DE2335842A1 - DEVICE FOR COMPARING THE SPECTRAL REMISSION OR TRANSMISSION OF A DUTY AND A STANDARD - Google Patents

Description

[LANDlS & GYR) LANDIS & GYRAG CH-63O1 Zug, Switzerland

Device for comparing the spectral remission or Transmission of a test item and a standard

introduction

The invention relates to a device for comparison the spectral remission or transmission of a test object and a standard, in particular for checking the authenticity of banknotes and other stamps, with a lighting device and a measuring device consisting of several light sensors for determining several, each only one narrow Measured values covering the spectral range at the same point on the test item and the standard, and with an evaluation device to compare the test measured values with the standard measured values.

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It is well known that the human eye is unable to determine which spectral colors a color stimulus is composed of. It is therefore possible that colors with different spectral composition produce exactly the same color sensation. The reproduction of a particular Color is comparatively light as long as it is the same physical impression is required. It is much more difficult reproduce a color with exactly the same spectral distribution. When comparing the remission of two colored Surfaces or when comparing the transmission of a test object and a standard, e.g. when checking the authenticity of banknotes, a complete spectral analysis is therefore a very strict test.

A device is already known which automatically carries out a spectral analysis of a document and a yes / no decision meets. Here, the same point of the test object and an original with a light source with a narrow Spectral range illuminated at the same time, with the help of two light sensors, the one from the test item and the one reflected from the original Light measured and the two measured values compared with each other. Then the same measurement is made in two repeated further narrow spectral ranges. The document is judged to be genuine if all three comparative measurements the difference between the test measured value determined on the test item and the standard measured value determined on the original does not exceed a specified value.

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The disadvantage of this known device is that for each spectral range to be included in the analysis . a separate light source is required; in the case of a larger number of spectral ranges to be recorded, a great technical effort. In addition, the working speed is relatively low because the individual Spectral measurements can only be carried out one after the other. There is also the risk that the measurement result will be damaged by instabilities the light sensor is falsified.

In another known apparatus for spectral analysis documents are illuminated with white light, the reflected light is spectrally split up with the help of a prism and directed onto several light sensors in such a way that each Light sensor is only hit by a selected spectral range of the reflected light. This requires a very precise adjustment of the optical system and undesirably large dimensions. In addition, with the known device only absolute measurements on the test item and not at the same time Comparative measurements can be carried out on a standard.

Task

The invention is based on the object of a device for comparing the spectral remission or transmission of a specimen and a standard to create that is not

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requires a separate light source for each spectral measurement, No special requirements are placed on the adjustment and stability of the light sensors, even if there are large numbers detectable spectral ranges is as simple as possible and the working speed is high.

Characteristics of the invention

The object set is achieved according to the invention by that the lighting device is set up to illuminate the test object and the standard with polychromatic light and that a light guide arrangement is provided, which is either that of the test object or that of the standard remitted or transmitted light through a filter device η throws light sensor, where η is the number of to be detected Spectral ranges means.

Description of the drawing

An exemplary embodiment of the invention is illustrated below the single drawing figure explained in more detail. Here is from the example of the application of the inventive concept in one Banknote validator run out.

In the drawing, 1 denotes a light source, its spectrum includes the total wavelength range to be analyzed. The light source can work in continuous or pulsed mode.

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This light source casts according to the position of an electromechanical Aperture 2 via light guide 3, 4 polychromatic light on a selected test point of one to be tested Banknote 5 (hereinafter referred to as the test item) or an original banknote 6 (hereinafter referred to as the standard). One Light guide arrangement 7 throws part of the light remitted by the test object 5 and the standard 6 via a filter device 8 to η light sensor 9, where η means the number of spectral ranges to be detected.

The light guide arrangement 7 has in the example shown two light guides 10, 11, the input of which is directed at the test item or the standard 6 and the output in one Mixing and distributing head 12 open. From the mixing and distribution head 12 - preferably an integrating sphere - η light guides lead to one filter area each of the filter device 8. This consists preferably from a graduated filter. According to the geometric arrangement of the outputs of the light guides 13 and this opposite light sensor 9 is of each Light sensor detects a selected narrow spectral range of the light reflected from the test object 5 or from the standard 6. Instead of a gradient filter, it goes without saying also a filter device consisting of η discrete individual filters Find application.

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^{A further light guide 13 1} leads from the mixing and distribution head 12 to a reference light sensor 14. A filter 15 can be arranged in front of the reference light sensor 14, the transmission range of which corresponds to the overall wavelength range to be analyzed.

