LHC Collimators Low Level Control System

The low level control system (LLCS) of the LHC collimators is responsible for accurate synchronization of -500 axes of motion at microsecond level. Stepping motors are used in open loop ensuring a high level of repeatability of the position. In addition, a position survey system based on resolver and LVDT sensors, verifies in real time the position of each axis at a frequency close to 100 Hz with some tens micrometers accuracy with respect to the expected position at a given time. The LLCS is characterized by several challenging requirements as high reliability, redundancy, strict timing constraints and compactness of the low level hardware because of the limited space available in the racks underground. The National Instruments PXI platform has been proposed and evaluated as real time low level hardware. In this paper the architecture of the LHC collimators low level control system is presented. The solution adopted for the motion control and positioning sensors reading implemented on the PXI platform are detailed.