– 8 –
8.0 EXTERNAL TRIGGERING
The Pocket-Strobe can be externally triggered.
The EXTERNAL TRIGGER jack (
F
) is DTL/ TTL compatible. It detects a square-
wave signal of 0 to +5 volts which is at least 800 nsec in duration. The signal delay
(the time it takes for the signal to cause the strobe to flash) is less than 5 µsec.
The EXTERNAL TRIGGER jack uses a standard 1/ 8” phono plug with the
configuration shown below:
NOTES:
Turn the Pocket-Strobe off when inserting or removing a trigger cable.
Whenever an external trigger is used, the ON/OFF switch and the
Flash Adjustment Knob are disabled.
WARNING:
Do not trigger the device with signals over 208 Hz.
1. The outer connection (barrel) is common.
2. The middle connection provides a
+5 V DC output to drive external
sensors which are not self-powered.
3. The center connection is the input signal,
which triggers the flash.
– 13 –
What is the actual rate of the fan? Images 1, 3, 5, 7, and 8 are all “frozen,” so the rate
could be taken as 3,300. 1,100, 825, 660 or 550. Which is correct?
In order to determine the fan’s actual speed, a mark is added to one
of the blades and the test is run again.
Image No.:
1
2
3
4
Flash Rate:
3.300
1,650
1,100
916.6
Image No.:
5
6
7
8
Flash Rate:
825
733.3
660
550
Using the orientation mark, it is now clear that the images appearing at 3,300, 825 and
660 RPM are multiple-image harmonics. In each of these cases, three identification
marks appear. On the other hand, a singular image appears at 1,100 and again at 550.
Here, only one mark appears. Recall that “a singular image always appears at exactly
one half of the object’s true RPM.” 550 is one half of 1, 100. Therefore, the rate of the
fan must be 1,100 RPM.
Example 2: (Within Range No Mark Needed)
This example illustrates how the actual speed of an object can be determined without
the use of an orientation mark—provided that the object has a suitable shape.
Assume that the speed of this cam is known only to be less than
7,000 RPM. Because it has a unique shape, it does not need an
identifying mark. As the flash rate is lowered from 7,000, the
following harmonic images (see page 14) appear.
F
Close-up of LCD
EXT illuminates when External Trigger function is activated.
