US3760185A - System for linearizing signals - Google Patents

Abstract

A system for linearizing a logarithmic signal provided by a colorimeter photocell or the like and for applying the linearized output signal therefrom to a strip recorder or other storage means, the system includes a double diffused transistor which is coupled to a plurality of amplifiers in a manner to utilize the logarithmic relationship between the emitter-base voltage and collector current of said transistor while at the same decreasing linearity error of said photocell.

Description

United States Patent 1 Green 1 Sept. 18, 1973 1 SYSTEM FOR LINEARIZING SIGNALS Primar Examiner-James w. Lawrence Assistant ExaminerT. N. Grigsby [75] Inventor Aaron Attorney-Donald Brown et al. [73] Assignee: Knobelsdorff Instruments Incorporated, Natsch, Mass. 7 I n [22] Filed: Aug. 18, 1972 [57] ABSTRACT 2 Appl 231 73 A system for linearizing a logarithmic signal provided by a colorimeter photocell or the like and for applying the linearized output signal therefrom to a strip re- 52] 0.8. CI. 250/226, 307/230 comer or other Storage means the System includes a [5 U f 0 1 3/34 350, 3 7/12 double diffused transistor which is coupled to a plural- [58] Field of Search 330/32; 324/124; y of amplifiers in a manner to utilize the logarithmic 307/230; 250/226 relationship between the emitter-base voltage and collector current of said transistor while at the same de- [56] References cued creasing linearity error of said photocell.

UNITED STATES PATENTS 3,237,028 2/1966 Gibbons 307/230 U 3,540,825 11/1970 Grojean 250/226 X 10 Claims, 1 Drawing Figure as LENS SAMPLE SCALE ADJUST. TO SLIDE REAGENT LOW l 34 g l3 I4 l RECORDER l5 n I HlGH 45 23c 23 24 24c '1' W V '1 24:. 1 W

I 4o 5 V 2; an 46 42 22 V I go PATENTEB SE?! 8 I973 mmomoomm BACKGROUND OF THE DISCLOSURE This invention is directed to a system for linearizing signals and is more particularly directed to a new and improved system for taking the logarithm of an input electrical signal such as a signal provided by a photocell of a system sold by Technicon Instruments Corporation, Chauncey, New York and distributed under the trademark AUTO ANALYZER.

The AUTO ANALYZER is a system which continuously measures and compares on a moving graph, the level of concentration of a given component in a test solution against a known concentration of that compo-' nent in a standard control solution.

In said system, samples to be analyzed are picked up, pumped along and mixed with a flowing stream of dilucut. The diluted sample then moves through a dialyzer where its diffusable constituents are separated and feed into a flowing reagent stream.

In one of its applications the stream is passed through a colorimeter for tests involving color reactions in which light is passed through the samples to generate a signal representing the intensity of light passing through the moving sample at specific wave lengths. The output signal from the AUTO ANALYZER is then plotted on a recorder (strip chart). For a more detailed explanation of said AUTO ANALYZER system refer ence may be had to the brochure entitled Automation Brought to Analytical Chemistry copyright 1958 by Technicon Instruments Corporation, Chauncey, New York.

Since concentration (according to Beers Law) is a logarithmic rather than linear function, the graphic presentation of the sample concentration is therefore normally a logarithmic presentation.

Although a logarithmic presentation maybe used it is difficult to convert since the output must be plotted on logarithmic paper and accordingly direct linear recording has become a necessity in order to increase the usability of the system data.

In order to produce the linearized output, Technicon Instruments Corporation as well as others have provided various schemes for linearizing concentration plots. Although such systems have found their place there has developed a need for a new and improved lower cost scheme for accomplishing the above, particularly one that could be sold for less than half the cost of presently available systems.

Accordingly, this invention provides a new and im proved system for linearizing logarithmic electrical signals. The system of this inventica is not only relatively inexpensive but may be easily installed in the AUTO ANALYZER system by the user without the requirement of experts. The system of this invention also enhances the ability of the user to make more accurate readings in less time as well as facilitating the ability of the user to trouble shoot the entire analytical train of the AUTO ANALYZER subsystems as well as the reagents used therein.

