The log file was analyzed for the reported date of event, (b)(6) 2018.After two hours in the case using volume mode the system detected two consecutive motor encoder check errors.Thereupon, according to the device safety concept, the system forced a shutdown of the automatic ventilation and posted the corresponding "ventilator failure" alarm.Manual ventilation and monitoring functions remain available in this case.After the event the motor was replaced and was made available for further investigation at manufacturer¿s site.An evaluation of the motor in the laboratory revealed that in several positions the motor did not provide mechanic power due to a mechanically abraded collector disc.In this case the electrical contact between the collector disc and the carbon brushes is partly disrupted.The consequence are fluctuations in the rotating speed so that the measured ventilator piston position does not match with the one calculated by the system's software.In this case to prevent from damages the system is designed to shut down as described above.Finally it can be concluded that the device has responded to a detected malfunction of a single component as specified.The repair exchange of the motor assembly has solved the reported symptom and the device was put back into operation without further problems reported.The number of similar cases, related to the same root cause, is within the expected range of the respective risk assessment and thus accepted.
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