An Overview of the LIGO Control and Data Acquisition Systems{*}

∗ Work supported by the National Science Foundation under Grant PHY-920038. Abstract Interferometric gravitational wave antennas are based on Michelson interferometers whose sensitivity to small differential length changes (for LIGO it is 1 part in 10) has been enhanced by adding multiple coupled optical resonators. These antennas are used to verify the theory of relativity by detecting gravitational waves from astronomical sources such as spiraling binary stars and black holes. Estimates for detection rates of such events by LIGO range from several events per month to several per year. The LIGO Control and Data system (CDS) features a tightly coupled and highly integrated control and data acquisition system. Control of the interferometers requires many Multiple Input Multiple Output (MIMO) control loops closed both locally and across the 4-kilometer interferometer arm lengths. In addition to providing the closed loop control, the control systems front end processors act as Data Collection Units (DCU) for the data acquisition system. Data collected by these front ends and the data acquisition system must be collected and time stamped to an accuracy of 1 microsecond and made available to on-line analysis tools such as the Global Diagnostics System (GDS)[1]. Data is also sent to the LIGO Data Analysis System (LDAS)[2] for long-term storage and off-line analysis. Data rates exceed 5 Mbytes per second per interferometer continuous. Connection between the various front end processors and the data acquisition system is achieved using fiber optic reflective memory networks. Both controls and data acquisition systems use VME hardware and VxWorks® operating systems. This paper will present an overview of the LIGO CDS and discuss key aspects of its design.