DE10245407A1 - Device for automatically measuring high cycle differences in permeable and optically birefringent media comprises a light source, a color filter, a polarizer a plate, a diffuser, an analyzer, and optical cables connected to a computer - Google Patents

Abstract

Device for automatically measuring high cycle differences in permeable and optically birefringent media with simultaneous digital Fourier analysis comprises a light source (1), a color filter (2), a sample (4) arranged between a polarizer (3) and an lambda/4 plate (5a), a diffuser (5b), an analyzer (6a) with three angle adjustments, and optical cables (7a) connected via photoreceivers (8a) and amplifiers (9a) to a computer (10) and a display (11). An Independent claim is also included for a process for automatically measuring high cycle differences in permeable and optically birefringent media with simultaneous digital Fourier analysis.

Description

The invention relates to a method and a device for automatic, contactless, fast, calibration-friendly and bright measurement of high path differences R of birefringent and permeable optical media or samples in small spaces according to Senarmont with simultaneous or successive digital Fourier analysis for at least two wavelengths, especially of fibers, filaments, foils, foil threads and other fabrics, both in the laboratory, on the microscope and on-line during the manufacturing process with fast or slow changes (ms or seconds range). According to the procedure and the device can all permeable Fibers, filaments, foils, foil threads and fabrics in the still molten state examined during manufacture or in the solid and dormant state become. These samples can measured even if they show false colors in white light.

[State of the art]

The Senarmont method is often used for the automatic and contactless determination of the path difference in the area up to a wavelength ( DE-AS 1097167 . DE 4123936 A1 . DE 4235065 A1 and DE 19529899 A1 ) that works with monochromatic light.

The Soleil-Babinet method is used for path differences greater than a light wavelength λ ( DE 4123935 A1 and DE 4235065 A1 ) that works with white light. There are polymers and other substances that show an abnormal color sequence of the interference fringes. The 0th order compensation strip is then no longer neutral black. In many cases, it cannot be decided between two adjacent strips which strip is the compensation strip. It is often neither of the two and there is no exact specification of the birefringence.

One way to fix this Difficulty is in making a bevel cut and counting of orders in monochromatic light. Such a process is natural no longer with an automatic and above all contactless as well as fast measuring procedures identical.

A way out in determining the The path difference when false colors are present offers the Senarmont method, but applied with two wavelengths.

For path differences R> λ, the minimum of the difference in the path differences of the two beams of different wavelengths is determined ( DE 4306050 A1 ). The disadvantage of this method, however, is that because of the time-consuming determination of the minimum, it is not fast enough, ie high sampling frequencies are not possible. In addition, the accuracy is limited due to the flat maximum. The space-consuming equipment cannot be used in small rooms.

High sampling frequencies and the measurement in small spaces but are necessary to e.g. of fibers and Filaments the rapid relocation of special appearances, e.g. the shoulder (neck point) during fast spinning or during the stretching process in tight spaces clear capture. Under the small dream i.d.S. one at any Place measuring range fixed in the vertical direction of the thread understood the dimensions in the millimeter range, preferably between 3-15 mm.

It also uses high sampling frequencies in the quality inspection, if e.g. a monofilament is unwound from the spool and the Orientation along of the thread at high take-off speed.

An elegant method to solve these problems is to use the Senarmont method with at least two wavelengths in a large number of angular positions of the analyzer ( DE 198 19 670 A 1 ).

If this latter method is used to measure the path difference of shiny and, for example, 15 μm thick fibers with minimal light scattering, then the simultaneous (simultaneous) measurement of the light intensities at at least two wavelengths in very many angular positions (e.g. 10 ) of the analyzer is very difficult because the scattered light is also distributed to a large number of receivers. In this case, calibration with a large number of channels (optical fibers), a large number of photo receivers and a large number of electrical amplifiers also proves to be very time-consuming.

This procedure is described So too weak and unfriendly to calibration.

Are known from DE 199 53 528 A1 and DE 199 53 527 A1 Single-wavelength method with evaluation of the signals from 2 channels of different polarization. The disadvantage of this method is that only path differences smaller than one wavelength can be measured. Samples with false colors cannot be recorded.

