Adapter module for improving the reliability of an alarm circuit

Abstract: In an alarm system having several alarm circuits (18 to 20) connected to the terminals (11,12) of a central control panel (10) both ends of the alarm loops (29,30) interconnecting the ends of the alarm circuits are connected to terminals (25,26;27,28) of an adapter module (22@ which connects these terminals (25 to 28) to the terminals (11,12) of the control panel. By connecting both ends of the alarm loops (29,30) to the control panel each kind of circuit break (34,35,36) in one or both alarm loops (29,30) cannot prevent the annunciator (20′,20″) from responding since it remains connected to the associated terminal (11,12) via the second end of the associated alarm loop (29,30).

Description: The present invention relates to alarm circuits and more particularly to an adapter module for converting a class B alarm circuit to more reliable class A operation. BACKGROUND OF THE INVENTION Various types of systems are called upon to signal an alarm condition when a specified event occurs. Examples of such systems are fire alarms and burglar alarms. Because of the reliance placed on such systems, steps must be taken to insure the reliability of the alarm circuit. One step which is commonly taken is the use of separate supervisory and alarm modes. In supervisory mode the alarm circuit is monitored to insure that it is in working order, i.e. has no broken wires or other open circuits. When an alarm condition occurs, the circuit shifts from supervisory to alarm mode, causing the alarm to be signaled. Such alarm circuits may be divided into two general groups. These are known as "class A" circuits and "class B" circuits (see for instance US-A-4224538). A class A circuit has certain fail-safe features not present in a class B circuit. If an open circuit condition occurs in a class B circuit the alarm will not function until the open circuit is repaired. In a class A circuit, however, an open circuit, while detectable by the supervisory mode of the system, will not prevent the alarm from sounding should an alarm condition occur. Class A circuits, therefore, have significant advantages over class B circuits in providing increased safety, by insuring that alarms will be sounded if an alarm condition arises before an open circuit can be repaired. Alarm systems commonly are designed with a central panel which acts as a controller and various remote sensors and alarms. The design of the central panel will determine whether a class A or a class B alarm circuit may be connected thereto. In some situations, however, it may be desirable to upgrade a system which has been previously installed with class B alarm circuits to class A alarm circuits. The invention as characterized in claim 1 provides an adapter module for converting class B alarm circuits to class A. It allows a central control panel designed to accept a class B alarm circuit to be upgraded to support a class A alarm circuit. Preferred embodiments are described in the subclaims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a class B alarm circuit; Figure 2 is a schematic diagram of a class B alarm circuit which has been converted to a class A alarm circuit using the adapter of the invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Figure 1 illustrates a typical class B alarm circuit. The portion of the alarm circuit enclosed by box 10 would typically be provided on a central control panel, while the remainder of the circuit would be external to such a panel. The portion of the circuit on panel 10 includes terminals 11 and 12 which connect to the external alarm circuitry at terminals 13 and 14 thereof, respectively. In supervisory mode circuit nodes 15 and 16 are electrically biased such that an electrical current flows from node 15 to node 16. In so doing, it will flow through load resistor 17, but diode 18 will prevent current flow through circuit branch 19 thus preventing the activation of annunciator 20. In supervisory mode, if there is an open circuit condition, such as that which is indicated at point 21 on the circuit, the current will be unable to flow and the presence of an open circuit will be indicated on the control panel. When an alarm condition occurs, nodes 15 and 16 will be electrically biased so that an electrical current will flow from node 16 to node 15. When this occurs, diode 18 will be forward biased allowing current to flow through circuit branch 19 thus activating annunciator 20. Annunciator 20 may be a bell, a horn, a light, or any other signaling device which will indicate the existence of an alarm condition. As may be seen, if an open circuit condition occurs, such as at point 21, no complete circuit will exist, preventing the signaling of an alarm condition. Turning now to Figure 2, the portions within box 10, i.e. the portions on the central control panel, match those of Figure 1. The portion within box 22 is a module which may be connected to terminals 11 and 12 in order to convert the circuit to class A operation. In a preferred embodiment the circuitry in box 22 would be provided on a printed circuit board which could be attached to the central control panel. The circuitry in box 22 includes terminals 23 and 24 which connect to terminals 11 and 12, respectively. The circuitry in module 22 further includes terminals 25, 26, 27 and 28 for connection to alarm loops. The circuitry also includes diodes 31, 32. and 33 and resistor 17′. Diodes 31, 32 and 33 are not required for proper operation of the circuit, but are preferred. Diodes 31, 32, 33 could be replaced by wire connections. Particularly, the reasons for preferring the presence of diode 32 are described in co-pending application EP-A-0251223. In operation loop 29 is electrically connected to terminals 25 and 26 while loop 30 is electrically connected to terminals 27 and 28. Alarm circuits 19′ and 19″ run between the two loops and include diode 18′ together with annunciator 20′ and diode 18″ together with annunciator 20″, respectively. As in the previous example, when the circuit of Figure 2 is in supervisory mode, nodes 15 and 16 are electrically biased so that an electric current flows from node 15 to node 16. This current may be used to detect open circuits at locations in the alarm loops. For example, open circuits at location 34, 35 or 36 would be detected. When an alarm condition occurs, the biasing on nodes 15 and 16 is changed so that current will flow from node 16 to node 15. As before, this will cause the annunciators to be activated. Unlike the circuit of circuit 1, however, an open circuit which has not been repaired at locations such as 34, 35, 36 or at similar locations on loop 30 will not prevent activation of the annunciators, therefore, producing a fail-safe system. By connecting both ends of the alarm loops 29, 30 to the control panel each kind of circuit break 34, 35, 36 in one or both alarm loops 29, 30 cannot prevent the annunciator 20′, 20″ from responding,since it remains connected to the associated terminal 11, 12 via the second end of the associated alarm loop 29, 30.

