Light Sensors
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Active Infrared Detectors Functional principles An Active Infrared Detector always comprises one transmitter and at least two receiver chips with high-quality optical systems. These are housed on the sensor PCBs (modular system) or in the preassembled housings (individual sensors). The scanning range is set by means of a mechanical mircro-speed unit by changing the angle between the transmitter and receiver. This optical procedure is called triangulation or optical differential measurement. Active Infrared Detectors are static, i.e. they only detect persons and objects if these are actually in the beam. Advantages of background suppression ■ Almost constant scanning range for reflective objects with diffuse reflectances which vary greatly Reliable detection of dark objects against light backgrounds Insensitive toward undesired reflection from objects in the background (aluminum channelled plates, marble floors etc.) Very high operating reserve Mobile installation possible (e.g. on elevator doors) System variants Available variants include autonomous Active Infrared Detectors with separate housings or systems in the form of a PCB with profile housings which can be assembled as desired (modular system). Autonomous Active Infrared Detectors Available as single-beam sensors with point detection beams, as four-beam area sensors or as count sensors also with four beams and intelligent evaluation electronics (see Fig.2). Fig. 2 The detection area consists of points and depends, to a large extent, on the optical centre-to-centre distances of the transmitter and receiver lenses. Several beams can be combined in the modular system (e.g. RMV/RMT) to form lines (vertical Light Curtains without counter-sensor) or a defined area (area Acitve Infrared Detector FLT 2800 or count sensor CLS 2000). Background suppression The following comparison determines which of the two receiver chips receives more light. Element in foreground receives more light; the object is detected Receiver Sacanning range In contrast to Active Infrared Detectors with background suppression (the signal changes when an object enters the scanning area), the systems with background analysis require a signal from the background in order to deactivate the output. The Detector will thus continue to function even in the event of vandalism, e.g. if the optical surface is partially or completely covered. Important information for Active Infrared Detectors with background analysis Object in scanning range Scanning area boundary Background analysis Element in background receives more light; the object is masked a) Direction of movement 1 b) Direction of movement 2 Scanning area boundary The sensor is installed and requires a background (floor/wall) – the output is deactivated. 2. The desired scanning range is set mechanically within the predefined possible distances. Light background As only the position of the object within the optically active range and not its reflectivity determines whether the element in the foreground or the element in the background receives more light, light and dark objects can be detected with the same degree of reliability. Only in the cross-over area between the foreground and background is there a difference between the scanning ranges for white and very black objects of a few percent of the nominal range. 3. Each object within the set scanning range is detected statically (see Fig. 2). Advantages of background analysis ■ As points 1–3 for background suppression Testing possible – contact-free protection alignment with test Ideal for safety locks as the optical system cannot be covered and it is not possible to push even flat objects (e.g. envelopes) between the floor and scanning field. Two light bundles are combined in each case to form one line of light. The movement signal is determined from the sequence in which the person passes through the lines of light. Modular Active Infrared Detectors These Active Infrared Detectors are designed as PCBs – each PCB has one detection beam. Versions with power supply units and output stages (master) are suitable for controlling and evaluating up to eight further PCBs without power supply units and output stages (slave). Detector PCBs can be installed directly behind covers (pay attention to the lens apertures, tightness, vibrations, contamination etc.) or can be mounted in the various aluminium support extrusion which we offer as a mechanical housing package with the sensor window and side caps for installation by the user. Typical applications Please refer to the individual product brochures.