QC PLOTS
	CURRENT	HISTORY
Grating stability
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Click on CURRENT to see the current trending (Health Check).    Click on HISTORY to see the historical evolution of the trending.

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 data are also used to monitor the simlamp efficiency.

SIMLAMP,TAL frame (closeup). There are five simultaneous calibration fibres, illuminated by the simultaneous arclamp.

The gratings are observed to have both thermal and non-thermal motions. To control the thermal motions, the temperature sensor TEMP53 is used, located on top of the grating table. It delivers a value into the header of each raw frame.

QC1 parameters

Trending

As a reference evalue, the temperature TEMP53 is plotted in box 1 and repeated in box 4 of the trending plot.

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.

QC1 parameters

Trending

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 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.

History

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