Chemical Analyzer

The present invention is directed generally to a chemical analyzer, and more specifically to an analyzer for the automated chemical assay of blood, urine and cerebrospinal fluids, particularly in vitro blood chemistry, coagulation and electrolyte analyses. By determining the concentration of key chemical factors in these fluids, data relating to the pathological status of the patient may be obtained which leads to early diagnosis and treatment.

The chemical analyzer of the present invention is designed to perform the chemical analysis by measuring the optical absorbance of species or the reaction products of species in the clinical sample, or the chemical activity of species or their reaction product of the sample using ion selective microelectrodes. Both types of tests are under control of a central processing unit such as a digital computer and particularly a microprocessor which monitors the test results and provides display capability of the test results in the form of a visual, graphical or plotted display. For example, the results of a particular test may be plotted as a bar graph or histogram. Similarly, the test data produced by the chemical analyzer may be integrated with other patient information stored in a host computer such as medical history or billing information.

The optical tests performed by the chemical analyzer are based on the ability of a particular chemical involved in the sample to combine with other chemicals, specifically reagents provided with the usual clinical test kit, to form a compound which absorbs light of a specific wavelength, usually in the ultraviolet or visible region. This chemical compound has a characteristic color, referred to as a chromagen.

The optical test section of the present invention includes a dual beam scanning monochromatic spectrophotometer which is used to measure the amount of light absorbed by the sample. The specific measurement parameters for the particular test such as temperature, time, and wavelength are set precisely under computer control. The test results may then be communicated to an appropriate output device.

For ion selective electrode experiments, the particular electrode sensitive to a species and a reference electrode are immersed in the sample and a potential measurement taken. This information may be stored within the computer memory space, or outputted for display to an appropriate display device.

The specific test parameters are inputted to the system by reading an optical bar code on the reagent package supplied for each test. The bar code is read from the reagent package by means of a wand, the data being under control of the central processing unit within the analyzer. For example, this bar code may provide information relating to the reagent, lot number, expiration date of the reagent, the type of experiment to be performed (i.e. optical or ion selective electrode), information regarding the calibration curve for the test, the clinical acceptable range, the units, the reagent number, quantity of reagent used, etc. In the case of an optical experiment, the specific wavelength required may be specified in the bar code, while in the case of an ion selective electrode experiment, the specific electrode number may be provided. With this approach, all of the information relating to a new experiment can be incorporated into the bar code, without the need to reprogram the chemical analyzer itself.

The specific circuitry and processing used in the present invention will become apparent from the detailed description which follows.

FIG. 1 is a block diagram of the chemical analyzer of the present invention.

FIG. 2 is a diagrammatic top plan view of a portion of the chemical analyzer of the present invention.

FIG. 3 is a diagrammatic side elevational view of a portion of the chemical analyzer of the present invention.

FIG. 4 is a schematic diagram of a portion of the electronic processing circuitry of the present invention.

FIG. 5 is a flow diagram of a portion of the processing of the present invention.

The block diagram of the chemical analyzer of the present invention is illustrated in FIG. 1, and the arrangement of the mechanical and electrical components of the present invention is illustrated, in FIG. 2 and FIG. 3. It will be understood that certain non-critical components of the chemical analyzer unnecessary to the understanding of its construction and operation of the analyzer have been deleted for clarity. Furthermore, for purposes of an exemplary showing the various mechanical and electrical components are illustrated as being mounted on a generally rectangular base plate P.

The physiological fluid, such as blood, urine or cerebrospinal fluid, to be anyalyzed is placed in an optical cuvette or precision test tube 1. The appropriate reagent or reagents necessary to carry out the particular chemical test procedure are also placed in the cuvette and mixed or incubated as required.

In order to maintain the test sample at the appropriate temperature during the analysis, one or more cuvettes 1 may be placed in an incubator 2 which forms part of a heated sample block 3.

As best illustrated in FIG. 2 and FIG. 3, sample block 3 comprises a solid block 4 of aluminum or other heat conducting material rigidly mounted to base P and which contains twelve vertically oriented side-by-side bores or receptacles of square cross section, one of which is shown at 5 arranged in three rows, with four receptacles in each row. Each of bores 5 is dimensioned to accept a cuvette 1 and hold the cuvette in an upright position during incubation. Although the incubator 2 described in connection with the present invention is provided with twelve cuvette-accepting bores 5, it will be understood that any number of such bores or receptacles may be provided.

