How to Retrofit Encoders on Old Motors

Posted by Brian Winter | View all of Brian's blogs on May 24, 2021 3:35:24 PM

If you need to retrofit encoders onto old motors that presently have analog tachogenerators mounted on them, what should you use?

• If your analog tachogenerators are BC46, BC42, or RE210 flange styles mounted on NEMA 56C face adapters, then often all you need to do is mount any solid shaft Avtron™ Encoder with a NEMA 56C face. This method allows you to retain the same coupling and mounting bolts. It is a direct mechanical replacement. Our AV485 is a typical example.

• For an even more durable installation, consider removing the flange adapters and couplings and installing a modular encoder with no bearings, couplings, or other moving, wearing parts. Examples include: AV125, AV850, AV56, and AV85.
  • • If foot mounted: all of the Avtron Heavy Mill and Severe Duty (HMD/SD) encoders (such as AV485) have the same shaft size and shaft centers as BC46/BC42 tachogenerators. The mounting base dimensions are identical so no modification to the mounting holes is required. These foot mounting kits are available to match the footprint of either Classic Avtron Encoders or analog tachogenerators. Simply specify the foot mount kit you need with your Avtron Encoder.
  • • If you have a 5PY analog tachometer, the AV44 can be used, or by replacing the stub shaft, a hollow shaft model such as HS35M can be fitted. The mechanical design of the AV44 allows for easy and convenient drop-in replacement.
  • • One important exception to the above procedures: Mill Duty (MD) or other motors or shafts that have sleeve or roller bearings that permit high axial movement. In these cases, the analog tachogenerator should be removed and replaced with a severe duty hollow shaft encoder such as AV685, along with the appropriate stub shaft. The tether mount of the AV685 will permit it to move with the axial thrust of the motor and give the longest life.
  • • If you need to maintain the analog voltage output of a tachogenerator to an older analog drive, Nidec-Avtron offers several Brushless tachometers (K660A, K661, K662) which can be combined with modern digital encoders to replace analog tachogenerators. Contact us at for assistance.




Topics/Tags/Categories: Retrofit Encoders, tachogenerators, Encoders

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