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Claims  |
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What is claimed is:
1. A measurement apparatus, including a sensor component and an analyzing
instrument component, said components being removably connectable, said
sensor component being operative to generate a signal in response to
certain environmental conditions and said instrument component being
operative to generate an output and calibration data interpretive of said
signal, comprising:
first memory means secured to said sensor component and interconnectable to
said instrument component for storing calibration data relating to said
sensor component, wherein said instrument component stores said
calibration data into said first memory means;
second memory means located within said instrument component for storing
calibration data relating to said instrument component; and
processing means for correcting said signal in accordance with said
calibration data stored in said first and said second memory means.
2. The measurement apparatus of claim 1, further comprising at least two
instrument components, each instrument component interchangeable with the
other and having respective memory means for storing calibration data
relating to said instrument components, said first memory means having
calibration data relating to said sensor component and necessary for said
signal to be correctly interpreted by said instrument components.
3. The measurement apparatus of claim 2, wherein said first and second
memory means are selected from the group consisting of RAM, PROM, EPROM
and EEPROM.
4. The measurement apparatus of claim 1 wherein said sensor component
generates an optical signal and wherein said first and said second memory
means store calibration data electronically.
5. The measurement apparatus of claim 1 wherein said sensor component
comprises at least one probe, insertable into a patient's vasculature,
said probe being responsive to the presence of a certain blood parameter
within said patient's blood supply and operative to fluoresce with an
intensity thereof being a function of the partial pressure of said
parameter and wherein said instrument component interprets such
fluorescence to generate an output directly in terms of said partial
pressure.
6. The measurement apparatus of claim 5, wherein the blood parameter to be
measured is selected from the group consisting of PO.sub.2, PCO.sub.2, and
pH.
7. The measurement apparatus of claim 1, wherein said first memory means is
removably secured to said sensor component.
8. An invasive optical blood gas analyzer, including a probe insertable
into a patient's blood flow, and an analyzing instrument, said probe and
instrument being interconnectable, said probe being operative to generate
fluorescent radiation, the intensity of said fluorescent radiation being a
function of the partial pressure of a certain gas in the patient's blood
flow, and said instrument being operative to convert the fluorescent
intensity into a measure of partial pressure, said analyzer comprising:
a first, non-volatile, semi-conductor memory device attached to said probe,
said first memory device interconnectable to said instrument and operative
to store calibration data specific to said probe relating to the
conversion of said fluorescent intensity into a measure of partial
pressure;
a second, non-volatile, semi-conductor memory device located within said
instrument and operative to store calibration data specific to said
instrument relating to the conversion of said fluorescent intensity into a
measure of partial pressure; and
a data processor located within said instrument for correcting the measure
of partial pressure in accordance with the calibration data stored in said
first and second memory devices.
9. The analyzer of claim 8, wherein said first and second memory devices
are selected from the group consisting of RAM, PROM, EPROM and EEPROM.
10. The analyzer of claim 8 wherein the probe is capable of generating
fluorescent radiation which is a function of the pH value of the patient's
blood.
11. The blood gas analyzer of claim 8, wherein said first memory device is
removably attached to said probe.
12. The blood gas analyzer of claim 8, wherein calibration data is stored
in said first memory device via an analyzing instrument interconnected
thereto.
13. The blood gas analyzer of claim 8, wherein the calibration data stored
in said first memory device is specific to the characteristics of said
probe.
14. A method for calibrating a group of instruments, said group including
at least a first and second instrument, each instrument operative to
interpret signals generated by remote sensors interconnectable thereto and
responsive to a certain environmental condition, said sensors including
memory means for storing calibration data and said instruments including
memory means for storing calibration data as well as processing means for
interpreting the sensor signals in accordance with calibration data stored
in said sensors' and said instruments' memory, said method comprising the
steps of:
selecting a first instrument, interconnecting said first instrument to a
first sensor, subjecting said first sensor to a first standard of said
certain environmental condition to generate a first signal, entering first
calibration data into the memory means of said first sensor, generating a
first measurement of said first standard;
selecting a second instrument, interconnecting said second instrument to
said first sensor and subjecting said first sensor to said first standard
to generate a second signal;
entering second calibration data into said second instrument's memory means
so as to correct said second signal to conform to said first measurement.
