Abstract: Apparatus for detecting the presence of an ink on a substrate comprises a number of LEDs (1) for irradiating the substrate (2) with radiation at at least two different wavelengths, at least one of the wavelengths being chosen to correspond to an absorption or relectance wavelength of the ink to be detected. A sequence generator (5) modulates the radiation at each wavelength in a respective, different manner. A radiation sensor (3) senses radiation emitted by the substrate (2). A correlator (7,8) correlates samples of the sensed radiation from the radiation sensor (3) with signals each of which is modulated by a respective one of the modulations applied to the radiation, to generate correlation signals. A monitor (9) monitors the correlation signals in order to detect the presence of the said ink.

Abstract: A monitoring system, particularly for use with document sorting apparatus, comprises a sensor assembly including a sensor for sensing a respective characteristic of an article and for generating a corresponding first output signal, and a detector controller for applying at least one of a predetermined set of algorithms to the first output signal from the sensor, in conjunction with data supplied to the detector controller, to generate one or more second output signals. A detector processor common to each of the sensor assemblies supplies the data and algorithm selection information to the detector controllers to control which of the set of algorithms is applied by the detector controller and to generate in response to the or each second output signal and reference data a third output signal representative of the characteristic of the article being monitored.

Abstract: This application discloses a method and apparatus for ascertaining the fitness of a document having some printed regions and some unprinted regions, by determining its degree of soiling. A sensor (16) provides reflectance signals representing the intensity of light reflected from a number of sensed elements on the face of the document. A signal processing circuit responsive to the reflectance signals includes means (26) for determining for each of a number of areas of the document, the number of elements in the area which result in a signal level exceeding a first threshold which represents the upper limit of brightness for printed areas on the document; and means (24,34,36) for determining whether the number of elements exceeding the first threshold reaches a given proportion of the total number of sensed elements for that area.