DE2201384A1 - Two-beam spectrophotometer - Google Patents

Description

Two-beam spectrophotometer

The invention relates to a two-beam spectrophotometer, in which a radiation source, an optical system containing a monochromator with entrance and exit slit, and a radiation receiver are provided, the optical system generating a measuring and a comparison beam, which are collected on the radiation receiver after passing through the monochromator.

Two-beam spectrophotometers are devices in which two light bundles, a measuring or sample beam, are produced from a light source and a comparison beam, go out. The sample beam passes through a sample cuvette that contains a sample to be examined Substance is filled, while the comparison light beam generally passes through a comparison sample cell. The two bundles are then arranged over suitable mirrors and a "chopper" alternating in time in a common beam path onto the entry slit of a monochromator directed. The chopper is a rotating sector mirror that lets through one light beam during one phase and during another phase the other light beam into the same

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Poetecheckkonto Essen 47247 · Commerzbank AG Düsseldorf, Deposltenkaaee main station

Direction reflected. The monochromator can be a grating monochromator be or a prism monochromator, which splits the radiation spectrally.

Radiation of a narrow wavelength range occurs at an exit slit the end. The exit slit is directed to a detector, e.g. a thermocouple, via mostly aspherical concave mirrors. pictured. By swiveling optical elements in the monochromator, e.g. the grating or a Littrow mirror, the spectrum is scanned.

Such dual-beam spectrophotometers are available as commercial devices. These are relatively large and heavy devices that are, for example, set up firmly on a laboratory table. Sample cell and comparison sample cell are in Arranged next to one another in a relatively large sample space, as viewed in the direction of irradiation, and specifically in separate Brackets. The sample space separates a lamp housing with the associated optics from the other parts of the optical system.

The known commercial two-beam spectrophotometers make it necessary to take samples of substances to be examined to the laboratory in which the device is installed. This is associated with loss of time and carries the risk of mix-ups in itself.

In the known spectrophotometers, the optical elements and thus the beam cross-sections are quite large. Do you want do not work with excessively large cuvettes, then you are forced to image the radiation source in the cuvette or in its immediate vicinity. This leads to the following disadvantages:

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a) The intermediate image of the radiation source requires additional optical components (taxation of the Spectrometer).

b) The intermediate figure requires because of the additional Fret cuts additional space, which makes the Spectrometer is enlarged.

c) In the image of the radiation source is the irradiance and thus the load on the sample, in particular the sample heating, quite large.

d) As a result of the additional bundle sections, the entire optical path length between the radiation source and receiver enlarged. As a result, the atmospheric radiation absorption is very high, which is known in Way (especially due to the absorption effect of atmospheric water vapor) to difficulties leads to how rapidly fluctuating radiant energy, incompensation, etc.

In the known spectrophotometers, it is customary for sample and comparison beams to run parallel to one another and, as already mentioned, place the two cuvettes next to each other in the radiation beam. It was too already mentioned that the cuvettes are arranged in a single and relatively large sample space and therefore require separate brackets. Such an arrangement is also disadvantageous in another respect: In order to align the two bundles parallel to one another, plane mirrors are often used. The merging of the Bundles aligned parallel to each other often happens

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with plane mirrors that deflect the bundle in a suitable manner. In addition - and now independent of the parallel run of the two bundles - plane mirrors are often used in the same beam path, e.g. immediately in front of or behind the monochromator.

The plane mirrors therefore either serve to be able to arrange sample bundles and comparison bundles parallel to one another, or to move the entire beam path closer together. Sometimes they are also required to make the different optical Groups such as the radiation source part, the sample space, the photometer part, the monochromator and the receiver part do not differ spatially to cross over. In contrast, these plane mirrors have no essential task for the function of the device, such as E.g. imaging of the radiation source on the entrance slit or on the receiver. So optical elements are used which require a certain amount of effort without being absolutely necessary for the function of the device.

With the known spectrophotometers it is still necessary to map the exit slit very much reduced on the receiver, since the signal-to-noise ratio is known The smaller the recipient, the cheaper it is. One large reduction requires special measures, such as the use of an ellipsoid mirror. Are ellipsoidal mirrors considerably more expensive than spherical mirrors.

It is necessary to change the slit width as a function of the wavelength in order to have an approximately constant radiation flux to let the recipient act. Of course, the intensity level can also be controlled as a function of the wavelength, for example will. In any case, control or re-

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gel systems are necessary so that the device can be used e.g. during registration can work under approximately the same energy conditions, because otherwise the display will temporarily turn on crawling behavior (if the energy is too low) or an overshoot (if the energy is too high). The known Regulation and control systems are quite complex. In addition, e.g. in the case of a gap width stiffening the gap jaws, which are moved in a known manner in the direction of the gap width, are moved very precisely, since the gap widths are generally very small. The required precision is in the order of magnitude of some around. It is evident that such a movement is very laborious.

Modern devices prefer to work with grids. The advantages over prism devices are well known: Higher dispersion and thus wider gaps and thus higher radiant power, or vice versa, with the same resolution same radiation power, higher resolution. In addition, gratings show a uniform dispersion than prisms, what leads to a less pronounced change in the spectral slit widths with the wavelength.

In comparison with prisms, however, gratings have the disadvantage that they have different orders, that is to say several wavelengths at the same time let the exit gap pass. It is therefore necessary to pre-decompose, e.g. by optical edge (for Working in the first order) or band filter (when working in higher orders). The filters must be one after the other be pivoted into the beam path at certain wavelengths. The filters therefore require their own Movement mechanism and its own control system. It is

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known for example, the filter in a holder to set, which are each connected to a rotary magnet. The rotary magnets are operated by microswitches switched on and off, which in turn are actuated by cams that move on one with the wavelength advance connected disc. This whole device is quite expensive.

