
calibration constants are derived in the laboratory by the master
gauge, and these newly derived master calibration constants are
then distributed to the field gauges in use. The master calibration
constants are loaded into each field gauge, and in each field gauge
the master calibration data is adjusted based upon the unique cross
relationship data which is stored in the field gauge. This is much
easier and quicker than requiring individual calibration of each
field gauge.
However, the calibration data transfer procedure of this invention
can also be utilized in instruments which are not specially
equipped for calibration data transfer, such as for example the
asphalt content gauges noted earlier, which have been produced by
applicant's assignee for many years. For use in these gauges, the
master calibration constants are obtained in the laboratory on a
master gauge and cross relationships between each field gauge and
the master gauge are established in the manner noted above. Then
the master calibration constants are adjusted for each field gauge
using the previously derived cross relationships for each field
gauge. This can be accomplished manually or preferably through the
use of a computer. Then the adjusted calibration constants for each
gauge are distributed to the respective field gauges and loaded
into the appropriate field gauge for use in performing subsequent
measurements. This permits the field units to stay in the field and
avoids the time consuming process of individually calibrating each
field gauge.
BRIEF DESCRIPTION OF THE DRAWINGS
Some of the features and advantages of the invention having been
stated, others will become apparent as the description proceeds,
and taken in connection with the accompanying drawings, in
which
FIG. 1 is a perspective view of a neutron gauge;
FIG. 2 is a perspective view of several sample pans filled with
samples to be tested in the neutron gauge;
FIG. 3 is a front cross section view of the neutron gauge of FIG. 1
illustrating its basic components;
FIG. 4 is a graph illustrating the general relationship of thermal
neutron counts to the asphalt content of a sample of
asphalt-aggregate paving mix and graphically representing the
calibration of a thermal neutron gauge;
FIG. 5 is a flow chart illustrating the basic procedures followed
by the present invention;
FIG. 6 is a flow diagram illustrating the detailed procedures
pursuant to one embodiment of the present invention where specially
equipped field gauges are employed; and
FIG. 7 is a flow diagram similar to FIG. 6 illustrating the
detailed procedure of an alternate embodiment of the invention
where standard field gauges are employed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will now be described more fully with
reference to the drawings, in connection with a particular type of
neutron gauge designed for measuring the asphalt content of
bituminous paving mixes. This invention can, however, be embodied
in many different forms and can be used with other types and
designs of instruments which use experimentally determined
calibration curves. It should be understood therefore that the
specific embodiments described herein are illustrative of how the
present invention may be practiced, and that the invention is not
limited to these specific embodiments.
A neutron gauge is generally indicated by the number 10 in FIG. 1
and comprises a generally rectangular housing 11 having a door 12
which provides access to a measurement chamber in which sample pans
are placed for measurement. A control unit 14 is provided,
including a keypad 15 for entry of data and for controlling the
functions of the gauge, and a display 16, which may be of any
suitable construction, such as a liquid crystal display. Referring
to FIG. 2, there is shown several sample pans 17 containing samples
of asphalt-aggregate paving mix. The sample pans are sized to fit
into the measurement chamber of the neutron gauge. Referring to
FIG. 3, a sample pan 17 is received within the interior of the
gauge. Located in the upper interior portion of the gauge is a
source 20 of fast neutrons. The source 20 may for example suitably
comprise a Am-241:Be source. In the lower interior portion of the
gauge beneath the sample pan are a series of detector tubes 21 for
detecting neutrons which have been slowed or thermalized by
interaction with hydrogen atoms present in the sample. The
illustrated detectors 21 are He.sup.3 detector tubes but .[.an.].
.Iadd.any .Iaddend.suitable thermal neutron detector will suffice.
The gauge also includes a data processor module 23 for controlling
the gauge and counting of thermalized neutrons.
To operate the gauge, the sample pan is filled with a sample of
material and inserted into the interior of the gauge. The door is
shut and fast neutrons from the source 20 are emitted down through
the sample in the sample pan 13. Hydrogen present in the sample
interacts with the fast neutrons, producing moderated or slowed
neutrons, and thermalized neutrons below a specified energy level
are detected by detectors 21. The thermalized neutrons are counted
for a predetermined period of time and a count is recorded in the
data processor module 23. The data processor module 23 then
correlates the number of counts to a moisture content or an asphalt
content calibration to indicate the result.
