Method of, and circuit arrangement for, function control of ultrasonic alarm installations
US4727522A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 23, 1985 |
| Grant date | Feb 23, 1988 |
| Priority date | — |
| Expiry date | Sep 23, 2005 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01S7/52004
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
In an ultrasonic alarm installation ultrasonic waves are continuously emitted into a monitored region and a frequency shift due to a moving object, e.g. an intruder, by virtue of the Doppler effect is evaluated for giving an alarm signal. The function control in this installation occurs during a test phase by means of brief aperiodic modulation of the emitted ultrasonic waves. The resulting brief frequency broadening generates in the same evaluating circuit a signal if the installation is functioning correctly. The time duration of the aperiodic modulation is selected to be so short that no standing waves can form, so that the function control can also work faultlessly if the installation, because of vectorial addition of the received ultrasonic waves, accidentally is in an insensitive state. Thus even coverings of the ultrasonic transmitter during a sabotage attempt can be recognized and distinguished from an insensitive state.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.