Tachometer Input

The tachometer signal, from the motor gear box, is applied to a differential receiver and a 30 Hz analog, low-pass filter. The signal is then digitized and added to the processor.

The differential receiver ensures that any common-mode signal, on both tachometer leads (for example power-line noise) is not falsely interpreted as antenna motion. If there is no analog tachometer, a virtual tachometer based on the differentiated position can be selected. See AXIS Command.

The drive levels that are computed by the processor are applied to a 14-bit D/A converter, scaled by the external analog amplifiers, and then applied to the motor power amplifiers.

note The D/A and A/D convertors are signed. They generate and accept both positive and negative voltage levels.

The drive signal is the sum of the following components:

  • A nominal level based solely on the requested velocity.
  • Feedback term based on the difference between the requested and actual velocities.

The 2 graphed transfer functions indicate how the drive levels are derived for each component.