Each light sensor 9 is connected to a maximum value memory 16 and the reference light sensor 14 is connected to a further maximum value memory 17 connected. Each Maxxmalwertspeicher 16 is connected to a first input of a comparator 18, whose Output is connected to a control input of an up-down counter 19. The maximum value memory is via an integrator 2O to the second input of the comparators 18 connected. A pulse generator 21 is connected to one counting input of each of the up / down counters 19. Each Up-down counter 19 is assigned a logic circuit 22, which are connected to a common decision logic 23.

A control circuit shown only schematically in the drawing 24 controls the program flow of the device; it switches the light source 1, controls the diaphragm 2, causes in the appropriate Time the deletion of the Maxxmalwertspeicher 16, 17 and the resetting of the up-down counters 19 and controls their counting direction.

The device described works as follows:

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At the beginning of the program, the diaphragm -2 is in such a position that the light source 1 over the light guide 3 throws polychromatic light onto test item 5. Part of the light remitted by the test object is transmitted by the light guide 1O detected, divided into the η light guides 13 in the mixing and distribution head 12 and from these via the filter device 8 thrown onto the η light sensor 9. Each of the light sensors 9 is of only a narrow spectral range of the from Test object struck with reflected light. The maximum value IL to U of the electrical generated by the light sensors 9 Signals is stored in the maximum value memories 16.

The reference light sensor 14 detects all of the light sensors 9 analyzed the spectrum and generates a reference measurement value that corresponds to the basic brightness of the test object 5. The maximum value U of this reference measured value is stored in the maximum value memory 17 stored and integrated by the integrator 20. At the output of the integrator there is a signal U. according to FIG Relationship U. = U. · T / τ, where t is the time and τ is the time constant of the integrator.

Simultaneously with the start of integration of the integrator 20, the up / down counters 19 are enabled and the pulses emitted by the pulse generator 21 are counted into the counters 19. The comparators 18 compare the signal U. with the measured values U ₁ to U _n ί If the signal U. the value U.

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reached, the comparator 18 speaks of the corresponding Measurement channel and the up / down counter 19 assigned to it is stopped. The following then applies:

U ₁ - U ₁ «-U _n * 1 / τ.

^U 1
and t _n = τ -1,

where t. the duration means during the pulses in the considered up-down counters have been counted into it. Similar relationships apply to the other measuring channels. Thus, in each of the pulse counters 19 during one of the associated measured value directly proportional and the reference measured value inversely proportional time pulses are counted. When the pulse frequency of the pulse generator 21 is constant, thus becomes the quotient of the measured values U "to U and the

1 η

Reference measured value U formed.

The maximum value memories 16, 17 are now deleted and the aperture 2 is set in such a way that then over the Light guide 4 of the standard 6 is illuminated. The previously described The measurement process is carried out in the same way on the Standard 6, but with the difference that now the Counting direction of the up-down counter 19 is reversed, i.e. the pulses from the pulse generator 20 are counted out from the counters 19. It is easy to see that at the end of the Measurement all counters 19 are back to zero when the test

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ling 5 corresponds exactly to standard 6 in all color nuances. Counters with a positive or negative count indicate a deviation in the remission of the relevant spectral range. For the counter reading N. of the counter 19 of the previously considered first measuring channel, the relationship N ₁ = (t .. -t *) · fg applies, where fg is the pulse frequency of the pulse generator 21 and t * is the duration during which the pulses from the considered Up-down counters have been counted out. The logic circuits 22 determine whether the count of the up / down counters 19 is within predetermined limits or not. The decision logic 23 finally emits a "good" signal if, for example, at least (n-2) of all counter readings are within these limits.

advantages

The device described is relatively simple, does not require any time-consuming adjustment, is hardly susceptible to interference and still allows a very precise comparison the spectral remission of a test object and a standard. Of course, transmission measurements can also be carried out; for this it is only necessary that the Light guide 10, 11 on the opposite of the light source 1 Side of the test item 5 and the standard 6 to be arranged.

The stability of the light source 1 and the light sensor 9 and 14 only low requirements are made. The sensation

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The light sensor only needs to be used during the two successive measurements remain constant. If, as described, the quotient from the measured values U. to U and the reference measured value U is formed, it is not even necessary that the intensity of the light source 1 emitted light is the same in the two measurements, if only the relative spectral energy distribution is obtained remain. This advantage is essential if a flash lamp is used as the light source, the flash intensity of which is known difficult to keep constant. By forming the quotient from the measured values and the reference measured value it is also achieved that a neutral, i.e. constant contamination over the entire analyzed wavelength range of the test object does not influence the measurement result.

variants

The solution described can be varied within wide limits without departing from the limits of the invention. Instead of a single light source 1 and a diaphragm 2, two separate light sources can of course be used. The diaphragm 2 can be arranged behind the test specimen and the standard with the same effect instead of in front of them. The light guide arrangement 7 can also be designed without a mixing and distributing head 12 if the light guide 10, 11 is a fiber bundle used and this on the individual output strands

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13 can be fanned out. However, the mixing and distribution head 12 ensures that all of the light captured by the light guides 10 _f 11 is distributed evenly to the individual channels.

