Technical Education Committee Member
Integrated Power Services, LLC
Tachometers are used to detect shaft speed for a variety of reasons; proper setup improves the quality of the measurement and ensures safe operation. Modern laser tachometers function best when the laser hits the pickup area at an angle other than straight at the centerline at 90 degrees. This is because the shaft does not reflect directly back to the laser at an angle; however, the tach pickup tape will. Pointing the laser directly at the shaft centerline at a 90 degree angle can cause reflections off the shaft thus providing noisy or inconsistent data. It is not recommended to use electrical tape to eliminate shaft reflection as it can come off due to centrifugal force and heat breaking down the adhesive in the tape. In the best case, this causes loss of signal. In the worst case, it can flail around as it comes loose and pulls things into the motor shaft. Another possible cause of erratic readings is fluorescent lighting, which generally shows up at 7200 rpm. This also may be mitigated by changing the angle of the laser so as not to pick up the light.