| 摘要 |
The invention is based on an electrical proximity switching device, operated by means of ultrasound, having a transducer and a control unit. To widen the field of application of this device, particularly for utilisation in dim light and darkness, this device is associated with a light-sensitive cell which can act on the control unit, particularly, however, on the oscillation generator, in such a manner that it can enable or disable the device. In particular, however, the cell should switch off the device in daylight.
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