In known spectrophotometers there are entry and exit slits of the monochromator is the same size. An optimal one Relationship between resolution and radiation flux can be do not achieve with it.

It is obvious that the rather large, movable components (Grid movement, measuring diaphragm movement, recorder drive) stable and therefore large transmission links and strong ones Require drive motors. The required electrical energy can only be achieved with relatively large and heavy components (e.g. transformers) are made available. The known devices are therefore necessarily quite large and difficult.

Sometimes it could also be perceived as a disadvantage that the devices are powered by an external power supply (mains connection). are dependent, although this disadvantage in the larger devices, which are generally fixed and installed, hardly matters.

The two-beam spectrophotometer according to the invention is characterized in that it is designed as a portable device (- £ 20 kg) of relatively small dimensions (volume < 30 1), the reduction in the light conductance and thus the

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Signal-to-noise ratio, which s in the device as compared with normal commercial equipment by reducing the dimensions and spacing erg ibt, by enlarging the aperture angle (V f / _BH <5 »8) and / or at least one of the two ( vertical and horizontal) field of view angle (f / h <18, spectral resolution> 1 cm with a wave number of 1000) is at least partially compensated, with "f" the collimator focal length, "B" and "H" width and height of the radiation beam at the grating and "h" is the gap height. The small dimensions have various advantages: The device is easy to handle and can be light and portable, since the small size alone makes it light. Since less material is used for almost all components, the price is reduced. Production is also cheaper in many cases. For example, a large number of small mirrors can be mirrored in one operation, while large mirrors can only be mirrored in small numbers at the same time or even have to be mirrored individually. Many components can be made very strong and robust with less effort compared to their size. Small components can sometimes be very simple in their construction. An example: A small mirror holder can essentially consist of a sturdy angle plate, while a larger mirror holder has to be made, for example, as a cast piece with reinforcing ribs.

It seems trivial to build a two-beam spectrophotometer of the known type very small. However, since the scaled Downsizing a spectrophotometer has a major negative impact on the specifications a small device is not obvious, especially for a specialist, but, on the contrary, is used when designing a new

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rates excluded from the start. The idea of the invention only makes sense if measures are taken to mitigate the negative effects on the specification. As a result, the specification reductions can be kept within such limits that a for many purposes still "A useful device is created. There is an interaction." between the measures mentioned, the small size of the device, the device price and the reduction in device specifications: The small device initially leads to a low price, but to reduced specifications, such that either the Specifications are completely inadequate or the price reductions are so small that they represent a loss of specification not equalize. The measures mentioned improve the specifications, downsize the device even further and lead partly also to a further reduction in price. In this way it is possible for the first time to have a small and cheap device to create with usable specifications, because one can find a usable compromise by means of the measures mentioned can choose between device dimensions, price and specifications.

It is evident that the use of light material leads to a further weight reduction of the device. Because of the small dimensions, lightweight materials can even be used there used where this is not possible with large devices for reasons of stability.

The use of light materials also appears trivial, but is initially not obvious, as it is with the known spectrophotometers For reasons of stability, for example, heavier materials often have to be used. Only the invention Small dimensions allow the use of lighter materials that would not be stable enough for large components.

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A spectrophotometer can be kept small by having a spectrometer of known make and size in its Structure and its essential components simply scaled down. It is known that the light guide value is reduced by the square of the reduction ratio. Reduced proportionally to the light guide value the signal-to-noise ratio, which is a measure of the performance of the device, among other things. Because this connection has obviously existed in the professional world, a technical prejudice to the effect that such Device would not provide usable spectra.

The light conductance can be calculated with dimensions otherwise given, in particular with given focal lengths and mirror distances, by increasing the opening angle and / or the field of view angle enlarged. These relationships are known per se. However, it is not necessary for large devices sometimes even undesirable, the opening angle and field of view angle up to the practically possible limit, because it also means expensive components, such as grids and aspherical ones Mirrors need to be enlarged. It's easier to just do the whole optical setup, especially the mirror spacing to enlarge, whereby, for example, one obtains wider gaps and thus a higher light guide value with the same resolution.

In contrast, the invention is based on the knowledge that in the case of small spectrometers, increasing the opening angle and / or field of view angle can achieve a very significant gain in performance without the need for components such as the grid will become excessively expensive. The cost of a grid can then still be a very small fraction of the cost for a grating of a spectrophotometer of the known size.

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The known spectrophotometers are very expensive. Such devices are therefore expected to have a high level of performance, e.g. with regard to the spectral resolution, even if for the majority of measurement problems a lower resolution is sufficient. The invention is based on the further knowledge that a small Waiver of resolution, which does not limit the usability of the device for most measurement problems, with one quite a considerable gain in light conductance is connected.

In the known spectrophotometers, the aperture angles and the vertical field of view angle (gap height) certain sizes. A further enlargement not only leads - as already mentioned - to an enlargement of the expensive components, such as grids, but also to a greater degree of blurring of the image, since the aberrations increase. The permissible uncertainty depends on the resolution, i.e. on the Gap width. Since the known spectrophotometers show a high resolution, the angles mentioned are also limited there.

It is known to use different spectrophotometers Set gap widths, e.g. in the form of switchable gap programs; however, the angles mentioned, which are based on the smallest gap width, remain constant. The radiation flux then changes proportionally to the square in a known manner the gap width.

