Note: Descriptions are shown in the official language in which they were submitted.
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INSTRUMENT PERFORMANCE VERIFICATION SYSTEM
BACKGROUND OF THE INVENTION
I. FIELD OF THE INVENTION
This invention relates generally to diagnostic testing
instruments, and more particularly, to an electronic system
and method incorporated integral to the diagnostic
instrument for verifying the performance of the instrument.
The instrument performance verification system is activated
periodically or manually to detect any changes in the
integrity of the diagnostic instrument, thereby assuring
and maintaining the accuracy of the analysis conducted by
the diagnostic instrument.
II. DISCUSSION OF THE RELATED ART
In order to confirm that a diagnostic instrument is
operating to specification, controlled tests must be run
periodically on the diagnostic instrument. In the past,
standardized control samples of known composition have been
used to determine whether the diagnostic instrument is
operating as expected. A blood analyzer is one example of
a diagnostic instrument that may use standardized control
samples to determine its operating quality. The typical
blood analyzer has electrochemical sensors that are used to
test for blood constituents such as blood gases and other
species in a sample.
Diagnostic systems are known in which a plurality of
electrochemical sensors have been built into a single use
disposable cartridge. These sensors can be used to make a
variety of measurements when in contact with, for example,
a sample of blood. The hematocrit, for example, of the
blood may be measured by determining the impedance (or its
inverse, conductance) of the blood as measured between two
electrodes of an electrochemical sensor.
A test unit for a system of this type is disclosed by
Zelin et al. in U.S. Patent number 5,124,661. In that
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device, a re-usable plug-in test cartridge is used that
introduces externally generated signals of known values
that mimic several expected sensor signals to the
diagnostic instrument. If the analyzing sensors and
circuitry of the instrument are functioning properly, the
expected signal output for each will be displayed.
The system disclosed by Zelin et al. impresses
simulated signals produced either from a single source and
voltage divider resistor network using matched resistors or
a second resistor network using multiple tied voltages.
These networks supply a voltage step or multiple voltages
to an amplifier or open circuit for testing. Simple
resistors are employed to produce high impedance. Low
voltage signals for simulating signals are produced by
amperometric, conductometric and potentiometric sensors.
Thus, although the test cartridge system of Zelin et al.
permits detection and discrimination between failures from
damaged CMOS amplifiers and failures from current leakage
in contaminated connectors, that system does not test for
circuit leakage, leakage current, A/D reference voltage,
temperature control, and edge connector contact resistance.
A pressure transducer incorporating an internal
control circuit has been disclosed by Reynolds et al. in
U.S. Patent number 4,557,269. In Reynolds et al.'s system,
the entire pressure transducer is discarded after one use,
requiring calibration of the instrument before each test.
The required calibration is patient specific and is not
interchangeable between patients. Additionally, although
the transducer includes an electronic circuit having
calibration resistors, the electronic circuit does not
verify instrument performance. By testing for leakage to
ground, pin to pin and background leakage, all potential
areas of failure due to leakage would be identified.
Hence, a system that tests for all types of leakage current
would be beneficial.
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Advantageously, a performance verification system for
such a diagnostic instrument would include an integral
system that automatically determines the integrity of all
aspects of the associated instrument, particularly a user
friendly system that minimizes the need for externally
connected testing devices. It would also be an advantage
if each test signal were independently generated and not
based on a common signal input. Further, it would be
desirable for the test range to exceed the voltage/amperage
range produced by the electrochemical sensors.
SUL~IARY OF THE INVENTION
The present invention overcomes the above and other
disadvantages of present diagnostic instrument verification
systems by providing a more comprehensive, user friendly
system and method of verifying the performance and
integrity of a portable diagnostic instrument of the class
including those for rapid blood analysis using single use
plug-in cartridges. Generally, a diagnostic instrument
incorporating the system of the present invention includes
a housing, a multi-channel connector, an electronic circuit
board, a power supply, a control panel, an instrument
performance verification system for analyzing output
signals, and user interface or output means to indicate
results obtained from said instrument performance
verification means. An external test cartridge is required
to test the temperature control and edge connector contact
circuit. The other verifications performed by the system
are performed without the necessity of external components.
The diagnostic instrument of the preferred embodiment
uses electrochemical methods of sample testing. Certain
species within the sample are identified by potentiometric
sensors and other species are identified by amperometric
sensors.