The measurement of the path difference R of the samples mentioned is important because the birefringence results from the thickness D of these samples Δn = R / D (1) results, which in many cases characterizes the orientation of the macromolecules in the fibers and films. This orientation determines technically and technologically important parameters such as the tensile stress at break, the elongation at break and the modulus of elasticity of the samples mentioned. If Δn _{max is} the maximum possible birefringence, then an average orientation angle α can be specified, which for fibers means the angle between the cylinder axis and the central longitudinal direction of the macromolecules as follows:

In the case of fibers, the birefringence Δn is always the difference in the refractive indices parallel and perpendicular to the fiber longitudinal axis, ie Δn = n || - n ⊥ , (3)

This applies analogously to the path difference R. In the case of optically uniaxial fibers with the diameter D, the path difference R is the difference in the optical light paths n _|| * D and n _⊥ * D, ie R = (n || - n ⊥ ) * D. (4)

In the first case (n _|| * D) the electrical vector of the light vibrates perpendicular to the direction of propagation, but parallel to the cylinder axis of the fiber. In the second case it swings perpendicular to it.

The path difference R is smaller than the vacuum light wavelength λ used, then called this area is the area of the 1st order (N + 1 = 1, so N = 0). If the path difference lies between the wavelengths λ and 2λ, then this is the area of 2nd order (N + 1 = 2, i.e. N = 1) etc.

OBJECT OF THE INVENTION

The object of the invention is Procedure for the automatic, non-contact and rapid measurement of high path differences R from birefringent and permeable Samples, especially of fibers, filaments, foils, foil threads and fabrics in small spaces, the one in white Light can also show false colors, this method should be bright and easy to calibrate, to develop. The integration times should be in ms or seconds lie.

• a) – der simultanen DFA in einem ersten Schritt ein Farbfilter mit der Schwerpunktwellenlänge λ₁ in den optischen Strahlengang schnell eingeschoben oder mit einem Spektrometer eingestellt wird, – bei dieser Wellenlänge der hinter dem Polarisator, Probe, Diffusor und der λ/4-Platte angeordnete Analysator mit n Winkelstellungen und den entsprechenden Photoempfängern die n Licht-Intensitäten über Lichtleitkabel photoelektrisch abtastet, – nach Verstärkung dem Computer zur Berechnung des Senarmontwinkels und des Gangunterschiedes zuführt, – und in einem zweiten Schritt der zweite Farbfilter mit der Schwerpunktwellenlänge λ₂ =< λ₁ – 10 nm oder λ₁ =< λ₂ + 10 nm in den optischen Strahlengang schnell eingeschoben oder mit einem Spektrometer eingestellt wird, und bei dieser Wellenlänge der gleiche Messvorgang abläuft wie bei der ersten und anschließend auf Grund der Beziehungen der digitalen Fourier-Analyse mit den gespeicherten Lichtintensitäten die Senarmontwinkel λ₁ und λ₂ und die entsprechenden Gangunterschiede Rλ₁ und Rλ₂ berechnet, die richtige Ordnung der Probe bestimmt und dadurch die richtigen Gangunterschiede angegeben werden, oder
• – b) – indem andererseits das Senarmont-Mess-Verfahren mit zeitlich sukzessiver DFA durchgeführt wird, indem wieder zu Beginn der Messung die Wellenlänge λ₁ mit einem Spektrometer eingestellt wird und bei dieser Wellenlänge die hinter dem Polarisator, Probe und λ/4-Platte angeordnete Analysator zeitlich nacheinander schnell in 1 bis n Winkellagen gedreht wird, indem dieser Analysator mit einem Miniatur-Servo-Antrieb verbunden ist, der für jede Winkellage einen spezifischen Impuls erhält, und die zu jeder Winkelage ₁ bis _n gehörende Lichtintensität I₁ bis I_n entsprechend dem Impuls ermittelt und gespeichert und in einem zweiten Schritt der zweite Farbfilter mit der Schwerpunktwellenlänge λ₂ =< λ₁ – 10 nm oder λ₁ =< λ₂ + 10 nm in den optischen Strahlengang schnell eingeschoben oder mit einem Spektrometer eingestellt wird und bei dieser Wellenlänge der gleiche Messvorgang abläuft wie bei der ersten und anschließend auf Grund der Beziehungen der digitalen Fourier-Analyse mit den gespeicherten Lichtintensitäten die Senarmontwinkel λ₁ und λ₂ und die entsprechenden Gangunterschiede Rλ₁ und Rλ₂ berechnet, die richtige Ordnung der Probe bestimmt und dadurch die richtigen Gangunterschiede angegeben werden.