In contrast, the feature of the invention of the angle enlargement is based on the knowledge that with optimal utilization of all optical data, a gain in light conductance value (or radiation flux) can be achieved which is considerably greater Dimensions than grows with the square of the gap width. Do you build

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borrowed a small, simple spectrophotometer that didn't it is only possible to optionally set a lower resolution, but rather that from the outset to a somewhat reduced one Resolution is designed, then you can see the opening angle and the vertical angle of view compared to the usual Increase values because you can adjust the blurring to the wider columns.

So here again there is an interaction between different ones features according to the invention: The device is scaled down. This reduces the light guide value. The gap width is increased slightly, which decreases the resolution a bit, but the light guide value is increased again. As a result of the wider column, the requirements for image sharpness are increased less. The gap height and the opening angle can be increased. This is the light guide value enlarged again.

The numerical examples given below will show in what strong and surprising even for a person skilled in the art The extent of the spectrophotometer of the known type and size has been reduced, taking into account the above relationships with only a slight reduction in performance.

First, however, the light guide value and the influence of the aperture angle and the field of view angle on the light guide value are explained in more detail.

The light conductance value is a quantity that links luminous flux and luminance in photometry. Located in front of a first diaphragm of the surface f. (aperture diaphragm of the optical system

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tems) is an area of luminance B, then the luminous flux through a second diaphragm (field of view diaphragm) of the area fp, which is opposite to the diaphragm diameter there is a sufficiently large distance a from the first diaphragm,

ca ^f 1 * ^f 2 . B If one sets the luminous flux in analogy to Ohm's law

equals an electric current and the luminance equals an electric voltage, then the expression corresponds

^f 1

a ²

a conductance, i.e. a reciprocal resistance. If a device is scaled down, e.g. by the factor 1/2, the two areas f, - and f ^ decrease to each 1/4, as well as the square of the distance. The conductance and thus the luminous flux is therefore reduced to 1/4, and the same applies to the signal-to-noise ratio. The signal-to-noise ratio but can be raised again by various measures. Namely, the opening angle can be increased once and on the other hand the angle of the field of view, i.e. slit width and slit height in relation to the focal lengths. That practically runs on a change of f ^. and f ~ in the above Relationship beyond. The possibilities of the two measures are limited by the requirements regarding image sharpness, spectral resolution, receiver size and aperture angle on the receiver. A widening of the column decreases for example the spectral resolution. However, both measures are very effective. The light guide value is proportional

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to the opening angle in the vertical section, to the opening angle in horizontal section and to the field of view angle in vertical section (gap height). It is still proportional to the square of the field of view angle in horizontal section (slit width). The gap width goes in as a square, because with one An increase in the width of the gap is associated with an increase in the spectral range used. However With the enlargement of the slit width, for precisely this reason, there is a reduction in the resolution, i.e. an increase the spectral width proportional to the angle of the field of view in the horizontal section.

In order to be able to estimate the possibilities quantitatively, the following numerical examples are given:

1. The mirror distances are reduced by half. All opening angles and field angles are enlarged by 20%. The spectral slit width increases by 20%. The luminous flux and thus the signal-to-noise ratio decreases 40%, i.e. it drops to 60%.

2. The mirror distances are reduced by half. The two opening angles and the vertical field of view angle is retained. The spectral slit width increases by a factor of 2 to. The radiation flux is retained.

3. The mirror distances are reduced to 1/4. The two opening angles and the vertical field of view angle are enlarged by 20%, the spectral slit width increases by a factor of 2. The radiation flux decreases by 58%, i.e. falls to 42%.

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4. The mirror distances are reduced to 1/4. The two opening angles and the vertical field of view angle remain. The spectral slit width increases by the factor 3. The radiation flux is reduced by 44%, i.e. drops to 56%.

5. The mirror distances are reduced to 1/4. The two opening angles and the vertical field of view angle remain. The spectral slit width increases by a factor of 4. The radiation flux remains.

These numerical examples show that if the mirror spacing is reduced to half or even to 1/4 still receives reasonable specifications for the device. In particular about the spectral slit width effectively compensate for the loss of radiation flux or at least keep it small. If no gas spectra but only liquid spectra are to be recorded and, in addition, no precision measurements, but only overview measurements are required, is an increase in the Spectral slit width around a factor of 2, 3 or 4 is quite acceptable.

In a known commercial device, the optical system occupies an area of about 50 cm 35 cm. At a Halving the linear dimension comes to about 25 cm χ 18 cm, if halved again to about 12 cm χ 9 cm. Albeit a reduction in the geometric dimensions the electrical and electronic components and the mechanical parts are not quite in the same proportion

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is achievable as with the optical system, it appears However, a reduction of the device dimensions to about 20 cm χ 15 cm with a height of 10 cm to 12 cm is quite possible. In this way, a portable, handy device can be produced without the optical properties of the device being impaired would be inadmissibly deteriorated.

The downsizing of the device while largely maintaining it the optical properties can be significantly increased by constructive measures with regard to the optical system be relieved.

These constructive measures can - individually or in combination or in partial combination - consist of the following:

a) The optical system of the device is used to image the radiation source one after the other only on the monochromator exit slit, the monochromator exit slit and the radiation receiver while avoiding further intermediate images.

b) Every optical element of the optical system either fulfills the function of a real image, or the dispersion or the superposition of the beam paths.

c) All images in the optical system are made by spherical mirrors.

d) The beam paths of the measuring and comparison beams are geometrically and optically congruent, and there is only a single rotating sector mirror (for bundling) used.

