Sensors with switching output (digital): Deviation of the switchpoint after often repeated switching, under identical conditions and with the same sensor.
Sensors with analog output: Change of the output value under the same conditions and with the same sensor. Value of the measured range indicated in percentage.
Protection against false connection.
All sensing ranges of photoelectric sensors and excess gain curves of retroreflective sensors mentioned in this catalog were determined with the BRT75 reflector. Retroreflectors are designed in such a way that light is reflected back in the same direction. The amount of light reflected back to the sensor depends on two factors:
1. The size of the reflecting surface
2. The reflector‘s reflectivity
Short distances require a reflector with Ø 25 mm which is capable of reflecting the light as good as a Ø 75 mm reflector. A Ø 75 mm reflector reflects up to nine times more light than a Ø 25 mm and is suited for longer distances.
Irregularities in the DC voltage may occur after the VAC mains voltage is rectified to a VDC voltage (due to the original sinusoidal wave of the mains voltage). The remaining wave troughs can be compensated (“smoothed”) by means of a capacitor connected in parallel to the load or a coil connected in series to the load. The remaining AC component after smoothing is called the ripple or hum voltage. 10% ripple (peak to peak) of supply voltage is usually tolerated.
2-wire sensors: The current which flows in non-active condition.
3/4-wire sensors: The current which flows in non-active condition between the output and 0 V (PNP output), resp. between output and supply voltage (NPN output).
Opposed mode sensors:The range listed is the maximum distance between emitter and receiver under perfect conditions.Retro-reflective mode sensors: The range listed is the maximum distance between the sensor and a BRT75 retro-reflector under perfect conditions.Diffuse mode sensors:The range listed is the maximum distance between the sensor and a 20 x 25 cm Kodak 90% reflectance white test card under perfect conditions.Convergent mode sensors:The range listed is the distance from the sensor lens to the focal point.Fixed-field sensors:The range listed is the distance to the cut-off point.The intensity of light falls off inverse squarely with distance; i.e., if you double the distance, you will get 1/4 of the light intensity. The lens arrangement on retro-reflective, diffuse and convergent sensors means that at very short ranges most of the light may be reflected back to the emitter, not the receiver; and so the intensity of light reaching the receiver may actually fall as the range decreases. This can be clearly seen on the excess gain curves; and, in such cases, the sensor should be used at the range which gives the maximum or required level of excess gain.
An object has to reflect sufficient light in order to be detected by a diffuse or a convergent mode sensor. The amount of light received, depends on the emitting power of the sensor and the reflectivity of the object. A dark object reflects less light than a bright one (see Excess gain). A smooth, mirror-like surface has to be aligned perpendicular to the sensor‘s axis. Otherwise, the light is not reflected back.
Retroreflective sensors host both emitter and receiver circuitry in the same housing. A light beam is established between the emitter, reflector and receiver. An object is sensed when it interrupts the beam. Retroreflective sensors share some advantages with opposed mode sensors such as good contrast and high excess gain. Moreover, only one device has to be installed and wired. Of disadvantage are short sensing ranges and objects with shiny surfaces when using devices without polarizing filter.
The switching distance of inductive ferrite core sensors depends on the material of the actuating element.
The maximum switching distance is attained with mild steel St37, whereas with other metals only smaller switching distances are achieved.
The reduction factor indicates to which fraction the switching distance is reduced by using other metals than St37.
Reduction factor, typical values: Steel (St37): 1; brass: 0.35…0.5; copper: 0.25…0.45; aluminium: 0.35…0.50; stainless steel: 0.6…1
uprox® and uprox®+ sensors have the same switching distance for all metals. The reduction factor is always 1.
Real switching distance (sr)
Sensors have a delay that suppresses possible error pulses at the output for the period between switching on the power and the operational readiness of the sensor; for example < 80 ms for standard inductive sensors, and < 250 ms for uprox sensors.
The rated switching distance is measured through the axial approach of a standard target. Manufacturing tolerances and external influences such as temperature and voltage are not considered. The tables only indicate the rated operating distances.
Rated operational current (Ie)