INT Sony Incremental focus transducer

On the TCS, use: PAGE ENC to check that the absolute and incremental encoders agree.  Move the focus in engineering mode and check that the encoders still agree. If they agree, type:  SHOW ENC to see which focus encoder is IN USE. If it is the absolute encoder, type: ENC ON FOC INC to switch to the incremental.

What to do if the encoders do not agree

If the encoders do not agree, use the absolute focus encoder until the problem is sorted out. Type:


then zeroset the incremental encoder with:


n.b.  You may have to repeat this command.

If the zeroset does not work, move the telescope to access park with: PARK AP1 and check that the control box on the top ring is set up correctly. Peel back the black tape to reveal the LCD display. If the box is displaying ------, power-cycle it and then check the settings. If you redo any connections, you must power-cycle the control box before checking the settings.

To check or change the settings, follow this procedure:

If the display is NOT flashing, hold the SET  key and press the MODE key for approx 2 seconds. The display will change to diSP and flash. Once the display is flashing, cycle through the items by pressing the MODE key. If an item is incorrect, press the up-arrow key until the correct value is displayed, then press SET to set it. Press MODE to continue to the next item. Press MODE after the item rEP to display the encoder value.

The correct settings are:

Once the settings are correct, zeroset again (possibly twice).

If the encoders are still different, there is probably a problem between the encoder and the TCS.

Things to check are:

  1. A problem with the RS422 line drivers (there are two; one within the SONY FOCUS control box, the other plugged directly into the 3340 CAMAC module in the CLIP centre) or more likely, the small PSU units that power them.
  2. The 3340 CAMAC module itself. This is located in the bottom crate ( B4 C3 N19 ).
  3. The Sony transducer or its control box. There are spares in the INT electronics workshop store.
Once the encoders are reading the same, move the focus in engineering mode and check that they still read the same value. If one encoder increases and the other decreases, check that the control unit setting rSL is set to -0.0005 (the minus sign MUST be present).

Once everything is OK, type:  ENCODER ON FOC INC to use the incremental focus for tracking.

This file:  ejm