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e) Two light beams emanating from the radiation source in opposite directions

. are symmetrical to one, the light source and a circumferential sector mirror containing plane arranged concave mirror once directly and once after reflection at the sector mirror on the monochromator entrance slit collected.

f) The monochromator is a grating monochromator in Czerny-Turner or Ebert arrangement, however preferably in an Ebert arrangement.

g) The exit slit of the monochromator is opened by a spherical concave mirror a radiation receiver, e.g. a thermocouple.

h) A sample cell and a comparison sample cell are one behind the other in the direction of irradiation symmetrical to the radiation source provided in between in the beam paths of the two Arranged light bundle.

i) For samples and comparison samples are separate Sample spaces are provided, the dimensions of which are essentially those of the sample cuvette and the Comparative sample cuvette correspond so that the cuvettes are held in it with a positive fit.

j) Sample and comparison sample cells are from above can be used in the rehearsal rooms.

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k) The sample chambers have funnel-like expansions in the area of the insertion openings, which make it easier to insert the cuvette.

1) ^ i _n tritts- and exit slit of the Ebert or Czerny-Turner monochromator are formed by diametrically opposed portions of circular-arc column in a Spaltrad. The split wheel can be rotated synchronously with the wavelength or the number of waves. The gap width changes according to the required gap program along the arc-shaped gap.

m) Optical pre-decomposition filters for suppression unwanted orders are firmly connected to the split wheel and occur when the split wheel rotates synchronously with the number of shafts one after the other in the beam path.

n) On the sector mirror, radial sector diaphragms are axially offset and provided on both sides of the radiation source immerse in the beam paths of the two light bundles and these with a frequency and phase position which cause the elimination of the sample's own radiation by measurement interrupt in relation to the sector mirror.

o) The device is operated by a battery.

p) The device contains a spring motor that drove the wave number of the spectrometer (rotation of the Grid, gap width control and abscissa feed of the recorder). Preferably

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the tensioning of the spring motor takes place in that after a previous registration the recorder is manually reset from the ending wave number to the starting wave number. Recorder, grille and gap width control are mechanically coupled to one another.

q) The radiation source is heated by a flame.

In a further embodiment of the invention, only those that are absolutely necessary for the function of the device are therefore used Light source images generated, i.e. on the monochromator entrance slit, on the monochromator exit slit and on the receiver. All other intermediate images, in particular also in the cuvette, are omitted. As a result, a true-to-scale reduction of a spectrometer is known In addition to its size, the following advantages are achieved:

The space requirement for the optical structure is further reduced because the additional radiation bundles which are not absolutely necessary and which of course take up a certain additional space, are not required for the intermediate images. The optical imaging elements required for this are also omitted, which not only results in a material . This leads to cost savings, but also simplifies the optical adjustment, the workload of which is approximately proportional to the number of optical elements. Inevitable imperfections in the adjustment have less of an effect, the fewer optical elements need to be adjusted. In addition, the entire optical path length between the radiation source and the receiver is no longer required for the additional intermediate images.

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lich bundle is further reduced, resulting in a large reduction in the adverse effects of the atmospheric Absorption (energy fluctuations, incompensation) leads.

The small bundle cross-sections allow an intermediate image dispense with the light source in the cuvette and place the cuvette e.g. near a pupil. Nevertheless, the cuvette does not have to be larger than in the known devices or can even be smaller. The relative excessive heating of the sample when the light source is imaged on the cuvette is avoided if such an image is not used. Here again there is a chain of favorable influences that do not exist with a normal reduction in size would be: The smaller bundles of radiation allow the usual intermediate image of the light source on the cuvette to eliminate, thereby the sample heating is reduced and the optical structure is in its entire dimensions even smaller and the device even cheaper; if the small device dimensions are given in terms of their size, you can increase the distance between the mirrors, focal lengths, etc. compared to a true-to-scale reduction and thus improve the specifications again a bit.

The influences of the inventive ideas are reciprocal. Neither the true-to-scale reduction nor the omission of intermediate images in the cuvette are each separate only makes sense because in one case there is none corresponding to the price Performance and with usable performance no drastic reduction of the device dimensions can be achieved and in the other case the cuvettes must be excessively large.

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The optical structure of the known devices does not only contain the absolutely necessary imaging elements still further imaging elements for further intermediate images, but also plane mirrors for bundle folding. These Planar mirrors that are not absolutely necessary for the function of the device are also omitted in the inventive concept Spectrometer. This also results in advantages, such as material reduction in price due to the elimination itself and relief adjustment.

The rotating sector mirror is also a plane mirror that serves for bundle folding. However, this bundle folding serves the purpose of the essential for the function of the device Beam merging. The rotating sector mirror is therefore not included in the mirror that is fundamentally dispensable and is also present in the device according to the invention.

In the known devices, aspherical mirrors are used, e.g. toroidal mirrors in photometer optics, parabolic mirrors in the Littrow monochromator and ellipsoid mirror in the receiver optics.

Since, in the device according to the invention, the light source is mapped directly onto the monochromator entrance slit, that is multiple images, whose image errors (e.g. spherical aberration) can add up, are omitted, and this one image only serves to illuminate the gap, spherical mirrors are completely sufficient for this purpose. as Monochromator, an Ebert monochromator is used, which also only requires a spherical mirror and even only shows its full potential with such a mirror. The same goes for a Czerny-Turner mono

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chromator with the only difference that then two spherical mirrors are needed. The use of a spherical mirror in the receiver optics can be as follows establish:

For a given radiated power, the smaller the receiver, the better the signal-to-noise ratio Recipient is. A practical, lower limit for the size of the receiver area is not only due to receiver technology Problems given, but also due to limitations in terms of illustration technology. The monochromator exit slit must be mapped to the receiver as much smaller as possible. This figure doesn't have to be absolutely be sharp, but the vast majority of the radiation must be concentrated on the receiving surface. When using a spherical mirror, the practically usable reduction ratio is mainly through the spherical aberration is limited. Something similar applies to an ellipsoidal mirror, but one can be said here Achieve a more favorable reduction ratio than with a spherical mirror. An even bigger reduction is in a very narrow framework, which is given by fundamental, physical relationships, in principle possible, but associated with an order of magnitude higher and not justifiable in practice. The optimum in terms of performance and effort is the use of the known spectrophotometers of an ellipsoidal mirror. For these reasons, one finds the known spectrophotometers in the receiver optics such mirrors. The receiving surfaces of the known receivers are adapted to these imaging conditions.

