JPH03111998A - Ionization type smoke sensor - Google Patents

Abstract

PURPOSE:To prevent sensitivity from being changed by accumulated dust on a dielectric by alternatively applying positive and negative voltage to be impressed to an ion chamber. CONSTITUTION:A radiation source 8 is provided in a cathode electrode (k) surrounded by an anode electrode (a) and an ion chamber 2 is formed by the anode electrode (a) and the cathode electrode (k). Air is ionized by the radiation source 8 and an ion current flows. However, when smoke flows into the ion chamber 2, the ion current is decreased. By using this fact, the smoke is detected. An output pulse I from an oscillation circuit 1 passes through a capacitor C1 and a resistor R1, becomes alternative positive and negative pulses like II and is impressed to the anode electrode (a). Thus, electric charges, which are formed by the dust accumulated in the ion room 2, to be charged to the capacitor are almost eliminated and the sensitivity of the smoke sensor is kept constant.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an ionization type smoke detector.

[Conventional technology]

Ionization smoke detectors generally have two ion chambers.
One chamber type and one ion chamber 2 as shown in Figure 4.
There is a one-chamber type with two types, and both have already been commercialized. The operating principle in the latter case is that a voltage is applied to the ion chamber 2 containing the radiation source 8, and when there is no smoke to be detected, an approximately constant amount of ion current flows through the ion chamber 2. When smoke flows in, the ion current becomes difficult to flow, the current value decreases, this is converted into voltage, and through amplification etc., the switching circuit 6 is activated and a signal is sent to the receiver. An actual circuit configuration to which this principle is applied is disclosed, for example, in Japanese Patent Publication No. 62-42319, and has the circuit configuration and waveform diagrams shown in FIGS. 4 to 6. The specific detection operation of this circuit is that a pulse voltage is applied to the ion chamber 2,
During the application period T1, an ion current 1 flows, and a voltage of ROXII (V) is generated across the resistor RO. Furthermore, if the current flowing through the ion chamber 2 during the period T2 when no current is applied to the ion chamber 2 is 12 (normally l2=0), ROXI2 (V) is applied to both ends of the resistor RO.
voltage is generated. Voltage difference (change) between these two points
VS - (ROX II - RO x Engineering 2) to amplifier circuit 3
After alternating current amplification is performed, a threshold circuit 5 connected at a subsequent stage performs discrimination and switching. The voltage difference between these two points S is the ionic current 1 as the smoke concentration increases.
1 becomes smaller, and as a result, the voltage difference vS becomes smaller, so that it becomes less than the threshold of the threshold circuit 5 and operates.

Now, if the ionization type smoke detector as described above is used for a long period of time or installed in a bad environment with a lot of dust, etc., dust 9 may accumulate in the ion chamber 2, as shown in Fig. 7. be. If this dust 9 is an electrical conductor, it will not affect the ionic current, but if it is lint, sand, etc., it is electrically insulating and has been confirmed to function as a dielectric, that is, a capacitor. This affects the current in the ion chamber. Now, as shown in FIGS. 8(a) and 8(b), if we consider the bump 9 to be equivalently a parallel circuit of a resistor RX and a capacitor CX, and the applied voltage Vp is the pulse voltage shown in FIG. 9, The voltage across the capacitor CX is constant at a certain value between 0 and 10 (applied voltage) (as shown in the lower part of FIG. 9). The reason is the equivalent resistance RX of the lump 9 and the ion chamber 2.
The overall resistance RI is very large, and the charging/discharging time constant of the capacitor CX is the period T1 when the voltage is applied and the period T when it is not applied.
This is because it is a very large value compared to 2.

Let VCX be the increase in constant voltage due to this dust 9.

With the lumps 9 deposited in this manner, the voltage applied to the ion chamber 2 space during periods TI and T2 is VTI =
10-VCX VT2=-VCX. Therefore, the voltage difference VS is 5=ROX (I of VTI - I of VT2). According to the measured values of the voltage-current characteristics shown in FIG. 1O, this relationship is not a straight line, so the value of Angline in the above equation varies depending on the VCXO value due to the bulge. And it becomes minimum when VCX is 0.

To summarize the above points: (1) When dust accumulates in the ion chamber, the voltage applied to the space of the ion chamber changes, and as a result, the ion current changes, and the voltage difference VS also changes.

(2) The direction of the change is such that the voltage difference VS always increases even if there are variations in the value of vCx due to dust, and the smoke sensitivity becomes less sensitive.

[Problem to be solved by the invention]

As mentioned above, the decrease in smoke sensitivity due to the accumulation of dust is a problem related to the basic function of a fire detector, and an immediate solution is desired.

This invention was devised by paying attention to the above-mentioned actual situation, and its purpose is to provide an ionization type smoke detector in which the smoke sensitivity does not change even if dust accumulates in the ion chamber of the ionization type smoke detector. The point is to get a smoke detector.

