At the AAT we use a gain = 8 and a time constant = 250 ms (Sept 96).
The remaining front-panel control are set as follows:
(X, Y, Z)_coarse = (0.0, 0.1, +5.0 *)
(X, Y, Z)_fine = (3.90, 8.00 #, 10.0 *)
(X, Y, Z)_Rbalance = (4.08, 3.70, 4.00)
These are used in addition to the following X and Y offsets
applied through software control:
X_soft = 20
Y_soft = 5
Values at the WHT are identical except for the following changes:
X_soft = -100
Y_soft = 0
Y_coarse = 0.0
At the WHT, scan FSR lengths are twice as long as those at
AAT, which means the CS100 controller there has half the scan range.
# Note 1: A value of 7.28 use to be set here. Try it if 8.00
appears non-optimal.
* Note 2: Plate parallelism can be established irrespective of the
values of Z used (since this only represents the spacing between the
plates.
The front panel fine and coarse offsets work the same way with
the coarse being approximately 10 times the fine. The
plate spacing in physical units (um) can be can estimated
from a September 1996 calibration by DHJ:
Z_um = Z_c + 0.105Z_f + Z_s/2048 + 5.488 (+ 0.0106) .
This calibration used (X, Y)_c = (0, 0.1), (X, Y)_f = (3.90, 7.28)
and (X, Y)_s = (0, 0); which differ from the standard settings above
in X_s, Y_s and Y_f. Using the calibration relation for X
Z_X = 0.2Z_c + 0.021Z_f + Z_s/4096
we can show the plates to differ in offset by 4.88e-3 um in X and
0.0163 um in Y. The relations for Z_x and Z_Y are identical.
Incorporating this as a mean offset in Z gives the additional term (+ 0.0106)
in the Z_um calibration. For most purposes, this corrective offset is
neglibible.
In all cases, self-calibration during an observing run is recommended for
precision measurements.
A look-up table
of (Z_c, Z_f, Z_s) vs. Z_um values (using the above
calibration) is available.
More details on the CS-100 XYZ
controls .
