| 摘要 |
<p>Method and Circuitry for the Function Control of Ultrasonic Alarm Systems In an ultrasonic alarm system, in which ultrasonic waves are continuously radiated within a surveilled area (R) and a frequency shift caused by a moved object, e.g. an intruder, is by virtue of the Doppler-Effect determined to be cause for the giving of an alarm, the function control of the system is effected during a test phase by means of brief aperiodic modulation of the ultrasonic waves. The resulting brief broadening of the frequency produces in the same east circuit a signal (S2) if the system is functioning normally. The duration of the modulation is chosen to be short enough so that no standing waves can form; this ensures the trouble-free operation of the function control, even if the system, as a result of the vectorial addition of the received ultrasonic waves, accidentally experiences a lack of insensitivity; in this manner even the covering of the transmitter during a sabotage attempt can be identified and differentiated from a state of insensitivity.</p> |
