Table 2
FLASH-RATE
DIAL
CALIBRATION
MARKS
Images
Revolutions
Per
Minute
1 1800 900 600 450 360 300 200
2 3600 1200 720 514 400
3 2700 1350 1080
4 2400 1440 1028 800
5 3000 2250 1500 1280
6 2160 1543 1350
Line
Frequency
Submultilple.
In the LINE-FREO-SUB-MULT mode the strobotac
will
flash at a rate equal
to
a submultiple
of
the line frequency
(i.e. 3600, 1800, 1200 .
..
240 fpm
with
an
accuracy equal
to
that
of
the 60-Hz line
within
0.
1%).
The strobe
automatically switches from one submultiple
to
another
as
the flash-rate control
is
varied over its
range
-the flash rate
does
not
vary continuously.
This mode
of
operation
can
be
used
to
accurately
measure
the slip
speed
of
motors. For example:
a. Mark the
end
of
the shaft
of
a 1750 rpm induction
motor.
b.
Set the strobotac
to
the first submultiple
of
the line
frequency
and
direct the strobe light on the shaft.
c.
Notice that the mark
appears
to
rotate (slip). To
determine the slip
speed,
count the number
of
revolutions
that occur in one minute. To determine the actual
speed
of
the n:'otor subtract the slip
speed
from 1800 rpm.
The submultiple of the line frequency at which the
strobotac
is
flashing
can
be
determined by
using
a synchro-
nous motor
in
the
above
procedure.
Set
the flash-rate dial
to
the high
end
and
depress
the LINE-FREO-SUB-MULT
button. Point the strobotac toward the outer surface
of
the disk
and
turn on the motor. Two
images
of
the mark should
be
seen
180° apart. Rotate the flash-rate
knob ccw until a single
image
appears.
This corresponds to
the first submultiple
of
the line frequency (60/2
flashes/min or 1800 rpm). The
second
submultiple (60/3)
will
be
a double
image
and
each
successive
image
will
alternate between a single
and
double
image,
down
to
approximately the 15th submultiple.
External
Trigger.
In the EXTERNAL-TRIGGER mode, the strobotac will
flash at a rate determined by the frequency
of
the
external-trigger device
(such
as
a
cam
operated micro switch
or a
camera
shutter). Refer
to
the STROBES
FOR
PHOTOGRAPHERS
para
.
for
an
application
of
this
mode.
NOTE
The trigger device must
be
a contact closure
with
both
sides
isolated from ground.
If
a contact device connected
to
the strobotac
is
operated at a frequency higher than 3780 fpm, the strobe
oscillator will automatically divide down
to
the approxi-
mate submultiple. The strobe
will
flash at a rate equal to
that submultiple.
Noise
is
usually generated by a contact-closure device
when the contacts
are
closed, due to contact bounce. The
circuit
design
is
such
that noise occurring up
to
15
ms
after
the initial contact closure will
be
filtered out. Information
on
how
to
increase
the time constant
of
this
filter
can
be
obtained from our service department
by
special request.
STROBES FOR PHOTOGRAPHERS.
GR
stroboscopes
are
widely employed in single
and
multiflash photography. .In
general
the
camera
used
should
have
a
"time"
or
"bulb"
connection
(for
multiple expo-
sure).
an
"X"
synchronization connection (for single
exposure).
an
adjustable aperture, a cable
release,
and
a
tripod mount. Polaroid
film
is
recommended.
Following
is
a procedure
for
making a single-flash
photograph
using
the
EXTERNAL
TRIGGER mode:
a. Find the guide number
for
the
film
speed
used
(see
Figure
3)
.
b.
Measure
the lamp-to-subject distance.
c.
Calculate the aperture setting using the following
Guide Number
formula: f/number =
-:--:-:----,--....,...,..-......,.,---..,..,--.
1 + lamp-to-subject distance (ft.)
d. Adjust the
camera
aperture to the calculated setting.
e.
Depress
the
POWER
and
EXTERNAL
TRIGGER
buttons
of
the strobotac.
f. Connect the
EXTERNAL
TRIGGER jack on the
strobotac
to
the shutter
release
on
the
camera.
Use
an
adaptor cable
with
a standard, two-conductor phone plug
on this
end
and
the appropriate connector
for
the
camera
end.
The setup
is
now ready
to
make
a single-exposure
photograph.
1000
500
100
a::
~50
:::1!
:;)
z
....
0
:;)
(!)
10
5
I
7
..,""
v
I"
10
50
100
500
1000
Fl
LM
SPEED-
ASA
Figure 3. Guide-number chart.
5000
10,000
1543-J
3
