Method and electronic control for the analyzation of serum chemistries

Abstract

An electronic control logic system for processing the results of a spectrophotometer analysis of a serum chemistry comprised of a serum and one or more chemical reagents. The spectrophotometer output representing air as a light path and another output representing the test chemistry as a light path are integrated and the air path integrated value allowed to exponentially decay until its value is equal to that of the integrated test chemistry path value. The decay time is converted into a train of digital pulses representative of the optical density of the test chemistry. These pulses are counted and their total stored for comparison with the corresponding optical density of a standard solution. The concentration of the element for which the particular test was designed to detect is known for the standard solution, so the percentage concentration of that element in the test chemistry may be thereby ascertained. Programable variations are provided to enable the evaluation of test results from a kinetic or an end point test. The results of the analysis, together with a test identification number and a patient identification number is selectively applied by a printer control logic section for suitable printing of the data.

We claim: 
     
       1. An apparatus for determining the concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises analyzation means for determining the light transmittance of .[.a.]. .Iadd.the .Iaddend.solution and for generating a first analog signal in accordance therewith; said analyzation means being .[.adaptable for determining the light transmittance of a reference substance and.]. .Iadd.also .Iaddend.for generating a .[.second.]. .Iadd.reference .Iaddend.analog signal .[.in accordance therewith.].; conversion means for generating a first digital signal from said first and .[.second.]. .Iadd.reference .Iaddend.analog signals, said first digital signal having a first numerical value associated therewith .[.as.]. representative of the optical density of said solution; and calculation means for calculating the .[.percentage.]. concentration of the .[.element.]. .Iadd.substance .Iaddend.in said solution from said first digital signal, said calculation means  .[.including.]. .Iadd.having .Iaddend.generation means for generating and storing a second digital signal having a second numerical value associated therewith representative of .[.the concentration of the element needed in said solution for said first numerical value to equal one;.]. .Iadd.a standardizing scale factor value, .Iaddend. a digital pulse generator for generating a first digital pulse train having pulses occurring at a predeterminable frequency and having first and second outputs.[.;.]..Iadd., .Iaddend.frequency alteration means coupled to said conversion means and said first .Iadd.pulse .Iaddend.generator output for altering said frequency in accordance with said first digital signal whereby a second digital pulse train is generated.[.;.]..Iadd., .Iaddend.first counting means coupled to said second .Iadd.pulse .Iaddend.generator output for counting the pulses occurring in said first pulse train.[.;.]..Iadd., .Iaddend.second counting means coupled to said frequency alteration means for counting the number of pulses occurring in said second pulse train.[.;.]..Iadd., .Iaddend.detection means for detecting when the number of said first pulse train pulses counted by said first counting means equals said second numerical value and for inhibiting said digital pulse generator when the equation occurs, whereby the number of pulses counted by said second counting means prior to the inhibiting of said generator represents the numerical value of the concentration of the .[.element.]. .Iadd.substance .Iaddend.in said .[.first.]. solution. 
     
     
       2. An apparatus as claimed in claim 1 wherein said analyzation means .[.includes.]. .Iadd.comprises .Iaddend.a spectrophotometer having light sensitive means for generating said first and second analog signals and automatic feedback means for adjusting the supply voltage to said light sensitive means in accordance with changes in the operating characteristics of said spectrophotometer. 
     
     
       3. An automatic method for determining the .[.percentage.]. concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises the steps of reading the value of the light transmittance of the solution; computing .[.the optical density.]. .Iadd.a .Iaddend.value .Iadd.representative .Iaddend.of the solution .Iadd.optical density .Iaddend.from said .Iadd.solution .Iaddend.light transmittance value; multiplying said .Iadd.representative .Iaddend.optical density value by a scale factor value, .[.said scale factor value being equal to the percentage concentration value of the element which would cause the optical density value to equal one,.]. said multiplying step .[.including.]. .Iadd.comprising .Iaddend.generating a first digital pulse train having pulses reoccurring at a predeterminable frequency.[.;.]..Iadd., .Iaddend.counting and storing the number of pulses generated in said first pulse train.[.;.]..Iadd., .Iaddend.generating a second digital pulse train identical to said first pulse train.[.;.]..Iadd., .Iaddend.altering the frequency of said second pulse train in accordance with the .Iadd.representative .Iaddend.optical density .Iadd.value .Iaddend.of said solution .[.;.]..Iadd., .Iaddend.counting and storing the number of pulses in the thereby altered second pulse train.[.;.]..Iadd., .Iaddend.comparing the stored number of pulses from said first pulse train with said scale factor value.[.;.]..Iadd., .Iaddend.and stopping the generating of said first and second pulse trains when the stored number of .Iadd.pulses .Iaddend.from said first pulse train equals said scale factor value, whereby the stored number of pulses having occurred in said altered .Iadd.second .Iaddend.pulse train represents the percentage concentration of the  .[.element.]. substance in the solution; and storing the resulting value of said multiplying step. 
     
