Fire alarm system

• US 4,525,700 A
• Filed: 10/27/1983
• Issued: 06/25/1985
• Est. Priority Date: 10/27/1982
• Status: Expired due to Term

• Current Assignee: Nittan Co. Ltd. (Old) (Secom Company Limited)
• Original Assignee: Nittan Co. Ltd. (Old) (Secom Company Limited)
• Inventors: Suzuki, Takashi, Tanaka, Seiichi, Kimura, Tetsuo
• Primary Examiner(s): Crosland, Donnie L.
• Application Number:
  US06/546,108
• Time in Patent Office: 607 Days
• Field of Search: 340/518, 340/505, 340/506, 340/500, 340/508, 340/511, 340/510, 340/514, 340/522, 340/537, 340/825.06, 340/825.07, 340/825.08, 340/825.09, 340/825.1 , 340/825.3, 340/825.54, 179/5 R
• US Class Current: 340/518
• CPC Class Codes: G08B 26/002 only replying the state of the sensor

Abstract

A fire alarm system has a main unit and a plurality of sensor terminals in accordance with a polling system. The plurality of sensor terminals are divided into a plurality of groups. When a given sensor terminal of a given group is accessed and transmits digital data as response data indicating a smoke concentration or a temperature to the main unit, and the response data exceeds a first reference value thereby indicating that a fire has broken out, the main unit accesses other sensor terminals of the given group. If some of the response data therefrom exceed a second reference value which is equal to or smaller than the first reference value, the main unit counts the number of such sensor terminals. When the number exceeds a predetermined number, the main unit displays information indicating the existence of a fire.

Claims

1. A fire alarm system comprising:

a plurality of sensor terminal means separately connected to a transmission line, each of said plurality of sensor terminal means transmitting digital data as response data by converting an analog sensor output indicating one of the parameters smoke concentration and temperature when the respective sensor terminal means is accessed by an address signal corresponding to an address of the respective sensor terminal means;

a main unit means connected to said plurality of sensor terminal means through said transmission line for cyclically accessing said plurality of sensor terminal means and for comparing the response data from each sensor terminal means with a first reference value; and

said plurality of sensor terminal means being divided into a plurality of groups, said main unit means comparing the response data from a given sensor terminal means of a given group with the first reference value and comparing the response data from the other sensor terminal means in the same group as the given sensor terminal means but excluding the given sensor terminal means with a second reference value when the response data from the given sensor terminal means exceeds the first reference value, and said main unit means determining that a fire has broken out when the number of sensor terminal means supplying response data exceeding the second reference value is greater than a predetermined number, and thereafter displaying information indicating existence of a fire.

2. A system according to claim 1 wherein the second reference value is smaller than the first reference value.

3. A system according to claim 1 wherein the sensor terminal means supplying the response data exceeding the second reference value are preset in a memory.

4. A system according to claim 1 wherein the sensor terminal means supplying the response data exceeding the second reference value are detected after the given sensor terminal in the same group which supplies the response data exceeding the first reference value is detected by said main unit means.

5. A system according to claim 1 wherein the first and second reference values are equal.

6. A fire alarm system comprising:

a plurality of sensor terminal means separately connected to a transmission line, each of the sensor terminal means transmitting digital data as response data indicative of presence of a fire when accessed by an address signal corresponding to an address of the respective sensor terminal means;

a main unit means connected to said plurality of sensor terminal means through the transmission line for repeatedly accessing the plurality of sensor terminal means and for comparing the response data from each sensor terminal means with a first reference value; and

when said main unit means determines that response data from one of the sensor terminal means exceeds the first reference value, the main unit means then compares the response data from other sensor terminal means with a second reference value, and said main unit means then determining that a fire has broken out when the number of sensor terminal means supplying response data exceeding the second reference value is greater than a predetermined number, and thereafter supplying information indicating existence of a fire.