MUTING CIRCUIT FOR A SECURITY ALARM SYSTEM PROVIDING A SONIC ALERT

• US 3,707,708 A
• Filed: 12/16/1970
• Issued: 12/26/1972
• Est. Priority Date: 12/16/1970
• Status: Expired due to Term

• Current Assignee: Carlo Dan
• Original Assignee: Carlo Dan
• Inventors: Dan, Carlo
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/098,588
• Time in Patent Office: 741 Days
• Field of Search: 340/213.1,213.2,326,327
• US Class Current: 340/503
• CPC Class Codes: H04M 11/04 with alarm systems, e.g. fire, police or burglar alarm systems

Abstract

An electronic circuit enabling an operator at a central station to mute a sonic alarm device energized in the event of an emergency condition occurring at a remote station under surveillance at any time from the moment the alarm is heard and identified at the central station to the time when a normal condition is restored. The circuit additionally includes means which reenergizes the sonic device automatically as soon as the normal condition is restored to remind the operator that muting had previously occurred and further requiring the operator to manually reset the circuit to deactivate the reenergized sonic alarm device.

Claims

1. A muting circuit for a sonic alarm device in a security alarm system and being powered by an electrical supply voltage applied thereto, comprising in combination:

input signal means;

first circuit means coupled to said input signal means and said sonic alarm device, being responsive to an input signal of a first and a second type coupled to said input means to become operative for energizing said sonic alarm device and remaining operative to supply electrical voltage to said sonic alarm device until reset;

reset means coupling said electrical supply voltage to said first circuit means and selectively rendering said first circuit means inoperative after being rendered operative by said input signal by interrupting said electrical supply voltage coupled thereto;

second circuit means coupled across said sonic alarm device, being normally inoperative but being rendered selectively operative in accordance with a first control voltage applied thereto for short circuiting said sonic alarm device and thereby muting said alarm device;

third circuit means including normally open electrically controlled switch means coupled to said second circuit means, being rendered closed to generate said first control voltage upon the application of a second control voltage fed thereto as well as a power voltage, and muting switch means coupled to said controlled switch means for selectively applying said second control voltage thereto and rendering said controlled means closed whereupon said controlled switch means remains closed as long as said power voltage is applied;

fourth circuit means coupled from said input means to said third circuit means, being responsive to said first type of input signal for applying said power voltage thereto for the duration of said first type of input signal;

an fifth circuit means coupled from said input means to said third circuit means being responsive to said second type of input signal for supplying said power voltage thereto for the duration of said second input signal, said second and said third circuit means however becoming inoperative upon the termination of said first and second input signal due to the absence of said power voltage whereupon said sonic alarm device agAin is rendered operative by means of said first circuit means, remaining energized until said first circuit means is rendered inoperative by said reset means.

2. The invention as defined by claim 1 and additionally including visual indicator means coupled to and energized by said first circuit means providing a visual indication of the presence of said first or second type of input signal at said input means.

3. The invention as defined by claim 1 wherein said first circuit means comprises:

a controlled rectifier having a first and a second current conducting electrode and a control electrode, and additionally including circuit means coupling said reset means to one current conducting electrode, the sonic alarm device to the other current conducting electrode, and said control electrode to said input means.

4. The invention as defined by claim 1 wherein said first circuit means comprises:

a semiconductor controlled rectifier having an anode, a cathode and a gate electrode including circuit means coupling said anode electrode to said reset means, said cathode electrode to said sonic alarm device and said gate electrode to said input means.

5. The invention as defined by claim 1 and additionally including current limiting means coupled between said first circuit means and said sonic alarm device.

6. The invention as defined by claim 1 wherein said second circuit means comprises a semiconductor switch and said electrically controlled switch means comprises a controlled rectifier having a first and a second current conducting electrode and a control electrode and including circuit means coupling one of said current conducting electrodes to a circuit terminal for the application of said power voltage, the other current conducting electrode to said semiconductor switch, said control electrode to said muting switch means, and said fourth and fifth circuit means to said circuit terminal whereupon said muting switch means is adapted to render said controlled rectifier conductive upon the application of said power voltage to said circuit terminal upon the appearance of either said first or second input signal at said input means and whereupon said other current conducting electrode couples said first control signal to said semiconductor switch.