15. The method of claim 14 further comprising the step of subjecting said
first sensor to at least one additional standard of certain environmental
conditions and interconnecting the first sensor subjected to each
additional standard to each of the first and second instruments, so as to
obtain additional calibration points to be stored in the memory means of
the sensor and instruments.
16. The method of claim 14, further comprising the step of entering an
interpretation from said first instrument of said first signal into said
first sensor's memory means for correction of an interpretation from said
second instrument of said second signal.
17. A method for calibrating an invasive optical blood gas analyzing
system, including a group of analyzing instruments, so as to enable a
transfer of probes, interconnectable to such analyzing instruments, from
instrument to instrument without recalibration, each of said probes
including a memory device for storing calibration data and each of said
instruments including a memory device for storing calibration data as well
as a data processor for modifying said instrument's output in accordance
with calibration data stored in said probe's memory and said instrument's
memory, comprising the steps of:
selecting a first probe for use as a transfer probe;
interconnecting said transfer probe to a first instrument of said group of
instruments and subjecting said probe to at least one calibration
standard;
entering said first instrument's output into said transfer probe's memory
device;
successively transferring said transfer probe, subjected to said
calibration standard, to every other instrument in said group, and
entering corrective data into each individual instrument memory device
such that each individual instrument's output is modified to conform to
said first instrument's output;
selecting a second probe, interconnecting it to any instrument of said
group of instruments and subjecting it to a calibration standard of known
values;
entering calibration data into said second probe's memory device for
modifying the output of the instrument interconnected thereto to conform
to said known values, whereby said second probe can then be interconnected
to any instrument in the group to yield an accurate output.
18. A method for calibrating a group of apparatuses including at least a
first and second instrument component and including at least a first and
second sensor component, each instrument component and sensor component
being associated with its own memory device capable of storing calibration
data values, each sensor component being configured to removably connect
to each instrument component, each sensor component configured to be
subjected to at least a first known standard of analytes for which each
sensor component is capable of detecting, said method including the steps
of:
connecting a first sensor component to a first instrument component;
subjecting the first sensor component to a first standard;
calculating calibration values associated with the first sensor component
when the first sensor component is connected to the first instrument
component and subjected to the first standard;
storing calculated calibration values into the memory device of the first
sensor component;
repeating said connecting, subjecting, and calculating steps for the second
instrument component connected to the first sensor component subjected to
the first standard, wherein new calibration values are calculated and
stored into the memory device of the second instrument component.
19. The method of claim 18, further comprising the step of repeating said
connecting, subjecting and calculating steps for the first sensor
component subjected to the first standard sequentially connected to each
instrument component, wherein calibration values are calculated and stored
into the memory device of each instrument component.
20. The method of claim 18, further comprising the step of repeating said
connecting, subjecting, calculating and storing steps, wherein the first
instrument component is connected to the second sensor component and the
second sensor component is subjected to the first standard.
21. A measurement system, comprising:
a first instrument component having first memory means for storing first
calibration data specific to said first instrument component; and
a sensor component removably connectable to said first instrument
component, said sensor component having second memory means for storing
second calibration data specific to said sensor component,
wherein said first instrument component generates and stores the first
calibration data into the first memory means,
wherein said sensor component generates a signal in response to certain
environmental conditions, and
wherein said first instrument component further includes processing means
for interpreting the signal generated by said sensor component, the
processing means utilizing the calibration data stored in the first and
second memory means to interpret the signal.
22. The measurement system of claim 21, further comprising a second
instrument component having third memory means for storing third
calibration data relating to said second instrument component,
wherein said sensor component is configured as a transfer probe for
calibrating said second instrument component,
wherein said first and second instrument components are interchangeably
connectable to said sensor component,
wherein said second instrument component generates and stores the third
calibration data into the third memory means, and
wherein the second and third memory means have calibration data necessary
for the signal generated by said sensor component to be correctly measured
by said second instrument component.
