(19)
(11) EP 1 174 835 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
05.03.2003 Bulletin 2003/10

(43) Date of publication A2:
23.01.2002 Bulletin 2002/04

(21) Application number: 01305973.8

(22) Date of filing: 11.07.2001
(51) International Patent Classification (IPC)7: G08B 3/10
(84) Designated Contracting States:
AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE TR
Designated Extension States:
AL LT LV MK RO SI

(30) Priority: 18.07.2000 GB 0017477

(71) Applicant: Rafiki Protection Limited
Cwmbran, Gwent NP44 5DB (GB)

(72) Inventor:
  • Lewinsky, John
    Gwent NP4 8DD (GB)

(74) Representative: Evans, Huw David Duncan 
Urquhart-Dykes & Lord, Three Trinity Court, 21-27 Newport Road
Cardiff CF24 OAA
Cardiff CF24 OAA (GB)

   


(54) Audible warning devices


(57) An audible warning device e.g. for a fire alarm system is arranged to generate an audible output signal having a first frequency 1/T1 and comprises an audible output transducer 10 and a driver circuit 12 for applying an alternating drive signal, having a second and higher frequency 1/T2, to the transducer 10 over successive distinct periods, the frequency of the periods being equal to the first frequency 1/T1. The (second) frequency at which the transducer 10 is driven is at or near the resonant frequency of the transducer 10. However, the (second) frequency signal is only applied in successive distinct periods at the (first) lower frequency and thus the transducer appears to produce an audible output signal at this lower frequency.
There is also disclosed a method of tuning the a transducer to output an audible output signal at the (first) lower frequency by determining the (second) frequency at which the audible output of the transducer is high and driving the transducer 10 with a drive signal at the determined (second) frequency over successive distinct periods, the frequency of the periods being equal to the desired (first) frequency.






Search report