The light guide 13 ', the filter 15, the reference light sensor and the maximum value memory 17 can be omitted if the input of the integrator 20 is connected to one of the maximum value memories 16. In this case, one of the readings will be

U., until U is used as a reference value. The forward-backward 1 η

counter of the channel concerned must then be completed after each Comparison measurement are at zero; If this is not the case, a malfunction of the arrangement is indicated.

When explaining the mode of operation of the illustrated embodiment it was assumed that the pulse frequency of the pulse generator 21 is constant. The up-down counter 19 register the measured values linearly. But since the error limit specified by the logic circuits 22 is constant, larger relative deviations are permitted for small measured values than for large measured values. To avoid this, the pulse generator 21 can be controlled in such a way that the pulse frequency during the pulse counting decreases steadily or in steps. In this way it can be achieved that in the case of small measured values despite a constant error limit the same relative deviation is permitted as with large measured values.

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The logic circuits 22 can also be designed in such a way that each counter reading has several different error limits is compared. Extreme deviations from the decision logic 23 can thus be rated correspondingly strongly.

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Claims (1)

Landis & Gyr AG. PATENT CLAIMS 1. \ Device for comparing the spectral remission or Transmission of a test item and a standard, in particular for checking the authenticity of banknotes and other stamps, with a lighting device and a measuring device consisting of several light sensors for determination several measured values, each covering only a narrow spectral range, at the same point of the Test specimen and the standard, and with an evaluation device for comparing the test measured values with the standard measured values, characterized in that the lighting device (1 to 4) set up to illuminate the test item (5) and the standard (6) with polychromatic light is and that a light guide arrangement (7) is provided, which is either that of the test item (5) or that of "standard (6) remitted or transmitted light through a filter inlet PA 1741 409882/0691 direction (8) on η light sensor (9), where η is the number of the spectral ranges to be recorded means. • 2. Device according to claim 1, characterized in that that the test item (5) and the standard (6) each have a light sensor (10, 11) for a mixing and distribution head (12) leads and that η light guide (13) from the mixing and distribution head (12) to a respective filter area of the filter device (8) lead. 3. Device according to claim 2, characterized in that the mixing and distributing head (12) is an integrating sphere is. 4. Device according to claim 1 or one of the claims 2 and 3, characterized in that the lighting device consists of a single light source (1), from which via a diaphragm (2) a light guide (3, 4) to the Test item (5) and the standard (6) leads. 5. Device according to claim 1 or one of the claims 2 and 3, characterized in that the filter device (-8) is a gradient filter. 6. Device according to claim 2, characterized in that the mixing and distributing head (12) is another PA 1741 409882/0691 Light guide (13 ¹ ) leads to a reference light sensor (14). 7. The device according to claim 6, characterized in that the evaluation device is set up to form the quotients from the measured values (U ₁ to U) determined by the light sensors (9) and the reference measured value determined by the reference light sensor (14). 8. Device according to claim 1 or one of the claims 2, 3 and 6, characterized in that a maximum value memory (16; 17) is connected downstream of each light sensor (9; 14) is. 9. Device according to claim 8, characterized in that each of the η Liehtsensor (9) is assigned an up / down counter (19) which is controlled by the maximum value memory (16) and a control circuit in such a way that it receives the values from a pulse generator (21 ) generated pulses during a time period proportional to the stored measured value (U ₁ to U) and inversely proportional to a reference measured value (U) when determining a test measured value in one counting direction and when determining a standard measured value in the other counting direction. 10. Device according to claim 9, characterized in that that each maximum value memory (16) is connected to a first input of a comparator (18) whose PA 1741 409882/0 6 91 Output with a control input of the assigned up / down counter (19) is connected, and that the second inputs of the comparators (18) to an integrator (2O) are coupled, the input of which is supplied with a reference signal (U). 11. Device according to claims 6, 7 and 1O, thereby characterized in that the input of the integrator (2O) is connected to the reference light sensor (14). 12. The device according to claim 9, characterized in that the pulse frequency of the pulse generator (21) is temporal is variable. 13. The device according to claim 9, characterized in that each up-down counter (19) has a logic circuit (22) is assigned to the count of the up / down counter (19) with several different Compares error limits. PA 1741 409882/0691