DESCRIPTION OF TI-IE DRAWINGS The single FIGURE illustrates both in block and schematic format the preferred embodiment of the invention used in conjunction with the AUTO ANALY- ZER system.

2 DETAILED DESCRIPTION OF THE DISCLOSURE Reference should now be had to the figure for a description of the preferred embodiment of the invention. At 10 there is shown in block form the construction of a typical colorimeter of the type sold by Technicon Instruments Corporation under lIIllC trademark AUTO ANALYZER.

The colorimeter comprises a source of voltage derived from a6 volt (without load) stabilizer 11 coupled to 115 volt AC. A lamp (prefocused) is shown at 12 and is coupled to the stabilizer 11.. The light from lamp 12 performs two functions, namely to generate a reference signal for a recorder of the typical AUTO ANA- LYZER system 36 and to permit light to be directed against an unknown sample or control sample passing in a flow curvette shown at 14 which is constructed to permit light focused thereon by a mirror 13 to pass therethrough and be detected by a photocell 15.

The light detected by the photocell 15 indicates transmission of light through the sample and thus provides a measure of sample concentration in terms of the logarithm of light passage through the sample.

The reference signal is at the same time developed using a columating lens system 16 and a photocell 17. The colorimeter also preferably includes interference filters (not shown) as well as focusing apertures all conventional in the AUTO ANALYZER system previously mentioned.

Reference should now be had to the Linearizing system of this invention shown at 19. The linearizer is in reality a logarithmic converter which converts the logarithmic signal provided by the colorimeter to a linear signal by taking the log thereof (it is well known and should be understood that the logarithm of a logarithmic signal to the same base provides a linear signal).

The logarithmic converter of this invention utilizes the logarithmic relationship between two double diffused transistors emitter-base voltage and collector current.

More particularly the linearizer comprises two operational amplifiers 21 and 22 (operated in the inverting mode) as for example of type LM 308 sold by Babylon Electronics of Pasadena, California, coupled to double diffused transistors 23 and 24 preferably of the type generally called dual NPNs sold conventionally as 2N 2060 or the like.

It should also be understood that other double diffused transistors having the aforementioned logarithmic relationship between emitter-base voltage and collector current may also be used.

In this circuit transistor 24 acts as the logging transistor to develop the logarithmic'function and thus linearizes the input signal while transistor 23 provides offset voltage for transistor 24 base-emitter turn on voltage.

As shown in this figure transistors 23 and 24 include emitters 23a and 240 respectively, bases 23b and 24b are collectors 23c and 240. The collector 240 of transistor 24 is coupled to photocell 15 as well as to the negative input of operational amplifier 21. At 27 and 30 there are provided capacitors which are inserted in the circuit to decrease loop gain at high frequencies to insure system stability. In addition, there are provided capacitors 25 and 26 coupled to operational amplifiers 21 and 22 respectively to provide for frequency compensation of the amplifiers 21 and 22..

The circuit also includes a resistor 28 coupled between the amplifier 21 output and the emitters 23a and 24a of the transistors 23 and 24 respectively, which provides for impedance matching between amplifier 21 and its loading ground referred and amplifier 22 output referred.

At 31 and 32 there are provided a pair of resistors for establishing the collector 230 current of transistor 23. Resistor 32 is preferably a semi log taper potentiometer (e.g., made by Ohmite) adjustable over several decades while resistor 31 establishes the maximum collector current of transistor 23. As may also be seen the base 23b of the transistor 23 is grounded.

A temperature compensation resistor is provided at 20 to compensate for the logging transistor 23 temperature sensitivity. The output from the linearizer is provided at one end of a divider resistor 29 and is derived from the base 24b of transistor 24 coupled to the resistors 29 and 20.

In operation the cell provides a current which flows into the amplifier 21 which acts as a zero impedance load. In its function as a zero impedance load, amplifier 21 maintains the voltage across the emitter-base junction of transistor 24 which is generated by the photocell 15 current passing through the collector 24c. This then allows logarithmic conversion of the input current to be reflected across the base-emitter junction of transistor 24 as a voltage.

