Tach/Position consistency shutdown algorithm

note This algorithm requires that the Tach be calibrated in degrees/second. If the tach gain potentiometer is adjusted, you must redo the tachometer calibration.
note If virtual tach is used rather than an actual tachometer, this algorithm is disabled.

When the Tach is properly calibrated, the observed change in the antenna position should match the integrated velocity. If these are inconsistent, this could indicate failure of either the Tach or the position sensing and continued operation could lead to antenna damage.

The following algorithm parameters, are defined as:

  • Permissible fixed error - 1.5°
  • Permissible relative error - 10.00 %

The watchdog algorithm computes the expected difference in position by integrating the velocity and comparing this to the observed position difference over the previous 1 second. The algorithm forces a shutdown of the antenna if the difference between the observed and the computed antenna displacements exceeds the larger of the fixed and the relative error.

For the antenna displacements greater than 15° in 1 second, the relative error of 10 %, for example, is used as the standard for the test, while for the displacements of less than 15°, the fixed error of 1.5° is used.

note The algorithm integrates over the prior one second interval and is updated 16 times per second.