JPH0449748Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention detects fire by sequentially connecting a plurality of fire detectors in parallel to a pair of power supply signal lines drawn out from a receiver, and also connects a pair of power supply signal lines The present invention relates to a fire alarm equipped with a disconnection detection function for detecting disconnection of wires or feed lines.

An example of a conventional device of this type is the one shown in FIG. A plurality of fire detectors 2a, 2b, . . . 2n, which detect fire by sensing the heat caused by the occurrence of a fire, are sequentially connected in parallel to a pair of power supply signal lines L1 and L2 drawn out from the receiver 1 by a feed line Lo. The line is monitored by connecting a terminating resistor Ro to the final end and constantly passing a monitoring current.
2 or when the feed line Lo is disconnected, the power supply from the receiver 1 is cut off, and the monitoring current no longer flows through the terminating resistor Ro. Here, the fire detectors 2a, 2
b,...2n are equipped with a detection contact that closes when it senses the heat caused by a fire. Under normal conditions, the detection contact is open and the impedance between the pair of power and signal wires is infinite, so it is not possible to detect a fire. vessels 2a, 2b,
...No current flows through 2n either. Therefore,
At the time of wire breakage, the monitoring current becomes zero, no current flows out from the receiver 1, and the detection voltage of the power supply detection circuit 4 becomes equal to the power supply voltage E, thereby determining whether the line is broken.

However, the fire detectors 2a, 2b,...2
In some cases, a smoke detector is used to detect a fire by sensing smoke caused by a fire outbreak. Fire detection is performed by converting the smoke into an electrical detection level, and even in normal times the smoke flowing into the chimney must be constantly monitored.In order to carry out this monitoring operation,
Each fire detector consumes a small amount of current.
Therefore, even if the line is disconnected, for example between the fire detector 2n and the terminating resistor Ro, and the monitoring current flowing through the terminating resistor Ro becomes zero, the fire detectors 2a, 2
b, . . . 2n perform a monitoring operation, and as a predetermined current consumption flows, the detected voltage of the voltage detection circuit 4 is not equal to the power supply voltage of the receiver 1, and the voltage changes between the disconnection and the normal state. There was a problem that it was not easy to detect line breakage due to the small number of wires.

In other words, to explain the changes in line voltage in normal conditions and disconnected conditions with respect to FIG. 1 using a calculation formula, as an example, the equivalent resistance of the fire detection circuit 5 is
1kΩ, multiple fire detectors 2 connected to receiver 1
Assuming that the combined equivalent resistance of a, 2b, ...2n is 40kΩ, the resistance value of the terminating resistor is 20kΩ, and the voltage supplied from receiver 1 is 24V, the line voltage Vn input to voltage detection circuit 4 during normal operation is calculated by the following formula: It is indicated by.

Vn=[24×{(40×20)/(40+20)}]/[{(40×20)/(40+20)}+1] =22.3[V] Next, disconnection of feed line Lo, for example, fire detector 2n
The line voltage Vc input to the voltage detection circuit 4 at the time of disconnection when the line is disconnected between the terminal resistor Ro and the terminal resistor Ro is determined by the following equation.

Vc = (24 x 40) / (40 + 1) = 23.4 [V] Therefore, the change in line voltage input to the voltage detection circuit 4 between normal and disconnected conditions (Vc - Vn) is: Vc - Vn = 23.4 - 22.3 = 1.1 [V], which is small, and the ratio A of this voltage change to the power supply voltage is determined by the following equation.

A={(Vc-Vn)/24}×100 =4.6(%) In this way, fire detectors 2a, 2b,...2n
Therefore, when using a so-called smoke detector that detects fire by detecting smoke caused by a fire,
Due to the small amount of current flowing through the line, the change in line voltage between normal and disconnected conditions is minute, and in order to detect such minute voltage changes, a detection element with excellent detection sensitivity must be used. First, the circuit configuration becomes complicated, resulting in high costs, and there is a risk of malfunction due to noise or fluctuations in the power supply voltage.

This invention was created in view of the above problems, and all types of fire detectors, including smoke detectors as well as thermal fire detectors, are connected in parallel to a pair of power supply and signal lines drawn out from the receiver. To provide a fire alarm equipped with a disconnection detection function that reliably detects a disconnection of a line with a simple circuit configuration even when the line is disconnected.

In order to achieve this purpose, the present invention inserts a resistance for disconnection detection into the line of the receiver that is compatible with the power signal line, and uses the voltage drop caused by the opening of a switch connected in parallel to this resistance to detect the disconnection during normal operation. The change in line voltage at the time of wire breakage is increased to reliably detect wire breakage.

