When the absolute encoder bulbs are functioning normally, absolute zerosets can be done for all axes from the TCS USER window:
- USER> ZEROSET ROT ABS
- USER> ZEROSET ALT ABS
- USER> ZEROSET AZ ABS
They can also be done by pressing ZA (zeroset absolute) for either AZIMUTH or ALTITUDE in the engineering control under the AXES menu.
Absolute zerosets are supposed to happen automatically on startup of the TCS, and even if the TCS isn't restarted the encoders shouldn't change, but it's good practice to do it at the start of every night anyway.
Target zerosets for AZ and ALT are done with the telescope close to zenith. The whole procedure can be done in ENG MODE.
- On the engineering console, from the MAIN MENU select the AXES menu then go to AZIMUTH (or ALTITUDE - the procedures are identical)
- Check that the current AZUMITH, as seen in the top of the central section called AZIMUTH CONTROL, is LOWER than the Zeroset Target Position New, found listed in the right section.
- Check also that the AZ Zeroset ZS1_B1 is showing a "0" and not a "1".
- Press ZT (zeroset target)
- Press YES to continue
- Using the AZIMUTH + button found just under the display screen, press this to move the azimuth in the positive direction until it passes through the target position (you will hear a beep from the TCS) AND the AZ Zeroset ZS1_B1 status changes from 0 to 1 and then back to 0. Now you can release the azimuth movement button.
- Check on the TCS that it says "zeroset azimuth complete".
- Repeat for ALTITUDE.
When no other method of zerosetting is possible, it can be done using a known position. This requires 2 people, one at the TCS and one under the telescope!