According to the invention, the object is achieved in that the Senarmont method is carried out in combination with simultaneous or successive digital Fourier analysis (DFA) with preferably three angular positions and at least two measuring wavelengths using fiber optic cables. The object is achieved by the developments of the invention which are advantageous in the main claim and in the subclaims, in that the Senarmont measurement method is carried out in succession with simultaneous or successive DFA at least at two wavelengths with a spacing of at most 10 nm

• a) - in a first step, the simultaneous DFA a color filter with the focal wavelength λ _{1 is} quickly inserted into the optical beam path or adjusted with a spectrometer, - at this wavelength the one arranged behind the polarizer, sample, diffuser and the λ / 4 plate Analyzer with n angular positions and the corresponding photo receivers, which photoelectrically scans n light intensities via fiber optic cables, - after amplification, feeds the computer to calculate the sensor angle and the path difference, - and in a second step the second color filter with the focus wavelength λ ₂ = <λ ₁ - 10 nm or λ ₁ = <λ ₂ + 10 nm is quickly inserted into the optical beam path or adjusted with a spectrometer, and at this wavelength the same measuring process takes place as for the first and then due to the relationships of the digital Fourier analysis the stored light intensities the Senarmontwi nkel λ ₁ and λ ₂ and the corresponding path differences Rλ ₁ and Rλ _{2 are} calculated, the correct order of the sample is determined and the correct path differences are thereby indicated, or
• - b) - on the other hand, the Senarmont measurement method is carried out with successive DFA, by again setting the wavelength λ ₁ at the beginning of the measurement with a spectrometer and at this wavelength the one behind the polarizer, sample and λ / 4 plate arranged analyzer is rotated quickly one after the other in 1 to n angular positions by connecting this analyzer to a miniature servo drive, which receives a specific pulse for each angular position, and for each angular position ₁ Light intensity I ₁ to I _n belonging to _n is determined and stored in accordance with the pulse and, in a second step, the second color filter with the focal wavelength λ ₂ = <λ ₁ - 10 nm or λ ₁ = <λ ₂ + 10 nm into the optical beam path quickly inserted or adjusted with a spectrometer and at this wavelength the same measurement process as the first and then due to the relationships of the digital Fourier analysis with the stored light intensities, the senarmont angles λ ₁ and λ ₂ and the corresponding path differences Rλ ₁ and Rλ _{2 are} calculated, the correct order of the sample is determined and the correct path differences are specified.

The device is shown in the drawings ( 1 to 4 ) and embodiments described.

In the Senarmont process with simultaneous DFA, three angular positions are preferably realized simultaneously and at least three fiber optic cables with an upstream λ / 4 plate and three polarizers needed. At the Senarmont procedures with successive DFA become only one Optical fiber, a photo receiver and an electrical amplifier needed. So that increases the light intensity across from the Senarmont process mentioned above with a lot of angular positions of the analyzer. During calibration just need the linearity, the zero and maximum intensities to be observed. The the former variant (simultaneous DFA) is faster than the latter Variant (successive DFA). In the latter case, the less material effort, the highest light intensity and the requirements the calibration is particularly minimal.

By the distance of the measuring wavelengths from at the most 10 nm, all samples with false colors are measured correctly.

To carry out the test procedure a device is used in which the birefringent Sample seen in the direction of light is located between a polarizer and a λ / 4 plate. Polarizer, sample and λ / 4 plate will be of a white Light source irradiated with a monochromatic filter or a laser.

In the Senarmont process with simultaneous inventive DFA will be available standing light intensity preferably in three channels divided into three angular positions (e.g. 0 °, 60 ° and 120 °) with three polarizers and then with a CCD line, CCD camera, PIN diodes or measured with SEV's (multiplier), in electrical Signals converted and evaluated. With the Senarmont process with time according to the invention successive DFA becomes by means of pulse-controlled and fast rotating Miniature servo drive the analyzer in preferably three different ones Angular positions rotated and the resulting intensities with or measured without fiber optic cable and photo receiver and from the results both the Senarmont angle and the path difference are calculated. The angular position and light intensity are assigned to each angular position belonging characteristic impulse.

The advantage of this multi-color Senarmont process is that there are also path differences greater than one wavelength (R> λ) and due to the small distance of the measuring wavelengths too Samples with false colors can be measured correctly.

