Evaluation of Electro Pneumatic Valve Positioners for LHC Cryogenics

Since about 1994 several manufacturers have been introducing a new generation of valve positioners. They are called digital positioners because they have integrated micro controllers (some manufacturers also call them "intelligent" positioners). They offer a range of features that could be of special interest for LHC: simple installation (Fieldbus reduces cabling and therefore costs) automatic start-up and calibration (self-adaptation to valve) means fast and therefore cheap maintenance communication capability (e.g. Hart, Profibus, etc.) remote configuration preventive maintenance planning using diagnostic data reduced air consumption. The use of this new generation of positioners could improve the overall reliability of the LHC cryogenic system as well as provide significant manpower savings. An analysis of the present and future cryogenic systems shows that the total number of control valves and their widespread distribution in the tunnel (and therefore the length of the access routes) will all be significantly different for LHC than they are for LEP. In LEP, all control valves are close to the access points. In LHC, the control valves will be distributed evenly along the whole tunnel. LHC will make use of about an order of magnitude more control valves in the tunnel than LEP.