8
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.
To select a flash rate from a Preset (memory) location:
1.
Press the
ALT FUNCTION
button and then the
MEMORY
button.
2.
READ
will be displayed.
3.
Turn the tuning knob to cycle through the preset flash rates.
4.
Once the desired flash rate is displayed, press the
MEMORY
button to select it. Press any other button to cancel.
5.
DONE
will be displayed.
To store the current flash rate in a Preset (memory) location:
1.
Press the
ALT FUNCTION
button and then the
MEMORY
button.
2.
READ
will be displayed.
3.
Do NOT turn the knob and press the
MEMORY
button again.
4.
STORE
will be displayed.
5.
Turn the tuning knob to cycle through the memory locations.
6.
Once the desired memory location is displayed, press the
MEMORY
button to store the current flash rate in that location.
Press any other button to cancel.
7.
DONE
will be displayed.
13
Example: Object Rotating at 5000 RPM
If the speed is outside the full scale range of the stroboscope (50,000 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
1/4 times
1/2 times
1 time
2 times
3 times
4 times
Flash Rate (FPM)
1250
2500
5000
10000
15000
20000