7. The invention as defined by claim 1 wherein said fourth circuit means comprises diode means coupling said first type of input signal to said electrically controlled switch, said input signal thereby comprising said power voltage.

8. The invention as defined by claim 1 wherein said fifth circuit means comprises:

capacitive means coupled to said input means and being responsive to said second type of input signal to be charged thereby, and amplitude sensitive circuit means, coupled to said capacitance means, being responsive to the amplitude of the voltage across said capacitive means and coupling said supply voltage to said electrically controlled switch when the voltage across said capacitor exceeds a predetermined amplitude, said supply voltage thereby comprising said power voltage.

9. The invention as defined by claim 8 wherein said amplitude sensitive circuit means comprises a Schmitt trigger circuit.

10. A muting circuit for a sonic alarm device adapted to be powered by a supply potential coupled from a power source comprising, in combination:

a first controlled rectifier coupled to said sonic alarm system and including circuit means for being rendered conductive upon the application of a steady state and a pulsating alarm signal coupled thereto to couple said supply potential therethrough to said sonic alarm;

reset means coupling said power source to said first controlled rectifier for supplying power thereto and for selectively rendering said first control rectifier non-conductive when actuated;

normally open switch means coupled to said sonic alarm device and being adapted to be rendered closed to short circuit said sonic alarm;

second controlled rectifier means coupled to said normally open switch means and additionally including circuit means for applying a control signal to said switch means when either said steady state or said pulsating alarm signal is coupled to said first controlled rectifier, and being adapted to be selectively rendered conductive only during the presence of said steady state or said pulsating alarm signal to close said switch means; and

muting switch means coupled to said second controlled rectifier for selectively rendering said second control rectifier conductive only during the presence of said alarm signals to cause said normally open switch means to short circuit said sonic alarm device, said second controlled rectifier automatically becoming non-conductive upon the disappearance of said steady state or said pulsating alarm signal and removing said control signal from said switch means causing said switch means to become open whereupon said first controlled rectifier reactivates said sonic alarm until said first controlled rectifier means is rendered non-conductive by said reset means.

11. The invention as defined by claim 10 wherein said first and second controlled rectifier means comprises a semiconductor controlled rectifier and said normally open switch means comprises a transistor.

12. The invention as defined by claim 11 wherein each said semiconductor controlled rectifier has a first and second current conducting electrode and a gate electrode and additionally including input circuit means coupling said steady state and said pulsating alarm signal to the gate electrode of said first semiconductor controlled rectifier, and circuit means coupling said muting switch means to the gate electrode of said second controlled rectifier whereby said muting switch means couples a trigger signal thereto when actuated.

13. The invention as defined by claim 12 wherein said reset means is coupled to one current conducting electrode of said first controlled rectifier and additionally including diode means coupled between said second current conducting electrode of said first controlled rectifier and said sonic alarm device;

and circuit means coupling a voltage to one current conducting electrode of said second controlled rectifier during the presence of either said steady state or pulsating alarm signals and the other current conducting electrode to said transistor.

14. The invention as defined by claim 13 wherein said last recited circuit means includes:

a capacitor responsive to said pulsating alarm signal and being charged thereby, a normally non-conductive transistor coupled between said power source and said one current conducting electrode of said second controlled rectifier, and an amplitude discriminator circuit coupled between said capacitor and said transistor, said transistor being rendered conductive by said amplitude discriminator when the charge across said capacitor exceeds a predetermined amplitude level to couple said supply potential to said one current conducting electrode of said second controlled rectifier; and

a semiconductor diode responsive to said steady state alarm signal, coupled to said one current conducting electrode of said second controlled rectifier and being selectively poled to apply said steady state alarm signal to said one current conducting electrode of said second controlled rectifier.