NOTE: There are maximum and minimum values in each mode
beyond which you cannot adjust. If you are adjusting the
rate and you reach a value which on the next increment would
exceed the maximum flash rate, the display will not increment.
The same is true if you try to adjust the flash rate below the
minimum flash rate.
To multiply or divide the current flash rate by 2:
In addition to the knob, there are two buttons on the back panel
marked x2 and ÷2. This enables the user to instantly double or halve
the reading on the display to the maximum or minimum values allowed.
This feature is useful for checking harmonics in the internal flashing
Alternate Knob Function (multiple by 2, 3, 4, 5, etc.)
The tuning knob functions differently when ALT. is displayed. The
current flash rate is used as an adder. The knob will add (counter
clockwise) or subtract (clockwise) that initial flash rate for each “click”
the knob is turned. This in effect allows the user to multiply the initial
flash rate by 2, 3, 4, 5, etc up to the maximum flash rate. This is very
helpful on fan blades. Using this feature, one can superimpose the
blades on top of each other and check for blade tracking, bent blades,
lead and lag tests, etc.
For example: A 3 bladed fan is spinning at 3600 RPM. The strobe is
flashing at 3600 FPM. Press the ALT FUNCTION button to display
ALT. Then turn the knob counter clockwise 2 clicks. The strobe will
now flash at 10,800 FPM (effectively 3600 times 3). The fans blades
will be all superimposed on each other. One can now see if the blades
are out of alignment, bent, etc. by viewing the blades from the front or
viewing from the side edge of the blades.
Example: object rotating at 5000 RPM
If the speed is outside the full scale range of the stroboscope (20,000 FPM),
it can be measured using the method of harmonics and multipoint calculation.
Start at the highest flash rate and adjust the flash rate down. You will
encounter multiple images so be aware of these. Note the flash rate of the
first SINGLE image you encounter, call this speed “A”. Continue decreasing
the flash rate until you encounter a second SINGLE image. Note this speed
as “B”. Continue decreasing the speed until you reach a third SINGLE
image at speed “C”.
For a two point calculation the actual speed is given by:
RPM = AB/(A-B)
For a three point calculation:
RPM = 2XY(X+Y)/(X-Y)2 where
X = (A-B) and
Y = (B-C)
If a Remote Optical Sensor or Magnetic Sensor is used to sense one pulse
per revolution (External mode), the readout will display directly in RPM
(FPM) without any adjustment required.
In instances when you can shut down the device and install a piece of
reflective tape, then an optical tachometer is easier to use for RPM
measurement. Stroboscopes must be used when you can’t shut down
the device. The human eye is not easily tricked into seeing a stopped image
by a stroboscope when the flash rate is slower than 300 FPM. Therefore,
stroboscopes are just about impossible to use below 300 FPM for inspection
or to measure RPM.
Stopped Image 1/3 times 1/2 times 1 time 2 times 3 times 4 times
Flash Rate (FPM) 1250 2500 5000 10000 15000 20000