Banner M12 Series—Visible Red LED - Manual (Page 2)

Banner Engineering Corp. • Minneapolis, MN U.S.A
www.bannerengineering.com • Tel: 763.544.3164 2
P/N 129721 rev. E
M12 Series Metal Barrel Sensors
Overview
Banner’s M12 family of sensors offers a full complement of sensing modes, all packaged in a
compact yet rugged metal housing. Their popular 12-mm threaded barrel design allows them
to mount easily into tight spaces, with the excellent performance expected of much larger
sensors.
The single-turn Gain potentiometer on most models and two Signal LEDs (positioned on either
side of the housing for visibility) provide easy alignment and configuration for reliable sensing
(see Figure 1). Note that when the signal LED is not ON, the green Power LED is visible
through all three LED ports.
Fixed-Field Mode Overview
M12 Series fixed-field sensors are powerful diffuse-mode sensors with far-limit cutoff (a type
of background suppression). Their high excess gain and fixed-field technology allow them to
detect objects of low reflectivity that are directly in front of another surface, while ignoring the
surface in the background.
The cutoff distance is fixed. Backgrounds and background objects must always be placed
beyond the cutoff distance.
Fixed-Field Sensing – Theory of Operation
In operation, the M12FF compares the reflections of its emitted light beam (E) from an object
back to the sensor’s two differently-aimed detectors R1 and R2 (see Figure 2). If the near
detector (R1) light signal is stronger than the far detector (R2) light signal (see object A, closer
than the cutoff distance), the sensor responds to the object. If the far detector (R2) light signal
is stronger than the near detector (R1) light signal (see object B, object beyond the cutoff
distance), the sensor ignores the object.
The cutoff distance for model M12FF sensors is fixed at 25, 50, or 75 mm (1", 2", or 3").
Objects lying beyond the cutoff distance are ignored, even if they are highly reflective.
However, it is possible to falsely detect a background object, under certain conditions (see
Background Reflectivity and Placement).
In the drawings and discussion on these pages, the letters E, R1, and R2 identify how the
sensor’s three optical elements (Emitter “E”, Near Detector “R1”, and Far Detector “R2”) line
up across the face of the sensor. The location of these elements defines the sensing axis (see
Figure 3). The sensing axis becomes important in certain situations, such as those illustrated
in Figures 6 and 7.
Fixed-Field Sensor Setup
Sensing Reliability
For best sensing reliability, the sensor-to-object distance should be positioned to maximize
excess gain. The excess gain curves for these sensors are shown on page 5. Sensing at
higher excess gains will make maximum use of the sensor’s available sensing power. The
background must be placed beyond the cutoff distance; more reflective backgrounds must be
placed further back. Following these two guidelines will improve sensing reliability.
Figure 1. Features
Green ON Steady Power ON
Green Flashing Output overloaded
Yellow ON Steady Light sensed
Yellow Flashing Marginal excess gain
Sensing
Axis
R1
R2
E
As a general rule, the most reliable sensing of an
object approaching from the side occurs when the
line of approach is parallel to the sensing axis.
Figure 3. Fixed-field sensing axis
R1
R2
Lenses
Object
A
Object B
or
Background
Sensing
Range
Cutoff
Distance
E
Receiver
Elements
Near
Detector
Far
Detector
Emitter
Object is sensed if amount of light at R1
is greater than the amount of light at R2
Figure 2. Fixed-field concept
Power LED
Signal LED
(one of two)
Single-turn Gain
Potentiometer