     
       4. An apparatus for determining the concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises analyzation means for .[.determining the.]. .Iadd.generating a first electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of the optical density of the .Iadd.test .Iaddend.solution, said analyzation means .[.including.]. .Iadd.having .Iaddend.optical means for .[.determining.]. .Iadd.generating an analog signal representative of .Iaddend.the light transmittance of the .Iadd.test .Iaddend.solution and .[.for generating an analog signal in accordance therewith.]., conversion means for converting said analog signal to .[.a digital.]. .Iadd.said first electrical .Iaddend.signal .[.representative of the value of the optical density of the solution.]., and first storage means for storing said .[.digital.]. .Iadd.first electrical .Iaddend.signal, said analyzation means also being for .[.determining.].  .Iadd.generating a second electrical signal having a value representative of .Iaddend.the optical density .[.value.].  of a standard solution having a known concentration .[.value.]. of the .[.element.]. .Iadd.substance .Iaddend.therein, and for .[.determining.]. .Iadd.generating a third electrical signal having a value representative of .Iaddend.the optical density .[.value.]. of a blank solution; calculation means for .[.determining a value for.]. .Iadd.automatically generating .Iaddend.a standardizing scale factor .[.representing the concentration of the element in the solution needed for said optical density value to equal one.]. .Iadd.signal.Iaddend., said calculation means .[.including.]. .Iadd.having .Iaddend.subtraction means .Iadd.comparing and .Iaddend.for taking the difference between .[.the optical density value of the standard solution and the optical density value of the blank solution.]. .Iadd.said second and third electrical signals .Iaddend.and for storing the difference value thereby obtained .[.in said first storage means.]., second storage means for .Iadd.generating and .Iaddend.storing .Iadd.a fourth electrical signal having a value representing .Iaddend.said known concentration .[.value.]. of .Iadd.the substance in .Iaddend.said standard solution, and division means for dividing .Iadd.the value of .Iaddend.said .[.known concentration.]. .Iadd.fourth electrical signal .Iaddend.by said difference .[.stored in said first storage means.]. .Iadd.value between said second and third electrical signals .Iaddend.to obtain said standardizing scale factor .Iadd.signal.Iaddend. ; .Iadd.and .Iaddend.multiplication means for multiplying said .[.determined optical density.]. .Iadd.first electrical signal .Iaddend.by said scale .[.factor value.].  .Iadd.factor signal .Iaddend.thereby .[.obtaining the .]. .Iadd.obtaining an output signal having a .Iaddend.value of the concentration of the .[.element.]. .Iadd.substance .Iaddend.in the .Iadd.test .Iaddend.solution.[.; and display means for presenting said concentration value.].. 
     
     
       5. An apparatus for determining the concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises analyzation means for determining .[.the.]. .Iadd.a .Iaddend.value .[.of.]. .Iadd.representing .Iaddend.the optical density of the solution; calculation means for .[.determining.]. .Iadd.generating .Iaddend.a value for a standardizing scale factor .[.representing the concentration of the element in the solution needed for said optical density value to equal one.].; multiplication means for multiplying said .[.determined.]. .Iadd.representative .Iaddend.optical density value by said scale factor value thereby obtaining the value of the concentration of the .[.element.]. .Iadd.substance .Iaddend.in the solution, .[.including.]. .Iadd.said multiplication means having .Iaddend.a digital signal generator .[.having.]. .Iadd.with .Iaddend.first and second outputs for generating a first digital signal having a predetermined frequency on said first and second outputs, a digital rate multiplier coupled to said first generator output and to said analyzation means for altering said digital frequency on said first output in accordance with said .Iadd.representative .Iaddend.optical density value to generate a second digital signal, first storage means for storing a third digital signal representative of said scale factor value, second storage means coupled to said digital rate multiplier for storing said .[.third.]. .Iadd.second .Iaddend.digital signal, said first storage means being coupled to said second generator output for receiving said first digital signal, and detection means for detecting when the value of said first digital signal equals the value of said third digital signal stored in said first storage means and for inhibiting said generator concurrently with such detection whereby the value of said second digital signal in said second storage means equals the concentration of the .[.element.]. .Iadd.substance .Iaddend.in the .Iadd.test .Iaddend.solution. 
     