Claims: An adapter module for a central control panel having first and second terminals (11, 12) for providing output signals to a class B alarm circuit (18,19,20), characterized in that said module comprises: a) support means for holding electrical components; b) first and second terminals (23, 24) for electrically connecting to said central control panel first and second terminals (11, 12), said module (22) first and second terminals being physically attached to said support means; c) third (25), fourth (26), fifth (27) and sixth (28) terminals for electrically connecting to class A alarm circuit, said third terminal (25) being directly electrically connected to said module first terminal mean (23), and said sixth terminal (28) being directly electrically connected to said module second terminal (24), said third, fourth, fifth and sixth terminals being physically attached to said support means; d) first connecting means (31) for electrically connecting said third terminal (25) to said fourth terminal (26); e) second connecting means (17′,32), including an electrical resistor (17'), for electrically connecting said fourth terminal (26) to said fifth terminal (27); f) third connecting means (33) for electrically connecting said fifth terminal (27) to said sixth terminal (28) whereat g) said first, second and third connecting means are physically attached to said support means. A module according to claim 1, characterized in that said second connecting means (17';32) includes a diode (32). A module according to claim 1 or 2, characterized in that said first (31) and third (33) connecting means each contain a diode (31,33). A module according to one of the preceding claims, characterized in that said support means is a printed circuit board. A module according to one of the preceding claims for connecting the central control panel to several alarm circuits which are connected in parallel between a first (29) and a second (30) alarm loop, with each alarm circuit including a diode (18′,18″) and an annunciator (20′ 20″) connected in series, characterized in that h) the ends of the first alarm loop (29) are connected to the third and fourth terminals (25,26) respectively and the ends of the second alarm loop (30) are connected to the fifth and sixth terminals (27,28) respectively; i) a first diode (31) is connected between the third and the fourth terminals (25,26) and a second diode (33) is connected between the fifth and the sixth terminals (27,28), with both the first and the second diode having the same flow direction as the diodes (18′,18″) in the alarm circuits (19′,18′,20′;19″,18″,20″); j) a resistor (17′) is connected between the fourth and the fifth terminals (26,27). A module according to claim 5, characterized in that a third diode (32) is connected in series with the resistor (17′) between the fourth and the fifth terminals (26,27), with said third diode (32) having a flow direction opposite to the flow direction of the first and second diodes (31,33).

Inventors: PRYSBY DANIEL G, PRYSBY, DANIEL G.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1987
Main classification: G08B29
IPC codes: G08B29, G08B25