Two Beam Alternating Light Colorimeter

The invention concerns a two beam alternating light colorimeter consisting of an illumination lens system and a control device, which, with the help of two stationary reflecting mirrors, deflects the measuring beam which is produced by a light source in alternating fashion through a first measuring cell and following this through a second measuring cell onto a common light sensitive element or cell. A measuring and evaluating circuit is also provided which is connected with the light sensitive element.

The advantage of a two beam alternating light colorimeter of this sort with respect to the other known one beam and two beam colorimeters consists in the use of a single radiation deflector in the form of a light sensitive element for the measuring and comparing beam signal. By means of the use of two measuring cells conducting the object liquid wherein one has a comparatively great thickness and the other displays only a half thickness, it becomes possible to compensate the measured value falsifications which are brought about by means of dirt accumulations of the cell windows. By means of the use of measuring cells of the same layer thickness wherein one contains the object liquid and the other contains a reactive fluid, it becomes possible to compensate the reactive components. By means of processing of the electrical measuring signals according to the photometric law of absorption, it becomes possible to determine the concentration of the components which are to be measured in the object liquid. The known two beam, alternating light colorimeters possess a control device which guides the measuring beam produced by an illumination lens system as an alternating pulse first through a first measuring cell and following this through a second measuring cell. For this, usually a rotary shutter (chopper disc) is used, where, by means of a mirror system, the measuring beam which was produced by the illumination lens system is directed to the cell windows of the two measuring cells. The measuring signal which was provided by the single photoresistor or respectively, light sensitive element is conveyed to a measuring circuit where the output voltage of the measuring circuit is a measurement for the concentration of the object liquid.

A two beam chopped light colorimeter of this kind became known through German OS 2,536,188, incorporated herein by reference, in the case of which in the path of the measuring beam which is coming from the illumination lens system, a semitransparent mirror is arranged at an angle of 45.degree.. In this way, the portion of the measuring beam which is reflected by the semitransparent mirror is deflected by 90.degree. relative to the portion of the measuring beam which is allowed to pass through. By means of a respective additional mirror in the optical path of both partial measuring beams, these are deflected to the light sensitive elements. Since both partial beams constantly act upon the light sensitive element, a rotating shutter is provided which brings the two beams into a chopped effect. Also, synchronizing switches must be provided which must be controlled in dependence upon the rotating shutter disc. With the help of these synchronizing switches, the output signals of the measuring beams are provided to corresponding analog memories from which they are supplied for further evaluation.

This known two beam alternating colorimeter requires a significant expenditure for the mechanical arrangement and electronics on the one hand because of the rotating shutter and on the other hand because of the storage of both signals.

It is an object of the invention to create a two-beam alternating light colorimeter which is less complex and expensive, and thus is also less susceptible to interference than the known colorimeters. This problem is solved according to the invention wherein the control device is a mirror which is pivotable into the beam path of the measuring beam. This mirror deflects the measuring beam which was produced by the light source by 90.degree. in a preferred embodiment.

With respect to the known two beam alternating light colorimeters, the one according to the invention displays the significant advantage that no rotating parts are used which necessarily are subject to maintenance and wear. Further, with respect to the colorimeter which became known with German OS 2,536,188 incorporated herein by reference, also the advantage is attained that no semitransparent mirror needs to be used. Since mirrors of this kind cannot divide the measuring beam in precisely the same fashion, additional adjusting techniques must be resorted to. Also, a particular advantage with respect to the known colorimeters is that in the case of the two beam-alternating light colorimeter according to the invention, only one measured value memory is used since neither oscillating parts nor rotary shutters are used.

In a manner which is essentially known, a current-voltage converter is connected after the photo sensitive element, the output of which converter is connectable in dependence upon the mirror position on the one hand directly via an analog memory and on the other hand indirectly to the inputs of a computing circuit. The computer circuit delivers an output voltage which corresponds to the function k.multidot.log (Um/Ur), whereby k is a constant and Um and Ur are voltages which are proportional to the intensity of the two measuring beams Ir and Im.

FIG. 1 shows the principle construction of the two beam-alternating light colorimeter of the invention;

FIG. 2 shows the principle of the cell filling; and

FIG. 3 shows a basic evaluating circuit.

