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MARQUAT sensors are devices that convert optical signals into electrical signals. Their operating principle is based on the photoelectric effect. The photoelectric effect refers to the phenomenon where electrons in a material absorb photon energy when light strikes certain substances, resulting in corresponding electrical effects. Based on the different manifestations of the photoelectric effect, it is classified into three categories: external photoelectric effect, internal photoelectric effect, and photovoltaic effect. Photoelectric devices include phototubes, photomultiplier tubes, photoresistors, photodiodes, phototransistors, and photocells. The performance and characteristic curves of photoelectric devices are analyzed.

MARQUAT sensor principles

Photoelectric sensors achieve control by converting changes in light intensity into changes in electrical signals. Generally, photoelectric sensors consist of three parts: transmitter, receiver, and detection circuit. The transmitter emits a light beam toward the target. The emitted light beam usually originates from semiconductor light sources, such as light-emitting diodes (LED), laser diodes, and infrared emitting diodes. The light beam is emitted continuously or with modulated pulse width. The receiver consists of photodiodes, phototransistors, and photocells. Optical components such as lenses and apertures are installed in front of the receiver. Behind it is the detection circuit, which filters valid signals and applies them. In addition, structural components of photoelectric switches include emitter plates and optical fibers.

MARQUAT sensor classification

1) Slot-type photoelectric sensor: A slot-type photoelectric sensor is formed by mounting a light emitter and a receiver face-to-face on opposite sides of a slot. The emitter can emit infrared or visible light, and the receiver can detect the light when unobstructed. However, when the detected object passes through the slot, the light is blocked, causing the photoelectric switch to actuate and output a switching control signal to cut off or connect the load current, thereby completing a control action. Due to limitations imposed by the overall structure, the sensing distance of slot-type switches is generally only a few centimeters. 2) Through-beam photoelectric sensor: Separating the emitter and the receiver increases the sensing distance. A through-beam photoelectric switch, abbreviated as through-beam switch, consists of one emitter and one receiver. The sensing distance of through-beam photoelectric switches can reach several meters or even tens of meters. When using a through-beam photoelectric switch, the emitter and receiver are installed on opposite sides of the path through which the detected object passes. When the object passes through and blocks the light path, the receiver actuates and outputs a switching control signal. 3) Retro-reflective photoelectric switch: The emitter and receiver are housed in the same unit, with a reflector plate installed in front. This configuration utilizes the principle of reflection to achieve photoelectric control and is called a retro-reflective (or mirror-reflective) photoelectric switch. Under normal conditions, the light emitted by the emitter is reflected back by the reflector plate and received by the receiver. Once the detected object blocks the light path and the receiver no longer receives light, the photoelectric switch actuates and outputs a switching control signal. 4) Diffuse-reflective photoelectric switch: The sensing head of a diffuse-reflective photoelectric switch also contains an emitter and a receiver, but there is no reflector plate in front. Under normal conditions, the receiver cannot detect the light emitted by the emitter. During detection, when an object passes through, it blocks the light and reflects part of it back. The receiver then detects the light signal and outputs a switching signal.

MARQUAT sensor application cases

1) Application of photoelectric sensors in laser weapons: Since photoelectric sensors are particularly sensitive to infrared radiation, visible light, or both, they are more likely to become targets of laser attacks. Furthermore, electronic systems and the sensors themselves are highly susceptible to interference from thermal noise and electromagnetic noise generated by lasers, preventing normal operation. Methods by which battlefield laser weapons attack photoelectric sensors mainly include the following: using a laser beam of appropriate energy to "blind" the sensor, rendering it unable to detect or continue tracking already detected targets. Alternatively, if the sensor is guiding a weapon toward a target, blinding will cause it to lose the target. In summary, because sensors play an increasingly important role on the battlefield and are vulnerable to laser attacks, they have become the preferred targets for low-energy laser weapons. 2) Application of photoelectric sensors in automatic meter reading systems: With the development of microelectronics, sensor technology, computer technology, and modern communications, photoelectric sensors can be used to develop automatic meter reading systems. The aluminum disk of an electricity meter rotates under torque generated by eddy currents and magnetic fields. Using photoelectric sensors converts the number of rotations of the aluminum disk into pulse counts. For example, by partially blackening a rotating shiny aluminum disk and pairing it with a reflective photoelectric emitter-receiver pair, pulses are generated at the blackened areas as the disk rotates. The rotations of the aluminum disk are sampled and converted into corresponding pulse counts, which are then sent via an optocoupler isolation circuit to the T0 port of the CPU for counting processing. Using optocoupler isolators effectively prevents interference signals from entering the microcomputer. Combined with other transmission methods, this forms an automatic meter reading system. 3) Application of photoelectric sensors in monitoring smoke and dust pollution: Photoelectric sensors are small electronic devices that detect changes in received light intensity, achieving control functions by converting changes in light intensity into changes in electrical signals. Due to characteristics such as non-contact operation, fast response, and reliable performance, photoelectric sensors are widely used in industrial automation equipment and robotics. We can utilize the characteristics of photoelectric sensors to detect smoke and dust conditions; thus, the strength of the output signal from the photoelectric sensor reflects changes in flue gas turbidity. 4) Hygienic washdown-resistant photoelectric sensors: Washdown-resistant sensors provide extremely high reliability and ease of use while minimizing operating costs. Equipped with IO-Link interfaces and the proTect+ sealing concept, which significantly extends service life, these two new sensors are suitable for demanding applications and represent an ideal solution for the food and beverage industry.

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