APPARATUS FOR PERFORMING OPTICAL MEASUREMENTS ON DYE BATHS

The present invention relates to an apparatus for performing optical measurements on dye baths.It is known that the Lambert-Beer law, also known as the law of Beer-Lambert Law or Beer-Lambert-Bouguer law, is an empirical relationship that correlates the amount of light absorbed by a mediumto the chemical nature, the concentration and the thickness of the medium traversed by the light. When a beam of light (monochromatic) of intensity I0goes through a layer of a medium of a thickness 1, a part of it is absorbed by the medium itself and a part of it is transmitted with residual intensity I1. The ratio between said intensities is expressed by the following relationship:I1I0=e−kλl=T=e−Awhere kλ is the absorption coefficient (which is a constant typical of the medium and depends on the wavelength λ) and 1 is the thickness of the solution traversed by the light.By defining the transmittance (T) as the ratio I1/I0and as absorbance (A) the opposite of the natural logarithm of the transmittance, the law assumes an even more simplified form:A=kλlthat for a solution is simplified as follows:A=ελlM;where ελis the molar extinction, M is the molarity of the solution and 1 is the geometric path. The value of ελis considered constant for a given substance at a given wavelength, although it may vary slightly withtemperature. Moreover, its constancy is ensured only within a given range of concentrations, above which the linearity between absorbance and concentration can be affected by chemical and physical phenomena (for example the precipitation of the colored chemical species). The measurement of the absorbance of chemical solutions at typical wavelengths is the principle on which the spectrometry analysis is based. For the control of the exhaustion of the dyes in the dye baths utilized for dyeing textile materials, use is made of control cells, in which is entered the dyeing bath to control, having variable thickness, or control cells with mobile walls, which are particularly complex and therefore expensive in relation to the current production requirementsUS2006/152730A1discloses an optical sensor for determining particle and/or dye concentrations in liquid or gaseous media and to a method for operating the same. The optical sensor comprises at least one measuring head. The measuring head consists of an emitter unit with a semiconductor emitting element, which emits visible emission light beams, and with a receiver unit with a semiconductor receiving element. The portion of the emission light beams, which pass through an absorption section containing liquid or gaseous medium, is guided onto the receiving element. An evaluating unit is coupled to the measuring head via electric leads, and the received signals, which are present at the output of the semiconductor receiving element, are evaluated inside said evaluating unit in order to determine the particle or die concentration.US2004/156036A1discloses a method for optically measuring black carbon in the atmosphere an aerosol particle collection area of a filter tape is continually illuminated by an illumination source with light of one or more wavelengths. Transmitted and reflected light fractions are measured at several precisely defined angles or angle ranges, such as of 0°, 12° to 140° and 165 to 180° by means of photodetectors arranged correspondingly relative to the illumination source, achieving maximum symmetry for the angles to be measured. The loading of the filter tape collection area with light absorbing aerosol material is continually determined from the change in the optical properties of the collection area with the aid of known algorithms from transmissivities and reflectivities as detected.US2005/133724A1discloses a system for conducting a polymerase chain reaction (PCR) assay upon a collection of samplesis disclosed. The PCR assay is performed by absorption detection. The system includes a multi-well plate which is adapted to retain a collection of sample wells. This system includes a thermal cycler for the multi-well plate. The system additionally includes a collection of photodetectors, and a corresponding number of light sources. The light sources are positioned such that light emitted from each of the respective light sources passes through a corresponding well retained in the multi-well plate and to a corresponding photodetector. The system also includes a processor or other means for analyzing the output signals from the photodetectors. In certain versions of the system, ultra-violet light is used.The present invention relates, in particular, to an apparatus that allows to correlate the aforementioned variables in a particularly simple, economical and effective way for applying the Lambert-Beer law to solutions containing coloring agents and used for dyeing textile materials in order to perform an assessment of the exhaustion of the dyes in the same solutions.This result is achieved, according to the present invention, by adopting the idea of making an apparatus having the characteristics indicated in claim 1. Other features of the present invention are object of the dependent claims.An apparatus in accordance with the present invention is particularly simple from the constructive point of view, economic, and reliable. Furthermore, the optical readings obtained using the present apparatus are more accurate.These and other aspects and advantages of the present invention will be best understood by anyone skilled inthe art thanks to the following description and to the attached drawings provided by way of example but not to be considered in a limiting sense, in which:Fig.1is a diagram showing an apparatus according to the present invention;Fig.2is a diagram showing an apparatus according to a further embodiment the present invention.Reduced to its essential structure and with reference to the accompanying drawings, an apparatus according to the present invention comprises a cell having a constant thickness or a variable thickness associated with one or more light emission and reception points positioned in correspondence of the various thicknesses, wherein each light emission point comprises a plurality of colored LEDs that cover the spectrum of visible light, wherein each light receiving point comprises a photodiode, and wherein to each group of light emitting LEDs is associated a photodiode which detects the light emitted by the light emitting LEDs of the group.With reference to the example shown inFig.1, the cell (1) has three different thicknesses, being formed by a succession of