Performance of the HADES ring recognition hardware

The operation and performance of the online ring recognition hardware which is a component of the second level trigger of the HADES detector is described. Its goal is to identify Cherenkov rings from electrons traversing a hadron blind RICH. This information is used in the second level trigger to select electron/positron pairs within a given invariant mass range. ng recognition hardware has been operated in several commissioning beamtimes. The obtained event rates are in accordance with expectations and the full system performance. For C+C collisions an event reduction factor higher than 15 can be achieved using only conditions on the online ring recognition. Higher reduction factors are reached using the full second level trigger functionality.