Banner OMNI-BEAM Series - Manual (Page 4)

OSBLVAGC
Sensor Head
DARK condition example: D.A.T.A.
system LEDs #1 and #2 lit. LIGHT condition example: D.A.T.A.
system LEDs #1 through #8 lit.
Contrast = 1.3x = 1.8
0.7x
4
(Setup Procedure continued from page 3)
2) With no load attached, apply power to the sensor. With the aid of an assistant if
necessary, hold the reflector at its approximate mounting position, directly facing the
sensor, and move it up/down and right/left while observing the D.A.T.A. display on
the sensor. Find the center of the zone of reflector movement within which the most
LEDs on the 10-element array remain "on". It may be necessary to decrease (rotate
ccw) or increase (rotate cw) the sensor's 15-turn GAIN control to produce the most
easily "readable" indications for fine tuning the reflector position. Mount the reflector
at the center of this movement zone, directly facing the sensor.
3) Present the object to the sensor at the sensing point. Adjust the 15-turn GAIN
control to light three LEDs on the D.A.T.A. array. Remove the object from the sensing
position and note the number of LEDs that light with the object absent. If six or more
LEDs are lit, optical contrast in the application is adequate. Four or more LEDs lit in
the "dark" condition and/or five or less in the light condition represent inadequate
sensing contrast and will trigger a warning from the sensor head. If possible,
experiment by presenting different "views" of the object to the sensor, for the purpose
of increasing contrast. The GAIN control should be set so that the "dark" signal does
not light more than three LEDs.
For example, if LEDs #1 through #8 come "on" in the
"light" condition and LEDs #1 and #2 come "on" in the
"dark" condition (as shown in the photos at right), the
contrast (referring to the table above) is calculated as
follows:
This value is expressed as "1.8:1" or "1.8-to-one".
The best sensor adjustment will cause all ten D.A.T.A.
LEDs to come "on" for the "light" condition, and will
cause no LEDs to come "on" in the "dark" condition. This
is rarely possible when sensing clear materials. However,
it is important to always adjust a sensor for the greatest
amount of contrast possible for any sensing situation.
The D.A.T.A. light system makes this easy. Suggestions
for maximizing sensing contrast in your application are
given in the Theory and Setup section on page 3.
Contrast is the ratio of the amount of light falling on the receiver in the "light" state as compared to the "dark" state. Contrast is also referred
to as "light-to-dark ratio". Optimizing the contrast in any sensing situation will increase the reliability of the sensing system. Contrast may be
calculated if excess gain values are known for both the light and dark conditions:
Contrast =Excess gain (light condition)
Excess gain (dark condition)
To determine the contrast for any sensing application, present both the "light" and "dark" conditions to the OMNI-BEAM, and read the D.A.T.A.
signal for each. Take the ratio of the two numbers (from the table above) that correspond to the highest D.A.T.A. light numbers registered for
the "light" and "dark" conditions.
The amplifier threshold is the point at which the sensor's output switches. The OMNI-BEAM's threshold corresponds to the #5 level of the
D.A.T.A. light array. That is, when LEDs #1 through #5 are lit, the excess gain of the received light signal is equal to "1x".
The table above (Relationship between Excess Gain and D.A.T.A. System Lights) shows how excess gain relates to the D.A.T.A. light array indication.
The OMNI-BEAM's D.A.T.A. lights may be used to measure the
excess gain and contrast in any sensing situation and during
installation and maintenance.
Excess gain is a measurement of the amount of light energy
falling on the receiver of a photoelectric sensor over and above
the minimum amount necessary to operate the sensor's amplifier.
Excess gain is expressed as a ratio:
Excess gain (E.G.) = light energy falling on receiver
amplifier threshold
D.A.T.A. light
LED number Excess
Gain D.A.T.A. light
LED number Excess
Gain
Relationship between Excess Gain and D.A.T.A. System Lights
#1 0.5x E.G.
#2 0.7x
#3 0.8x
#4 0.9x
#5 1.0x
#6 1.1x
#7 1.2x
#8 1.3x
#9 1.7x
#10 2.2x (or more)
Measuring Excess Gain and Contrast
This curve shows the excess gain of the OSBLVAGC sensor
when it is used with different size retroreflectors. It also shows
the maximum sensor-to-reflector distance for each reflector.
The larger the reflector, the higher the excess gain, the greater
the possible sensor-to-reflector distance, and the wider the
effective beam. If the objects to be sensed are small, a smaller
(or partially masked) reflector might provide better optical
contrast than a larger one. This is because the larger the
reflector used, the larger the sensor's effective beam. Refer to
Figure 1 (page 3). A larger reflector might cause light to "spill"
around the edges of a small object and increase the light signal
that the sensor sees in the "dark" condition.
10
1
SENSOR-TO-REFLECTOR DISTANCE
100
.1 FT
,03 m 1 FT
,3 m 10 FT
3,0 m 100 FT
30 m
E
X
C
E
S
S
G
A
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N
OSBLVAGC
with various reflectors
with
BRT-3
with
BRT-1.5
with
BRT-1
with
BRT-.6