The advantage of the device is in that by the simultaneous measurement in preferably three angular positions of the analyzer with three fiber optic cables or through successive measurements of light intensities achieves a higher light intensity in three different angular positions of the same analyzer will (opposite e.g. n = 10 angular positions with other methods), even in small spaces quickly can be measured and only the linearity, the zero and the maximum intensities of three or one photo receiver must be observed i.e. the device is fast, miniaturizable, bright and kalibrierfreundlich.

The method and the device can for automatic, contactless and rapid measurement of the path difference of birefringent samples (also in small rooms) can be used without ambiguity of the results.

The method and the device are suitable for measurement in laboratory operation, for fast (simultaneous measurement) and slowly changing operations (successive measurement over time) with an integration time in ms and in the seconds range and to track the change in gear difference of microscopic samples.

[Examples]

Exemplary embodiments for the method and the device

To measure the _path difference R _λ1 for a film at the wavelength λ ₁ according to the described method, the arrangement of the parts along the optical axis must be observed, as shown in 1 for simultaneous DFA and in 2 for which successive DFA is specified.

The in are perpendicular to the optical axis 3 the specified polarization and angular positions.

1. Procedure for a 2-1 / 4 λ plate (without False color)

Table 1 shows the intensities resulting for the different wavelengths and angular positions of the analyzer, which were determined either simultaneously or successively in time (device according to 1 and 2 ), compiled.

Table 1: For the 2-1 / 4 λ plate (without false colors) for the different wavelengths and angular positions (0 °, 60 ° and 120 °) the resulting relative intensities and the calculated path differences R (see below)

The calculation is subsequently used for the wavelengths 486 and 506 nm (table, lines 1 and 2 ) For the wavelength λ ₁ = 486 nm (line 1 ) results from the equations for the Senarmont method with digital Fourier analysis (DFA) the Senarmont angle
ε ° = 28.648 ° arctg b / a + 45 ° (1 + a / | a |), a = I ₁ - 0.5 (I ₂ + I ₃ ) and
b = 0, 866 (I ₂ + I ₃ ) as well
with the numerical values in Table 1 (row 1 )
a = 144.5 and
b = 26.85
to
ε ° = 95.3 °
as well as the gear difference

For the wavelength λ ₂ = 506 nm (line 2 ) results (analogous to the calculations for the wavelength 486 nm)
a = 207,
b = -109.12 and
ε ° = 76.1, that is

The minimization calculation shows the following differences | ΔR (N = 0) | = | R 1 - R 2 | = 43.4 (1st order) | ΔR (N = 1) | = | ΔR (N = 0) + (λ 1 - λ 2 ) | = 23.4 | ΔR (N = 2) | = | ΔR (N = 0) + 2 (λ 1 - λ 2 ) | = 3.4 | ΔR (N = 3) | = | ΔR (N = 0) + 3 (λ 1 - λ 2 ) | = 16.6 | ΔR (N = 4) | = | ΔR (N = 0) + 4 (λ 1 - λ 2 ) | = 36.6.

The minimum is in the 3rd order, ie with N + 1 = 3
the following values for the path differences:

In Table 1, the wavelength differences were deliberately chosen to be 20 nm to show that samples without false colors do not necessarily have to be set to 10 nm. As the wavelength spacing increases, the requirement for the measurement accuracy of the intensity measurement also decreases. The Ehringhaus number is determined here (see Table 1)

This corresponds to the factual experience that for Ehringhaus numbers | NE | > 30 there are no false colors.

2. Procedure for a false color film

The situation is completely different if the film arranged between the crossed polarizers (polarizer and analyzer) shows false colors and the wavelength difference used is still 20 nm:

Die Ehringhauszahl ergibt sich analog zu Pkt. 2 zu

Here there are very different path differences R for the wavelengths used from 486 to 676 nm (R values in the range of approx. –70 to 1500 nm!). Only for the wavelength distance of 10 nm used in the measurement does a physically sensible gradation result, as is shown in the following and last table

The number of Ehringhaus is analogous to point 2

This order of magnitude means existence of false colors that are correctly captured by the Ehringhaus number! requirement for the correct measurement of the path difference of samples with false colors is the small wavelength difference of the two laser diodes of 10 nm.

