Large Scale Experience with Industrial Stepping Motor Controllers and
Resolver Read- out Systems at SPS and LEP

R.J. Colchester, J.J. Gras, R. Jung,
J. Koopman, J.M. Vouillot
CERN

J. Feres, B. Lopez
MIDI Ingenierie

Some 340 stepping motors and 210 resolvers are used in SPS and LEP for beam instrumentation purposes. These motors drive very different instruments, ranging from heavy Tungsten blocks used for beam collimation purposes to lightweight Beryllium mirrors used in Synchrotron Light Telescopes and are located in the SPS and LEP rings and transfer channels. Most of these instruments are beam intercepting and therefore require very reliable drive electronics. As the SPS commenced operation in 1976 and the LEP in 1989 they had, up till recently, completely different control systems. However, with the upgrading of the SPS controls in 1993 and the planned energy upgrade in the LEP which requires an additional 80 collimator blocks, it was decided that this was the ideal opportunity to change to an industrial system which would fulfil the requirements for both machines in the most economical way. The major problem we have encountered with industrial stepping motor control electronics was the high level of EMI noise generated by the chopper type power electronics. Additional problems are caused by the long distances between the motors and the electronics (up to 1500 m), and the restricted space in the underground caverns. The interface to the control system had to be of the type RS 232 or RS 422 so as to be able to interface to different environments, currently PCs in the SPS and VME crates in LEP and possibly other systems in the future. The system had to be reasonably modular for good maintainability. Detailed specifications were written and a company selected for the procurement. 210 motors and 80 resolvers have so far been equipped and have been running for more than one year without any failures. The components for the complement have been received and will be installed at the end of 1995. Details of the hardware, software and experience with the systems are presented.