Means are also provided for maintaining incubator 2 (and the cuvettes retained therein) at a constant temperature. As illustrated in FIG. 3, this heating means includes an electrically operated heating element 6 secured to the lower portion of incubator 2 so as to underline the bottom of bores 5. In the preferred embodiment illustrated, heater 6 comprises a number of resistive heating elements embedded in a flexible silicon rubber so as to form a pad-like heater. Heater 6 is secured by a suitable adhesive or the like in heat exchange relationship with metallic block 4 so as to uniformly heat the block, and the sample containing cuvettes deposited therein.

Electric current is supplied to heater 6 by means of a block heater control, shown generally at 7 in FIG. 1, as is well known in the art. The control 7 which may be electronic in nature, may be included as part of the electronics associated with the chemical analyzer and indicated generally at 8 in FIG. 2.

The temperature of the heat conducting block comprising incubator 2 is monitored by means of two temperature sensors 9 embedded in block 3, in order to maintain the temperature of the incubator at a constant temperature, preferably 37 C..+-.0.5 C. This close temperature control provides the proper temperature environment for incubation of the test sample, and is particularly important in blood, urine and cerebrospinal fluid in vitro chemistry analysis, notably with respect to coaggulation or electrolyte analysis, which may be particularly temperature dependent. It will be observed that one of temperature sensors 9 continuously monitors the temperature of the sample block 3 while the other temperature sensor operates to cause block heater control 7 to disable heater 6 in the event the temperature of the sample block reaches a predetermined limit, e.g. 38 C.

The remaining portion of sample block 3 comprises the sample test station, indicated generally at 10. Test station 10 is formed from a block 11 of heat conducting material, such as aluminum, and shares a portion of heater 6, so that block 11 is also maintained at a relatively constant temperature of about 37 C..+-.0.5 C. If desired, block 11 may be formed as an integral part of block 4, both of which are rigidly secured to base plate P.

Block 11 comprising test station 10 contains a pair of spaced vertically extending bores 12 and 13, similar to bores 5 in incubator 2, for accepting and holding a sample cuvette 14 and reference cuvette 15, respectively. That is, bore 12 forms a sample well into which the sample cuvette is manually placed, while bore 13 forms a reference well into which a reference cuvette, either with or without reagent, is manually deposited. These wells are utilized in connection with the optical analysis section of the chemical analyzer as will be explained in more detail hereinafter.

As noted briefly hereinabove, one of the principles used in the chemical analyzer of the present invention is the ability of certain chemical substances to absorb a specific band or bands of light in the ultraviolet or visible regions of the spectrum. Thus, the chemical composition of the substance may be defined by a characteristic color, based on the ability of the substance to absorb light of specific wavelengths or color. Ideally, the concentration of the substance is proportional to the depth of the characteristic color, as governed by the absorbance of certain bands of light. These principles are well known in blood, urine and cerebrospinal fluid analysis.

In many types of chemical analysis associated with blood, urine or cerebrospinal fluids, it is necessary to react the sample with exact amounts of certain specified reagents to form a chromogen. The optical chemical analysis section of the chemical analyzer of the present invention is designed to measure the amount of light that the particular resultant chromogen absorbs.

In the preferred embodiment of the chemical analyzer of the present invention illustrated in FIG. 2 and FIG. 3, the optical analysis section includes a dual beam scanning monochromatic spectrophotometer, illustrated generally at 16 in FIG. 2 as rigidly mounted to base plate P, which is designed to measure the amount of light that the chromogen absorbs, i.e. its color intensity. The monochromatic spectrophotometer 16 operates by passing a beam of filtered light through an optical cuvette which contains the chromogen. The beam of filtered light is then projected on a photodetector or photosensor, which produces an electrical current corresponding to the amount of impinging light. This current is then used to provide a measure of the absorbance of the sample in the cuvette.

In the preferred embodiment illustrated, the light source associated with the spectrophotometer comprises a tungsten filament incandescent lamp 17 which produces usuable light energy in the ultraviolet and visible ranges, principally 300-780 nm. The lamp 17 may be turned on or off by appropriate control signals by means of a lamp control 18 (see FIG. 1) as is well known in the art. The voltage applied to lamp 17 by lamp control 18 is carefully controlled through a conventional well regulated power supply or the like so that the intensity of the lamp is substantially constant.

The light rays, indicated generally at 19, emitted from lamp 17 pass through a prefocus or collimating lens 20 which is mounted horizontally oriented base 20a in a lens mounting block 21. Mounting block 21 is slidably supported on three horizontal mounting rails 22 secured to plate P so as to be slidable toward and away from lamp 17. This enables the focus of prefocus lens 20 to be manually adjusted.