3. Device for the Senarmont process with simultaneous DFA

In 1 the scheme of the device is shown, according to which a light source ( 1 ) with or without color filter ( 2 ), (without color filter when using two different lasers), the polarizer ( 3 ) and the λ / 4 plate ( 5a ) between which the sample ( 4 ) is arranged, whose scattered light over the λ / 4 plate ( 5a ) and the diffuser ( 5b ) on the analyzer ( 6a ) with the three angular positions analogous to 3 acts and with or without the three fiber optic cables ( 7a ) with the three photo receivers ( 8a ) scanned photoelectrically and via the amplifier ( 9a ) in the computer ( 10 ) processed and displayed ( 11 ) or forwarded to regulate the manufacturing process.

4. Device for the Senarmont procedure with successive DFA

In 2 the scheme of the device is shown, according to which a light source ( 1 ) with or without color filter ( 2 ), (without color filter when using lasers), the polarizer ( 3 ) and the λ / 4 plate ( 5a ) between which the sample ( 4 ) is arranged, whose scattered light over the λ / 4 plate ( 5a ) on the quickly rotating analyzer ( 6b ) with the three angular positions analogous to 3 acts and with or without the three fiber optic cables ( 7b ) and with the photo receiver ( 8b ) scanned photoelectrically and via the amplifier ( 9b ) in the computer ( 10 ) processed and displayed ( 11 ) or forwarded to regulate the manufacturing process.

5. Device for the Multi-color Senarmont process for Filaments in small spaces with simultaneous DFA

In 4 is the device for the multi-color Senarmont process with simultaneous DFA for filaments ( 4 ), the two laser diodes ( 1a and 1b ) over the polarization divider cube ( 1c ), the beam expansion ( 1d ) and the polarizer ( 3 ) on the filament or filaments ( 4 ) works. The light scattered by 40 ° is then, as in l shown, forwarded and evaluated.

The device is suitable for a quasi-simultaneous DFA in the manner shown by the two laser diodes ( 1a and 1b ) over the polarization divider cube ( 1c ) act alternately in the sense of multiplexing. The monochromate filter ( 5c ) can then be omitted.

However, if the two laser diodes act simultaneously (evaluation according to real simultaneous DFA), the channel from 5a to 11 must be used twice, whereby the two monochromate filters ( 5c ) are designed once for the measuring wavelength λ ₁ and for the second measuring wavelength λ ₂ .

1

White light source with monochromatic filter or laser

1a

Laser diode for the wavelength λ ₁

1b

Laser diode for the wavelength λ ₂

1c

Polarizing beam splitter cube

1d

Beam expansion optics

2

Color filter changer for the wavelengths λ ₁ and λ2.

3

polarizer

4

sample (Foil or other birefringent sample

[Sheet]); in 4 the filament or filaments

5a

λ / 4 plate

5b

diffuser

5c

Monochromatfilter

6a

analyzer with three angular positions at the same time

6b

Fast rotating analyzer with three

Angular positions

7a

optical cable L1, L2 and L3

7b

optical cable L

8a

PH1 photoreceiver, PH2 and PH3

8b

Photo receiver PH

9a

Amplifier V1, V2 and V3

9b

Amplifier V

10

computer with storage of the measured

Light intensities and Calculation of the Senarmont angles and

Path differences

11

display of the measurement results and if necessary

forwarding to the control room for the regulation of the

manufacturing process

Claims (9)

