Monarch Instrument Vibration Strobe - Manual (Page 8)

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To set-up for balancing or phase measurement, a data collector or vibration analyzer must be used
that is capable of interfacing with the Vibration Strobe. The instrument must then be set up to obtain
and record the phase information supplied to it from the strobe and the reference transducer.
As a general set-up guideline for the data collector or analyzer, in order to be triggered properly and
to read phase properly, check the following:
1. Set the instrument to accept an external tachometer trigger signal. The strobe light will
provide this signal.
2. Set the frequency range for order analysis (10 orders full scale works best). This insures
the 1X frequency will be centered in the 1X (first order) filter which is a must for repeatable
phase measurements.
3. Set the instrument to display averaged spectrum and phase data (4 or 8 averages).
4. Set transducer power to On.
NOTE: Application Notes are available for some data collectors that describe their particular set-
up configurations. Check the Owners Manual for your data collector for proper setup
configurations.
Connect the proper interconnect cable between the strobe and the data collector or analyzer. See
wiring diagram to build the cable. The Input (Up Arrow) and Output (Down Arrow) jacks are
located on the left side of the strobe. Connect the vibration transducer (this may be a separate cable
or an integral cable) to the strobe cable.
NOTE: The vibration transducer provides the signal the strobe uses as a phase trigger source and
therefore is the input to the strobe. The vibration transducer also provides the vibration
signal to the data collector or analyzer. The interconnect cable provides a “TEE” connection
to both. The strobe provides the phase referenced tachometer signal (output) which is
used as an input to the data collector or analyzer for triggering.
Now you are ready to go to work!
Follow the operating instructions outlined at the beginning of this section for tuning the strobe to 1X
running speed. After the reference mark has been “frozen” (as nearly as possible, but slight rotation
is acceptable), place the Mode Selector Switch in the LOCK/TRACK position. The flash rate is
now derived from the vibration transducer. Phase information is only valid when operating in
the Locking (LOCK/TRACK) mode.
Select the Phase Angle orientation that is desired (0-360 or ±180 degrees) by pulling or pushing the
Phase Angle control knob. Using the Phase Angle control knob, position the reference mark to a
“convenient viewing location”. The data collector can now be employed to receive and process the
phase information as supplied to it by the strobe and the transducer. After the information is received,
simply release the trigger on the strobe, proceed to the next point, and then repeat the process.
NOTE: The trigger must stay depressed until the data collector or analyzer is through processing
the data.
For certain data collectors that do not provide constant power out to transducers that so
require, it may be necessary to command the analyzer to begin taking the data before the
phase image becomes stable enough to allow it to be placed at a reference location. It
may also be noted that slight adjustment of the Phase Angle control knob may be required
before each measurement, to assure that the reference location is repeated.
If the data collector you are using does not respond to the phase reference signal supplied to it by
the strobe, it is possible that the Trigger Set-up in the data collector may be reversed. If so, change
the set-up from “positive” trigger slope to “negative”, or vice versa, and try again.
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When the strobe is tuned in the Internal (INT) mode, and then switched to LOCK/TRACK, the filter
in the strobe will track slight changes in speed. If the speed changes too much or too fast, the strobe
will lose LOCK/TRACK and stop flashing. It will be necessary to switch back to Internal (INT)
mode and repeat the adjustments. Also, try switching the Narrow and Wide Bandwidth switch to
optimize results. Generally, the Wide Bandwidth will give best tracking results but the Narrow
Bandwidth will give better stabilization.
NOTE: When it is necessary to have repeatable phase measurements, it is necessary to write
down the transducer locations used. Also, the transducer mounting method should be the
written down. Stud mounting or magnetic base mounting is preferred since data taken
with hand-held transducers may lead to significant phase differences.
PHASE ANALYSIS
The Vibration Strobe can be used to measure movement of parts of a machine, couplings and
machine cases in a machine train. The direction of movement (Phase) reveals important information
about looseness, unbalance and alignment.
This section is not intended to be a comprehensive review of these measurements. Refer to one of
the many training notes and application notes written over the years on these techniques.
This section outlines the preparations and use of the strobe light in order to be assured the
measurements you are making are correct.
NOTE: A data collector or vibration analyzer is not needed in order to do phase analysis. You do
need a method of powering the vibration transducer, or you can use a self-generating
velocity transducer to “drive” the strobe light.
General preparation for phase analysis is as follows:
1. It is important to use a magnetic mounting base on the vibration transducer.
2. Use a transducer cable that is long enough to allow you to get some distance away from
the strobe light.
3. Mount the strobe light on a tripod so it can be left standing.
4. Connect the vibration transducer to the strobe light (using a power source or a
data collector).
5. Start all measurements with the vibration transducer mounted on a bearing housing in the
vertical direction. (This is a good habit to get into). Aim the strobe light at the selected
reference mark and turn it on. Adjust the flash rate to running speed and then set it to the
Locking (LOCK/TRACK) mode. Using the Phase Angle control, position the reference
mark to the 12:00 o’clock position.
Do not move the strobe between measurements.
Checking for looseness:
1. Keeping the vibration transducer in the vertical direction, move the vibration transducer
from the foundation, to the base plate, to a foot, to an area above any split line, to the
bearing cap. Note the phase at each of these locations.
2. The reference mark should stay at the 12:00 o’clock position for each of these
measurements. If phase changes (probably to 6:00 o’clock) at any of these measurement
points, there is looseness at the mechanical joint.