Large scale test and performances of the RPC trigger chambers for the ATLAS experiment at LHC

Resistive plate chambers will be used as trigger detectors in the barrel region of the muon spectrometer of the ATLAS experiment at the LHC. The total number of RPC units to be installed is greater than 1000, covering a total surface of about 3650 m/sup 2/. Three cosmic rays test stands have been designed and built in Naples, Lecce and Rome "Tor Vergata" INFN laboratories in order to carry out the quality assurance tests on the ATLAS RPCs. Although the three test stands are based on different setups and use different techniques to trigger and to reconstruct cosmic rays, the same tests are performed, in order to have the same quality criteria. Since august 2002 more than 600 units have been tested, mainly in the Naples site. This large number of RPC units tested allows to perform a statistical evaluation of the uniformity and stability of the main RPC performance characteristics over such a large scale production. Most of the tested RPCs satisfied the required specifications and only a small fraction of them had to be rejected.