JPS598873B2 - Ionic smoke detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion type smoke detector that detects smoke generated during a fire.

Conventionally, in principle, ion type smoke detectors have lower sensitivity to smoke caused by smoldering than photoelectric type smoke detectors.

For this reason, increasing the sensitivity of the sensor increases the number of malfunctions caused by cigarette smoke and the like. In addition, in order to prevent malfunctions caused by cigarette smoke, etc., a storage type sensor that activates when the concentration of smoke exceeds a predetermined level for a certain period of time can be used to prevent malfunctions caused by cigarette smoke. This had the disadvantage of delaying the process and increasing the risk. This invention eliminates these drawbacks and provides an ion-type smoke detector that prevents malfunctions caused by cigarette smoke, etc., operates reliably even in the case of smoldering fires, and has a quick response speed in the case of flaming fires. was provided.

Hereinafter, the ion type smoke sensor of the present invention will be explained in detail based on the drawings.

FIG. 1 shows an ion type smoke detector of the present invention, in which an ion chamber 1 for detecting smoke, an impedance conversion circuit 2 for converting the impedance of this ion chamber 1, and based on the output of the impedance conversion circuit 2, A low sensitivity level detection circuit 3 that detects high smoke concentration, a high sensitivity level detection circuit 4 that detects low smoke concentration, a timer circuit 5 that starts operation by the output of this high sensitivity level detection circuit, and Resistors R3 and R2 for applying voltage to the ion chamber 1 based on the output, a switching circuit 6 such as an SCR that becomes short-circuited based on the output of the low sensitivity level detection circuit 3, and an operation indicator such as a light emitting diode. It is composed of T.

The ion chamber 1 consists of an internal ion chamber ch into which outside air ionized by radioactive isotopes cannot easily enter, an external ion chamber ch 2 through which outside air can freely flow in, an intermediate electrode m disposed in between, and an external electrode n. It is formed from etc.

The impedance conversion circuit 2 is formed from a field effect transistor F whose gate is connected to an intermediate electrode m, and a transistor Q3 connected to this field effect transistor F. The low sensitivity level detection circuit 3 is formed from a series circuit of a Zener diode ZD3 and resistors R3 and R4. High sensitivity level detection circuit 4
is formed from a resistor R5, a transistor Q2, and a Zener diode ZD2. The timer circuit 5 includes resistors R6 to R9, a transistor Q2, a diode D, and a PUT (
A) The Zener diode ZD, which is formed from the capacitor C and is supplied with a standard voltage based on the Zener diode ZD2 at the time of detection by the high-sensitivity level detection circuit 4, has a Zener voltage higher than that of the Zener diode ZD2. is used. Power is supplied to the terminals P and N from the receiver via a pair of lines (not shown).

The receiver is configured to detect an increase in the operating current supplying the sensor and issue an alarm. The operation of the ion-type smoke detector constructed in this way will be explained next. As shown in Figure 2, in the case of a fire, the external ion chamber Ch2 When smoke enters the electrode, the ionic current decreases, and therefore, as time T increases, the voltage at the intermediate electrode m increases slowly, but does not become very high. The voltage of the intermediate electrode m is the reference voltage V. When the voltage rises from 1 and reaches voltage 1, the potential of the emitter electrode of transistor Q1 rises,
Resistor R5 and transistor Q2 of high sensitivity level detection circuit 4
Between the base of the emitter electrode and the Zener diode Z
Current flows through the circuit of D2, and transistor Q2 becomes conductive. As a result, the transistor Q3 of the timer circuit 5 also becomes conductive, and the capacitor C connected to the anode electrode of the PUA 4 starts charging via the resistor R8. PUT
A reference voltage based on a Zener diode ZD is applied to the gate electrode in (A). And 30-60
Over a certain period of time T, set to about seconds, the transistor Q
2 is conductive, the charging voltage of capacitor C is PUT
(A) becomes higher than the gate voltage of PUT (A), and PUT (A) becomes conductive, discharging the charge in the capacitor C through the resistors Rl and R2. As a result, a predetermined voltage is applied to the external electrode n due to the voltage drop across the resistor R1. Therefore, the voltage of the intermediate electrode m becomes as shown by curve A5 in FIG. 2, and exceeds the voltage 2 at which the low sensitivity level detection circuit 3 operates. That is, the voltage at the emitter electrode of the transistor Q becomes higher than the Zener voltage of the Zener diode ZDl, and a current flows through the series circuit of the Zener diode ZDll resistors R3 and R4. Then, a switching circuit 6 such as an SCR is triggered to short-circuit the terminals P and N. Since a current larger than the current flowing during monitoring flows through the operation indicator light 7, it lights up to indicate that the sensor has operated. That is, even if the smoke detection level is low, it operates if it is above a predetermined level set by the high-sensitivity level detection circuit 4 for a certain period of time t1.

In the case of a flaming fire, the voltage V of the intermediate electrode m generally increases rapidly with time T, as shown by the curved line in FIG.
Before a predetermined time t1 has elapsed after reaching the voltage 1 at which the high sensitivity level detection circuit 4 operates, the voltage V2 at which the low sensitivity level detection circuit 3 operates is reached and the sensor operates.

That is, the voltage at the emitter electrode of transistor Q increases, and current flows through the series circuit of Zener diode ZD and resistors R3 and R4, triggering switching circuit 6 such as an SCR, and creating a short circuit. The operation indicator light 7 lights up to indicate that the sensor has operated. In the case of smoke such as cigarettes, although the smoke concentration may reach a level at which the high-sensitivity level detection circuit 4 operates, it rarely continues for a long time.

The timer circuit 5 is restored immediately when the output of the high-sensitivity level detection circuit 4 disappears, that is, when the transistor Q2 is cut off, the charge in the capacitor C is discharged through the diode D1 and the resistor R. For this reason, the high sensitivity level detection circuit 4 is set by the timer circuit 5. fixed time t
Even if the output is issued multiple times for a period shorter than 1, the sensor will not be activated. Therefore, malfunctions caused by cigarette smoke can be prevented. As explained above, the ion type smoke detector of the present invention prevents malfunctions caused by smoke such as cigarettes, reliably detects smoke from smoldering fires, and quickly detects smoke from smoldering fires. Since it can be detected and operated, it is extremely useful for disaster prevention.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the ion type smoke sensor of the present invention, and FIG. 2 is a diagram for explaining the operation of the sensor shown in FIG. 1... Ion chamber, 2... Impedance conversion circuit, 3... Low sensitivity level detection circuit, 4
... High sensitivity level detection circuit, 5 ... Timer circuit, 6 ... Switching circuit, 7 ...
...Operation display Chl...Inner ion chamber, Ch2...Outer ion chamber, m...Middle electrode, n...Outer electrode, R1 ~9...
・Resistance, F... Field effect transistor, Q, ~
3...Transistor, ZDl-ZD2...
... Zener diode, D... diode,
C... Capacitor, A... PUT, P
・N terminal.

Claims (1)

[Claims] 1 Equipped with an ion chamber whose ion current changes depending on the presence or absence of smoke, a field effect transistor that converts the impedance of the ion chamber, and a switching circuit such as an SCR that short-circuits terminals with low impedance in response. In the ionic smoke detector, a low sensitivity level detection circuit operates the switching circuit when the detection signal is relatively high based on the output of the field effect transistor; and a detection signal based on the output of the field effect transistor. a high-sensitivity level detection circuit that emits an output signal when An ion type smoke sensor characterized by being provided with a timer circuit for changing the output voltage of the ion chamber.