23. The measurement system of claim 22, further comprising a second sensor
component removably connectable to said first instrument component and
said second instrument component, said second sensor component having
fourth memory means for storing fourth calibration data relating to said
second sensor component,
wherein said second sensor component generates a signal in response to
certain environmental conditions,
wherein the first and fourth memory means have calibration data necessary
for the signal generated by said second sensor component to be correctly
measured by said first instrument component, and
wherein the third and fourth memory means have calibration data necessary
for the signal generated by said second sensor component to be correctly
measured by said second instrument component.
24. A method for calibrating at least two instruments, each instrument
having memory means for storing calibration data, each instrument being
interconnectable to at least one sensor responsive to an analyte, each
sensor having memory means for storing calibration data, and each
instrument having means for processing the calibration data, said method
comprising the steps of:
(a) subjecting the first sensor to a first analyte;
(b) interconnecting a first instrument to the first sensor;
(c) generating a first signal from the first sensor;
(d) calculating first calibration data from a first measurement of the
first signal;
(e) entering the first calibration data into the memory means of the first
sensor;
(f) interconnecting a second instrument to the first sensor;
(g) generating a second signal from the first sensor; and
(h) entering second calibration data in the memory means of the second
instrument to calculate a second measurement from the second signal which
conforms to the first measurement.
25. The method of claim 24 further comprising the steps of subjecting said
first sensor to a second analyte and repeating steps (b) through (h) to
enter additional calibration data into the memory means of the first
sensor and the second instrument.
26. The method of claim 24 further comprising the steps of selecting a
second sensor and repeating steps (a) through (e), wherein the second
sensor is used in place of the first sensor.
27. The method of claim 24 further comprising the steps of configuring the
first sensor as a transfer probe for calibrating each of a plurality of
instruments, and repeating steps (f) through (h) for each of the plurality
of instruments.
28. A method of calibrating a group of instruments including, at least, a
first and a second instrument, each instrument operative to measure and
interpret signals from remote sensors interconnectable thereto, said
sensors being responsive to an analyte partial pressure or concentration,
said sensors including memory means for storing calibration constants
related to said sensor performance and said instruments including memory
means for storing calibration constants relating to the correction of said
instruments as well as processing means for correcting the measured
intensity signals, said method comprising the steps of:
selecting a first instrument, interconnecting said first instrument to a
first sensor, subjecting said first sensor to a first analyte standard to
generate intensity signals, storing calibration constants in said first
instrument's memory means;
selecting a second instrument, interconnecting said second instrument to
said first sensor, subjecting said first sensor to said first analyte
standard to generate intensity signals; and
entering calibration data into the memory means of said second instrument
to correct said intensity signals of said second instrument to conform to
the intensity signals of said first instrument.
29. A method of calibrating a group of instruments including, at least, a
first and a second instrument, each instrument operative to measure and
interpret signals from remote sensors interconnectable thereto, said
sensors being responsive to an analyte partial pressure or concentration,
said sensors including memory means for storing calibration constants
related to said sensor performance and said instruments including memory
means for storing calibration constants relating to the correction of said
instruments as well as processing means for correcting a measured signals,
said method comprising the steps of:
selecting a first instrument, interconnecting said first instrument to a
first sensor, subjecting said first sensor to one or more analyte
standards to generate intensity signals related to known analyte levels,
storing calibration constants into said first instrument's memory means;
selecting a second instrument, interconnecting said second instrument to
said first sensor and subjecting said first sensor to one or more analyte
standards to generate intensity signals related to known standards; and
entering calibration data into the memory means of said second instrument
to append said calibration data to the memory means of any sensor
subsequently calibrated by the second instrument.
30. A method for calibrating at least two instruments each having memory
means for storing calibration data, each instrument interconnectable to at
least one sensor responsive to an analyte, each sensor having memory means
for storing calibration data, and each instrument having means for
processing the calibration data, said method comprising the steps of:
(a) interconnecting a first sensor and a first instrument;
(b) subjecting the first sensor to a first analyte;
(c) generating a first signal from the first sensor;
(d) storing a representation of the first signal into the memory means of
the first instrument;
(e) interconnecting the first sensor and a second instrument;
(f) generating a second signal from the first sensor;
(g) storing a representation of the second signal into the memory device of
the second instrument; and
(h) utilizing the first signal and second signal representations in the
memories of the first and second instruments to maintain the accuracy of
calibration of all subsequent sensors calibrated on the first instrument
and subsequently moved to the second instrument. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates generally to the calibration of measurement
devices and more particularly pertains to the calibration of measurement
systems wherein remote sensors optically interact with analytical
instruments.
