High-frequency contrast sensors
High-frequency contrast sensors for UV, VIS and IR range
The SPECTRO-1 sensors are contrast sensors that are able to record even slightest brightness differences almost in real time. The sensor features analog and digital signal outputs. With the optical fibre types (FIO) inspection can be performed both in transmitted-light and in reflected-light mode.
► Information on the range of types
► Measuring principle SPECTRO-with SPECTRO1-Scope
Transmitter and receiver optics are focused to the same distance. The transmitter optics is integrated in the receiver optics, which allows a highly compact design. The -COF type especially is characterised by a small light spot size at a large distance, which means that even small objects can be reliably detected at a large distance ( < 1000mm ). In addition to the white-light types there also are versions that operate in the UV range (UV-A light is used at the transmitter side, and the visible wavelength range is evaluated at the receiver side; -COF-UV types thus can be used for the inspection of fluorescent objects), and versions that operate with red laser light (-COF-LAS and -COF-LAS-CYL, which generate spot sizes in the tenth millimetre range at a large sensor distance and allow very narrow-band optical filtering).
–DIF (diffuse light with volume diffusor)
The light that is emitted by the transmitter LED is extremely diffused, which results in extreme gloss reduction. The sensor thus recognises a glossy black surface as black, and there is no gloss-related grey value shift towards higher values.
The objective is to reduce the gloss effect. Direct reflection has a disturbing effect on grey value determination (contrast), which means that glossy black surfaces also may be detected as grey, i.e. they may appear brighter than they normally are. Direct reflection can be reduced by using a surface diffusor, because the rate of diffuse transmitter light is increased.
The transmitter LEDs are arranged in a ring. They converge with the narrow-band light cones at a distance that is defined by the sensor unit (with -50-FCL e.g. at 50 mm sensor distance from the object). Both diffusely and directly reflected light can reach the receiver optics, which means that a combined evaluation of grey value (contrast) and gloss is performed. For this sensor system a glossy black object thus differs from a dull black object. In addition to the white-light LED version there also is an IR type (860 nm) which, among others, can be used for dullness inspection.
The sensor system features a polarisation filter both at the transmitter and receiver side. The polarisation directions of the two filters are rotated by 90° with respect to each other, which means that light of the same polarisation direction cannot pass the receiver filter. Since the polarisation direction exclusively is changed by diffuse reflection and not by direct reflection, this sensor type is excellently suited for gloss suppression, but also for the detection of transparent plastic films (whose direction of rotation also can be detected), because such films also show a certain polarisation effect.
With this sensor type the UV light that is emitted by the transmitter LEDs is partially converted into the visible wavelength range by fluorescent objects, and can then be detected at the receiver side.
An extensive selection of optical-fibre transmitted-light and reflected-light versions is available. In combination with the respective attachment optics spot sizes starting from a diameter of 0.2 mm with an object distance of 10 mm up to object distances of 500 mm and spot sizes of 50 mm can be realised in reflected-light operation, and transmitter-receiver distances of up to 2000 mm can be covered. In addition to a white-light LED version there also are versions that operate in the UV-A, blue, red, and IR wavelength range (dullness inspection with 860 nm).