Last updated on 28-Aug-2001 2:11 PM

Calibration Unit Mechainism Maintenance

The calibration unit mechanism module contains the mechanisms which insert any one of the following components in front of the cryostat window.

1.  Folding Mirror
2.  Window shutter or flat field plate
3. One of two waveplates for polarimetry

This procedure assumes that the calibration unit has already been removed from the cryostat (see removing the calibration unit).
   Before disassembly if installed the polarimetry optics should now be removed as follows.

Check the current status of the mechanisms by looking through the aperture, the copper shutter plate should be in position.
Manually retract the shutter and insert the first waveplate into position in front of the aperture by turning the handles on the ends of the motor shafts. Insert the protective cover into the top of the waveplate clamp, undo the six M3 countersink screws and using the protective cover withdraw the clamp ring through the aperture.
The waveplate can now be removed from its holder through the aperture and stored safely, remember also to remove the wave spring.
If a second waveplate is installed move the carriage on to the next position by further turning the handle on the end of the motor shaft and repeat the process of removing the waveplate as before.

In order to get access to the calibration unit mechanism assemblies it is necessary to separate the module as follows.

Undo ten M3 countersink screws and remove the top access cover.

Depending on whether the module has been configured for UKIRT or GEMINI Undo six M4 socket head screws or five M4 countersink screws and remove the end plate opposite the motors.
Undo the ten M4 socket head cap screws on the top plate and the three at the end with the two motors.

Apart from the two umbilical cables the top plate is now free of the main housing.

Without disconnecting the two cables, Carefully lift the top plate squarely from the main housing, turn it through 180 degrees and place it down flat over the top end of the main housing.
The folding mirror is now exposed and should be removed from the mirror slide carriage and stored safely.

Both carriage mechanisms are now readily accessible for any maintenance or repair.