Banner OMNI-BEAM Series - Manual (Page 7)

7
Figure 11. Excess gain: OASBFX
Figure 14. Fiber optic angular
displacement of specular surface
Figure 12. Linear displacement with rectangular fibers
Figure 13. Fiber optic angular displacement
measurement
Figure 9. Displacement Measurement
1
.1
DISTANCE
10
100
1 IN 10 IN 100 IN 1000 IN
OASBFX
E
X
C
E
S
S
G
A
I
N
I
Opposed mode
with IT23S fibers
no lenses
4
2.7
.25
Max. NULL
Min. NULL
1
.1
DISTANCE
10
100
.1 IN 1 IN 10 IN 100 IN
Range based on 90%
reflectance white test card
OASBCV
E
X
C
E
S
S
G
A
I
N
I
Max. NULL
4
2.7
.25
Min. NULL
Figure 10. Fiber optic opposed distance measurement
Figure 8. Convergent mode,
depth-of-field
Figure 7. Excess gain curve: OASBCV
be seen far beyond the normal
depth of field, and small changes
in viewing angle can cause com-
plete loss of the received light
signal.
Model OASBCV uses a visible
red (650nm) light source. Con-
sequently, this sensor may be
used successfully in some ap-
plications to monitor the
reflectivity differences contrib-
uted by a change in object color.
However, a convergent beam
sensor may be used to monitor
such color changes only if the
sensing distance and other fac-
tors contributing to the object's
surface reflectivity remain con-
stant. Color monitoring appli-
cations always require a feasi-
bility study. Your Banner Field
Sales Engineer or Factory Ap-
plications Engineer can assist
with testing.
Fiber Optic Sensing
Modes:
models OASBF,
OASBFX, OASBFV,
OASBFP
Fiber optics offer many possibili-
ties for analog sensing and con-
trol. Individual fiber optics may
be used for opposed or mechani-
cal convergent sensing. Bifur-
cated fiber optics may be used for
diffuse mode sensing. Selection
of fiber diameter (plastic fibers)
or fiber bundle diameter (glass
fibers) affords a means of cus-
tomizing the sensing optics for
optimum analog response. Fiber
optics also offer ease of sensor
mounting, especially in tight lo-
cations.
Individual fiber optics:
Glass or plastic individual fiber optics are used in an opposed configuration for distance
measurement (Figure 10). If a pair of fibers are kept in alignment with one another while
moving apart, the decrease in excess gain is predicted directly by the inverse square law.
This fact is illustrated by the straight-line excess gain curves for opposed mode sensors
(Figure 11). Long distance measurement is accomplished by adding lens assemblies to
individual fiber optics with threaded end tips. Give consideration to the warnings about
flexing of glass fiber
optics whenever a fi-
ber optic is repeatedly
moved back and forth
over a long distance.
A pair of fiber optics
with a small fiber or
fiber bundle will offer
highly accurate mea-
surement over short
distances.
One way to accurately
measure small dis-
placements is to posi-
tion a pair of opposed
fiber optics so that the
displacement be-
tween two surfaces
causes misalignment
of the two fibers.
Figure 12 illustrates
how linear displace-
ment may be moni-
tored. Rectangular
glass fiber optic as-
semblies can be used
to monitor displace-
ment over a long dis-
tance with relative
fiber movement
occuring along the
length of the rectangular bundle termination. Figure 12 also illus-
trates how opposed glass fiber optics with rectangular sensing ends
may be used for very precise displacement measurement with
movement across the width of the rectangular termination. Figure
13 shows how opposed fiber optics are used to measure angular
displacement within any specified plane of rotation.
A pair of individual fiber optic assemblies may be used in the
specular reflection sensing mode for monitoring the angular dis-
placement of a specular (shiny) surface (Figure 14). Two threaded
fibers are used and
both are fitted witha
lens assembly. The
lenses are threaded
into each fiber sens-
ing end until the end
of the fiber (or fiber
bundle) comes into
sharp focus (appear-
ing magnified) as
viewed throught the
lens. The two fiber/
lens assemblies are
then mounted at
equal and opposite
angles (e.g. 45 de-