With amperometric sensors, a potential is generated
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across a working electrode and a reference electrode. The
reference electrode is set to a first potential and
stabilized by a counter electrode used to source the
current. The potential between the electrodes causes a
chemical reaction to occur proximate the electrode
surfaces. The electrodes and generated potential are
selected such that the current generated across the
electrodes is proportional to the amount of the selected
analyte present in the sample.
To ensure that the amperometric sensor circuit is
functioning properly, a DAC voltage is applied through a
resistor of known resistance and the output is applied to
the amperometric sensor input (at the working electrode).
The sensor circuit output is measured and compared to an
expected value and a range of inputs are tested to assure
linearity over the entire circuit's range.
To ensure that the potentiometric sensors are
functioning properly, the potentiometric operational
amplifiers are tested at levels that exceed expected
operating levels, thereby verifying that the operational
amplifiers exceed the requirements necessary to measure the
outputs from the potentiometric sensors. A DAC voltage is
directed through a resistor of known resistance and the
output is applied to the selected operational amplifier.
The output from the operational amplifier is measured and
compared to the expected value.
The multi-channel connector is fixed to the housing as
part of a system designed for mechanical and electrical
connection to a mufti-function disposable sensor cartridge
device. The electronic circuit board within the diagnostic
instrument is electrically coupled to the mufti-channel
connector and power supply, and is contained within the
housing. The electronic circuit board includes a means for
analyzing output signals transmitted through said multi-
channel connector and other components of the electronic
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circuit.
The instrument performance verification system of the
present invention is a software controlled system that
utilizes digital-to-analog converters (DACs) to apply
voltages to measure high impedance regions and detect
leakage current between channels. The DAC signal is
generally a higher voltage signal than those produced by
electrochemical sensors. DACs are further used to provide
a low impedance signal for performance checking or checking
the operation of the front-end amplifier system. Each
signal is generated separately and is not tied to any
other. The software determines the value of each applied
signal. While the test signal sources connect to common
conductors, the test signals are not sent through a
mechanical connector device.
The verification system may include but is not limited
to one or more of the following subsystems: a means for
testing a calibration of the cartridge temperature control
system, means for detecting leakage to ground within the
electronic circuit, means for detecting failure in
operational amplifiers electrically coupled to the
electronic circuit, means for detecting leakage between
pins electrically coupled to the electronic circuit, means
for determining failure in an amperometric sensor circuit,
means for determining failure in an operational amplifier
electrically coupled to the electronic circuit, means for
determining failure in a conductivity sensor circuit, means
for detecting failure in an AC source of a conductivity
sensor circuit, and means for detecting failure in a band
pass filter of a conductivity sensor circuit.
The electronic circuitry of the verification system is
electrically coupled to a display or output means that
indicates performance verification results. In operation,
normally, the user activates the test sequence from a
control panel, thereby initiating the internal test
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sequence to test the circuit integrity and performance of
the diagnostic instrument.
The internal test routine includes the following
steps: activating a test cycle, measuring various amounts
of leakage current within the electronic circuit, analyzing
the various amounts of measured leakage current, and
indicating the results obtained from analyzing the various
amounts of leakage current. Other tests may include
determining the A/D reference voltage of the electronic
circuit, comparing the A/D reference voltage with a
predetermined expected value, determining an integrity of
the potentiometric sensor circuit (reffered to as an Ion
Selective Electrode (ISE) in the drawings) operational
amplifier electrically coupled to the electronic circuit or
other potentiometric circuit operational amplifier,
comparing the integrity of the potentiometric circuit
operational amplifier with a predetermined expected value,
testing the performance of an amperometric sensor circuit,
testing the performance of a hematocrit sensor circuit,
testing a temperature control circuit coupled to the
electronic circuit, and measuring an edge connector contact
resistance of said electronic circuit. The internal tests
allow the diagnostic instrument to be checked periodically
or manually to insure that the circuitry and connectors are
functioning properly, thereby avoiding inaccurate
diagnostic measurements.
OBJECTS
It is accordingly a principal object of the present
invention to provide a performance verification system for
a diagnostic instrument that automatically checks the
performance of the electronic circuitry and electrical
connections of the instrument.
Another object of the present invention is to provide
a method of internally checking the integrity of the
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electronic circuit.
Still another object of the present invention is to
provide a passive external card for verifying the
performance of the temperature control and edge connector
contacts.
Yet another object of the present invention is to
provide a diagnostic instrument that includes an internal
means of checking the performance of the electronic
circuit.
