One Plane Balancing with a Strobe Light
dataPAC User’s Guide
167
If the speed is outside the full scale range of the stroboscope (14,000 FPM for the dB+), 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)
When the dataPAC is used with the strobe (External mode), the readout displays directly in
RPM (FPM).
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 impossible to use below 300 FPM for inspection or to measure RPM.
Taking the Initial Vibration Measurement
1.
Connect the strobe light to the dataPAC using the connector cable provided. The mini-
jack plugs into the strobe as shown below, and the 9-pin D connector attaches to the
DATA I/O plug of the dataPAC.
2.
Attach a transducer to a bearing housing.
3.
When the machine is stopped, mark the rotor by making a mark on one rotor that serves
as a reference when using the strobe light. It is also possible to use an existing mark on
the rotor as the reference mark, such as a key or keyway.
Note:
If the rotor has multiple positions (vanes or fan blades), the reference mark must be at
one of the blade positions.
9-PIN “D” connector
goes to the “DATA I/
O” plug on the
dataPAC
mini jack
Entek IRD dataPAC
strobe light
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Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