The light rays leaving prefocus lens 20 pass through a narrow vertically disposed entrance slit 23 in the side of box-like casing 24a of the monochronometer 24.

Monochronometer 24 includes a defraction grating 25 mounted within the monochronometer 24 by means of a control shaft 26 which rotatably extends through the end of the monochronometer housing 24a. It will be understood that monochronometer housing 24a is generally light-tight. The opposite end of control shaft 6 is connected to a drive shaft 27a of a multiple position stepping motor 27, which is used to control the angular position of the defraction grating 25. Angle input information to stepping motor 27 is provided by a stepping motor control 28 (which may generally comprise part of electronics 8), as is well known in the art. Consequently, by providing the properly encoded digital input signals to stepping motor control 28 as will be described hereinafter, the stepping motor, and consequently the defraction grating 25, may be moved to any desired angular position with respect to the incoming light beam. In the specific embodiment illustrated in the present invention, the monochronometer is usable over the ultraviolet range of 340-400 nm and the visible range of 400-780 nm. Furthermore, for purposes of exemplary showing, it will be understood that monochronometer 24 may comprise a conventional monochronometer unit, such as Model SMC1-03 manufactured by PTR Optics.

The monochromatic light leaving defraction grating 25 passes through a narrow vertically disposed exit slit 29 generally in-line with entrance slit 23 and a focusing lens 30 which serves to collimate the light beam. Focusing lens 30 is mounted in a horizontally extending base 31a formed in a lens mounting block 31 which is also slidably mounted on three parallel 32 horizontally extending rails secured to base plate P and similar in construction to rails 22, thereby permitting manual focusing of lens 30. This adjustment would normally be made by the manufacturer, and not by the user.

The collimated light from focusing lens 30 impinges on an optical beam splitter 33 mounted in close proximity to sample test station 10. A portion of the collimated beam is directed by the beam splitter toward sample well 12, while the remainder of the collimated beam is deflected toward reference well 13. The portion of the beam directed toward the sample well passes through an opening 34 in block 11 which communicates with sample well 12. After passing through sample cuvette 14, the monochromatic light beam exits sample well 12 through an opening 35 in block 11, and impinges on sample photosensor or photodiode 36. As will be explained in more detail hereinafter in connection with the electronic schematic diagram illustrated in FIG. 4, the amount of current produced by sample diode 36 an output line 36a provides a measure of the absorbance of the chromogen contained in sample cuvette 14 at the particular monochromatic wavelength produced by monochronometer 24.

The monochromatic collimated light beam deflected toward reference well 13 passes through an opening 37 communicating with reference well 13 through block 11. After passing through the reference well, the light beam exits sample test station 10 by means of an exit opening 38 and impinges on reference photodiode or photosensor 39. As will be explained in more detail hereinafter in connection with the electronic schematic diagram of FIG. 4, the amount of current produced by reference photodiode 39 on output line 39a is used in conjunction with the amount of current produced by sample photodiode 36 to calculate the absorbance of the sample material within sample cuvette 14.

It will be understood that in some instances, it may be necessary to place a reference cuvette 15 within sample well 12 in order to calibrate the optical path for specific chemical tests. In other types of tests, the material forming the reference cuvette will have no significant effect on the reference optical beam, and thus may be eliminated.

The chemical analyzer of the present invention is also provided with a plurality of ion selective electrodes, one of which is illustrated diagrammatically at 40a in FIG. 3, for performing other chemical analyses. The construction and operation of such electrodes is well known in the art, and need not be described in detail. In the present invention, each electrode 40a is connected by means of a wire or cable 41 to a plug 42 which mates with one off several jacks 44 mounted on a jack panel 45. It will be understood that jack panel 45 may be provided with a plurality of jacks 44, each adapted to mate with a connecting plug 42 of an associated ion selective electrode 40a. In the embodiment illustrated, jack panel 45 is vertically mounted vertically adjacent incubator block 2 so that one or more of the electrodes may be inserted into the test solutions contained within the cuvettes 1 mounted in the incubator as indicated diagrammatically by arrow 40c in FIG. 3. There is also one reference electrode 40b (see FIG. 4) which must be present in the sample in conjunction with any individual sensor electrode 40a. The specific type of ion selected electrode will be chosen for the particular chemical analysis to be performed as is well known in the art.