At the same time there is provided a reference current source adjustable over several decades to correspond to the reagent base level of imput current which would be present in the system when light passes through the curvette 14 in the presence of reagent alone. This is preferably set before putting through samples with reagent by adjusting the output to zero by adjustment of resistor 32 in the presence of reagent alone passing through the system.

Thus reference current is fed into amplifier 22 also operating as a zero impedance load and thus causes a voltage to be generated across the base-emitter junction of transistor 23. The voltages thus generated across both transistor 23 and 24 (base to emitter junction) are subtracted one from the other and generates an output signal at the junction of resistor 29 and amplifier 22 which represents the logarithm of the input logarithmic signal to the same base as a linear output.

As a further improvement in this invention there is provided a new and improved transformerless passive voltage regulated supply 40 which may be coupled directly across and be operated from the colorimeter exiter lamp voltage (4.8 V.AC in the Auto Analyzer System).

In the preferred embodiment thereof the exciter lamp voltage is converted to i- 7 volts DC by two diodes 41 and 42 each of which charges a separate high capacitance electrolytic capacitor shown at 43 and 44 to the peak value of the original AC signal. Filtering is then accomplished using current regulating diodes 45 and 46 having very high dynamic impedances, connected in series with integrated circuit zeners (diodes) 47 and 48 having very low dynamic impedance.

in this manner a very large noise and ripple reduction is then realized on the signal across the zeners and in addition the integrated circuit zeners afford good voltage regulation due to their exceptionally sharp voltage knees at the current levels in the circuit (about 4 rn.a.). The voltage supply 40 is coupled to the linearizer 19 as shown at V+ and V.

The linearizer output is then coupled to the Auto Analyzer recording system or recorder 36 which will now plot a linearized curve representing sample concentration. The linearizer of the invention may be coupled to the recorder 36 by making a few minor wiring changes as shown generally at 34 so that now the colorimeter, linearizer and recorder are coupled together as shown through the scale adjust (10 turn) potentionmeter already present in the Auto Analyzer recorder and a zero set resistor 34 also already present in the Auto Analyzer recorder. The input line marked slide indicates connections to the recorder slide wire whereas the lines marked high and low indicate inputs to the chopper present in the Auto Analyzer recording system.

Thus by a few simple changes in the Auto Analyzer recorder (recording system) wiring, the linearizer of this invention may now be directly coupled between the Auto Analyzer colorimeter and recorder to provide a linear graphical presentation.

Although it is to be understood that many modifications may be made to the above circuit, the following circuit values may be utilized to provide the logarithmic converter 19 and the power supply 40.

Transistors 23 and 24 A Dual NPN 2N 2060 Operational amplifiers 21 and 22 LM 308 Resistor 31 68 K ohms Resistor 32 25 K ohms 10 percent to center Resistor 20 1 K ohms 0.3 percent C Resistor 28 3.3 K ohms Resistor 29 6.8 K ohms Capacitors 30 and 27 0.033 mf Capacitors 26 and 27 330 pf Current Regulator Diodes 4S and 46 MCL1304 Zeners 47 and 48 LM 103 Capacitors 43 and 44 500mf 10v Diodes 41 and 42 la, 50v

It will thus be seen that the objects set forth above and those made apparent from the preceding description are efficiently obtained and since certain changes may be made in the above devices without departing from the scope of the invention, it is intended that all matter contained in the above description as shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

I claim:

1. A system for linearizing signals for use with a system including a colorimeter or the like providing a first logarithmic signal representing the passage of light through the combination of a sample and a reagent, the converter comprising a first double diffused transistor for taking the logarithm of said logarithmic signal to generate a first signal, means coupled to said transistor for generating a reference signal representative of the amount of reagent in combination with said sample, and means for subtracting the reference signal from said first signal to provide a third signal representing the properties of the sample in a linearized presentation.

2. A system according to claim 1 which includes a second double diffused transistor forming part of the means for generating the reference signal, said second transistor coupled to said first double diffused transistor, the transistors being coupled in circuit so that the voltage developed across the base to emitter junctions of the transistors are subtracted one from the other.

