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Setup/installation photoelectric sensors

Diffuse sensors with background suppression

The diffuse sensor must be aimed at the object. The sensing distance must be set to a distance between the target and the background. The background must be located behind the adjusted sensing distance by at least the distance of the sensing distance reduction of the sensor to black.

 

For diffuse sensors with background suppression, the sensing range diagram is specified for the optimum adjustment. This indicates the sensing range reduction as a function of the sensing range to white for different degrees of remission. This means the distance by which the sensing distance to black or gray is reduced in comparison with white. When the adjusted sensing range to white is entered on the X axis of the diagram, the reduction of the sensing distance to black or gray can be read off on the Y axis. The sensing distance reduction also indicates the minimum distance a black or gray object must be separated from a white background.

The direct reflection from glossy or reflective objects must not impinge on the receiver. This can be avoided by slightly tilting the sensor.

It should be ensured that the object to be detected approaches the active area of the sensor from the side, which avoids malfunctions caused by deflection of the light beam at edges.


Light barriers without reflector

The SmartReflect light barrier has to be aligned with a machine part within its sensing range. This machine part is then set using the teach-in.

It should be noted that there is a dead band directly in front of the machine part that is set automatically during teach-in. The dead band is determined by the specification of the sensing range (Sa) as a percentage (%)of the background position (Sde).

It should be noted that an object to be detected must approach the active range of the sensor from the side in order to avoid switching errors.


Diffuse sensors with intensity difference

With diffuse sensors operating by the intensity difference principle, the relative receiving signal is specified. This represents the signal level received from a white object as a function of the distance. Using this diagram, the sensing range can be determined for an object which is not white. The correction factor of the respective material is required for this purpose.

 

Correction factor

The material and surface properties of the object (representing the reflectivity) influence the switching distance of a diffuse sensor with intensity difference. To determine the corrected switching distance, the following values must therefore be applied to the relative receiving signal (KFs) or in approximation to the distance (KFd).


Retro-reflective sensors

Each sensor has a separate excess gain curve. As the operating reliability depends heavily on the ambient conditions, it must be ensured that the sensor operates with the highest possible excess signal gain.

With narrow light beams as used in laser sensors, the size of the light spot on the reflector in relation to the triple structure is crucial factor when it comes to choosing the reflector or the reflective type. A special reflective type or reflector for laser sensors should be used for spot diameters of up to 1,5mm, while the use of reflectors with microstructures is recommended for spot diameters of up to 3 mm. It should also be ensured that the reflective type or reflector is not placed close to the focus.

The reflector is aligned and centered.

The reflector may not be tilted by more than 15°.

For a correct function, the object must cover the reflector or at least have the size of the beam diameter on the distance.


Through beam sensors

The emitter and receiver must be aimed at each other. The narrower the angle of radiation and reception, the more accurately this must be conducted.


Distance measuring sensors

 
   With all distance measuring sensors, it must be ensured that the laser spot can be seen directly by the optical system of the receiver and that no obstructions are in front of the receiver.
 

With glossy or reflective objects, the direct reflection must not impinge on the receiver. This can be avoided by slightly tilting the sensor.

 

For optimum measurement results, the sensor must be installed at right angles to the movement of the object. A simple rule applies for triangulation sensors that the distance between the sensor and the object should be kept as small as possible for each application. The shorter the range, the better (more than proportional) the resolution and accuracy. Note on electromagnetic compatibility: ground the sensor and use a shielded connecting cable.