An important part of the present invention is the bar code reader illustrated generally at 46 in FIG. 1. The bar code reader 46 is used in conjunction with a wand to be described hereinafter to read a 28 character bar code supplied with the reagent container. This bar code contains all of the information about the reagent and the particular test being performed. As illustrated in FIG. 2 and FIG. 3, for example, the reagent container 47 supplied as part of a test kit for a particular chemical test is provided with a label 48 bearing printed indicia 49 describing the type of test, type of reagent, etc., as well as a conventional bar code 50. The bar code 50 encodes information relative to the reagent and test such as the lot number and expiration date of the reagent, the type of experiment to be performed (i.e. optical or ion selective electrode), the calibration curve for the test, the clinical acceptable range, the units, the reagent number, quantity of reagent to use, etc. In the case of an optical experiment, the wavelength may be specified in the bar code, and in the case of an ion selective electrode experiment, the channel number or electrode number may be given (i.e., which of the several electrodes 40 should be immersed in the sample solution). With this approach, all of the information relating to a new experiment can be incorporated into the bar code, without the need to reprogram the chemical analyzer itself.

The bar code is read by means of a wand 51 which may be a Hewlett Packard Type HEDS-3050 and, which is connected to electronics 8 by means of a suitable cable 52. For purposes of an exemplary showing, bar code reader 46 may comprise a Hewlett Packard type HEDS-1050 bar code reader which produces suitable data on line 46a (see FIG. 1) according to the information read from the bar code 50. The specific utilization of the bar code reader in connection with the chemical analyzer of the present invention will be described in more detail hereinafter.

The block diagram summarizing the signal processing components of the present invention is illustrated in FIG. 1, where the elements similar to those previously described have been similarly designated.

System operation is controlled by a data processor comprising a central processing unit or CPU 52 which may be any suitable type of digital computer, such as a 6809 or other microprocessor based system. The control program, particularly the processing for the chemistry experiments, is stored in system ROM 53 and control ROM 54, which may be implemented as "firmware" in a suitable integrated circuit chip. A suitable program listing for this purpose is described in Appendix I hereto. Read/write memory is supplied by RAM 55.

Information is inputted to processor 52 by means of a conventional keyboard 56, associated with host computer 69, and output information may be displayed by means of a CRT display 57, incremental plotter 58, or the like. An additional parallel printer port 59 and a serial terminal 60 are also provided.

The foregoing processing elements communicate by means of an internal computer buss 61, as is well known in the art. In addition, communication is provided through the internal computer buss 61 with bar code reader 46, block heater control 7, lamp control 18 and stepping motor control 28, as will be described in more detail hereinafter.

The photosensors 36 and 39 associated with monochronometer 24 and the ion selective electrodes 44, both designated by block 62 in FIG. 1, communicate with internal computer buss 61 through experimental digital buss 63 and experimental buss digital link 64. That is, as will become apparent from the detailed description which follows, the information obtained from the monochronometer and ion selective electrodes is converted to a digital format for use by CPU 52 in conjunction with its operating program. Digital link 64 may be implemented by means of tristate gates which isolate the experimental digital buss from the internal computer buss.

The analog information produced by the photosensors and electrodes comprising block 62 communicates with the internal computer buss 61 as will be explained hereinafter through an analog data buss 65, an eight channel multiplexer 66, and a thirteen bit analog/digital converter 67. The A/D converter 67 permits the analog voltages to be presented on the internal computer digital buss as is well known in the art. The analog information from block heater control 7 and temperature sensors 9 also communicate with the system through the analog data buss 65.

There is also associated with the chemical analyzer of the present invention three sixteen bit timers 68 which control some of the timing functions associated with the experiments, such as the prothrombin coagulation time analysis experiment.

The chemical analyzer of the present invention may also communicate through internal computer buss 61 with an external host computer 69 so as to integrate the chemical analysis information with other patient information. For example, the results of specific in vitro blood, urine and cerebrospinal fluid chemistry or electrolyte analyses may be integrated with the patient's medical history or billing and insurance information stored in the host computer. Likewise, data associated with the patient and relative to the particular diagnostic test such as age, weight, height, sex, and so forth, may be called from the host computer data base management system and used as input information to the diagnostic test being performed. The host computer 69 may also be used to control the overall operation of the chemical analyzer according to the specific instructions contained in the message code from the host computer, such as commands for setting the monochronometer 24 to a particular wavelength, interrogating the temperature of sample block 3, reading the voltage produced by a particular ion selective electrode, etc. Examples of each of these functions will be given in greater detail hereinafter.

