A set of frames is measured daily to monitor
the stability of the gratings and of the fiber system. These frames carry the DPR
TYPE SIMLAMP,TAL (TAL = thorium-argon lamp) and are created by the arclamp of the
simultaneous calibration unit. The arc lamp is used to illuminate the simultaneous
calibration fibres. The signal is correlated both in X (cross-disperion) and Y (dispersion)
against a reference frame. There is a set of six such health check measurements,
one (using the LR grating) for each slit system (Medusa1 and 2, IFU1 and 2, Argus),
plus one for the HR grating and the Medusa1 slit system.
The GIRAFFE gratings have some minor thermal motions, and occasional non-thermal jumps.
To control the thermal motions, the temperature sensor TEMP53 is monitored here, located on
top of the grating table close to the grating.
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one, always check the link 'HC'.
Each of the Health Check data is correlated in X and Y to a reference frame. The set
of reference
frames is arbitrarily taken from date 2003-07-24. The difference (X_new - X_ref)
is plotted vs. time. The same is done for the Y (dispersion) direction.
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one, always check the link 'HC'.
Boxes 2 and 3 of the trending
plot display the X motions of the HR and LR grating (selected is the Medusa1 frame),
boxes 5 and 6 the Y motions. Box 4 repeats the temperature record from
box 1 for comparison.
Stability trending plot, panel 1 .
On top there is the trending of the temperature (in degree Celsius), and below
are the plots for the shift in X direction, both for the HR and the LR grating.
The temperature sensor selected is TEMP53 ('surface table temperature top').
A similar column is plotted for the Y shifts (panel 2).
The scoring thresholds in plots #2 and #5 (for the HR grating) and #3 and #6 (LR) are set such as to indicate a) a sudden, non-thermal
jump, or b) a slow drift towards critical values for the position of the
gratings (critical because the pipeline then might loose parts of the fibre
signal). The positions have no particular physical meaning but are relative
and based on historical behaviour.
The incremental grating motions due to temperature are well visible in the
correlation plots #7-10 (see below). The correlation slope is very stable over
time, indicating clearly non-thermal motions (interventions, earthquakes).
The third panel shows the shifts in X and Y versus temperature TEMP53.
For both directions, there is essentially the same (anti-) correlation with temperature.
Correlation plot. Boxes 7 and 8 show the shift of the grating in X direction, in pixels, versus the temperature
drifts (TEMP53 as above). X-axis: grating shifts in X; Y-axis: TEMP53 in degrees
Celsius.
Boxes 9 and 10 display the same for the Y shifts.
Note that the Giraffe gratings occasionally show sudden non-thermal
shifts. These are detected in the trending plot as corresponding shift of the correlation
pattern in X direction.
*Class: KPI - instrument performance; HC - instrument health; CAL - calibration quality; ENG - engineering parameter
**There might be more than one, always check the link 'HC'.
The scoring thresholds in plots #2 and #5 (for the HR grating) and #3 and #6 (LR) are set such as to indicate a) a sudden, non-thermal
jump, or b) a slow drift towards critical values for the position of the
gratings (critical because the pipeline then might loose parts of the fibre
signal). The marked and scored position thresholds are based on historical experience and represent the best spectral format, in terms of
resolution and accuracy of the dispersion solution.
earthquake; non-thermal jump of HR grating in X (+1) and Y (+2) pixels
2011-03-14
earthquake, non-thermal jump in Y direction; adjusted backto the old values on 2011-04-01; no science files affected
2011-06-10
earthquake, non-thermal jump in X and Y direction; adjusted back to the old values on 2011-06-22
2011-06-27
earthquake, non-thermal jump in X; adjusted back on 2011-06-30
2015-11-27
earthquake, non-thermal jump of HR in X by +8 px, LR in Y by more than 1 px; adjusted back begin of 2015 Dec; required new reference dispersion solutions for Medusa2
2018-09-24
earthquake, non-thermal jump of HR in X by +4 px, no shift of LR grating; see PPRS 073865
2018-10-13
HR grating brought back to previous X position
2018-10-25
HR grating brought back to previous Y position
2019-03-29
low-risk EQ, caused X and Y shifts in both gratings (PPRS-075667); HR successfully re-adjusted 2019-04-01, LR on 2019-05-12 PPRS-076088
2020-02-12
medium-risk EQ, caused X and Y shifts in HR gratings, Y in LR grating (PPRS-078544)