3. A system according to claim 2 in which direct current power for the system is derived from the colorimeter.

4. In combination, first and second double diffused transistors having their emitters coupled together, means for coupling the collector of the first transistor to an input signal, means for coupling a reference signal generating means to the collector of the second transistor so as to develop a reference voltage between the emitter and the grounded base of the second transistor, and means for subtracting the emitter-base voltage developed by said second transistor from the emitter-base voltage developed by said first transistor.

5. A combination according to claim 4 in which an operation amplifier operating in the inverting mode is coupled at its input to the means for coupling the collector of the first transistor to an input signal and at its output to the emitters of both transistors by an impedance matching resistor.

6. A combination according to claim 4 in which the base of the first transistor is coupled to the junction point of a pair of resistors and in which one of the resistors is coupled to the output of a second operational amplifier having an input thereof coupled to said reference signal generating means.

7. A combination according to claim 5 in which one of the pair of resistors is constructed to compensate for temperature change current effects occurring in the first transistor.

8. In combination, a colorimeter having an exciting lamp developing an AC voltage accross the leads thereof, a DC rectifier system for providing and DC voltages, sad rectifier system comprises rectifier means for providing DC positive and negative voltages, current regulating diodes coupled to the positive and negative voltages to filter the voltage, said diodes having very high dynamic impedances, and said diodes coupled in series with a pair of series connected zener diodes having very low dynamic impedances and means powered by the rectifier system for taking the logarithm of signals provided by said calorimeter.

9. In combination according to claim 7 in which the zener diodes are of the integrated circuit type.

10. In a combination according to claim 8 in which the zener diodes are coupled to each other such that the p doped region of one is coupled to the n doped region of the other.

Claims (10)

1. A system for linearizing signals for use with a system including a colorimeter or the like providing a first logarithmic signal representing the passage of light through the combination of a sample and a reagent, the converter comprising a first double diffused transistor for taking the logarithm of said logarithmic signal to generate a first signal, means coupled to said transistor for generating a reference signal representative of the amount of reagent in combination with said sample, and means for subtracting the reference signal from said first signal to provide a third signal representing the properties of the sample in a linearized presentation.

2. A system according to claim 1 which includes a second double diffused transistor forming part of the means for generating the reference signal, said second transistor coupled to said first double diffused transistor, the transistors being coupled in circuit so that the voltage developed across the base to emitter junctions of the transistors are subtracted one from the other.

3. A system according to claim 2 in which direct current power for the system is derived from the colorimeter.

4. In combination, first and second double diffused transistors having their emitters coupled together, means for coupling the collector of the first transistor to an input signal, means for coupling a reference signal generating means to the collector of the second transistor so as to develop a reference voltage between the emitter and the grounded base of the second transistor, and means for subtracting the emitter-base voltage developed by said second transistor from the emitter-base voltage developed by said first transistor.

5. A combination according to claim 4 in which an operation amplifier operating in the inverting mode is coupled at its input to the means for coupling the collector of the first transistor to an input signal and at its output to the emitters of both transistors by an impedance matching resistor.

6. A combination according to claim 4 in which the base of the first transistor is coupled to the junction point of a pair of resistors and in which one of the resistors is coupled to the output of a second operational amplifier having an input thereof coupled to said reference signal generating means.

7. A combination according to claim 5 in which one of the pair of resistors is constructed to compensate for temperature change current effectS occurring in the first transistor.

8. In combination, a colorimeter having an exciting lamp developing an AC voltage accross the leads thereof, a DC rectifier system for providing + and - DC voltages, sad rectifier system comprises rectifier means for providing DC positive and negative voltages, current regulating diodes coupled to the positive and negative voltages to filter the voltage, said diodes having very high dynamic impedances, and said diodes coupled in series with a pair of series connected zener diodes having very low dynamic impedances and means powered by the rectifier system for taking the logarithm of signals provided by said colorimeter.

9. In combination according to claim 7 in which the zener diodes are of the integrated circuit type.

10. In a combination according to claim 8 in which the zener diodes are coupled to each other such that the p doped region of one is coupled to the n doped region of the other.

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