Process for automatic, non-contact, fast, calibration-friendly and bright measurement of high path differences of transparent and optically birefringent media according to Senarmont with simultaneous or successive digital Fourier analysis (DFA), in particular of fibers, filaments, foils, foil threads and flat structures that are in white Light can also show false colors and be in small spaces (miniaturized), characterized in that the multi-color Senarmont measurement method is carried out in combination with simultaneous or successive DFA at least at two wavelengths with a distance of at most 10 nm according to I. a) - in a first step the quasi-simultaneous DFA a color filter with the focal wavelength λ _{1 is} inserted into the optical beam path or adjusted with a spectrometer - at this wavelength the one behind the polarizer, sample, diffuser and the λ / 4-plate Ordered analyzer with n angular positions and the corresponding photo receivers which photoelectrically scans n light intensities via fiber optic cables, - after amplification, feeds the computer to calculate the sensor angle and the path difference, and I b) - in a second step, the second color filter with the focus wavelength λ2 = <λ ₁ - 10 nm or λ ₁ = <λ ₂ + 10 nm is inserted into the optical beam path or adjusted with a spectrometer, - at this wavelength the same measuring process is carried out analogously to a), - and then the Senarmont angles λ ₁ and λ ₂ and the corresponding path differences Rλ ₁ and Rλ _{2 are} calculated, or according to Ic) - the real simultaneous DFA, the steps mentioned in Ia and Ib are carried out simultaneously, or according to II. a) - the Senarmont measurement method with successive time DFA the wavelength λ _{1 is set} with a spectrometer at the beginning of the measurement, - with this Wavelength the analyzer arranged behind the polarizer, sample and λ / 4 plate is rotated successively in 1 to n angular positions, - this analyzer is connected to a miniature servo drive, which has a specific one for each angular position Receives momentum - at every angular position ₁ light intensity I ₁ to I _n belonging to _n is determined and stored in accordance with the pulse via light guide cable and II b) in a second step the second color filter with the focus wavelength λ ₂ = <λ ₁ - 10 nm or λ ₁ = <λ ₂ + 10 nm is inserted into the optical beam path or adjusted with a spectrometer - at this wavelength the same measuring process takes place analogously to I a and - the Senarmont angles λ ₁ and λ ₂ and the corresponding path differences Rλ ₁ and Rλ _{2 are} calculated. A method according to claim 1, characterized in that for the analyzer of 0 °, 60 ° and 120 ° n = 3 angular positions are used to measure the three light intensities I1 to I3, the Senarmont angle clearly from the relationships ° = 28.648 ° * arctg b / a + 45 ° (1 + a / | a |) in angular degrees or = 0.5 * arctg b / a + / 4 * (1 + a / | a |) in radians, a = I ₁ - 0.5 * (I ₂ + I ₃ ) and b = 0, 866 * (I ₂ - I ₃ ) are calculated and the path difference R = (° / 180 ° + N) * λ = (/ + N) * λ is given if the order N + 1 is known or is calculated using a minimization calculation from the results of the measurements with the two wavelengths. A method according to claim 2, characterized in that only linearity, zero and maximum intensity are required to calibrate the measurement become. Method according to one of the preceding claims, characterized characterized that for Fibers and filaments the beam path between light source, polarizer and birefringent sample on the one hand and the optical measuring channel on the other hand, consisting of λ / 4 plates, quickly rotatable analyzer and fiber optic cable with photo receiver, angled is, preferably with a deflection angle of 40 °. Method according to Claim 4, characterized in that the relationship R ₄₀ / R ₀ = 100-0.5 * D _μm exists between the determined gear difference R40 and the correct gear difference R ₀ . Method according to one of the preceding claims, characterized characterized that for optically active samples worked without λ / 4 plates and the determination of the twist angle is carried out according to claim 2. Device for automatic, non-contact, fast, calibration-friendly and bright measurement of high path differences of transparent and optically birefringent media according to Senarmont with simultaneous digital Fourier analysis (DFA), in particular of fibers, filaments, foils, foil threads and flat structures, which are also false colors in white light show and can be in small spaces, characterized in that after 1 to a light source ( 1 ) with or without color filter ( 2 ), (without color filter when using two different lasers), the polarizer ( 3 ) and the λ / 4 plate ( 5a ) between which the sample ( 4 ) is arranged, then the diffuser ( 5b ) and the analyzer ( 6a ) with the three angular positions analogous to 3 follow and with or without the three fiber optic cables ( 7a ) with the three photo receivers ( 8a ) photoelectrically arranged and via the amplifier ( 9a ) with the computer ( 10 ) and display ( 11 ) are connected. Apparatus according to claim 7, characterized in that one works with successive digital Fourier analysis (DFA), whereby after 2 to a light source ( 1 ) with or without color filter ( 2 ), (without color filter when using lasers), the polarizer ( 3 ) and the λ / 4 plate (5a) follow, between which the sample ( 4 ) is arranged, then the quickly rotatable analyzer ( 6b ) with the three angular positions analogous to 3 follows and with or without the three fiber optic cables ( 7b ) with the photo receiver ( 8b ) via the amplifier ( 9b ) to the computer ( 10 ) and the ad are connected ( 11 ). Device according to one of the preceding claims, characterized characterized in that for measuring the light intensity a CCD cell, CCD camera or PIN diodes can be used.