     
       6. An apparatus for determining the concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises analyzation means for .[.determining the.]. .Iadd.generating a first electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of a parameter characteristic of the .Iadd.test .Iaddend.solution .[.and the value.]. .Iadd.and for generating a second electrical signal having a value representative .Iaddend.of said parameter for a standard solution having a known concentration of the .[.element.]. .Iadd.substance .Iaddend.therein; .Iadd.storage means for generating and storing a third electrical signal having a value representing the known concentration of the substance in said test solution; .Iaddend.calculation means .[.for determining a value for.]. .Iadd.automatically generating .Iaddend.a standardizing scale factor .[.representing the concentration of the element in the solution needed for said parameter value to equal a predetermined value.]. .Iadd.signal.Iaddend., said calculation means .[.including.]. .Iadd.having .Iaddend.arithmetic means for operating on .Iadd.the values of said second and third electrical signals .Iaddend..[.said parameter value for said standard solution.]. in computing said standardizing scale factor .[.value.]. .Iadd.signal.Iaddend., said arithmetic means also being for operating on said .[.parameter of the solution with.]. .Iadd.first electrical signal and .Iaddend.said standardizing scale factor .Iadd.signal .Iaddend.to .[.compute.]. .Iadd.obtain an output signal having a value of .Iaddend.the concentration of the .[.element.]. .Iadd.substance .Iaddend.in the .Iadd.test .Iaddend.solution. 
     
     
       7. An apparatus as claimed in claim 6, wherein said analyzation means .[.includes.]. .Iadd.also comprises .Iaddend.means for .[.determining the.]. .Iadd.generating a fourth electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of said parameter for a blank solution, and wherein said arithmetic means .[.includes.]. .Iadd.comprises .Iaddend.means for operating on .[.said parameter value for said blank solution in addition to said parameter value for said standard solution.]. .Iadd.the values of said second, third, and fourth electrical signals .Iaddend.in computing said standardizing scale factor .[.value.]. .Iadd.signal.Iaddend.. 
     
     
       8. An apparatus as claimed in claim 6, wherein said analyzation means also .[.being.]. .Iadd.comprises means .Iaddend.for .[.determining the.]. .Iadd.generating a fourth electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of said parameter for a blank solution, and said arithmetic means .[.includes.]. .Iadd.comprises .Iaddend.subtraction means for .Iadd.comparing and .Iaddend.taking the difference between said .[.standard solution parameter value and said blank solution parameter value.]. .Iadd.second and fourth electrical signals .Iaddend.and for storing the difference value thereby obtained, .[.storage means for storing said known concentration value of said standard solution,.]. and division means for dividing .Iadd.the value of .Iaddend.said .[.known concentration value.]. .Iadd.third electrical signal .Iaddend.by said difference value .[.stored in said subtraction means.]. .Iadd.between said second and fourth electrical signals .Iaddend.to obtain said standardizing scale factor .Iadd.signal.Iaddend.. 
     