The electronic interface associated with the photosensor and electrode section 62 is illustrated schematically in FIG. 4. A high impedance electrometer amplifier, shown generally at 70 in FIG. 4, is connected to each of the ion selective electrodes 40a. It will be understood that in connection with the described embodiment of the present invention, there are eight ion selective electrodes, each having its own high impedance amplifier 70. It will be further understood that the second to fourth electrodes and the amplifiers associated therewith are represented by the block designated 71, while the fifth through eighth electrodes and the amplifiers associated therewith are designated by block 72. A reference electrode 40b is connected to analog signal ground. The gain of each amplifier 70 may be adjusted by variable resistor R1 in order to calibrate each of the ion selective electrode channels 1-8. This calibration is made during manufacture.

Each of the high impedance amplifier channel outputs 70a-70h is connected to an analog input of analog multiplexer 73. The output of multiplexer 73 is connected through buffer amplifier 74 to analog data busss 65. The selection of the eight ion selective electrode channels by means of analog multiplexer 73 is under the control of digital command signals produced by CPU 52 appearing on experimental digital busss 63. Consequently, by the appropriate digital input code to analog multiplexer 73, any one of the ion selective electrode channels may be read and this analog information outputted on analog data busss 65 via output line 74a.

As illustrated in FIG. 4, sample photodiode 36 is reversed biased to approximately -2.48 volts via bias voltage source 85c, and the current output of the photodiode converted to a voltage by means of operational amplifier 75. The feedback impedance 75a for operational amplifier 75 (designated "gain" in FIG. 4), is digitally controlled by CPU 52 through experimental digital buss 63. Consequently, the gain of operational amplifier 75 may be adjusted under computer control.

An active network is also provided to suppress or compensate for the photodiode dark current. This network includes a fixed resistor R2 connected between the inverting input of amplifier 75 and the junction of resistors R3, R4 and variable resistor R5. The remaining terminal of resistor R5 is connected to ground. The remaining terminal of resistor R4 is connected to the output of sample digital-to-analog converter ("sample DAC") 76, which is responsive to digital command signals on the experimental digital buss 63 from CPU 52. The remaining terminal of R3 is biased to approximately -5.00 V by bias voltage source 85b, which also provides the reference voltage for sample D/A connector 76. Consequently, the voltage produced on output line 76a by sample D/A converter 76 is under control of CPU 52 and operates to suppress the dark current for sample photodiode 36 as will be described in more detail hereinafter.

The output of amplifier 75 is connected to the non-inverting input of amplifier 77. The inverting input of amplifier 77 is connected to ground through variable resistor R6. The gain of amplifier 77 is determined by feedback resistor R7. The output of amplifier 77 forms one of the inputs on line 78a to an analog multiplexer 78, and is also connected to the input of log ratio amplifier 79.

A somewhat similar arrangment is used for biasing and dark current suppression of reference photodiode 39. This diode is reverse biased to approximately -2.48 volts. The current from the diode is converted to a voltage by means of amplifier 80, the gain of which may be adjusted by varying the value of feedback impedance 80a (marked "gain" in FIG. 4) under control of digital signals produced by CPU 52 on experimental digital buss 63. The dark current of reference photodiode 39 is suppressed by the network comprising resistors R8-R11, and reference digital-to-analog converter 81 ("Ref. DAC"). In a manner similar to that previously described, appropriate digital signals produced by CPU 52 on experimental digital buss 63 will cause reference D/A converter 81 to produce a voltage on output line 81a to suppress the dark current produced by reference photodiode 39.

The output of amplifier 80 is connected to the non-inverting input of amplifier 82, while the inverting input of this amplifier is connected to ground through variable resistor R12. The nominal gain of amplifier 82 may be set by feedback resistor R13.

The output of amplifier 82 is connected to log ratio amplifier 79, and also forms one input 78b to analog multiplexer 78. The output from amplifier 82 is also supplied as an input to a voltage comparator formed by amplifier 83. The trigger point of the comparator may be set by the voltage divider formed by fixed resistors R14 and R15, and variable resistor R16. The digital output from the comparator is applied to analog data buss 65 on line 83a.

It will be understood that the gain and bias conditions on sample photodiode 36 and reference photodiode 39 may be calibrated by adjustment of variable resistors R5, R6, R11, R12 and R15 to compensate for the sensitivity and dark current differences in various photodiodes.