According to FIG. 1, the two beam alternating or chopped light colorimeter consists of a housing 1 with an illumination lens system 2 which is installed in a wall portion. The illuminating lens system consists of a lamp 3, in particular a halogen lamp, two lenses 4 and 6, a shutter 5, and an interference filter 7. The optical axis of the measuring beam is designated 8. The measuring beam 8 is guided directly to a measuring cell 9, from which it exits after corresponding absorption, as a reference beam Ir, which is guided via a reflecting mirror 10 to a photo sensitive element 11.

In the vicinity of the optical axis 8 of the measuring beam, a mirror 13 is arranged which is pivotable around an axis 12 by 45.degree. relative to the optical axis 8 of the measuring beam. The measuring beam now experiences a deflection of 90.degree. and is guided via a further stationary mirror 14 to a measuring cell 15 with double the thickness of the measuring cell 9. From here it also proceeds as measuring beam Im to the photo sensitive element 11. In a separated space 16 the electronics are housed so that the total device forms a compact unit which can be housed relatively easily in an automatic analysis unit.

As FIG. 2a shows, the two measuring cells 9 and 15 are connected via hose pipes 17 and 18 with a common suction pipe 19 which dips into a container 20 in which the liquid to be tested is located. The container 20 can be a titrating container which can be provided with a stirring apparatus or such. The upper part of the two measuring cells 9 and 15 is connected via connection pipes 21 and 22 with a common pipe 23 connected with a syphon 24, which, for example, can be a dosaging syringe. With the help of the syphon 24, the sample is taken from the container 20 and conveyed into the cells 9 and 15.

The two measuring cells 9 and 15 can, however, also be connected one after the other and when necessary can also have the test liquid flowing through continuously.

As FIG. 2b shows, the measuring cells 9 and 15' can have the same layer thickness wherein the measuring cell 9 contains the measuring solution 20 and the measuring cell 15' contains a reference solution 20'. For this system a further dosaging syringe 24' is necessary.

FIG. 3 shows the measuring and evaluating circuit. The photo sensitive element 11 is connected with the input of a current-voltage converter 25. The output of the converter 25 is, on the one hand, connected directly via a line 26 with the one input of a computing circuit 27 and also is connected via a switching element 28 and an analog memory 29 with a second input of the computing circuit 27. The analog memory 29 consists of a capacitor 30 and an amplifier 31 with high resistance input. The switch 28 is activated corresponding to the position of the pivoting mirror 13. The switch position of the switch 28 according to FIG. 3 corresponds to the position of the mirror 13 according to FIG. 1. This means that the light beam, which is directed via the optical axis 8, penetrates only the measuring cell 9 and then proceeds via the mirror 10 to photo sensitive element 11.

The intensity Ir produces a current which is changed via the current-voltage converter 25 into a voltage Ur which corresponds to this. Via the closed switch 28, also the capacitor 30 is charged with this voltage. This voltage also is entirely present at the output of the amplifier 31 and it is supplied to the computing circuit 27. After the capacitor 30 has stored the voltage value Ur, the mirror 13 is pivoted into the position indicated by the broken line according to FIG. 1, whereby the light beam which enters via the optical axis 8 is conducted on to the mirror 14 and from there further through the measuring cell 15 to the photo sensitive element 11. With activation of the mirror 13 the switch 28 is opened, so that the corresponding signal Um which was released by the current-voltage converter is placed directly at the disposal of the computing circuit 27. The activation of switch 28 by the position of mirror 13 may be accomplished by any well known mechanical linkage. The computing circuit 27 now evaluates both signals. It is designed such that at the output, a signal U is released which is proportional to the product k.multidot.log Um/Ur. This signal is so constructed that it is proportional to the absorption of the solution and thus to the concentration of the substance which brings about the measured color intensity. This is attained by means of corresponding programming of the computing circuit 27. Such a computing circuit is known from U.S. Pat. No. 4,092,069 at A6 in FIG. 1, incorporated herein by reference.

Although various minor modifications may be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon, all such embodiments as reasonably and properly come within the scope of our contribution to the art.