LVDT conditioning on the LHC collimators

The position readout and survey system of the LHC collimators has to monitor in real-time (RT), at a frequency close to 100 Hz, the position of the 555 synchronized axes with an accuracy of 20 mum. Radiation hard linear variable differential transformers (LVDT) are used as absolute position sensors for their ruggedness, intrinsic accuracy and infinite resolution. Because of the radioactive environment the conditioning electronics is located in safe zones up to 800 meters far from the sensors. In these conditions, standard conditioning techniques cannot guarantee the accuracy requested by this application because of cable impedance, noise immunity, crosstalk between signals of different sensors passing in the same cable, temperature stability. A fully digital approach based on a sine-fit algorithm has been followed and will be described showing the excellent results measured up to now. Particular attention is devoted to the RT implementation of the algorithm on the PXI platform from National Instruments.