Log ratio amplifier 79 uses the voltages produced by sample and reference photodiodes 36 and 39, respectively present on lines 78a and 78b, to calculate the absorbance of the chromogen under test. As is well known the absorbance is defined as the products of the extinction coefficient, path length and concentration associated with a particular solution. This may also be defined as the logarithm of the ratio of the sample intensity to the reference intensity. In the present invention, log ratio amplifier 79 operates to divide the value of the voltage produced by sample photodiode 36 by the value of the voltage produced by reference photodiode 39, and takes the logarithm of this ratio to calculate the absorbance. This absorbance value is provided as an analog input to multiplexer 78 on line 78C.

The output current from each of the temperature sensors 9 (which is representative of the actual temperature of sample block 3) is converted to a voltage by means of an associated amplifier 84 and resistors R17 and R18, and the resulting voltages applied as inputs 78d and 78e, respectively, to analog multiplexer 78 and to analog data buss 65. The bias voltage for the temperature sensors 9 is produced by bias voltage source producing means 85a and applied to the non-inverting input of amplifiers 84a and 84b, and as an analog input 78f to multiplexer 78.

The photodiode bias voltage at the anodes of photodiodes 36 and 39 is provided as an input to analog multiplexer 78 on line 78g for mounting the bias conditions of the the photodiodes. Similarly, the bias voltage at the junction of resistors R3 and R9 is supplied as an input to multiplexer 78 on line 78h.

The output of analog multiplexer 78 is connected through voltage follower amplifier 86 to analog data buss 65 via line 816a.

It will be observed that any of the inputs 78a-78h to analog multiplexer 78 may be selected by appropriate digital commands from CPU 52 communicated on experimental digital buss 63. Consequently, CPU 52 may be used to select either of the temperature sensor outputs or their bias voltage, either of the sample or reference photodiode outputs or their bias or dark current suspension reference voltages, or the absorbance value produced on output line 78C of log ratio amplifier 79.

As noted hereinabove, the operation of the chemical analyzer of the present invention is under control of CPU 52 and host computer 69. An exemplary program which may be used to control the processing associated with the chemical analyzer is summarized in the flow diagram of FIG. 5 and is set forth in detail in Appendix I. This program is particularly adapted for use with a 6809 based system running under the 0S9 operating system. It will be understood that this program may be implemented as "firmware" in system ROM 53 or control ROM 54. Each of the program instructions is stored at a memory location between 0000 and FFFF (expressed in hexadecimal notation. For example, most of the application programs are located between about 0000 and 1FFFF. RAM is located at about 2000-27FF and 8000-8800, with system RAM at about F800-F8FF. I/O is located at about 3000-4800.

With reference to FIG. 5, the system processing first proceeds through an initialization sequence in which certain system parameters are verified and pointers set (see, e.g. memory locations 0F80-0FF00). A check is then made to determine whether or not all system supply voltages and bias voltages are within tolerance utilizing the instructions located in memory at about 0CC6-OCEA in the exemplary program described in Appendix I. Next, incandescent lamp 17 is turned on by means of lamp control 18. For example, a digital "1" produced by CPU 52 will turn the lamp on, while a digital "0" produced by the CPU will turn the lamp off.

CPU 52 then produces signals on experimental digital buss 63 which changes the gain of reference photodiode amplifier 80 via impedance 80a until the lowest sensitivity or output voltage on line 78b is obtained.

CPU 52 then causes stepping motor control 28 to rotate defraction grating 25 by means of stepping motor 27 toward the lower wavelengths. At a particular angle, as measured between the defraction grating and the incident light beam from entrance slit 23, the grating in effect acts as a mirror, reflecting essentially all of the incident light toward exit slit 29. This angle is defined as the zero order angle, i.e. a position in the monochrometer spectra in which an intense spectral line is produced. When this point is reached, there is a sudden voltage increase from amplifier 82 which is applied to the voltage comparator formed by amplifier 83. This causes the output of amplifier 83 to change state and apply a signal or output line 83a to analog data buss 65. The position of stepping motor 27 when this sudden intensity increase occurs is stored in RAM 55 as the zero order spectral line. This provides a basepoint from which angular increments of monochronometer 24 may be measured. Consequently, any other wavelength may be unambiguously located relative to this zero order position of the defraction grating 25. The instructions for this processing are located in memory locations of about 0D13-0D64, as shown in Appendix I.