These and other objects, as well as these and other
features and advantages of the present invention will
become readily apparent to those skilled in the art from a
review of the following detailed description in conjunction
with the accompanying claims and drawings in which like
numerals in the several views refer to corresponding parts.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of an analytical
instrument which may incorporate the instrument performance
verification system of the present invention;
Figure 2 is a perspective view of a test card used to
verify the calibration of the temperature control system
and performance of edge connector contacts of the
instrument;
Figure 3 is an exploded view of a test card of the
type shown in Figure 2;
Figure 4 is a schematic block diagram showing elements
of a system employed in carrying out the invention;
Figure 5 is a flow chart showing a test routine for
the performance verification system of the present
invention;
Figures 6-7 together present a schematic diagram of a
portion of the electronic circuit of the performance
verification system of the present invention; and
Figure 8 is a schematic diagram of the electronic
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circuit of the test card of Figures 2 and 3.
DETAILED DESCRIPTION
In conjunction with the several views of the figures,
details of representative embodiments will next be
presented. Figure 1 shows generally a diagnostic
instrument 10 which incorporates the electronic instrument
performance verification system of the present invention.
The diagnostic instrument 10 includes a housing 12, display
14, control panel 16, power supply 18, cartridge receptacle
20, cartridge temperature control contacts 24, infrared
(IR) probe 26, an array of card or cartridge connector
contacts 28-46, and electronic circuit (not shown).
Figures 6-7 illustrate details of the portion of the
electronic circuitry used to verify instrument performance.
Figure 2 and 3 together show the test card used to
verify the performance of the temperature control system
and edge connector contacts of the diagnostic instrument
10. The test card 48 includes a cover 50 and base 52. A
test circuit board 54 is retained between the cover 50 and
base 52. An end of the circuit board 54 having lead
connector pads 58-74 extends and protrudes beneath the
cover 50. An IR transparent probe window 76 (see Figure 3)
is provided in base 52 to enable temperature sensing of the
test circuit board 54. Guide rails 78 and 80 guide the
test card 48 into contact with the diagnostic instrument
10, wherein the connector contacts 28-46 engage the lead
connector pads 56-74. When the test card 48 is engaged with
or plugged into the diagnostic instrument 10, the IR probe
window 76 aligns with the IR probe 26, allowing IR probe 26
to sense the temperature of the test card circuit board 54.
Resistive heaters 82 electrically coupled to the ceramic
test circuit board, are used to heat the board 54 to a
control temperature. The temperature of the board 54 is
also measured by a thermistor 84, and the thermistor signal
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is compared to the corresponding value sensed by the IR
probe as a check on the performance of the IR probe 26.
Figure 4 further identifies the various components of
the electronic circuit of the diagnostic instrument 10 of
the present invention. As discussed below in greater
detail, an integrated circuit 86 is electrically coupled to
the display 19, control panel 16, digital to analog
converters (DACs) generally represented by numeral 88,
analog to digital (A/D) converters generally represented by
l0 numeral 90, beeper or alarm 92, printer 94, internal modem
96, and serial port interface 98. The DACs 88 are
electrically coupled to the sensor interface circuits 100
and temperature controls 102. A barometric pressure sensor
104 is coupled to the A/D converter 90.
An overview of the process steps for controlling the
verification system of the present invention is represented
in block form by the flowchart of Figure 5. The user
activates the test cycle using the control panel 16 (see
block 110). When the test cycle has been activated, a
message will appear on the display 14, prompting the user
to remove all sensor cartridges inserted in the diagnostic
instrument 10. The instrument performance verification
system checks to make sure that the connector contacts 28-
46 within the cartridge or card receptacle 20 are open.
Alternatively, the test cycle may be activated
automatically when a cartridge is removed from the
cartridge receptacle 20, when a test card is inserted and
the instrument is energized, or when the diagnostic
instrument 10 is otherwise energized.
The entire test routine is preferably implemented
automatically once a cartridge is removed from the
cartridge receptacle 20. A prompt on the display 19 may
change, indicating to the user the progress of the test.
At the end of the test, the results are indicated on the
display 14 and optionally printed on an attached printer
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94. Preferably, the results are also stored within
internal memory of the integrated circuit 86 for later
recall or for down-loading to an external data management
system or information system, thereby allowing the user to
document and maintain test records. If the test indicates
a failure of components of the diagnostic instrument 10,
instructions may appear on the display 14, instructing the
user on how to proceed to repair the failed components or
device. Error codes giving specific failure information
are stored for later recall, to assist in further
diagnosing any problems detected.
