| 摘要 |
A method and configuration for maintaining a constant flow of air to a protective helmet (4) from a fan (3) in a battery powered fresh air unit. The fan (3) is a radial fan with a filter (5) positioned on the suction side of the fan and is operated by a brushless continuous current motor (2). With the aid of signals from position sensors (30) in the motor (2), a control unit (12) can determine the speed of the fan (3). The control unit also detects the motor's power consumption and compares this and the speed with a characteristic curve for the motor (2) for a given flow from the fan, which is stored in a memory (14). In the event of any deviation, the control unit (12) regulates a change of the voltage supply to the motor (2) so that the deviation is reduced. In this way the flow is maintained constant at the desired, adjustable level independent of the blflcking and battery voltage of the filter (5). The control unit (12) emits signals (qs), Vs to a warning indicator light and buzzer (40, 42) in an alarm unit (38) in the fresh air unit if the battery voltage falls below a predetermined minimum safety level. |