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The situation is different in the case of the one according to the invention small spectrophotometer. The monochromator exit slit is smaller from the start than with the known ones Devices. You can now also work with an optimal reduction and use smaller receivers. This has the advantage of increasing the signal-to-noise ratio. This use of ellipsoidal mirrors and a lot small receivers is well within the scope of the invention. But since the known receivers use the larger spectrophotometers are adapted and the creation of very small receivers requires considerable development effort, it is also sensible and, at least for the time being, particularly advantageous to use the existing receivers. Of the The exit slit then only needs to be mapped onto the receiver in a relatively small size. A spherical mirror, which is considerably cheaper than an ellipsoidal mirror, is sufficient for this. So it belongs to an embodiment of the invention to use only a spherical mirror in the receiver optics.

Here, too, a chain of favorable influences of the individual inventive ideas on one another can be seen. the Small dimensions of the optical structure also include a correspondingly small exit slit. This little one Gap only requires a relatively weakly reducing image on the receiver. This weakly diminishing Figure in turn allows the use of a spherical mirror, which in turn is associated with a price reduction is. This price reduction - along with other price reductions - allows the purchase of a to make small devices with somewhat reduced specifications worthwhile.

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With the known spectrophotometers one takes care that that the same number of reflective surfaces is present in the two beam paths in order to make the reflection losses in both beam paths equal to one another. However, the reflection losses on a mirror are on the one hand very low and on the other hand largely independent of the wavelength, so that there are no difficulties in finding different losses in the two beam paths e.g. Compensate trim panels. It simplifies the optical structure, the reflection of one bundle on the rotating sector mirror not to be compensated by an additional reflection of the other bundle. Accordingly, there is another Embodiment of the invention is to provide a different number of reflections in the two beam paths and in particular to allow the number of reflections to differ by 1, namely the reflection on the sector mirror in a beam path.

In this way, an additional mirror is saved, which is necessary with the known spectrophotometers, to optically compensate for the reflection losses in the two beam paths. Like the embodiment shows below, it is even possible to set up the photometer part in a particularly simple and compact manner. Even this measure is therefore used to make the device even smaller and cheaper without additional influences on the specifications close.

The known photometer optics can be divided into two groups:

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a) The radiation is already at the light source

divided into two bundles and behind the sample space by means of a rotating sector mirror spatially brought together again. The two beam paths are geometrically and optically mirror images of each other, so that the imaging errors even after the spatial merging (e.g. coma) have a mirror-image effect, which together with the subsequent optics become unequal Imaging errors. This fact, in turn, adversely affects all of the symmetry dependent phenomena, such as incompensation, curvature in the 100 line, etc.

b) The radiation is taken from the light source in the form of a single beam, which then divided by means of a first sector mirror and again by means of a second sector mirror is merged. This arrangement is congruent from a geometrical-optical point of view (both Beam paths deliver congruent imaging errors after merging), but is the use of two sector mirrors that are synchronous have to run to each other, quite time-consuming.

Compared to these known arrangements, the invention is characterized in a further embodiment by the Arrangement of a geometric-optical congruent beam path when using only a single sector mirror. This is achieved in a preferred embodiment of the invention if the two beam paths are between the light source and sector mirrors in their spatial arrangement in

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"With respect to the sector mirror level, they are mirror images of each other selects, whereby the light source sits in the sector mirror plane and the bundle splitting is already at the light source he follows. Since a page reversal occurs in one beam path as a result of the reflection at the sector mirror, provides the spatial mirror-image arrangement of the two beam paths after the congruence of the union the aberration. The bundles run according to the association as if they came from the same optical arrangement.

The spatially mirror-inverted arrangement of the sector mirror level is not a mandatory requirement for achieving this a geometrically-optically congruent beam path, but only a particularly simple and preferred arrangement. You basically get the same geometrical-optical effect if you get one originally spatially mirror-image structure by means of additional plane mirrors folds so that the mirror-image symmetry in space Structure is disturbed. The only thing that matters is that after the beam paths have been unfolded at all plane mirrors (including the sector mirror) two congruent beam paths are created. In this general sense is to understand the feature of the invention discussed here, which will now be summarized once again:

The bundle splitting takes place at the light source, only one sector mirror is used (to merge bundles), and the beam path is geometrically and optically congruent.

The geometrical-optical congruence of the beam paths has a favorable effect on the photometric accuracy. Man

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The described arrangement achieves specification features that are otherwise only found in expensive two-chopper devices finds. Compared to two-chopper devices, the arrangement according to the invention is considerably simpler, cheaper and Saves space, because a two-chopper device requires an additional common beam path in front of the first chopper and in general an additional intermediate image of the light source, preferably in the vicinity of the first Choppers.

In the known spectrophotometers, the cuvette and comparison cuvette are in a single, relatively large sample space used in special holding devices. Inserting the cuvettes requires a certain amount of skill. For example, a plate on the cuvette must be pushed into a correspondingly narrow rail guide. Insertion takes place within a sample space that hinders handling. In addition, the construction of the special holding devices naturally associated with a certain amount of effort.