The correlation between counts and asphalt content is unique for
each gauge. This is because each fast neutron source 20 emits
neutrons at its own particular rate and the detectors also have
variations in efficiency and design from unit to unit. Therefore,
each gauge must be calibrated in order that the data processor
module 23 can convert the number of counts into a value for the
asphalt content of the sample. To calibrate the gauge in accordance
with conventional methods known in the art, several samples are
carefully prepared with known asphalt contents and are used in the
gauge to generate counts. The correlation can be done in several
different ways. For example, as shown in FIG. 4 the relationship
between observed counts and known asphalt content can be graphed.
Then, a linear or other form of equation can be formulated to fit
the data. Other ways include the creation of a "look up" table
where the various asphalt contents are cross referenced with a
number of counts.
Calibration is best and most easily accomplished in the lab. This
way, the known sample mixtures can be carefully prepared and the
most precise calibration can be obtained. However, if the user has
a number of these gauges in use in the field, which is often the
case, returning the gauges to a lab each time calibration becomes
necessary is most inconvenient and would seriously interfere with
the user's operations.
The present invention eliminates the necessity of returning field
gauges to the lab for calibration by providing a system by which
calibration data can be transferred from a lab-based master gauge
to one or more field gauges. Illustrated in FIG. 5 is the general
process of the system. The first step 31 is to establish a cross
relationship which establishes the variance between the thermal
neutron counts detected by the master gauge and the counts detected
by the field gauge when measuring the same sample. This is
accomplished by taking counts on various samples with both the
master gauge and the field gauge. The composition of the samples is
not critical, although it is desirable that the samples have a
hydrogen content generally similar to that of the material which
are to be measured during use of the gauge. Most desirably, several
samples are used having a hydrogen content which spans the range of
measurement of the gauge. For example, standard blocks of solid
polyethylene or polyethylene/metal laminates such as that shown in
commonly-owned U.S. Pat. No. 4,152,600 may be employed. The second
step 32 involves performing a conventional calibration procedure
with the use of the lab-based master gauge to obtain master
calibration constants. This calibration procedure would be carried
out whenever calibration is required, such as due to the use of a
new type or variation of paving mix. In order for the master
calibration constants to be usable in the field gauge, they must be
adjusted or converted to take into account the differences in
measurement between the field gauge and the master gauge. As
indicated at 33 in FIG. 5, adjusted calibration constants are
created by applying the previously derived cross relationship
between the master gauge and field gauge to the master calibration
constants to thereby obtain adjusted calibration constants specific
for the particular field gauge. The final step 34 of the process is
to use the adjusted calibration constants in the field gauge on the
material to obtain measurements of the amount of the constituent of
interest.
In accordance with one embodiment of the present invention, the
calibration data transfer procedure is used on gauges which are
specially equipped to store the previously defined master
gauge/field gauge cross relationship and to receive unmodified
calibration constants from the master gauge and to internally
adjust the constants based upon the stored master gauge/field gauge
cross relationship to produce adjusted calibration constants which
are specific for the particular field gauge and which can be used
thereafter for determining percent asphalt based upon a thermal
neutron count.
For this purpose, the data processor module 23 includes a stored
calibration transfer procedure or subroutine which can be called
whenever the calibration transfer procedure is to be run. This
procedure permits manual entry of the master gauge/field gauge
cross relationship by the operator and stores this data in memory
for subsequent use. It also permits entry by the operator of the
new master calibration constants, either manually or via a suitable
transfer media such as magnetic disk or EPROM. Additional data,
such as background readings, explained more fully below, can also
be entered at this time. After entry of all needed data, the
calibration transfer subroutine carries out a mathematical
computation to adjust the master calibration constants based upon
the stored master gauge/field gauge cross relationship to create
adjusted calibration constants which are thereafter stored and used
by the field gauge in converting thermal neutron counts into values
for percent asphalt. The method and apparatus in accordance with
this embodiment of the present invention is advantageous in that
the calibration procedure is quite simple and is essentially
automated. Since the master gauge/field gauge cross relationship is
stored in the field gauge, accuracy is assured in converting or
adjusting the master calibration constants to establish adjusted
constants for the specific field gauge.
When the calibration data transfer procedure of the present
invention is used with conventional thermal neutron gauges which
are not specially equipped for receiving and internally storing the
master gauge/field gauge cross relationship, the adjustment of the
master calibration constants is performed before the calibration
data is physically transferred to the field gauge. This may be
suitably accomplished at the laboratory either manually or by a
computer program which executes a procedure or subroutine similar
to that described above. After adjusting the master calibration
constants using appropriate master gauge/field gauge cross
relationship, the adjusted calibration constants are then
physically transferred to the appropriate field gauge. Depending
upon the specific gauge and how it is designed to receive
calibration data, the entry of the adjusted calibration data into
the field gauge may be by manual entry or by other means, such as
electronically.
