Guest Post by Bob Dunn from I&E Central, Inc.

A customer was having difficulty balancing the rotor shown above. They had made multiple corrections, some contradictory, and were worse than when they started. In that this is on a shop stand and under controlled conditions, something was not right. Looking at the photo, I saw a couple of likely issues.

1. The shaft is pretty reflective itself, it is doubtful that they were getting a good or consistent phase reading. I recommended they put a ring of black tape on the shaft, with the reflective tape on the black.
2. The tach sensor is pointing at the shaft at about a 90-degree angle. Optical sensors and reflective tape works better if the sensor is aimed at an angle – 30 degrees or so.
3. The tach sensor is pretty close to the rotor. In this case, it is not too close, but you can be too close. A sensor like this will work from several feet away, if you are having problems, try moving the speed sensor further away.

The customer applied the tape and adjusted the tach position. The rotor was balanced in a single run.