MODS agw.ini files and MODS-AGw recommissioning

This page describes the agw.ini files which are on the instrument server (mods1 and mods2) and are read by the agw service. These files contain information on the AGw stage position which corresponds to the guide camera hotspot and the AGw-to-PCS transform, and hence these must be updated whenever the guide camera needs to be realigned or a new transform needs to be installed. See BGTechProcedures for instructions on how to align the guider hotspot with the rotator center and how to collect AGw transform data.

The most recent updates to both MODS1 and MODS2 agw.ini files were made in September 2018, after the glycol-soaked lens on the MODS1-AGw guide camera was replaced and, in November 2018, after new transforms were determined. For MODS2 the new transform was determined with an improved RDG rotator zeropoint (RZP = 26.95 deg instead of 27.55 deg) that should more closely align the slit with the N-S axis.

Measurement of the rotator zero point

The Direct Gregorian rotator zeropoint is set, in the PCSInstrument.conf configuration file, so that the masks and longslits are aligned with the top and bottom perfectly along the N-S axis for a position angle, PA=0. The rotator zeropoint has not changed from one mounting to the next. For MODS1, the original rotator zeropoint measured during AGw commissioning is still in use. For MODS2, the original rotator zeropoint was soon found to be inaccurate by ~0.7 degrees. An improved zeropoint was measured, but we were unable to obtain a transform with this zeropoint until Nov 2018.

Instrument	L/R DG Rotator Zero Roint	Comments
MODS1	27.63	AGw Commissioning
MODS2	26.79	Nov 2018, was 27.55 from AGw Commissioning

Alignment of hotspot with center of rotation on guide camera

PCS-to-AGw stage transform

-- OlgaKuhn - 29 Nov 2018