LWS
Chop-nod Parameters
Specifications for the chop and nod parameters our presented below. Standard operating parameters are supplied as a guide.  

F/25 Chopping Secondary parameters.

Modes
GUI Name
Displacement
Angle
degrees
Frequency
Hz
Min 1 (")
Max (")
center-off
manual
5
70
360
<50
symmetric
automatic
5
140
360
<50

Typically, the F25 secondary is opperated in ceter-off or "manual" mode with 10 arcsec chop throws and oscillating at 2.5 Hz. For throws larger than 20 arcsec, the choping rate should be slowed. Currently, the chopping angle is offset from the observer specified angle by < 3 degrees. For large throws, the offset should be measured at the beginning of each night by observing a standard star in chop-nod mode. The chopper calibration requires a few extra minutes at the beginning of each night. For small throws (5-10 arcsec), the guider will correct for the angle offset.

Nodding Parameters.

Modes Displacement Angle Frequency
chop-nod set to chop
displacement 		set to chop
angle 		TBA Hz
quad-chop any any TBA Hz
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Last modified: 8 Apr  2002