In all automated processes sensors are necessary to provide the PLC with information. They supply the necessary signals for positions and limits, or serve as pulse pick-ups for counting tasks or for monitoring rotational speed. They offer ideal characteristics compared to mechanical switches: non-contact operation free from any wear and tear, high switching frequencies and accuracy. In addition, they are insensitive to vibration, dust and moisture. Inductive sensors detect all metals without contact.
Capacitive sensors are used for the non-contact detection of any objects. In contrast to inductive sensors, which only detect metallic objects, capacitive sensors can also detect non-metallic materials.
Magnetic sensors are used for the detection of positions without contact or wear and tear in control technology. They are used where inductive proximity switches reach their limits. The advantage: Compared to inductive switches magnetic switches have a considerably higher sensing range and smaller housings.
Only prerequisite: The object to be detected must be equipped with a magnet because the switch only responds to magnets.
Cylinder sensors are used to sense the position of pistons in pneumatic cylinders. They are directly mounted onto the cylinder. The ring magnet at- tached to the piston is sensed through the housing wall of non-magnetisable material (e.g. aluminium, brass or stainless steel).
ifm electronic offers different solutions for various cylinder types.
A diffuse reflection sensor is used for the direct detection of objects. The sensor transmits an ultrasonic pulse which is reflected by the target object and received and evaluated by the sensor. With this system the time of flight of the ultrasonic pulse from the sensor to the object and back again is evaluated. As opposed to photoelectric sensors colour, transparency or the object's surface shine do not play a role.
The system consists of two separate components: a transmitter and a receiver. The transmitter emits pulsed light in the infrared or visible red wavelength range. The receiver detects the light beam and immediately converts a beam interruption caused by an object in the sensing zone into a switched signal.
As is the case with through-beam sensors transmitter and receiver are arranged face to face. Both components are permanent parts of a fork or an angle, i.e. they do not have to be aligned towards each other.
If an object enters the detection zone, the light beam is interrupted and a switching signal is generated. Optical fork and angle sensors use a particularly fine light beam and are thus suitable for the detection of tiny objects.
The system consists of two separate components: a transmitter and a receiver. The transmitter emits a fine laser beam which is received by the receiver. The interruption of the laser beam is evaluated. The small beam diameter allows detection of tiny objects and their exact positioning.
Fibre optics can be considered to be a prolongation of the optical components of the fibre-optic amplifier. Through-beam and diffuse reflection versions are available depending on the detection task. Fibre optics with glass fibres and metal sheath can be used in hot applications. For standard applications inexpensive fibre optics with acrylic fibres are available.
Contrast sensors detect marks the colour of which is in contrast to the colour of the background. The decisive factor for operational reliability is the difference in contrast between mark and background and the constant distance between sensor and colour mark. The material of the background is of no importance.
The range of available sensors covers position feedback on quarter-turn actuators, sensors with integrated connection for solenoid valves, sensors with AS-i bus connection and versions for hazardous areas as well as continuous position detection for linear valves.
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