General Balance Procedure

Equipment Utilized

  • Optical tachometer
  • Weight set with tooling
  • Scale
  • Accelerometer data acquisition system and means to measure acceleration amplitudes (OVMS roaming accelerometers can be used)

Test Procedure

We plan to follow the method commonly referred to as "the four-run method", which requires only a single accelerometer, utilized to measure the magnitude of the equipment-induced vibration. The accelerometer should be placed on the fixed part of the equipment, perpendicular to the shaft. If the equipment is mechanically isolated, the accelerometer should be mounted on the same side of the isolator as the rotating element. Localized non-linear dynamics should be avoided.

Step 1: With the equipment stopped, mark the key-phase position (i.e. zero angle) on the rotating element. Also, place a piece of reflective tape on the rotating element.
Step 2: With the equipment moving in steady state, measure and record the amplitude of the vibration (units are irrelevant). Also measure and record the rotation speed using the optical tachometer.
Step 3: Stop the equipment and place a test weight at a know location on the rotating element. Repeat Step 2.
Step 4: Stop the equipment and move the test weight to a second known location at the same radius about 120 degrees from the position in Step 3. Repeat Step 2.
Step 5: Stop the equipment and move the test weight to a third known location at the same radius about 240 degrees from the position in Step 3. Repeat Step 2.
Step 6: Stop the equipment and remove the test weight.
Step 7: Utilized the attached MATLAB script to reduce the four measured amplitude and the test angles to compute the optimal weight size and mounting phase necessary to correct the imbalance.


Step 8: Mount the permanent correction weight of the optimal magnitude at the optimal phase angle. This may require trimming a standard weight.

Note 1: The above procedure may be performed in two planes (i.e. on either end of a rotating shaft) to fully balance a rigid piece of equipment. The accelerometer should be mounted in the same plane as the test weight moves in.

Note 2: The measured speed should be identical for all four runs.

Note 3: The analysis tool can be used with an arbitrary number of test runs.

Note 4: The optimal test weight is one that induces vibrations similar to that of the imbalance. Some experimentation will be necessary to find a weight that can influence the amplitude of the vibration without overwhelming the imbalance.

Note 5: The test weight indices an imbalance moment so the effect can be doubled by doubling the radius.

Results

Upper Right Treehouse

Air Handler

Left side of squirrel cage

Test weight mass: * gram

Test weight mounting radius: * mm

Condition Weight Location (degrees) Frequency (Hz) Signal Amplitude (g)
Run 1 (Baseline) - * *
Run 2 * * *
Run 3 * * *
Run 4 * * *

Solution: mass: *g, radius: *mm, phase: * degrees

Final Vibration Amplitude: *g @ *Hz

Right side of squirrel cage

Upper Left Treehouse

Air Handler

Lower Right Treehouse

Air Handler

Lower Left Treehouse

Air Handler

-- DaveAshby - 03 Oct 2012
Topic revision: r2 - 04 Oct 2012, DaveAshby
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