Hereinafter, embodiments of the present invention will be described based on the drawings.

FIG. 2 is a circuit diagram of a fire alarm showing an embodiment of the present invention. First, to explain the configuration, 1 is a receiver, and a plurality of fire detectors 2 are connected to a pair of power signal lines L1 and L2 drawn out from the receiver 1.
a, 2b, .
The monitoring current at this time is set to a value at which the fire detection circuit 5 does not perform a detection operation.

Next, the circuit configuration of the receiver 1 will be explained. E is a power supply, which supplies a power supply voltage of 24V, for example, as in FIG. 4 is a voltage detection circuit, which is composed of voltage detection elements such as relays or transistors, and detects changes in line voltage between normal times and disconnections, and detects disconnections in the pair of power signal lines L1 and L2 or the feed line Lo. Discern. 5 is a fire detection circuit, which is composed of a relay with a coil resistance of 1 kΩ, etc., and connects multiple fire detectors 2a, 2b,
...2n detects a fire and the pair of power signal lines L1 and L2 are made low impedance, the fire detectors 2a, 2b, ...2n operate by detecting the flowing line electrode. Receive fire signals from. Rc is a resistance for detecting disconnection,
As an example, the resistance value is set to 3kΩ, and a pair of power signal lines L1 and L2 or a feed line Lo
The line voltage change caused by the disconnection is captured and sent to the voltage detection circuit 4. A switch 6 is connected to both ends of the resistor Rc for detecting disconnection, and during normal fire monitoring, the switch 6 is closed to short-circuit the resistor Rc, and during testing, it is opened to detect disconnection.

Next, the operation of the present invention will be explained in comparison with the conventional device shown in FIG.

First, when a test is conducted with the switch 6 open in normal conditions, a voltage drop occurs due to the resistor Rc and the fire detection circuit 5, and is input to the voltage detection circuit 4. Here, like the conventional device shown in FIG. 1, a plurality of fire detectors 2a, 2b, .
The combined equivalent resistance is 40kΩ, and the resistance value of the terminating resistor Ro is
Line voltage input to voltage detection circuit 4 as 20kΩ
Vn is determined by the following formula.

Vn=[24×{(40×20)/(40+20)}]/[{(40×20)/(40+20)}+3+1] =18.5[V] Next, the terminating resistor Ro is disconnected and the wire becomes disconnected. I will explain the operation when it gets old. Voltage detection circuit 4 when conducting a disconnection test by opening switch 6
The line voltage Vc input to is determined by the following equation.

Vc = (24 x 40) / (40 + 3 + 1) = 21.8 [V] Therefore, the change in line voltage (Vc - Vn) between normal and disconnected conditions is as follows.

Vc - Vn = 21.8 - 18.5 = 3.3 [V] The ratio A of this voltage change to the power supply voltage is determined by the following equation.

A = {(Vc - Vn) / 24 x 100 = 13.8 (%) In this way, when the line voltage Vc is input to the voltage detection circuit 4 at the time of disconnection, the ratio of voltage change (Vc - Vn) to the power supply voltage is A As the voltage is significantly improved to 13.8%, the voltage detection circuit 4 composed of voltage detection elements such as transistors and relays operates reliably, and a disconnection is indicated by a relay contact (not shown).

As explained above, according to the present invention, a resistor for disconnection detection is inserted into the signal line that also serves as the power supply of the receiver, and a resistor switch is connected in parallel, so that when the switch is opened during a disconnection test, the voltage drop due to the resistance is reduced. By using this method, the amount of change in the line voltage between the normal state and the time of disconnection is increased, so that the voltage detection circuit can reliably detect a disconnection because the amount of change is large.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional fire alarm, and FIG. 2 is a circuit diagram showing an embodiment of a fire alarm according to the present invention. 1...Receiver, L1, L2...Power supply/signal line, 2a, 2b,...2n...Fire detector, 4...
...Voltage detection circuit, 5...Fire detection circuit, 6...Switch, E...power supply, Lo...feeding line, Rc...resistance, Ro...terminal resistor.

Claims (1)

[Claim for Utility Model Registration] Multiple fire detectors are sequentially connected in parallel by a feed line to a pair of power supply/signal lines drawn out from a power supply built into the receiver via a fire detection circuit, and terminated at the final end. In a fire alarm connected to a resistor, a resistor and a parallel circuit of a switch that is closed during normal monitoring and opened during a disconnection test are connected in series to the fire detection circuit, and a series combined resistance of the resistor and the fire detection circuit, and the terminal are connected in series. A fire alarm characterized by being equipped with a voltage detection circuit that detects fluctuations in divided voltage with a resistor.