     
       9. An automatic method for determining the .[.percentage.]. concentration of .[.an element.]. .Iadd.a substance .Iaddend.in a .Iadd.test .Iaddend.solution, which comprises the steps of .[.reading the.]. .Iadd.generating a first electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of a parameter characteristic of the .Iadd.test .Iaddend.solution; .[.reading the.]. .Iadd.generating a second electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of said parameter for a standard solution having a known concentration of the .[.element.]. .Iadd.substance .Iaddend.therein; .[.calculating a value for.]. .Iadd.generating and storing a third electrical signal having a value representing the known concentration of the substance in said standard solution; generating .Iaddend.a standardizing scale factor .[.representing the concentration of the element in the solution needed for said parameter of the solution to equal a predetermined value.]. .Iadd.signal with calculation means .Iaddend. .[.by.]. arithmetically operating .Iadd.automatically .Iaddend.on said .[.parameter value for said standard solution.]. .Iadd.second and third electrical signals.Iaddend.; multiplying .Iadd.with multiplication means .Iaddend.the .[.calculated.]. scale factor .Iadd.signal .Iaddend.by .[.the value of said parameter for said solution.]. .Iadd.said first electrical signal to obtain an output signal.Iaddend.; and storing .[.the result of said multiplying step whereby said result is the.]. .Iadd.and presenting said output signal, said output signal having a .Iaddend.value of the .[.percentage.]. concentration of the .[.element.]. .Iadd.substance .Iaddend.in the .Iadd.test .Iaddend.solution. 
     