Generally, as depicted in the chart of Figure 5, once
the test cycle has been activated, the system is first
directed to test for leakage current within the internal
electronic circuitry of the instrument 10 and the
connections to the instrument 10 (see block 112). Leakage
current within the circuitry may include background
leakage, sensing-circuit leakage, pin to pin leakage,
and/or pin to ground leakage. The A/D reference voltage is
also determined and compared with the expected value at
block 114. Accuracy of the A/D reference voltage is
important since the measurements made by the instrument are
based on the A/D reference voltage.
As further described below, the integrity of each
potentiometric circuit operational amplifier is tested at
block 1I6. They are tested at levels that exceed expected
operating levels to verify that the potentiometric circuit
operational amplifiers exceed the requirements necessary to
measure potentiometric sensor outputs. Various tests to
determine the condition of the amperometric and
conductometric (possibly hematocrit) sensor circuits are
also performed to ensure that those sensor circuits are
within predetermined tolerances at blocks 118 and 120. The
barometric pressure circuit of barometer 104 is tested at
122.
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A prompt next appears on the display 14, instructing
the user to insert a test cartridge or card 48. Once the
test card 48 is inserted into the cartridge receptacle 20,
the temperature control circuit is tested to make sure that
the temperature calibration is consistent with the actual
temperature of the card 48 determined by the thermistor 84
on the test card 48 (see block 124). The edge connector
contacts are also tested to determine the integrity of the
contacts at block 126. Once the tests and measurements or
l0 comparisons have been performed and processed at 128, a
message corresponding to any necessary action required of
the user is indicated on the display 14 at block 130.
Figures 6-7 together represent a schematic of a
portion the electronic circuit that those skilled in the
art will recognize as useful to perform the various tests
described above. Immediately below is a more detailed
discussion of the various diagnostic tests, with reference
to the portion of the electronic circuit used to conduct
the related test.
A portion of the circuit shown in Figure 7 is used to
detect leakage current from sensor connector contacts 28-46
to ground. At times the area between each sensor contact
28-46 and ground path may become contaminated, creating a
leakage path between the contacts and ground path. Leakage
between the contacts 28-46 and ground causes an incorrect
measurement of the potential, thereby distorting related
measurement values. In order to detect leakage between the
contacts 28-46 and the ground path, a digital to analog
convertor output from DAC 132 of 0.010 Volts (10 mV) is
directed through a 1.0 M ohm resistor 134 and multiplexor
136 to the potentiometric sensor connector, for example
contact 28. The current at the sensor connector is
measured and compared to the expected value of 10 n Amps.
If the measured current is lower than expected, a leakage
path is likely between the sensor connector and the ground
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path. The accuracy of this detection method is not
affected even when the potential directed through the
sensors approximates the ground potential.
A portion of the circuit used to detect leakage
between contacts is also shown in Figure 7. Contamination
and, hence, leakage between the contacts 28-46 may cause an
incorrect measure of potential, current or both, thereby
leading to inaccurate output. Contamination between the
various sensor's connectors or contacts 28-46 may be
to detected by directing an output signal from DAC 132 of, for
example, 1.0 volts through 1.0 M ohm resistor 134 and
multiplexor 136 to a first selected contact, for example
contact 30. The current at a corresponding potentiometric
sensor lead 142 is measured and compared to the expected
value of less than 0.1 n Amps. If a leakage is present
between the two selected sensor contacts, the measured
current value will be greater than expected. If a leakage
between sensor contacts is present, the specific sensor
contact is identifiable. By pinpointing specific sensor to
sensor contact leakage paths, one can be especially
sensitive to those leakage paths that are known to give
difficulties in performance.
The portion of the electronic circuit used to detect
failure in the potentiometric sensor operational amplifiers
within the electronic circuit is further shown in Figure 7.
Electrostatic discharge (ESD), for example, within the
integrated circuit may damage the operational amplifiers.
In order to detect damage to the operational amplifiers, a
DAC voltage from DAC 132 is directed through 1 M ohm
resistor 134 and through multiplexor 136 to operational
amplifiers 140-150. The output is measured and compared to
the expected value.
The potentiometric reference electrode contact 40 must
be at ground potential, since all contact measurements are
performed with respect to the reference electrode. The
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provided DAC voltages should span a range that exceeds the expected
range of the sensor outputs to sufficiently test the limits of the circuits.
