21—a Photoelectric Instrument for the Assessment of Fabric Appearance and Structure

A description is given of a simple apparatus for the detection of defects such as barré, streakiness, and irregularities due to structure or chemical composition in fabrics. The image of a slit illuminated by a small lamp is focussed on to the fabric and either the reflected or transmitted radiation analysed. Reflected radiation is collected by an integrating sphere and detected by two photomultipliers, one sensitive to the green and the other to the near infra-red. A phototransistor is used for the detection of transmitted light. Detector signals are processed and displayed by a millivolt pen recorder or an electronic counter. The resolution of the instrument is good enough to resolve single threads in the fabric. Inhomogeneities in depth of colour for a blude shade show up in the response of the green-sensitive photomultiplier but not in the response of the infra-red detector (which is insensitive to the dye) or the phototransistor. Other ‘faults’ can be detected by all three detectors. It is possible to obtain a quantitative measure of barré and streakiness with the aid of the electronic counter.