In a further embodiment of the invention, an Ebert monochromator is used used with the gap arrangement described below. This slit arrangement is also on a Czerny-Turner monochromator applicable, but an Ebert monochromator is preferably used, which only has a single spherical Mirror needed. In such monochromators, both gaps are curved in the shape of an arc of a circle and constitute sections one and the same circle. It is therefore possible and has already been proposed to lengthen the column so far, that they each describe almost a semicircle. Both gaps are arranged on a rotatable disc. Limit apertures immediately in front of or behind this pane

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the height of the column is so strong that only the one in the monochromator usable gap height is optically effective. If you make both gaps wedge-shaped, you leave one end of the gap Over the semicircle to the other end of the gap, the gap width grow continuously, in such a way that in each case opposite parts of the two columns are the same width, then you can turn the split wheel the change the effective gap width. The optically effective gap sections are then also slightly wedge-shaped, however, in each case the narrower end of the entry gap becomes onto the narrower end of the exit slit and the wider end of the entry slit onto the wider end of the exit slit pictured. The accuracy of the gap width is mainly due to the accuracy of the semicircular Given split jaws. The gap setting, on the other hand, occurs when the splitting wheel rotates in the longitudinal direction of the column takes place is not critical. A deviation in the angular position of the split wheel has only a minor error Resulting gap width, while in the usual arrangements the movement of the gap jaws takes place transversely to the gap length and goes directly into the accuracy of the width setting.

This already known gap arrangement is used to adjust the gap width in the sense that the displacement of the split jaws against each other in the usual arrangements by the Rotation of the split wheel is replaced. In contrast, the arrangement according to the invention differs in that not only the slit width adjustment, but also the slit width programming depending on the number of waves through the Split wheel is made. The split wheel is rotated synchronously with the wave number feed of the monochromator. For each

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the angular position of the split wheel belongs to a gap width, which is assigned to the respective wavenumber. The semicircular gaps therefore already contain the splitting program. As a result, the complicated control devices in the known gap program devices are avoided, what leads to a considerable reduction in price.

It has already been proposed (patent application P 19 23 005 8-51) »Entry and exit slits are not the same .to make them wide, but rather to set their widths in such a ratio that an optimal ratio between Resolution and radiant flux is achieved. This optimal ratio depends on the number of waves. One realization is for this reason very difficult with the known gap arrangements and can generally only be optimal for one Simply perform wavelength.

In contrast, the inventive programming of the gap width offers the possibility of setting the gap width ratio for to design each wave number optimally, without additional control measures are required. Heard accordingly it becomes an embodiment of the invention, the optimal gap width ratio for all wave numbers on the split wheel to be taken into account, i.e. to be implemented in the shape of the column.

In a further embodiment of the invention, the optical filters, which are used for pre-decomposition, are on the Split wheel fixed in such a way that when the split wheel is rotated, the correct filters enter the beam path. This avoids the special pivoting mechanisms and control devices that would otherwise be required. which again results in a considerable reduction in the price.

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In addition, there are filter spikes that "when swiveling in quickly the filter of the well-known spectrophotometer in the registry, avoided because the filter only relatively slowly into or out of the beam be swiveled out of the beam.

A method for eliminating the sample's natural radiation has already been developed in the case of spectrometers following the optical Work zero principle, proposed. A special embodiment of this proposal is the splitting of the bundles make aH of the light source and close the first sector mirror by means of periodically effective diaphragms replace, which chop the two bundles with a certain frequency and a certain phase position. This suggestion leaves can be implemented very easily in the spectrometer according to the invention if - as is the case with an embodiment of this Invention belongs - the radiation source lies in the sector mirror plane. Then you need that according to the invention Sector mirror wheel is only to be provided with a suitable aperture ring, which puts the two bundles close behind the radiation source chopped up in the required manner. Here, too, the effort is extremely low because neither has its own Drive mechanism still requires synchronization measures. The attached bezel is at the same time driven by the sector mirror wheel and is inevitably synchronized with it.

Small components require little power to drive them. According to the invention, a small spectrometer can also be included powered by a battery.

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In order to reduce the electrical energy requirement even further, the abscissa drive (monochromator, column, Recorder) by spring force. The spring must be tensioned by hand before each registration. Preferably the device for tensioning the pen is coupled to the pen in such a way that the pen after a registration by hand against the spring force of the final wave number the starting wave number must be set.

Requires a not inconsiderable proportion of the energy requirement the radiation source, especially in the case of infrared spectrophotometers. This proportion of the energy requirement can at least partly by flame heating the radiation source be replaced.

The invention is based on an exemplary embodiment below explained in more detail with reference to the accompanying drawings:

Fig. 1 shows a plan view of a device according to the invention with the optical system.

Fig. 2 is a side view of the device.

Fig. Λ 3 shows in front view an embodiment of the slit arrangement in the optical system of FIG. Omitting the filter.

Figure 4- is a front view of the gap assembly with filters.

209833/0669

Pig. 5 is a perspective view of the sector mirror with radial sector diaphragms.

The housing 10 of the two-beam spectrophotometer, which Shown in Figures 1 and 2 at approximately 1: 1 scale, contains a chamber 12 which houses the optical system. Behind the chamber 12 is a chimney 14 in which the electronics are housed. Below the chamber 12 is a chamber 16 for receiving the mechanical parts, one Power supply, transformer, etc. With 18 is a comparison sample room and 20 denotes the sample space. These sample spaces correspond in their dimensions to the dimensions of the Comparison sample cuvette or the sample cuvette, so that this can be inserted into the sample chambers with a fairly precise fit. The rehearsal rooms are arranged and with extensions Provided in the area of the insertion openings that the cuvettes can be easily inserted from above.