Measuring devices often comprise multicomponent systems wherein a remote
sensor or probe component generates a signal in response to a certain
condition and a processing or analyzing instrument is employed to convert
such signal into meaningful data. Both the sensor component as well as the
processing component are typically subject to variation in that the actual
signal generated by a sensor in response to a given condition may vary
from sensor to sensor and the output generated by the instrument in
response to a given signal as received from a sensor may vary from
instrument to instrument. It is therefore necessary to calibrate the
sensor component, the instrument component or both such that accurate
results are obtained in response to given conditions. Calibration efforts
are considerably more complex in systems wherein any of a plurality of
probes are intended to interact with any of a plurality of instruments.
Calibration efforts are further complicated in systems wherein the raw
signal generated by the probe is at least partially dependant upon
instrument input. Additional problems are inherent in systems wherein
electronic and optical componentry is combined.
Certain invasive optical blood gas analyzers are examples of measurement
systems subject to all of the above set forth complexities relating to
calibration. Such systems present a selected fluorescing medium to blood
flow, irradiate the medium to induce fluorescence and compare the
excitation radiation's intensity with the intensity of the resulting
fluorescence. The medium is selected such that its rate of fluorescence is
quenched by the presence of a certain gas to render the resulting
intensity ratio a function of the concentration of such gas. A probe
employing the described medium, when introduced into a patient's
vasculature, can therefore provide real time indications of the partial
pressures of certain gasses within the patient's blood supply. Because
such probes cannot be reused, the system must be designed to render their
disposability economically feasible.
The type of invasive optical blood gas analyzing system especially
difficult to calibrate is a system wherein the excitation signal is
generated within the analyzing instrument, conducted to the probe via an
optic fiber, and fluorescence, emitted by the probe, is returned to the
instrument via the optic fiber for analysis. By retaining a substantial
portion of the optical hardware within the instrument, the cost of the
probe is substantially reduced but considerable calibration problems are
introduced as a direct result of such a separation of the optics.
Variations inherent in the probe include the sensitivity of the particular
deposit of fluorescing medium employed therein and the transmission
qualities of the optical conduit and optical coupler. Variations inherent
in the instrument include the output of the radiation source, the
sensitivities of the sensors measuring the outgoing and incoming radiation
intensities as well as the transmission qualities of the optical conduits
and couplers. Simply calibrating the probe will not compensate for
variation in the instrument and vice versa. In order for the system to
produce accurate results, all these sources of variation must be
compensated for with respect to each individual instrument and probe
combination.
While the calibration of each probe and instrument combination just prior
to use would ensure accurate results, such calibration efforts are not
always practical or even possible in the environment where and under the
conditions which such blood gas analyzers are typically put to use. It is
often desirable to be able to transfer a particular probe from one
instrument to another without the need to recalibrate the new probe and
instrument combination upon transfer. Such situations arise when
transferring a patient from an operating room to a recovery area where the
movement of the analytical instrument is impractical. It is most desirable
to be able to leave the probe in position within the patient's
vasculature, disconnect the probe from the instrument located in the
operating room, transfer the patient into any of a number of recovery
areas and immediately reconnect the probe to an instrument located there.
Removing the first probe and inserting a new probe calibrated to the
second instrument is contraindicated due to the increased probability of
infection and the additional effort involved. A number of calibration
techniques have heretofore been suggested in an effort to overcome this
"transportability" problem inherent in this type of analytical equipment,
but each suffers from substantial shortcomings as set forth in more detail
below.