three zones (A, B, C) gradually increasing in height from an input side (10) for the solution to be controlled towards an outlet side (11) from which the same solution flows out. On each of said zones (A, B, C) of the cell (1) is arranged and acting a set of three light emitting LED (12A, 12B, 12C) and, on the opposite side (below the lower base of the cell 1 inFig.1), is arranged and acting a corresponding light-receiver photodiode (13A, 13B, 13C). Said photo-emitters and said photodiodes are located outside of the cell (1). The walls of the latter where the photo-emitters and photodiodes arepositioned are transparent to the light emitted by the photo-emitters. Each of the photo-emitters emits light of a predetermined color and each photo-emitters of each set produce, in cooperation with each other, visible light. For example, said photo-emitters can emit R, G, B light. Each set of photo-emitters (12A, 12B, 12C) is associated with an additional photodiode (14A, 14B, 14C) placed on the same side of the same photo-emitters of the set with respect to the cell (1) (above the upper base of the cell 1 inFig.1). Moreover, a screen (15A, 15B, 15C) can be provided behind each of the additional photodiodes (14A, 14B, 14C).Fig.1shows also a programmable unit (2) which activates the light emitting LEDs (12A, 12B, 12C) and receives the signals of the photodiodes (13A, 13B, 13C) and (14A, 14B, 14C) and processes them according to a program based on the law of Lambert-Beer. The diagram ofFig.1also shows sensors (3,4) for controlling the pH and conductivity values of the solution that flows through the cell (1) and a recirculation pump (5) intended to re-enter the solution in the dyeing machine from which it is taken. The solution fed into the cell (1) is, for example, a dyeing bath drawn off by a dyeing machine (known per se) and then put back in the same dyeing machine. The multiplicity of the thicknesses of the cell (1) allows to perform a more effective control even if such thicknesses are individually constants, taking into account the fact that when a solution is more concentrated, i.e. contains larger amounts of dyes, the thickness of the cell must be smaller to allow light emitted by the light emitters to reach the other side of the cell in amount sufficient to be interceptedby the respective photodiode and subsequently processed.The additional photodiode (14A, 14B, 14C) associated with the photo-emitters (12A, 12B, 12C) allows to send to the programmable unit (2) signals exactly corresponding to the intensity of light emitted by the photo-emitters.Figure 2shows a simplified version of the apparatus, in which the cell (1) has only one zone (A) of constant thickness. This version of the apparatus can serve, for example, to control the transparency of the washing water introduced into the dyeing machine.In more general terms, an apparatus adapted to perform optical measurements on dye baths according to the present invention, comprises a cell (1) with an inlet (10) and an output (11) to allow the dye bath to flow through the same cell (1), light emitting means (12A, 12B, 12C) adapted to produce a light intended to pass through the dyeing bath and placed in a predetermined area of the cell (1), light-detecting means (13A, 13B, 13C) adapted to intercept the light produced by said light emitting means and placed on the opposite side of the cell with respect to the latter, and programmable means (2) adapted to drive said light emitting means (12A, 12B, 12C) and to process electrical signals emitted said light-detecting means (13A, 13B, 13C) on the basis of a predetermined processing program, and to said light emitting means (12A, 12B, 12C) are associated additional light-detecting means (14A, 14B, 14C) placed on the same side of the light emitting means (12A, 12B, 12C) with respect to the cell (1) and also connected to said programmable means (2) that receives the signals emitted by the additional light-detecting means andprocesses them according to the predetermined processing program.Thus, the programmable means (2) receive, through the additional light-detecting means (14A, 14B, 14C), electric signals that can be compared with the electric signals emitted by the light-detecting means (13A, 13B, 13C) on the basis of the predetermined processing program and that correspond to the light emitted by the light emitting means (12A, 12B, 12C). It is noted that without said additional light-detecting means (14A, 14B, 14C) the processing unit (2) would process the signals coming from the light-detecting means (13A, 13B, 13C) assuming that the light emitted by the light emitting means (12A, 12B, 12C) remains constant over the time. This assumption is incorrect because, due to their structural and functional characteristics, the LEDs emit a light that is not constant over the time (for example, it is influenced by the temperature). In other words, the arrangement disclosed above ensures that the measurement is executed on the basis of real data, not on the basis of assumptions.In the examples described above the light emitting means (12A, 12B, 12C) are constituted by groups of individual LED diodes and the cell (1) can have either a constant height or a not constant height so as to be ideally divided into several zones (A, B, C) having different heights. Furthermore, in the above examples the apparatus is inserted in a closed circuit which includes the dyeing machine so as to allow to perform optical measurements without interrupting the dyeing process.From the foregoing description are also clear the advantages offered by the present apparatus, both in terms of construction simplicity and in economicterms, which implies the further advantage to allow a greater diffusion than the more expensive conventional devices and, therefore, to allow for a greater extend control of dye baths also in industry and not only in laboratories.It is also evident that the present apparatus can be equally advantageously used to control the color of liquids other than those mentioned above, such as the color of beverages, perfumes, etc.Still another advantage lies in the simplicity of the connection of the apparatus to the dyeing machine that should not be modified.In practice the details of execution may vary in any equivalent way as for what concerns the arrangement and the conformation of the individual elements described or illustrated, without thereby departing from the scope of the adopted solution and thus remaining within the limits of the protection conferred by the this patent. 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