High Precision Strain Gauge Based Sensor for Monitoring Suspension Forces at CERN

At the end of 2007, the world's largest particle accelerator, the LHC (Large Hadron Collider), will be ready to collide first particles. Protons will be accelerated in a ring of 27 km circumference, contained inside an evacuated pipe of 60mm diameter. At four interaction points, where the large particle detectors are placed, this beampipe is made from beryllium in order to limit the multiple scattering of particles on their way from the interaction point to the detector. In order to keep the sag in the pipe to acceptable levels, accurate monitoring of the forces in the cables, which hold the beryllium beampipe in place, is required. The beampipe is installed in an environment of 0.5 T magnetic field and is expected to absorb a dose of 1 Mrad in ten years. These special constraints and the lack of accessibility preclude most standard monitoring systems. Previous work has shown that strain gauge based systems work well under the described conditions. This report shows that the monitoring system for the ALICE beryllium beampipe requires a minimum sensor size which results in μ V effective range for the signal. The device provides the requested resolution of 1 N.