The system then causes stepping motor 27 to rotate the defraction grating 25 to the angular position corresponding to 500 nm. The angular position associated with this wavelength may be stored as a discrete number of stepper motor steps in control ROM 54, for example. This processing is defined by the program instructions stored in memory locations 0C5D-0CC6.

The processing then enters a loop waiting for the temperature of the sample block 3 to stabilize at 37C.+-.0.5C, as monotored by temperature sensors 9 (memory locations 08E8-0900). It will be observed, as illustrated diagrammatically in FIG. 1 and FIG. 2, that the optical sensors comprising sample photodiode 36 and reference photodiode 39 are physically connected to and in heat exchange relationship with sample block 3 so that their temperature remains constant. This helps to stabilize the dark current of the photodiodes, and permits supervision of the dark current as described hereinabove.

When the sample block temperature has stabilized, lamp 17 is turned off and the gain of sample photodiode amplifier 75 and reference photodiode amplifier 80 adjusted via feedback impedances 75a and 80a to the highest sensitivity by appropriate digital commands on experimental digital buss 63 from CPU 52. The output voltages from sample D/A converter 76 on line 76a and reference D/A converter 81 on line 81a are set to approximately half-scale by appropriate digital signals on experimental digital buss 63. The output voltage from amplifier 77 on line 78a representing the dark current produced by sample photodiode 36 is selected by multiplexer 78 and applied to analog data buss 65. This voltage is then selected by eight channel multiplexer 66, converted to a digital voltage by A/D converter 67, and applied to internal computer buss 61. The voltage produced on line 76 by sample D/A converter 76 is then adjusted by appropriate commands on the experimental digital lines 63 until the value of the dark current-produced voltage on line 78a is less than about three millivolts. This thus serves to null or compensate for the dark current produced by the sample photodiode (see memory locations 0D13-0D3B). Since the photodiode is maintained at a relatively constant temperature, this dark current value will remain substantially constant.

A similar procedure is followed in connection with reference photodiode 39 in order to adjust reference D/A converter 81 to compensate for or null the reference dark current (see memory locations 0D3C-0D6i3). The resulting settings of the reference and sample D/A converters resulting in minimum dark current are stored in RAM 55.

Following these calibration checks, the system is ready to perform a desired chemical analysis. This may be accomplished, for example, by a prompt to host computer 69 to indicate that the system is ready for operation (see memory locations 0B97-0BB0).

Each possible command from host computer 69 is in the form of a message comprising a string of characters. The first character of the message comprises the destination code, i.e. the particular output device. The remainder of the command represents an instruction or data followed by an end of message character. For example, the particular destination code may direct certain instructions or data to CRT display 57, incremental plotter 58 or the chemical analyzer of the present invention (see, e.g., the instructions defined by memory locations 1802-1B20). In the exemplary implementation of the present invention, several possible instruction codes are utlized as further described in the exemplary program listing set forth in Appendix I.

For example, the instruction "T" queries the temperature of sample block 3. Consequently, an appropriate digital code is produced by CPU 52 on experimental digital buss 63 which selects, through multiplexer 78, the voltage produced by either of temperature sensors 9. This voltage is directed to analog data buss 65, converted to a digital signal by A/D converter 67, and communicated to CPU 52. Hence, the system may respond by a reply on CRT display 57 that the temperature of the block is, e.g. 3701*, i.e. 37.01C. This operation is controlled by the instructions at memory location 0BB1-0BC0 in Appendix I.

Another command is "L 0,:", which turns lamp 17 off, or "L 1,:", which turns the lamp off (see memory locations 0D76-0D7E).

The photodiode dark current null routine described hereinabove, may be initiated by the command "N", as defined by the instructions stored in memory locations 0D13-0D63.

The monochronometer 24 may be positioned at a new wavelength by means of the command "W", followed by a stop wavelength value. In other words, the command "W540", for example, directs CPU 52 to produce appropriate signals on internal computer buss 61 to cause stepping motor control 28 to rotate the defraction grating 25 a calculated number of steps from the current position described hereinabove corresponding to a final wavelength of 540 nm (see memory locations 0A30-0A61).

