The two Allen-Bradley 843ES safety encoders on the telescope must be properly homed to ensure safe operation.

Because the safety encoders are multi-turn and are never normally decoupled from the telescope axis they should not normally require adjustment. However, loss of power or loss of connectivity may require that they have the safe home function actuated.

How to home the telescope safety encoders

In the engineering section of the HMI there are momentary pushbuttons to accomplish this.

1. Navigate to the Engineering – Safety Encoders screen on the GIS HMI.

2. Verify that the position value in ‘Target Home Position’ is correct.

3. Press ‘Set Safety Encoder Home Position’ push button.

4. Verify that the value in ‘AB Encoder Current Position’ is correct.

5. Verify that any warnings associated with 'Encoder not homed' have disappeared.

How to adjust the Telescope Safety Encoders.

The adjustment of the safety encoders are affected by two constant values in the Telescope LIC. ALT_ZERO_OFFSET and ALT_SCALE_FACTOR for the Azimuth Axis and AZ_ZERO_OFFSET and AZ_SCALE_FACTOR for the Azimuth Axis. Normally these should never require adjustment, especially the scale factor term.

But if the encoder was removed for repair or replacement then the zero offset term will likely require adjustment.