The cuvettes in the sample spaces 18 and 20 are in the direction of irradiation arranged one behind the other. The light source 22 sits symmetrically between the sample spaces 18, 20 and Cuvettes. A comparison light bundle 24 passes from the light source 22 through the comparison sample cuvette and a sample light bundle 26 through the sample cell. The cuvettes are located in the pupil, i.e. they are directly removed from the bundle irradiated without an intermediate image of the light source 22 taking place on the sample, as in the case of the previously known devices .

Two spherical concave mirrors are symmetrical to the light source 28 and 30 are arranged, which the two light bundles 24

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- 52 -

and 26 collect. In the central plane passing through the light source a chopper 32 is arranged in the form of a rotating sector mirror, which alternates the sample light beam 26 to the entrance slit 34 of a grating monochromat 36 lets through or, during the other phase, the Comparison light bundle 24 reflected in the same way onto entrance slit 34. At 38 is a photoelectric clock denotes which is operated by the chopper 32 and a reference voltage for a phase sensitive rectification of the detector signal supplies.

The monochromator 36 is a grating monochromator in an Ebert arrangement formed with a grating 40 and a spherical concave mirror 42. The spectrally split light becomes collected in the plane of an exit gap 44. An interference filter 46 is arranged behind the exit slit. The exit slit 44 is shaped by a spherical concave mirror 48 on a photoelectric receiver 50 collected by a thermocouple.

in the

The gap arrangement is shown in Figures 3 and 4 / individually:

FIGS. 3 and 4 show the gap structure in a front view, the filters being omitted in FIG. In a split disk 52 circular arc-shaped gaps 54, 56 are arranged. The width of the gap changes in the peripheral direction, in accordance with a wavelength-dependent gap program. The gap widths are in diametrically opposite points of the circular arc-shaped gaps 54 and 56 equal to each other. Between firmly connected to the housing

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and diaphragms 58, 60 or 62, 64 arranged directly in front of or behind the split wheel are then of the circular arc-shaped Columns of the entry slit 66 and the exit slit 68 of the monochromator are formed. The split disk 52 is continuously rotated with the wavelength or wave number feed, whereby due to the different gap widths correspondingly different widths of the effective entry and exit gap 66 and 68, respectively, can be obtained.

Like from Pig. 4 as can be seen, there are various filters on the gap disk 52 in front of the arc-shaped gap 56 70, 72, 74, 76 and 78 attached. These filters are automatically one after the other as the split disk 52 rotates depending on the wavelength moved into the beam path and serve to suppress the undesired Orders on the grating monochromator.

In this way, the device for changing the gap width also serves as a filter changing device. One own filter changing device is omitted, and the split disk 52 is also the filter wheel.

As shown in FIGS. 1 and 5, the two-beam spectrophotometer according to the invention can be designed in this way with little effort that a suppression of the sample's own radiation takes place.

With a two-beam spectrophotometer with optical zero adjustment, the sample's own radiation can be measured Eliminate, if one sees the temporally alternating bundle splitting and bundling merging into a certain phase relation puts. To do this, one has to divide the Wechnellioht period into four

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Divide equally long periods of time. In each time period, the radiation from the radiation source is determined in accordance with the table below directed into the measuring beam path or into the comparison beam path and the measuring light bundle or the comparison light bundle directed onto the radiation receiver with the interposition of the monochromator. The Radiation from the radiation source can also be completely blocked. The last column of the table below indicates which radiation is effective at the radiation receiver, where P is the sample's own radiation and P is the radiation of the Means light source in the measuring beam path and, mutatis mutandis, V and V mean the same for the comparison beam path.

division Together-
guide Recipient Cf. or blocked Measuring Measuring Measuring P + P
Q Measuring or blocked comparison comparison comparison V + V

4-

In line 1, for example, the following can be seen: The merging device directs the sample radiation on the radiation receiver. Because the light source radiation is blocked or directed into the comparison beam during the split will (and then at the point of merging is blocked), only the sample's own radiation P is applied the radiation receiver.

In the second line, the sample's own radiation is also directed onto the radiation receiver. However, since the light source radiation is directed into the measuring beam path during the division, the sum P _Q + P appears at the radiation receiver. The last two lines are to be interpreted accordingly.

209833/0669 - 35 -

In the optical scheme of FIG. 1, the beam is split already at the radiation source 22, that is, not only by means of a rotating sector mirror. The steering The radiation into a particular beam then occurs by blocking the other beam. Column 2 is to be interpreted accordingly. "Measurement" in line 2, column 2 means, for example, that the comparison radiation is already is blocked in front of the comparison cuvette and only the sample cuvette Receives radiation. The expression "blocked" in the next line means that the Radiation in front of the sample cell is blocked, so that neither of the two bundles of radiation from the radiation source receives.

In Figures 1 and 5 it is shown how the alternating blocking of the two light bundles 24 and 26 with respect to the sector mirror 32 takes place. On the sector mirror 32, the extends over an angle of 180 °, a double diaphragm ring 80, 82 is attached, the diaphragm blades Rotate in two planes and (in FIG. 1) walk past the light source 22 on the left and right and so alternately in each case block one of the two bundles 24 and 26. In the In the position of FIG. 1, the diaphragm blade 80 is blocking the comparison light beam 24, while the other diaphragm blade 82 faces away from the light source 22 and does not obstruct the measuring light beam 26. After a rotation of the sector mirror 32 by 180 °, the diaphragm blade 80 gives the comparison light bundle 24 free, while the diaphragm blade 82 assumes the position shown in dashed lines and the measuring light beam blocked.

