For the investigation the logfile and the results from the tests done on site were analyzed.The described problem could be retraced.It was found that the device forced a shut down due to high current consumption of the ventilator motor.Root cause was most likely a faulty light barrier cable.The light barrier on the ventilator shall signalize when the piston reaches its lower limit during active ventilation to ensure that further movement into downward direction is stopped.In case of a faulty light barrier cable the piston may move further downward and gets stuck in end position.The motor current increases significantly during the attempt to drive the piston up again which triggers the safety shutdown then.In this case the device will generate an audible alarm and, the alarm message "ventilator fail" will be displayed.The user can switch to manual ventilation as described in the instructions for use.Monitoring is still functional.The service engineer replaced the light barrier cable on-site.The device was tested according to manufacturer's specification and was released into use.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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