European Southern Observatory New Technology Telescope

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Observations :
Operations :

EMMI Blue Grating Encoder Calibration Procedure

This is a procedure to determine the correspondence between the Zero Order position of a blue grating and the Encoder Value when this is unknown after the replacement of the unit's encoder.

Install a grating or a mirror in the unit.

Initialize EMMI.

Put Standby/Online the EMMI OS Control Panel.

Setup the instrument with the following configuration:

grating wavelength = 0

slit width = 1.0

slit length = 300.0

window x = 1 to 1024

window y = 400 to 600

binning x = 1

binning y = 1

readout mode = normal

exposure time = 1 sec

Take a look to the grating cell. For the Zero Order, the grating position should be close to the vertical (Rotator at 0 deg.) and the grating under test facing toward the instrument.

On ins@wemmi start a ccseiMsg window under the configuration shown below:

Environment: lemmi

Process: emmilcuServer

Command: STATUS (Par)> grtb

Calculate the approximate offset between the actual grating position and the Zero Order position defined above, by computing 10.000 encoder/units per degree. The command STATUS given to the ccsei pannel, shows the absolute encoder value for the actual position of the grating. This value will be taken as the reference when moving the cell to the Zero Order position from the ccsei.

Move the grating to the calculated position by the command:

Command: MOVE (Par)> grtb,1923403 (the last parameter is the value found)

On the Adaptor B Control Panel, put the Calibration Unit IN.

On the ccsei change the configuration in order to control the Calibration Lamp by setting:

Environment: lemcal

Process: nttclbServer

Command: CLON (Par)> 1

Command: OPESHU (Par)> 1

Command: SELCL (Par)> 1

Note: This ensures that the Lamp and the Shutter remains ON permanently.

Take an exposure from the EMMI OS panel by pressing [start] (Do Not Press Setup).

Inspect the image and compute the offset of the Zero Order Image with respect to column 562 (+/- 5 pixels) The factor is 16.0 e/u per pixel.

Change again the configuration of ccsei to:

Environment: lemmi

Process: emmilcuServer

Move the grating again by:

Command: MOVE (Par)> grtb,1924483 (the last number is the value found)

Take another exposure pressing [start] on the OS panel.

Compute the offset again, move the grating and take another exposure, until the image of the Zero Order is centered on column 562 (+/- 5 pixels).

Once the Zero Order is found, modify emouifConfig.pan in order to implement the new reference encoder values for all the gratings available for the blue side, changing the previous values by the same offset constant.

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