Figure 5 shows the sector mirror 3? - with the attached Aperture ring 80, 82 in a perspective view. Of the

209833/0 6 69 -36-

- pb -

Sector mirror on the one hand and the two diaphragm blades on the other are offset from one another by 90 °. The two diaphragm blades 80 and 82 are 180 against each other offset.

The circumferential surface 84 can be used as a running surface for a drive belt to serve.

In this embodiment, the diaphragm blades 80 and 82 mutually block one of the two bundles 24 and 26. If the mode of operation indicated in the table by the terms "blocked" is to be implemented, then each of the diaphragm blades 80 and 82 must be lengthened on one side by 90, and although in Figure 5 one diaphragm wing at the top and the other diaphragm wing at the lower end.

The diaphragm blades 80 and 82 can also be used instead of the sector mirror 32 simultaneously serve to control the photoelectric clock generator 38.

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Claims (18)

Claims M-y two-beam spectrophotometer, "in which a radiation source, an optical system containing a monochromator with entrance and exit slit, and a radiation receiver are provided, the optical system generating a measuring and a comparison beam, which after passing through the monochromator on the radiation receiver, characterized in that it is designed as a portable device (^ 2O kg) of relatively small dimensions (volume "5 JO 1), with the reduction in the light guide value and thus the signal-to-noise ratio, which is by reducing the dimensions and spacing in the unit as compared with normal commercial Gerä erg th ibt, by increasing the öff-1 / -au <5i8) and / or at least one of the two (vertical and horizontal) field angle (f / h <18, spectral resolution> 1 cm at a wave number of 1000) is at least partially compensated, where f is the collimator focal length, B and H the Width or height of the radiation beam at the grating and h is the height of the gap. 2. Two-beam spectrophotometer according to claim 1, characterized in that that through the optical system of the device an image of the radiation source (22) successively only on the Monochromator entrance slit (3 * 0> the monochromator exit slit (44) and the radiation receiver (50) takes place while avoiding further intermediate images. - 38 -209833/0669 3. Two-beam spectrophotometer according to claim Λ or 2, characterized in that each optical element of the optical <see system fulfills either the function of a real image or the dispersion or the superposition of the beam paths. 4. Two-beam spectrophotometer according to one of claims 1 to 3, characterized in that all images in the optical system by spherical mirrors (28, 30, 42, 48)
take place. 5. Two-beam spectrophotometer according to one of claims 1 to 4, characterized in that the beam paths of measuring
and comparison beam bundles (24 or 26) are geometrically-optically congruent, and that only a single rotating sector mirror (for merging the bundles) is used. 6. Two-beam spectrophotometer according to claim 5 »characterized in that two in opposite directions from the radiation source (22) outgoing light bundles (24, 26) through
two arranged symmetrically to a plane containing the light source (22) and a circumferential sector mirror (32)
Concave mirror (28, 30) are collected once directly and once after reflection on the sector mirror (32) on the monochromator entrance slit (34). 7. Two-beam spectrophotometer according to one of claims 1 to 6, characterized in that the monochromator (36) is a
Grating monochromator is in Ebert arrangement. 8. Two-beam spectrophotometer according to one of claims 1 to 7, characterized in that the outlet gap (44) of the 209833/0669 -39- Monochromator through a spherical concave mirror (4-8) to a radiation receiver, e.g. a thermocouple (50) is imaged. 9. Two-beam spectrophotometer according to claim 6, characterized in that that a sample and a comparison sample cuvette are symmetrical one behind the other in the direction of irradiation to the radiation source (22) provided in between in the beam paths of the two light bundles (24, 26) are arranged. 10. Two-beam Sepktrophotometer according to one of claims 1 to 9, characterized in that for sample and ■ comparison sample separate sample spaces (18, 20) are provided, the dimensions of which are essentially those of the sample cuvette and correspond to the comparison sample cuvette, so that the cuvettes are held in it in a form-fitting manner. 11. Two-beam spectrophotometer according to claim 10, characterized in that that sample and comparison sample cuvette can be inserted into the sample chambers from above. 12. Two-beam spectrophotometer according to claim 11, characterized in that that the sample spaces have funnel-like widenings in the area of the insert openings. 13. Two-beam spectrophotometer according to claim 7 or with one Lattice monochromator in a Czerny-Turner arrangement, characterized in that that entry and exit slit (34 and 44) of the monochromator from diametrically opposite one another Sections (54, 56) of circular arc-shaped column in a gap • wheel (52) are formed so that the split wheel (52) wavelength 209833/0669 -40- or is rotatable synchronously with the number of shafts and that the gap width varies according to the required gap program along the arc-shaped column (5 ^, 56) changes. 14. Two-beam spectrophotometer according to claim 13, characterized in that that optical pre-decomposition filter (70, 78) for the suppression of undesired orders firmly with the Split wheel (52) are connected, which in the shaft-synchronous rotation of the split wheel (52) one after the other in the beam path reach. 15 · Two-beam spectrophotometer according to claim 6, characterized in, that on the sector mirror (32) axially offset radial sector diaphragms (80, 82) are provided on both sides the radiation source (22) immerse in the beam paths of the two light bundles (24-, 26) and these with a the metrological elimination of the sample's own radiation causing the frequency and phase position in relation to the sector mirror (32) interrupt. 16. Two-beam spectrophotometer according to one of claims 1 to 15, characterized in that it is by means of a battery is operated. 17. Two-beam spectrophotometer according to claim 16, characterized in that that the device contains a spring motor that drives the spectrophotometer's wave number (rotation of the grating, gap width control and abscissa feed of the recorder). 18. Two-beam spectrophotometer according to claim 16 or 17, characterized characterized in that the radiation source (22) is heated by a flame. 209833/0669 Blank page