The spectra of a sample may be scanned by the "F" command followed by a stop wavelength value. As an example "F 760" would cause the monochronometer to scan the wavelength from its present position to 760 nm in steps of approximately 1 nm. Following execution of each step of the scan, an absorption reading is taken. This is accomplished by causing multiplexer 78 through appropriate signals on experimental data buss 63 to select the analog output on line 78a from log ratio amplifier 79, and apply this voltage to analog data buss 65. This voltage is then converted to a digital signal, and routed to the appropriate output device for displaying or printing the absorbance value at that particular wavelength. The system response, as determined by the voltage produced by log ratio amplifier 79 may be, e.g. 2136*, representing a reading of 2.136 absorbance units. The scan will continue with the absorbance being provided for every step of the monochronometer until the stop wavelength is reached. This value can then form part of the diagnostic report associated with the chemical analysis. This processing is defined by the instructions in memory locations 0A7A-0AD4.

A more involved command involving the monochronometer 24 is represented by "0", followed by the monochronometer wavelength and delay in tenths of a second. For example, the command "0 462, 300:" directs the system to move the monochronometer to 462 nm, wait 30 seconds, and then take an absorbance reading as described hereinabove. The time duration is determined by 16 bit timer 68 under control of CPU 52. This processing is defined by memory locations 0CEA-0CF2.

For an ion selective electrode experiment, after one or more of the electrodes 44 have been placed in the sample cuvette, the command "I 3:" is entered. This causes the system processing to select via analog multiplexer 73 the channel associated with electrode number 3, i.e. the signal on line 70C, for example, and place that voltage on the analog data buss 65. This voltage is then converted to a digital signal, and displayed on one of the output devices in an appropriate format (see, e.g., memory locations 0C24-0C33).

The chemical analyzer of the present invention also includes the capability to measure prothrombine coagulation time. As is well known, this test measures the time necessary for coaggulation to occur in an in vitro blood test sample. In the processing of the present invention, the test sample is inserted in sample well 12, and the command "N:" entered. This causes the system to step monochronometer 24 to a particular wavelength and start the timing of timer 68. The output from log ratio amplifier 79 on line 78C is then selected by analog multiplexer 78 and applied to analog data busss 65. This value is converted to a digital signal by A/D converter 67 and monitored by CPU 52 for a sudden decrease in output intensity. This sudden decrease in intensity or drop in light transmitted marks the prothrobine time. At this point, the elapsed time associated with timer 68 is read, and the time transmitted to the appropriate output port. For example, a particular in vitro blood sample, the system will respond with an output such as "P97", indicating a prothrombin time of 9.7 seconds. These steps can be carried out using the processing defined by memory locations 0C3A-0C57 in Appendix I.

The command "R:" inputs information from bar code reactor 46. This instruction causes information contained in the bar code to be stored in RAM 55 for use during the diagnostic test procedures (see, e.g., memory locations 0DC8-0DFC). As noted hereinabove, information contained in this code establishes the experimental conditions for the particular test such as wavelength for optical experiments or the electrode channel member for ion-selective electrode experiments. The information stored may also relate to incubation time, reagent and sample volume units, calibration information for a particular reagent lot, lot number, expiration date, clinical significant range and test title. For example, the bar code may contain a slope and interrupt valves for synthesizing a straight-line calibration curve to correct for the particular reagent barch being used. In this way, new tests may be provided by the test reagent manufacturer without requiring changes in the instrumentation or software associated with the analyzer of the present invention, but only in the bar code associated with the reagent package or container.

The system is also provided with certain primitive instructions so that new input/output devices or capabilities may be added without the need to change the system software. For example, these commands provide the expansion capability for new experiments. One such primitive command is "K" followed by an address and value which permits the value to be transmitted to any location in the experimental I/O space of the system (memory locations 0F55-0F64). The command "D" followed by a numerical value provides a time delay in tenths of a second via timer 68 (memory locations 0CEA-0CFF). The command "C" followed by a numerical value 0-7 permits any individual channel of analog multiplexer 73 to be selected (memory locations 0BF1-0C23). Finally, the command "A" obtains a reading from A/D converter 67 (memory locations 0C58-0C5C). These primitive commands may be combined with those noted hereinabove to produce more complex instructions for carrying out any particular test.

It will be observed that the results of the particular test may be displayed by any of the output devices described hereinabove. For example, all or part of the test may be displayed in the form of a histogram or bar graph on CRT display 57. In lieu of or in addition to such display, such results may be graphed by means of incremental plotter 58.

As noted above, a complete program listing for an exemplary program to control the processing described in connection with the chemical analyzer of the present invention, is listed in Appendix 1. It will be understood that this program may be stored on any suitable storage media, such as disc or tape, and read into RAM 55 when appropriate. Alternately, the program may be stored as "firmware" in system ROM 53 or control ROM 54.

It will be further understood that various changes in the details, steps, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. ##SPC1##