     
       10. A method as claimed in claim 9 including the step of .[.reading the.]. .Iadd.generating a fourth electrical signal having a .Iaddend.value .Iadd.representative .Iaddend.of said parameter for a blank solution and said .[.calculating step includes.]. .Iadd.step of generating said scale factor signal comprises .Iaddend.the steps of .Iadd.automatically .Iaddend.subtracting .[.the standard solution parameter value from the blank solution parameter value.]. .Iadd.with subtraction means the value of said second electrical signal from said fourth electrical signal and.Iaddend., storing the difference value .Iadd.thereby .Iaddend.obtained .[.in said calculating step, storing the value of the known concentration of said standard solution.].  and dividing .Iadd.the value of .Iaddend.said .[.known concentration value.]. .Iadd.third electrical signal .Iaddend.by said difference value to obtain .[.the value for.]. said standardizing scale factor .Iadd.signal.Iaddend.. .Iadd. 11. An apparatus as claimed in claim 1 wherein said second numerical value has a value representative of the ratio of the concentration of the substance in said solution over the optical density of said solution. .Iaddend..Iadd. 12. An apparatus as claimed in claim 1 wherein said second numerical value has a value representative of the ratio of the concentration of the substance in a standard solution having a known concentration of said substance therein over the optical density of said standard solution. .Iaddend..Iadd. 13. An apparatus as claimed in claim 1 wherein said analyzation means also comprises means for determining the light transmittance of a standard solution having a known concentration of the substance therein and for generating a second analog signal in accordance therewith, and for determining the light transmittance of a blank solution and for generating a third analog signal in accordance therewith; said conversion means being also for generating a third digital signal from said second and reference analog signals having a numerical value representative of the optical density of said standard solution and for generating a fourth digital signal from said third and reference analog signals having a numerical value representative of the optical density of said blank solution; said generation means comprising subtraction means for taking the difference between said fourth digital signal value and said third digital signal value, first storage means for storing the difference value thereby obtained, second storage means for storing a value representative of the known substance concentration in said standard solution, and division means for dividing said representative known substance concentration value by said stored difference value, and means for generating and storing said second digital signal having said second numerical value from the result of said division. .Iaddend..Iadd. 14. An apparatus as claimed in claim 1 wherein said analyzation means also comprises means for determining the light transmittance of air, said reference analog signal being generated in accordance therewith. .Iaddend..Iadd. 15. An automatic method as set forth in claim 3 with the additional steps of reading the light transmittance value of a standard solution having a known concentration of the substance therein, computing a value representative of the standard solution optical density from said standard solution light transmittance value, and calculating the value of said standardizing scale factor from said standard solution representative optical density value. .Iaddend..Iadd. 16. An automatic method as set forth in claim 15 wherein said standardizing scale factor has a value representative of the ratio of the concentration of the substance in said standard solution over the optical density of the standard solution. .Iaddend..Iadd. 17. An automatic method as set forth in claim 3 with the additional steps of reading the light transmittance values of a standard solution having a known concentration of the substance therein and of a blank solution, computing representative optical density values for said standard solution and said blank solution from their respective light transmittance values; and calculating said scale factor value by taking the difference between the representative standard solution and blank solution optical density values, and dividing the difference value thereby obtained into a numerical value representing the known concentration of the substance in said standard solution to obtain said scale factor value. .Iaddend..Iadd. 18. An apparatus as claimed in claim 4 with the addition of display means for presenting the value of said output signal. .Iaddend..Iadd. 19. An apparatus as claimed in claim 5 wherein said analyzation means also comprises means for determining a value representing the optical density of a standard solution having a known concentration of the substance therein, said calculation means comprising arithmetic means for operating on said representative standard solution optical density value to compute the value of said scale factor. .Iaddend..Iadd. 20. An apparatus as claimed in claim 5 wherein said standardizing scale factor value has a value representative of the ratio of the concentration of the substance in a standard solution having a known concentration of said substance therein over the optical density of said standard solution. .Iaddend..Iadd. 21. An apparatus as claimed in claim 5 wherein said analyzation means also comprises means for determining a value representing the optical density value of a standard solution having a known concentration of the substance therein and for determining a value representing the optical density of a blank solution; said calculation means comprising subtraction means for taking the difference between the representative standard solution and blank solution optical density values, and division means for dividing the difference value thereby obtained into a value representing the known substance concentration in the standard solution to obtain said scale factor value. .Iaddend. .Iadd.22. An apparatus as claimed in claim 6 wherein said parameter value for said test and standard solutions comprises a value representative of the respective optical densities thereof, and said standardizing scale factor signal has a value representative of the ratio of the concentration of the substance in said standard solution over the optical density of said standard solution. .Iaddend..Iadd. 23. An automatic method as claimed in claim 9 wherein said standardizing scale factor signal has a value representative of the ratio of the concentration of the substance in said standard solution over the value of said parameter for said standard solution. .Iaddend..Iadd. 24. An apparatus for determining the concentration of a substance in each of a plurality of test solutions, comprising analyzation means for generating a first electrical signal having a value representative of a parameter characteristic of a blank solution and for generating a second electrical signal having a value representative of said parameter for a standard solution having a known concentration of the substance therein, storage means for generating and storing a third electrical signal having a value representative of the known concentration of the substance in said standard solution, and calculation means for automatically operating arithmetically on said first, second, and third electrical signals to generate a standardizing scale factor signal, said analyzation means being also for successively generating a fourth electrical signal having a value representative of said parameter for each of said test solutions, and said calculation means being also for arithmetically operating successively on each of said fourth electrical signals and said scale factor signal to obtain an output signal for each of the test solutions having a value of the substance concentration in each test solution. .Iaddend..Iadd. 25. An apparatus as claimed in claim 24 wherein said standardizing scale factor signal has a value representative of the ratio of the concentration of the substance in said standard solution over the difference between the standard solution and blank solution parameter values. .Iaddend..Iadd. 26. An apparatus as claimed in claim 24 wherein said analyzation means comprises optical means for respectively determining the light transmittance of each of said