Abstract: In optical mark recognition apparatus the light transmitter has two light sources 11, 12 which can be selectively switched on and which transmit light beams of different spectral compositions. A semi-permeable mirror 15 directs the light beams 13, 14 of both light sources 11, 12 along a common optical path 16 (FIG. 1).

Abstract: An electronic apparatus has an input stage (11) with a binary signal output (19). This signal output is connected to a relay control circuit which deenergizes or energizes the relay (15) in dependence on the output signal (0 or 1). The relay (15) can be held in the energized condition over a wide voltage range, without being overloaded, by a periodically limited energizing current. This is achieved, by way of example, by energizing the relay via a semiconductor switching device (transistor 14) which can be switched on and off by a Schmitt trigger (12) connected to the binary signal output. A capacitor (17) charged in dependence on the energizing current flowing through the relay is used to override the signal from the binary output (19) to switch the transistor (14) via the Schmitt trigger (12) so as to periodically energize the relay (15) (FIG. 1).

Abstract: Pulsed light barrier apparatus is driven directly from an a.c. supply voltage connected to the terminals L and M with the terminal M being earthed. A storage capacitor 14 is charged during the positive half wave of the a.c. supply voltage and is discharged at a time determined by a programmable unijunction transistor 13 through a photodiode 11 to emit a flash of light which passes across a region monitored by the light barrier to a photoreceiver 26. A Zener diode limits the voltage across the storage capacitor 14 to a value less than the peak a.c. supply voltage. As soon as the voltage across the storage capacitor has reached the Zener breakdown voltage the excess energy from the a.c. supply voltage is directed through a rectifier diode 18 to a smoothing capacitor 19 where it forms a positive operating voltage for the light receiver arrangement. During the negative half wave of the a.c.

Abstract: A light transmitter directs light via a first polarizing filter, so that it is polarized in one plane, to a retro-reflecting device across a region to be monitored and the retro-reflector produces depolarization, or rotates the plane of polarization of the light, prior to directing it to a light receiver positioned adjacent the light transmitter. A second polarizing filter crossed relative to the first is positioned in front of the light receiver so that the light receiver will only recognize light whose plane of polarization has been appropriately rotated by the retro-reflector but not light reflected from a strongly reflecting object which interrupts the light barrier. Threshold circuitry evaluates whether a signal from a photoelectric convertor embodied in the receiver lies above or below a given threshold. Weakly reflecting objects are not recognized, because light reflected therefrom will be too weak to generate a signal above the required threshold. Various polarizing arrangements are described.

Abstract: An adjustment device for aligning a group of cyclically switched transmitters or receivers with a single receiver or transmitter of the kind in which a series of spatially spaced beams pass between the transmitters and the receiver, or alternatively between the transmitter and the receivers. In a preferred form the adjustment device is used to ensure alignment of a row of infra-red transmitters which direct beams of light to a photoelectric converter arranged at the focus of a concave mirror. The adjustment device features a coincidence circuit the outputs from which indicate that signals transmitted from the end transmitters of the row are received at the photoelectric converter. The outputs are used to energize respective adjustment indicating lamps. In a particularly preferred arrangement threshold circuitry is used to produce winking of the lamps when approximate adjustment has been achieved; continuous lighting of the lamps shows that accurate adjustment is present.

Abstract: A photoelectric detection system which has two sequential photoelectric receivers to determine the precise moment at which the boundary between two contrasting fields passes beneath the detectors irrespective of the relative contrast between the two fields. The signals from the two photoelectric detectors which change as the boundary progressively obscures their respective fields of view are firstly subtracted to produce a difference signal. The difference signal is then passed to a gated maximum value store which is operative during each difference pulse to store the maximum value of the difference occurring during that pulse. A fraction of this maximum value is then taken and compared with the instantaneous value of the difference as this value reduces, when these two values are equal an output pulse is generated and this output pulse always occurs at the same position of the boundary relative to the photoelectric receivers irrespective of the respective levels of contrast on either side of the boundary.

Abstract: Bottle color identification apparatus with a light beam passing through the bottle, in which the light beam passing through the bottle is supplied to a spectral decomposition arrangement which emits a signal characteristic of the bottle color.A special application of the invention is the sorting of returnable bottles having the same size and shape but different colors.

Abstract: A photoelectronic instrument for measuring the length of an object by means of a slim scanning beam of light which, when not interrupted by the object, activates a photoelectric transducer, wherein, for the purpose of determining trigger points when half the light beam is obscured at the beginning and reemerges at the end of the period of cut-off, irrespective of the absolute magnitude of the light flux of the unobscured light beam, a circuit is provided for differentiating, with respect to time, a signal obtained from the photoelectric transducer and proportional to the magnitude of the light flux (light flux signal U.sub.1), a signal proportional to the differential quotient (dU.sub.1 /dt) thus obtained being rectified, multiplied by a preset factor (p.T), and the product of the multiplication and the light flux signal (U.sub.1) being applied to the inputs of a comparator functioning as a coincidence circuit for generating an output signal (U.sub.

Abstract: A light barrier system is provided which includes a light transmitter, a light receiver to receive the light beam transmitted over a predetermined path, an indicator unit which is connected to the light receiver and produces a signal when an obstacle is detected in the path, and a power unit supplying the light transmitter, light receiver and indicator unit. The power unit consists essentially only of a rectifier. A pulsed light source is employed, operated by the discharge of a capacitor in the rectifier output.