Method of, and circuit arrangement for, function control of ultrasonic alarm installations
US4729120A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 23, 1985 |
| Grant date | Mar 1, 1988 |
| Priority date | — |
| Expiry date | Sep 23, 2005 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG08B29/14
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
In an ultrasonic alarm installation, ultrasonic waves are continuously emitted into a monitored region and a frequency shift caused by a moving object, e.g. an intruder, is received by an ultrasonic receiver and evaluated by virtue of the Doppler effect for generating an alarm signal. For testing the ultrasonic alarm installation the emitted ultrasonic waves are modulated by a plurality of modulation frequencies in the range of the frequency shifts effective for triggering the alarm signal. Thus, the function test can be carried out using the same electrical evaluation circuit as for generating the alarm signal. The plurality of modulation frequencies conjointly with the switch-off of the transmitter signal has the effect that the reflected signals, which arrive at the ultrasonic receiver with different phase relationships, are not vectorially added to the ultrasonic transmitter signal to yield zero, so that a reliable function control is always ensured. Furthermore and for determining changes in the monitored region, the time decay of the modulation-caused signal is compared with a reference signal in the electrical evaluation circuit after switch-off of the modulation signal.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.