It has been suggested that upon arrival in the recovery area, a blood
sample would be drawn for analysis and that the second instrument's output
would then merely be adjusted to conform to the lab results. This however
assumes that the second instrument's calibration is merely in need of an
offset adjustment and ignores any slope changes that may in fact be
necessary. Moreover, the patient's blood gasses may be subject to
substantial fluctuation during the time elapsed between the time when the
blood sample was drawn and the time when the instrument is actually
recalibrated. Such errors would most likely occur in the case of an
unstable patient while it is precisely the unstable patient that is most
dependent upon accurate information.
An alternative approach has been proposed wherein a dual sensor probe
component is used in conjunction with appropriately modified analyzing
instrumentation. One of the sensors is intended for introduction into the
patient's vasculature while the second sensor remains available for
calibration at all times. This approach, however, requires the two sensors
to be identically responsive to the presence of the gasses being tested
for, which may introduce considerable if not insurmountable manufacturing
problems. Moreover, such modification would add considerable cost to that
component of the system which is intended to be disposed of after every
use. Adaptation of the analyzing instrument to accommodate an additional
sensor and to process information generated thereby would further add
considerable cost to the system. Finally, although such approach allows a
probe to remain within a patient and provide accurate information when
interconnected to a succession of instruments, a skilled labor-intensive
calibration effort is nonetheless required with each transfer.
Alternatively, it has been suggested to integrate the optical components of
the instrument in a portable optics module that remains interconnected to
the probe residing within the patient at all times. Upon transfer, the
optics module is disengaged from the analyzing instrument and transported
to the recovery area where it is simply plugged into the second
instrument. Incorporation of such a feature would, however, add cost to
the instrumentation, as this approach does require that extra equipment be
transported with the patient and logistical problems are posed by the
necessity of keeping track of numerous such modules throughout a typical
medical facility.
Another alternative approach involves the use of a universal standard to
which all of the instruments in use would be calibrated such that a given
signal received from any probe would yield the same value on every
instrument. Since instrument performance is subject to drift and
degradation, calibration of the instruments would have to be performed on
a periodic basis and cannot simply be permanently accomplished at the time
of manufacture. Return of the instruments to a central facility for
periodic recalibration would be an impracticable alternative, so this
approach would require the development of calibration standards which
could engage the instruments in the field. Such calibration standards
would have to be sufficiently stable so as to be transportable all over
the world, yet capable of exactly representing actual probes in all
optical respects. The development and production of such a universal
standard is a formidable undertaking. The necessity for acquiring and
maintaining such standards would add cost to the system.
The prior art is devoid of a practical solution for maintaining a plurality
of analyzing instruments of the type described in calibration. An approach
is called for that allows a probe to be transferred from instrument to
instrument without the need to undertake any recalibration efforts and
that achieves such function without a substantial increase in cost and
complexity.
SUMMARY OF THE INVENTION
The present invention provides for the calibration of measurement devices,
such that a disposable sensor probe can be transferred from instrument to
instrument without the need to recalibrate each successive probe and
instrument combination. The approach does not add substantial cost to the
disposable probe component nor to the analyzing instrument component, and
requires relatively little effort to implement.
The present invention calls for each instrument to be provided with a
non-volatile memory and computing capability and each sensor probe to be
provided with a non-volatile memory accessible by any instrument to which
the sensor is interconnected. No special calibration probes are needed and
no complex calibration procedures are employed.
Any probe that would normally be utilized in conjunction with the
instrumentation may be arbitrarily chosen to function as a transfer probe
for calibrating all of the instruments in a particular group of
instruments. Such group may for example include all of those instruments
in a particular medical facility. In order to implement the calibration
process of the present invention, the selected probe is interconnected to
any arbitrarily chosen first instrument of the group of instruments and
subjected to a first calibration standard. The calibration standard
consists of a mixture of analytes, including analytes to which the probe
is sensitive. The actual concentration values of analytes need not be
known for the purposes of the instrument calibration routine.
During the calibration routine, the first instrument's output is stored in
the transfer probe's memory, such output may or may not accurately reflect
the actual value of the calibration standard's particular mixture of
analytes. The probe is subjected to a second calibration standard
containing a different mixture of the same analytes and the second output
is stored in the transfer probe's memory. Two or more data points for each
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