Automatic thickness control system for the ATLAS electromagnetic calorimeter absorber plates

We describe an automated precision thickness measurement system which has been developed to control the quality of the 6160 lead plates forming the absorbers for the ATLAS electromagnetic Lead-Liquid Argon calorimeter. By using an ultrasound measurement technique combined with automated scan tables and pneumatic operation, robust, low cost, fast and easy to operate systems have been built. The required accuracy is at the level of a few microns per measurement point, with about 500 points per plate.