The instrument control electronics of the ESPRESSO spectrograph @VLT

Abstract

ESPRESSO, the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, is a super-stable Optical High Resolution Spectrograph for the Combined Coudé focus of the Very Large Telescope (VLT). It can be operated either as a single telescope instrument or as a multi-telescope facility, by collecting the light of up to four Unit Telescopes (UTs). From the Nasmyth focus of each UT the light is fed, through a set of optical elements (Coudé Train - CT), to the Front End Unit (FEU) which performs several functions, as image and pupil stabilization, inclusion of calibration light and refocusing. The light is then conveyed into the spectrograph fibers. The whole process is handled by several electronically controlled devices. About 40 motorized stages, more than 90 sensors and several calibration lamps are controlled by the Instrument Control Electronics (ICE) and Software (ICS). The technology employed for the control of the ESPRESSO subsystems is PLC-based, with a distributed layout close to the functions to control. This paper illustrates the current status of the ESPRESSO ICE, showing the control architecture, the electrical cabinet’s organization and the experiences gained during the development and assembly phase.