The procedure in accordance with the first embodiment of the
invention is illustrated in more detail in FIG. 6. The broad steps
or operations described above with reference to FIG. 5 are shown in
the broken line boxes and bear the same reference numbers. The more
detailed steps or operations are shown in the solid line boxes.
Thus, one step in establishing the master gauge/field gauge cross
relationship includes taking a background reading on each of the
master gauge and field gauges, as indicated at 41. The background
readings are to eliminate the possible error for the day to day
differences in the field and lab conditions and also the changes
that occur over time in the source 20. The background reading is
made by taking a count without any sample in the gauge. The master
gauge original background reading is specified as MOBG and the
field gauge original background is specified as FOBG. As earlier
discussed, several samples are measured by the master and field
gauges as indicated at 42 and a cross relationship is established
as indicated at 43. Preferably, the cross relationship is
established by selecting a minimum of five samples covering the
range of percent asphalt used. The readings from the five samples
are recorded as R.sub.M1, R.sub.M2, R.sub.M3, R.sub.M4, and
R.sub.M5 for the master gauge and R.sub.F1, R.sub.F2, R.sub.F3,
.[.P.sub.F4 .]. .Iadd.R.sub.F4 .Iaddend., and R.sub.F5 for the
field gauge. A cross relationship between the two gauges can now be
established by fitting the counts from one gauge against the other.
Please note that only the linear form of this process is considered
here, but this procedure can be performed with other equations.
Thus,
where j=1, 2 . . . 5. The cross relationship, which includes
E.sub.1, E.sub.2, MOBG and FOBG, is stored in the field neutron
gauge or more particularly the central processing module 23, as
indicated at 44.
At subsequent times, when it is necessary to calibrate a field
gauge, which is most often done when a different type or variety of
material is used, calibration is performed using the master gauge.
The master gauge is used to generate a background count on the
empty gauge chamber as indicated at 45. The background count is
specified as MBG. The master gauge is then used to test carefully
prepared samples of a particular variety of the asphalt-aggregate
paving mix, as indicated at 46, and the samples are used to
generate master calibration constants as indicated at 47. A minimum
of two samples are employed covering the range of asphalt used.
This will give readings R.sub.1 and R.sub.2. The counts R.sub.1 and
R.sub.2 are now used with the known asphalt content samples to
establish the master calibration constants A.sub.1 and A.sub.2,
using the relationship
where R.sub.M is master gauge count and %AC is asphalt content.
The master calibration constants, which include A.sub.1, A.sub.2
and MBG, are then transferred and input into the field neutron
gauge, or more particularly the central processing module 23 as
indicated at 48. Then as indicated at 49, the field gauge creates
adjusted calibration constants AA.sub.1 and AA.sub.2 by adjusting
the master calibration constants A.sub.1 and A.sub.2 based on the
cross relationship stored in the field gauge.
The following discussion explains how the adjusted calibration
constants are derived. Using the equation
to account for any changes in the gauge counts since the time of
cross calibration the stored background counts have to be used in
the above equation, so
wherein DBG is the field gauge daily background count. R.sub.M is
calculated Master Gauge count, and R.sub.F is the measured Field
Gauge Count. Rewriting equation (3)
For simplicity let
and
now
Substitute R.sub.M into equation 1 to get
or
let
and
Finally, the constants stored in the Field Gauge are AA1 and
AA2.
In use, daily background measurements specified as DBG are taken
from the field gauge as indicated at 50 and the field gauge is used
to obtain measurements of the asphalt content of an
asphalt-aggregate paving mix as indicated at 51 such that
The process of transferring the calibration to the standard gauges
is substantially similar to the process described above, and is
illustrated in FIG. 7. To avoid repetition, the procedures or steps
shown in FIG. 7 which correspond to those previously described in
FIG. 6 are identified with corresponding reference characters, with
prime notation added. Basically, the fundamental difference in this
procedure is that the adjusted calibration constants AA.sub.1,
AA.sub.2 for the field gauge are produced outside of the field
gauge (e.g. at the laboratory). Then the adjusted calibration
constants AA.sub.1, AA.sub.2 (rather than the master calibration
constants) are transferred to the field gauge as indicated at 48'
in FIG. 7.
* * * * *