solutions, generation means for generating an analog signal in accordance with said respectively determined light transmittances, and conversion means for generating said first, second, and fourth electrical signals from said analog signals, said first, second, and fourth electrical signals each having a value representative of the optical density of their respective solution and corresponding with the value of said characteristic parameter for their respective solution. .Iaddend..Iadd. 27. An apparatus as claimed in claim 24 wherein said calculation means comprises subtraction means for comparing and taking the difference between said first and second electrical signals and for storing the difference value thereby obtained, and division means for dividing the value of said third electrical signal by said stored difference value to obtain said standardizing scale factor signal. .Iaddend..Iadd. 28. An apparatus as claimed in claim 24 wherein said calculation means comprises multiplication means for successively multiplying each of said fourth electrical signals by said scale factor signal. .Iaddend..Iadd. 29. An automatic method for determining the concentration of a substance in a succession of test solutions which comprises the steps of generating a first electrical signal having a value representative of a parameter characteristic of a blank solution and generating a second electrical signal having a value representative of said parameter for a standard solution having a known concentration of the substance therein, generating and storing a third electrical signal having a value representing the known concentration of the substance in said standard solution, generating a standardizing scale factor signal with calculation means for arithmetically operating automatically on said first, second, and third electrical signals, successively generating a fourth electrical signal for each of said test solutions, each of said fourth signals having a value representative of said parameter of its respective test solution, and multiplying with multiplication means the scale factor signal by each of said fourth electrical signals to obtain a succession of output signals each having a value of the substance concentration for one of said test solutions. .Iaddend..Iadd. 30. An automatic method as claimed in claim 29 wherein said standardizing scale factor signal has a value representative of the ratio of the concentration of the substance in said standard solution over the difference between the standard solution and blank solution parameter values. .Iaddend..Iadd. 31. An automatic method as claimed in claim 29 wherein said step of generating said scale factor signal comprises the steps of comparing and taking the difference between said first and second electrical signals and dividing the difference value thereby obtained into the value of said third electrical signal to obtain said standardizing scale factor signal. .Iaddend..Iadd. 32. An apparatus for determining the concentration of a substance in each of a plurality of test solutions comprising analyzation means for generating a first electrical signal having a value representative of a parameter characteristic of a first blank solution and for generating a second electrical signal having a value representative of said parameter for a standard solution having a known concentration of the substance therein, storage means for generating and storing a third electrical signal having a value representing the known concentration of the substance in said standard solution, and calculation means for automatically operating arithmetically on said first, second, and third electrical signals to generate a standardizing scale factor signal, said analyzation means being also for successively generating a series of fourth electrical signals each having a value representative of said parameter for one of said test solutions and a series of fifth electrical signals each having a value representative of said parameter for one of a plurality of second blank solutions each corresponding with one of said test solutions, and said calculation means also comprises subtraction means for successively comparing and taking the difference between each of said fourth electrical signals and the fifth electrical signal corresponding thereto and means for arithmetically operating on said successively obtained difference values with said scale factor signal to generate a series of output signals each having a value of the substance concentration in one of said test solutions. .Iaddend..Iadd. 33. An apparatus as claimed in claim 32 wherein said standardizing scale factor signal has a value representative of the ratio of the concentration of the substance in said standard solution over the difference between said standard solution and first blank solution parameter values. .Iaddend. .Iadd. 34. An automatic method for determining the concentration of a substance in a succession of test solutions which comprises the steps of generating a first electrical signal having a value representative of a parameter characteristic of a first blank solution and generating a second electrical signal having a value representative of said parameter for a standard solution having a known concentration of the substance therein, generating and storing a third electrical signal having a value representing the known concentration of the substance in said standard solution, generating a standardizing scale factor signal with calculation means for arithmetically operating automatically on said first, second, and third electrical signals, successively generating a fourth electrical signal for each of said test solutions and a fifth electrical signal for each of a plurality of second blank solutions each corresponding with one of said test solutions, said fourth and fifth signals each having a value representative of said parameter of its respective solution, successively comparing and taking the difference between each of said fourth signals and the fifth electrical signal corresponding thereto, and arithmetically operating on said successively obtained difference values with the value of said scale factor signal to obtain a series of output signals each having a value of the substance concentration in one of said test solutions. .Iaddend. .Iadd. 35. An apparatus for determining the rate of reaction of a known reagent with a sample solution having a quantity of a reacting substance therein, comprising analyzation means for generating a first electrical signal having a value representative of a parameter characteristic of a standard solution having a known concentration of the substance and said known reagent therein, and for generating a second electrical signal having a value representative of said parameter for said standard solution at the end of a preselected time interval after generation of said first electrical signal; storage means for generating and storing a third electrical signal having a value representative of the known concentration of the substance in said standard solution; calculation means for automatically operating arithmetically on said first, second, and third electrical signals for generating a standardizing scale factor signal; said analyzation means being also for generating a fourth electrical signal having a value representative of said parameter for a test solution having the sample solution and said known reagent therein, and for generating a fifth electrical signal having a value representative of said parameter for said test solution at the end of a preselected time interval after generation of said fourth signal, said test solution time interval being equal to the standard solution time interval; and said calculation means also comprising subtraction means for comparing and taking the difference between said fourth and fifth electrical signals and arithmetic means for arithmetically operating on said difference value with said scale factor signal to obtain an output signal having a value of the rate of reaction of the reagent with the sample solution. .Iaddend..Iadd. 36. An apparatus as set forth in claim 35 wherein said calculation means comprises subtraction means for comparing and taking the difference between said first and second electrical signals, and division means for dividing the resultant difference value into the value of said third electrical signal to obtain the value of said standardizing scale factor signal.