Overview of Leuze DRT25 Series CAT (Contrast Adaptive Teach) Sensor
The Leuze DRT25C.3/L6-M12 sensor with its new, Contrast Adaptive Technology (CAT), is designed to reliably sense the presence of virtually any target moving along on a “conveyor” (a background). The sensor sets its reference on the conveyor, and not the target, so its sensing is independent of the nature of the target itself.
This new technology is to be distinguished from a sensor with background suppression, which would instead set up on the target, and ignore any object beyond the target’s distance. Since a background suppression sensor prox’s off the target, it must reliably sense the target during its passage in order to avoid multiple triggers per target, as would occur for a target with a multi-faceted surface facing the sensor.
The Leuze sensor with CAT uses its “teach” button is used to recognize the conveyor, and any object which is not the conveyor is by default, sensed as the target present. Three different sensitivities (or tolerances) can be selected depending on how long the teach button is depressed; 2-7 seconds (yellow & green LED flash simultaneously), 7-12 seconds (yellow & green LED’s flash alternately), or >/= 12 seconds (only the green LED flashes), from least sensitivity (most tolerance of any variance in the conveyor) to highest sensitivity (least tolerance of any variance in the conveyor), respectively.
With the Robust Setting (high tolerance/least sensitivity), the sensor will tolerate near infinite variations in the conveyor’s contrast, from extremes of white to matt-black, and accept that variation as being the conveyor. With the Sensitive Teach (most sensitivity) setting, most variations in the conveyor’s contrast are allowed as being the conveyor, but extreme black on the conveyor may cause the sensor to falsely believe it sees a target on the conveyor.
Interestingly, for either situation above, the intended target needs to be approximately ¼ inch high off the conveyor to be sensed. It is significant to note that if the “conveyor” itself is intentionally moved that same approximate ¼ inch closer to the sensor it will activate the sensor’s output as though the target was present. This unique performance suggests that the sensor sets a sensitivity or tolerance for the conveyor “at some defined distance”, and that if that distance is reduced by an approximate ¼ inch, it will see the conveyor as a target, independent of the conveyor’s contrast, color, or reflectivity.
A distinct advantage of the Lueze sensor with CAT is that the target can have either a flat or a multi-faceted surface and be reliably sensed over the duration of the target’s passage without multiple triggers per a given target.
A flat plane piece of glass, if presented parallel to the conveyor (perpendicular to the sensor’s beam of light), will not be sensed, independent of distance off the conveyor, as the light passes through the glass with minimal reflectivity at this angle. If however, that glass is NOT normal to the beam of light from the sensor, the light beam is reflected away from returning to the sensor by the glass surface and is reliably sensed as a target present.
The sensor projects three [3] visible red spots along a single plane, and for most applications, all 3 spots must fall upon the target to sense the target and switch output states depending on the sensitivity/tolerance setting selected.
The portion of the duty-cycle between consecutive targets (“t’) is a function of the teach setting:
“Robust Teach” (“High tolerance”/low sensitivity): t = 20-80 milliseconds
“Standard Teach” (“normal sensitivity”): t = 120-180 milliseconds
“Sensitive Teach”(low tolerance/”high sensitivity”): t = 220-280 milliseconds.
Factory recommendations:
- If either the distance to the conveyor has changed, or the conveyor has been replaced, that the sensor needs to be re-taught for the conveyor.
- Max distance from the sensor to the conveyor is 2-8 inches (50-200 mm), but the best rate of detection is to keep the distance to the target as small as possible.
- If the conveyor is a very glossy surface, it may be beneficial to tilt the sensor as to be 5-7 degrees off normal to the conveyor.
Both Q1 and Q2 outputs are push-pull, with I/O Link on output Q1. Both Q1 & Q2 outputs are defined as light switching PNP; dark switching NPN.
Sensor “response time is 0.66 milliseconds” (660. micro-seconds); which is apparently time to switch output states from conveyor sensed to target sensed for a single event. But note that the minimum “t” time for consecutive targets (explained below) is 20 milliseconds.
The sensor has a 4-pin M12 female connector on its body and is rated IP69K/IP67.
The Leuze DRT25C.3LT (with a suffix “T”) model offers a lock-out of the teach button by remotely holding the teach input high for > 20 milli-seconds.
Conclusion:
The sensor does perform in a very unique manner, and with its ability to ignore extreme variations in conveyor contrast, as well reliably sensing smooth to multi-faceted target surfaces, may offer a solution where other sensors do not. Generally speaking, the target must be at least ¼ inch high off the conveyor to be sensed, and the non-target portion of the duty-cycle (“t”) should be factored if either extremely fast-moving targets and/or consecutive targets that are closely spaced together.