Lyot Stop The CIRIM Instrument Introduction

Filter Wheels

CIRIM contains 3 stacked filter wheels which contain a total of 33 filter positions. To change to a given filter one types a command of the form filter name (e.g. filter k). This will command all three wheels to move to the proper positions for a given named filter. (Note to users of other WILDFIRE instruments: this command is different from the filt to xx command you are used to, because three filters wheels are involved, as well as a different motor controller.) If you are using the PostScript version of this manual, please check the cirim web page for the current filter list.

If you want to use a combination of wheel positions which is not named you can position individual wheels with the command ``mov f? pos'', where f? is the filter wheel number (i.e. f1, f2 or f3) and pos is the filter position on the wheel (i.e. 0 to 10). A typical command to move a single filter wheel would be mov f1 5 to select the K filter in wheel 1. Due to the different thickness of our filters there are significant focus offsets at the faster f-ratios.

If the filter wheel motor controller loses the current position of the motors they can be reinitialized with the command fwinit. Note, fwinit leaves the filter wheels in the 0,0,0 position (i.e. open). During normal operation this is not usually needed. The status of all the motors can be readback in a rather cryptic format using the command mtrinfo. A typical motor entry would be ``sf1 5 25000 0 1 25578''. The first entry (sf1) is the motor name (sf1, sf2, sf3, slr, slt for filter wheels 1 through 3 and the Lyot rotation and translation). The second entry (5) is the current position while the third entry (25000) is the current motor microstep position. The fourth entry (0) tells you if the motor is actively moving (1=yes, 0=no). The sixth entry (1) tells you if the motor is initialized (1=yes, 0=no) and the final entry tells you the number of microsteps it took to reach the initialization position.

Since CIRIM is a new instrument we do not have much experience with the reliability of the filter wheels. Thus, we suggest that at the beginning of each night (or if you have any doubts), you perform the following test; First, type filter open, then enter fwinit, finally, type mtrinfo and note the value of the fifth field for each of the three filter wheels (they should be close to 600, 600 and 400). If the number of motor steps needed to reach the initialization position (fields 5) differs from these values by more than 50 then one or more motor steps have been lost and you should contact your support astronomer.

Lyot Stop The CIRIM Instrument Introduction