JPS58213397A - Fire sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention prevents a drop in the power supply voltage to the detection circuit due to high resistance, applies a high constant voltage to the detection circuit, and easily limits the rush current when the power is turned on. To provide a fire detector capable of connecting a large number of detectors to one line without causing a receiving circuit to react due to transient current flowing through a capacitor when a plurality of detectors are connected in parallel to one line.

FIG. 1 shows a fire detector B according to the present invention, and this fire detector B! ! ' A thyristor SCR as a switching element that conducts to a low impedance value in response to a fire detection signal from the detection circuit
It is configured as a bypass circuit consisting of two circuits. When a voltage is first applied between the positive and negative electrodes in this circuit, the current flows from the positive pole of the power supply to the receiving relay R terminal a to the positive pole of the rectifier circuit BG → transistor Q1 → resistor R2 – capacitor C – rectifier circuit B
It flows to the negative terminal of G and the negative terminal of the power supply to charge the capacitor C in the sensor B.

The configuration and operation of the present invention will be explained in more detail below.
In Fig. 1, R2 is a low resistance inserted in series on the positive side of the detection wire connected from terminal a, and a cyrisk SCR is connected to the positive and negative sides of the detection wire on the receiver A' side from the low resistance. However, a capacitor C is also connected to the sensor B side. A constant voltage circuit consisting of a transistor Q1 and a Zener diode ZDI is connected to the receiver A side of this capacitor C, and the above-mentioned voltage is connected between the control electrode, that is, the base, of the transistor Q1 of the constant voltage circuit and the positive side of the above-mentioned detection line. A bypass circuit consisting of a transistor Q2 is connected, which is activated when the voltage drop across the low resistance R2 reaches a predetermined value.

As described above, in the circuit in which the low resistance R2 and the transistor Q2 are connected as described above, a current flows through the Zener diode ZD from the power supply through the detection line and through the resistor R1.
A pass current flows to the transistor Q1 from the connection point between the resistor R1 and the Zener danauto ZD, and a collector current of the transistor flows. This collector current reduces the resistance R.
When the voltage across the transistor Q2 becomes higher than the VBE of the transistor Q2, the base current of the transistor flows, the collector current of the transistor flows, the base current of the transistor Q1 decreases, and the collector current of the transistor also decreases. This collector current decreases to be lower than the VBE of transistor Q2 across low resistance R2 (then the base current of the transistor decreases and the transistor is turned off, the collector current of the transistor decreases, and the The base current increases.By repeating such alternating on and off of transistors Q1 and Q2,
Current is supplied to capacitor C. The maximum value of this current, that is, the inrush current, can be considered as the transistor Q2.
The current value is determined by VBE/R2 of , and is unrelated to the voltage of the power supply.

Claims (1)

[Claims] 1) Connected between the power supply and signal lines drawn out from the receiver,
A fire detection device that has a switching element that maintains a relatively high impedance value between the lines in normal conditions and transmits a fire signal by conducting at a low impedance value when a fire occurs, and a capacitor that stores potential by supplying power. In the device, a low resistance is inserted in series with one of the lines, and the low resistance connects the switching element between the lines on the receiver side, and connects the switching element to the detection circuit side.
At the same time, a constant voltage circuit consisting of a transistor, a resistor, and a Zener diode is connected to the line on the side of the receiver from the capacitor, and a control electrode of the transistor of the constant voltage circuit is connected to one of the lines. A fire detector characterized in that a bypass circuit is connected which is activated when the voltage drop occurring across the low resistance reaches a predetermined value.