Automatic spectrophotometric absorption analyzer

Claim 1

An automatic spectrophotometric absorption analyzer for continuous determination of a plurality of components of a fluid sample and comprising: a light source, a vessel with transparent faces which contains said sample and is placed on the path of the light emitted by said source, a device for modulating at a predetermined frequency the intensity of the light beam transmitted by said vessel, a monochromator comprising a diffraction grating which receives the light transmitted by the vessel, a photoelectric converter so arranged that the light beam emerging from the monochromator falls on the sensitive element of said converter, an amplifying system to which the alternating-current output signal of said converter is applied, a demodulating circuit connected to the output of said amplifying system in order to deliver a direct-current signal whose level is substantially proportional to the intensity of the light beam transmitted by the vessel at the wavelength which is determined by the monochromator, a unit for automatically controlling the position of said diffraction grating in order to determine cyclically N stop positions defining N wavelengths having different predetermined values of which N - 1 wavelengths referred-to as measuring wavelengths correspond to the absorption lines of N - 1 components of the sample and of which the last wavelength referred-to as the reference wavelength does not correspond to any of said absorption lines, and means for automatic computation from the signal which is delivered by the deomdulating circuit in respect of each stop position of the diffraction grating which defines a measuring wavelength and from the same signal which is delivered when the stop positIon of the grating defines the reference wavelength and which is stored during each cycle in order to determine the optical density of the sample at said measuring wavelength and the concentration of the component which corresponds to said wavelength wherein the unit for automatically controlling the position of the diffraction grating comprises: an electric motor for driving said grating in rotation about the center thereof, an angle coder driven by said motor and continuously indicating the angular position of the grating, a system for preselecting N angular stop positions of the grating and signalling the coincidences between the position of the grating as indicated by the coder and each of the N positions which are displayed, each coincidence being signalled by setting one among N flip-flops, a scaler which defines the serial number of the stop positions of the grating and the forward displacement of which is controlled by automatic computation means, a coincidence matrix which delivers at three different outputs a signal for stopping the motor if coincidence occurs between the number displayed by the scaler and the serial number of the set flip-flop, a signal for initiating the movement of rotation of the motor in one direction corresponding to the rotation of the grating in the direction of scanning of wavelengths from position No. 1 to position N if the scaler displays a number other than ''''one'''' and if the serial number of the set flipflop is lower by one unit than the number displayed by said scaler, and a signal for producing the rotation of the motor in the other direction corresponding to rotation of the grating in the direction of direct return from position N to position No. 1 if the scaler displays the digit ''''one'''' and if the serial number of the set flip-flop is other than ''''one,'''' and a device for controlling said motor comprising a switch which defines the direction of rotation thereof and to which are connected the three outputs of the coincidence matrix.