[Means to solve the problem]

In the second invention, the following measures were taken to achieve the above object.

That is, the ionization type smoke sensor according to the present invention includes a power supply circuit having a constant voltage circuit, an oscillation circuit, an ion chamber to which an output pulse of the oscillation circuit is applied, and a voltage at a reference point of the ion chamber that In an ionization type smoke detector consisting of a threshold circuit that outputs an output to operate the sensor when a reference voltage is exceeded, the output pulse of the oscillation circuit applied to the ion chamber is approximately The structure is characterized in that it includes a conversion circuit that changes the polarity between positive and negative values with equal absolute values.

[For production]

In the present invention, a pulse voltage having equal positive and negative peak values is applied to the ion chamber, and the pulse voltage is also applied to dust having a capacitor component in the ion chamber, but positive and negative pulses are applied alternately. As a result, there is no accumulation of electricity in the capacitor component of dust, and no change occurs in the electric field in the ion chamber, eliminating sensitivity deterioration due to aging due to dust accumulation.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

The structure of the ionization type smoke detector A is similar to that shown in Fig. 7, and includes a printed circuit board p with a circuit section mounted inside the body b.
An anode electrode a and a cathode electrode k surrounded by the anode electrode 11ia are provided to constitute an ion chamber 2. A radiation source 8 is attached to the cathode electrode k. The body b and the anode electrode a are provided with holes through which smoke flows.

On the other hand, the overall circuit is substantially the same as that of the conventional example shown in FIG. 4, and can be realized by converting only the main parts to that shown in FIG. 1. To explain the circuit shown in Fig. 4, 1 is an oscillation circuit consisting of an astable multi-channel, flip-flop, etc., 2 is an ion chamber as a sensor, and 3 is an AC (change) component of the ion current consisting of FET, operational amplifier, etc. Amplification circuit, 4 is a capacitor, a resistor,
A signal rectifier circuit including an analog switch, etc.; 5 a threshold circuit having a comparator for comparing the signal voltage with a reference voltage; and 7 a power supply circuit including a constant voltage circuit, a diode bridge, etc.

FIG. 1 shows a circuit diagram of the main part, in which an oscillation circuit 1 includes a capacitor C1 and a resistor R1, and the pulse period TL =
If the period T2 is set and CI According to the above configuration, since the charging and discharging conditions are completely symmetrical, almost no charge is charged to the capacitor component CX due to the lump, and as shown in FIG.
■The CX value is maintained at approximately Ov, eliminating the negative effect of dulling the sensitivity of ionization smoke detectors.

〔Effect of the invention〕

According to the present invention, a power supply circuit having a constant voltage circuit, an oscillation circuit, an ion chamber to which an output pulse of the oscillation circuit is applied, and a voltage at a reference point of the ion chamber lower than the reference voltage due to the presence of smoke. In an ionization type smoke detector, the output pulse of the oscillation circuit applied to the ion chamber is set to a positive or negative value with substantially the same absolute value with respect to the ground potential. Since a conversion circuit is provided to change the smoke sensitivity, even if dielectric dust accumulates in the ion chamber, the electric field inside the ion chamber does not change, so the smoke sensitivity remains unchanged and the original smoke sensitivity can be maintained.

[Brief explanation of drawings]

Figures 1 to 3 show embodiments of the present invention. Figure 1 is a circuit diagram of the main part of an ionization smoke detector, Figure 2 is a waveform diagram of the circuit, and Figure 3 is a waveform diagram and CX voltage diagram. It is a relationship diagram. Figures 4 to 10 show conventional examples, Figure 4 is a circuit diagram of an ionization type smoke detector, Figure 5 is a main circuit diagram, Figure 6 is a waveform diagram, and Figure 7 is an ionization type smoke detector. A cross-sectional view of the sensor, Fig. 8 is an equivalent circuit, Fig. 9 is a waveform diagram and a relationship diagram of CX voltage, Fig. 1
Figure 0 is a voltage-current relationship diagram. DESCRIPTION OF SYMBOLS 1... Oscillation circuit 1.2... Ion chamber, 3... Amplification circuit, 4... Signal rectification circuit, 5... Threshold circuit, 6...
...Switching circuit, 7...Power supply circuit, 8...Radiation source, 9...Fluff.

Claims (1)

[Claims] (1) A power supply circuit having a constant voltage circuit, an oscillation circuit, an ion chamber to which the output pulse of the oscillation circuit is applied, and a voltage detected when the voltage at the reference point of the ion chamber exceeds the reference voltage due to the presence of smoke. In the ionization type smoke detector, the output pulse of the oscillation circuit applied to the ion chamber is changed to positive or negative by approximately equal absolute values with respect to the ground potential. An ionization type smoke detector characterized by being equipped with a conversion circuit.