Using a Strobe as Phase Reference for Balancing

The information provided is for help with Commtest Instruments products:

• vb instrument

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QUESTION

Can I perform a balancing job using a strobe as a phase reference?

ANSWER

Yes, and you do not need to stop the machine for reflective tape placement when making the initial run.

Connect your strobe light's TTL output to the tachometer input of your instrument. You need to use a custom-designed cable for this task, as described in FAQ 11678.

Note: We have tested the Monarch Nova-Strobe DB-Plus 115 and found it to be suitable for this application.

1. Start an Initial Run and shine the strobe onto the rotor.
2. Adjust the strobe flash frequency to stop the rotor at an easily identifiable point, like a key, keyway, or bolt. Stop the rotor at a known and repeatable point; for example, at a keyway at 3 o'clock. See the illustration below.

   

3. Record an Initial Run. Typically, the transducer is set up to read displacement on the instrument and to determine the heavy spot by the relative phase angle measurement. In the illustration above, the heavy spot on the rotor is shown at 270°. (This is for illustration purposes only, as the initial phase measurement is arbitrary. However, all subsequent measurements will be relative to the initial reading.)
4. Stop the rotor and attach a calibration trial weight at a known location – either at a specific angle or positioned away from the selected reference point as noted in step 2.

   Note: Remember the 30/30 rule. That is, the trial weight must change the vibration reading's amplitude by 30% or the phase angle by 30°, or both. If the trial weight size is too small, the instrument will notify the user.

5. Start the rotor again and activate the strobe. Adjust the strobe flash rate until the contact point lines up at exactly the same location you selected in step 2.
6. Record the Trial Run.
7. Stop the rotor and remove the trial weight (as originally set up in the balancing parameters).
8. Continue to the next step for Correction Weight call out.
9. Place the specified correction weight at the angle identified, paying close attention to the angle being measured from the point of reference as identified in step 2.
10. Start the rotor, take a reading, then proceed to Trim Weight if necessary.

Repeat the steps above as required. In each progressive run, it is important to finely adjust the strobe flash rate so that the rotor is 'frozen' at the exact same point of reference chosen in step 2.

FAQ ID: 19246 Last Reviewed: 2 November 2007