Site engineer guide to setting up etalons and demonstrating
that charge shuffling is working.
How do I balance the etalons?
Go out to Cass cage and put etalon into light table with pupil 8
in light table as well. This is the first thing that meets you when you
enter the Cass cage. Screw on the Ne lamp after opening top and bottom
At the s/w level, there are 6 etalon ports, with 3 and 6 clear. Put
your etalon in 1, 2, 4, or 5, and then drive this etalon to the access
port (light table) using the SMS control window.
It would be useful to add a figure here of what one sees. Show Y axis
as normal x-axis, and vice versa.
i) power up s/w control and select etalon then external=off
ii) switch to R balance, balance needles using R control
iii) switch to error signal, time const highest 1.6ms, gain lowest at
iv) balance all needles with the coarse/fine control. Since the etalon
is not servo'd, the needle will flick through zero. Just get the needles
near zero using the controls. Some etalons are not able to be balanced
but will still servo at the appropriate positions.
v) change time const 250ms and gain of 32 (loop is open here)
vi) close loop and integrate
vii) if loop overloads, reduce gain setting
viii) optimize by eye
ix) external = on, and away we go.
What causes large etalon oscillations?
What do we do if the etalon will not servo?
(i) incorrect gain or time constant
(ii) large unbalanced R offsets
(iii) open or short-circuited etalon connector
(i) can you balance the etalon? more to come.
How do we test that the shuffling is working o.k.?
We will now initiate an 80-step shuffle where the TTF is stepped through
80 unique plate spacings, and the slit image is shifted down the CCD 80
For TTF, turn on CuAr or Ne lamp depending on filter; for other etalons,
turn on D lamp. These are chimney lamps and do not the secondary mirror.
set pupil = 8
set aperture = 3 (thin slit)
put an etalon in the beam
You will need a blocking filter in the focal plane whose width will
depend on the etalon gap. If TTF, use one of the TTF filters, say 670 (Ne
lamp) or 710 (CuAr lamp). The UNC 19um requires a 45A blocker, say the
H-alpha filter. The 125um and 200um etalons require something narrower
than 10A, preferably at H-alpha. If not available, just recognize that
there will be order confusion in the output spectrum creating more lines
than you would expect.
startup- (? on any line gives help)
ccd_shuffle (looks up instrument sequencer)
preexpose_info 3_1000_100 (2 = 0.1ms; 3 = 1ms clock rate)
(1000 = min phase time for bias frames clock cycles)
(100 = delay time for external device. Leave these!)
cycle_count <<1>> (no. of cycles where exposure time in .csx file)
setup_array <<true>> (option 2: generate gap numbers; see below)
etalon_start <<0000>> (start gap in option 2)
etalon_incremt <<0010>> (increment in gap in option 2; no. of steps in .csx file)
In the CCD window, you can always return to normal mode to do a glance,
say, with "method default". Probably best to do this after every shuffle
since bombing in shuffle mode is not good. "Method shuffle" gets you back
after "method default".
Figure 1: (A) The shuffle image in Fig. 1 comprises 80 separate
images of the slit where each image is taken at different TTF plates spacings,
i.e. wavelengths or frequencies (f1, f2....fN). (B) The raster image illustrated
in A produces a long-slit spectrum where the degree of curvature in the
lines is directly proportional to the gap spacing (the TTF has little curvature
at the smallest spacings; the 200um has huge curvature).
File translated from TEX by TTH,