Several measurement points should be used aver the range to confirm
linearity of the relation over the entire circuit range. By testing the
circuit
in a manner that exceeds the requirements necessary to measure
potentiometric sensor outputs, the chances of identifying or catching a
sensor circuit that is marginal is improved.
Figure 6 shows a portion of the electronic circuit used to determine
failure of any switches or operational amplifers corresponding to DAC
bias output switches 156, 158, 160, 162 used to set the amperometric
sensor bias and source current within the electronic circuit. To detect such
a failure, an MF pin 164-170 associated with each switch is connected to
an A/D converter 172 which is monitored. The DAC bias 174-180 is set
to a predetermined value, preferably 2 Volts. When each of output
switches 156-162 is closed and the circuit is operating properly, the
control monitor reading corresponding to each switch equals the DAC bias
output ~ tolerance. When each output switch 156-162 is open, the value
indicated on the control monitor or display should be zero. Then when
each corresponding feedback switch 182-188 is open the monitor reading
should be t rail (2.5 Volts).
Figure 6 also illustrates a portion of the electronic circuit used to
determine failure in a condutometric resistance measurement within the
electronic circuit. A resistor divider method is used to determine the
conductance. In order to detect damage to the resistor 190, the output
from the heater low control 192 is connected to multiplexor 194. The
output from the multiplexor 194 is monitored through A/D converter 196.
In use, the heater low control 192 is connected to graurad tlaraugh resistor
197, and then the output from the 1 K
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resistor 190 is monitored and compared to expected results.
The top portion of the circuit in Figure 6 is a
portion of the electronic circuitry used to detect failure
in the AC source 198 or band pass filter 200 of the
hematocrit sensor within the electronic circuitry.
Electrostatic discharge, for example, may damage the clock,
causing the AC source 198 to clock incorrectly or the band
pass filter 200 may center on the wrong frequency. In
order to detect damage to the clocks, the output of the
l0 bandpass filter 200 is connected directly to the DC
converter producing a signal represented as RMS/DC. The
RMS/DC signal is sent to a serial A/D 196 which is
connected to the display 14.
In use, the Band Pass Filter 200 is set to a desired
frequency, for example 71 kHz, and then the AC source 198
is adjusted over several frequencies including those above,
below and at the desired frequency. The RMS/DC signal is
then monitored for desired results. If the AC source 198
is functioning properly, the 71 kHz RMS/DC signal will
correspond with the "71 kHz" AC source signal. The AC
source 198 is then set at the desired frequency, for
example 71 kHz, and the Band Pass Filter 200 is adjusted
over several frequencies including those above, below, and
at the desired frequency. The RMS/DC signal is then
monitored for desired results. If the Band Pass Filter 200
is functioning properly, the 71 kHz RMS/DC signal will
correspond with the "71 kHz" Band Pass Filter signal.
The circuit used to detect failure in the temperature
control system is illustrated in Figures 6 and 8.
Temperature control failure may be caused, for example, by
a damaged operational amplifier or obstruction of the
infrared probe 26. To test the temperature control system,
a test card 48 is inserted into the cartridge receptacle
20. The test card 48 circuitry shown in Figure 8 includes
heaters 82 connected in series to simulate a resistance
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heater contained in an actual diagnostic cartridge. A
thermistor 84 is also connected to the test card circuitry,
wherein a signal corresponding to the temperature of the
card is transmitted to A/D converter 202. The temperature
controller is activated to heat to a desired set point,
normally 37°C for processing bodily fluid samples. Once the
set point has been reached, the temperature value of the
thermistor signal is determined and compared with that of
the IR probe output 204. If the value indicated by the
thermistor and that of the IR probe output 204 deviate
beyond a predetermined margin of error, a temperature
control failure message will be displayed on the monitor.
The tolerance typically used is ~ 0.5 °C.
An output from the amperometric sensor circuit is
measured to determine whether a failure condition exists in
that portion of the circuit. In this manner, output from
DAC 206 is directed through multiplexor 208 to the
amperometric sensor circuit. The amperage at A/D
converters 210-214 is measured and compared to the expected
value for corresponding amperometric sensor. If the
measured amperage deviates from the expected amount,
failure in the corresponding amperometric sensor is likely.
This invention has been described herein in
considerable detail in order to comply with the patent
statutes and to provide those skilled in the art with the
information needed to apply the novel principles and to
construct and use such specialized components as are
required. However, it is to be understood that the
invention can be carried out by specifically different
devices, and that various modifications, both as to the
equipment details and operating procedures, can be
accomplished without departing from the scope of the
invention itself.
What is claimed is:
