OPBA2QD BANNER ENGINEERING, OPBA2QD Datasheet - Page 6

• Manufacturer Part Number: OPBA2QD
• Description: POWER BLOCK
• Manufacturer: BANNER ENGINEERING

Specifications of OPBA2QD

• Accessory Type: Power Block
• Function: Module, Power Block
• Technology: Photoelectric
• For Use With: OMNI-BEAM Sensors
• Lead Free Status / Rohs Status: RoHS Exempt Product

6
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 installa-
tion and maintenance.
Excess gain
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:
Contrast
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:
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.
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 at the top of this page) is calculated as
follows:
This value is expressed as "6:1" or "six-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. In this situation (such as
an application in which a box breaks a the beam
of an opposed mode emitter and receiver):
Standard OMNI-BEAM Sensor Heads
Relationship between Excess Gain and D.A.T.A. System Lights
Measuring Excess Gain and Contrast
*NOTE: the scale factor is selected by programming switch #4 inside the sensor head (see page 7). "OFF" = STANDARD; "ON" = FINE.
Use the FINE scale only for setup and monitoring of close-differential sensing applications where LOW hysteresis is required.
Excess gain (E.G.) = light energy falling on receiver
Contrast is greater than 3.7x = 15:1
Contrast =
D.A.T.A. light
LED number
Contrast = 2.2x = 6
is the ratio of the amount of light falling on the receiver in
#1
#2
#3
#4
#5
is a measurement of the amount of light energy falling
Excess gain (light condition)
Excess gain (dark condition)
0.35x
amplifier threshold
STANDARD
scale factor
0.25x E.G.
0.35x
0.5x
0.7x
1.0x
0.25x
FINE*
scale factor
0.5x E.G.
0.7x
0.8x
0.9x
1.0x
Of course, it is not always possible to adjust a sensor to maintain this much contrast.
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. The
Contrast Values and Corresponding Guidelines table (above) gives general guidelines for
contrast values.
DARK condition example: D.A.T.A. system
LEDs #1 and #2 lit.
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 below (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.
Contrast Values and Corresponding Guidelines
Contrast Ratio
1.2 or less
1.2 to 2
2 to 3
3 to 10
10 or greater
D.A.T.A. light
LED number
#6
#7
#8
#9
#10
Unreliable. Evaluate alternative sensing
schemes.
Poor contrast. Use the LOW hysteresis
setting and the FINE scale factor.
Low contrast. Sensing environment must
remain perfectly clean and all other sensing
variables must remain stable.
Good contrast. Minor sensing system
variables will not affect sensing reliability.
Excellent contrast. Sensing should remain
reliable as long as the sensing system has
enough excess gain for operation.
STANDARD
scale factor
1.3x
1.7x
2.2x
2.9x
3.7x (or more)
LIGHT condition example: D.A.T.A. system
LEDs #1 through #8 lit.
Recommendation
FINE*
scale factor
1.1x
1.2x
1.3x
1.7x
2.2x (or more)