Installation Notes
Conventional retroreflective photoelectric sensors are extremely easy to align. Beam angles are wide, and retro targets are forgiving to
the light beam’s angle of incidence. The beam of this laser sensor is very narrow, compared with the beam of most retro sensors. As
Figure 6 indicates, the effect of angular misalignment can be dramatic. Alignment is critical because the beam may miss the retroreflec-
tive target unless the target is large.
Sensing Distance = X
Ø = Misalignment Angle
Y = X(tan Ø)
Y
Figure 6. Beam Displacement per degree of misalignment
Sensor-to-Target Dis-
tance (X)
Beam Displacement (Y)
for 1º of Misalignment
1.5 m (5')
25 mm (1")
3 m (10')
50 mm (2")
6 m (20')
100 mm (4")
15 m (50')
250 mm (10")
30 m (100')
500 mm (20")
For example, with one BRT-51X51BM mounted at a distance of 6 m (20') from the sensor, one degree of angular misalignment will cause
the center of the laser beam to miss the center of the target by 100 mm (4").
Alignment Tip
When using a small retroreflective target at medium or long range, it is often useful to temporarily attach (or suspend) a strip of retrore-
flective tape (e.g., BRT-TVHG-2X2) along a line that intersects the actual target. The visible red laser beam is easily seen in normal room
lighting on such tape. Sight along the beam toward the target (from behind the sensor). Move the sensor to scan the laser beam back
and forth across the retro tape strip. Use the tape strip to guide the beam onto the target.
Consider using sensor mounting bracket model SMB30SC (see page 11). This swivel bracket can simplify multiple-axis alignment. Align-
ment is complete when the visible image is centered on the retro target. The perpendicularity of the laser beam to the face of the retro
target is forgiving, just as it is with a conventional retroreflective sensor.
Effective Beam Size
Unlike conventional retroreflective sensors, the retroreflective laser has the ability to sense relatively small profiles. Figure 7 indicates the
diameter of the smallest opaque rod which will reliably break the laser beam at several sensor-to-object distances using sensor model
QS30LLP(Q). These minimum object sizes were measured with the sensor aligned to a BRT-51X51BM reflector and the gain set to
maximum using the Max Excess Gain SET. This sensor is typically recommended for long-range applications of relatively small targets
that will completely break the beam.
Figure 7. Minimum object detection size vs.
distance from sensor, model QS30LLP(Q)
Sensor-to-Object
Distance (X)
Minimum Object De-
tection Size
0.3 m (1')
2.5 mm (0.10")
1.5 m (5')
5.0 mm (0.20")
3 m (10')
7.0 mm (0.28")
18 m (59')
13 mm (0.52")
Smaller objects can be detected by using model QS30LLPC(Q), adjusting the
sensor gain down using the Manual Adjust, or performing a Low-Contrast SET
of the reflector. Objects as small as 2.0 mm can be reliably detected after per-
forming the Low-Contrast SET at ranges up to 6 m (18'). This sensor is typically
recommended for shorter-range applications detecting very small targets that
may break only a portion of the beam.
Note that the shape of the beam is elliptical. The minimum object sizes listed
assume passage of the rod across the major diameter of the ellipse (worst
case). It may be possible to detect objects smaller than the sizes listed if the
direction in which the objects pass through the beam can be controlled.
Retroreflector Recommendations
• BRT-51X51BM recommended for beam-block applications up to 18 m range.
• BRT-TVHG-2X2 recommended for applications up to 2 m range. (This retroreflector is an adhesive-backed sealed tape with micro-
prism geometry.)
WORLD-BEAM QS30 LLP and LLPC
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