JPS586993B2 - Amplification circuit for ionization smoke detector - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an amplification circuit for an ionization type smoke detector, and the amplification circuit increases the output in proportion to the amount of smoke, and only when the power source is a positive voltage. The purpose of this invention is to obtain an operable differential amplifier circuit.

A conventional ionization type smoke detector as shown in Figure 5 uses an inverting amplifier A using a differential amplifier, but in such a circuit, the operation of the amplifier A requires a positive voltage. Two power supplies, one with negative voltage and one with negative voltage, are required, and the voltage required is the sum of the voltage applied to ion chamber B and the voltage at which the output changes to the negative side, making low voltage operation impossible. In other words, the utilization rate of the power supply decreases. In addition, the signal voltage is highest when there is no smoke, and approaches zero in proportion to the amount of smoke, which has the disadvantage of complicating signal processing in subsequent stages.

In view of these problems, the amplification circuit for the ionization type smoke detector according to the present invention constitutes an inverting amplifier in which feedback is applied to the negative side input with high resistance from the output, and the negative side of the inverting amplifier is An ion chamber is connected to the side input terminal to amplify the ion current in the ion chamber, and the power supply voltage is divided to the positive input terminal of the inverting amplifier to obtain the product of the ion current and the high resistance. It is characterized by applying a voltage corresponding to .

The present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

Reference numeral 1 denotes a single-power-operated inverting amplifier, which is constructed by feeding back its output to the negative input via a resistor 2.

Reference numeral 3 denotes an ion chamber for smoke inflow, which is connected to the negative input terminal of the inverting amplifier 4, thereby amplifying the ion current.

5 and 6 are resistors that divide the power supply voltage at the connection point a, and apply a voltage corresponding to the product of the ion current in the ion chamber 3 and the high resistance 2 to the positive input terminal of the inverting amplifier 4. It is something to do.

7 and 8 are constant voltage diodes and thyristors that constitute the switching circuit 9.

The present invention is constructed as described above, and its operating state will now be described.

When feedback is applied from the output end of the inverting amplifier 4 to the negative input, the inverting amplifier 4 operates so that the potential difference between the negative input and the positive input is always zero.

Now let the ion current I be 100 PA, and the resistance value R of high resistance 2
If is 10,000MΩ, the potential at point a is 100PA x 10,000M
The resistance value of the resistor 6 is set so that Ω=1V.

In this way, since the positive side input of the inverting amplifier 4 is 1V, the output changes so that the negative side input also becomes 1V,
When the output becomes 0V, the negative side input also becomes 1V, and the operation is stable.

If smoke flows into the ion chamber 3 and the ion current becomes, for example, 70 PA, it will stabilize when I × R + output = 1 V, so from 70 PA × 10,000 MΩ = 0.7 V, the inversion amplifier 4 The output will be 0.3V.

In other words, with this constant, an output of 0.1V will be output to the inverting amplifier 4 for a decrease of 10 PA in the ion current.

Therefore, the output of this inverting amplifier 4 is an output voltage proportional to the amount of smoke, so the operating voltage Vs of the switching circuit 9 connected to the rear stage of the single power supply operation inverting amplifier 1 is appropriately selected. , the smoke amount S1 at that time becomes the operating level, and since both the voltage applied to the ion chamber 3 and the output are positive, only the positive voltage is required.

FIG. 3 shows the second embodiment of the present invention, but the first embodiment
This shows a circuit that is a practical improvement on the circuit shown in the figure.

Components corresponding to those in FIG. 1 are given the same reference numerals.

In this figure, resistor 2 is a highly stable and relatively small resistance value, and the problem of the signal voltage becoming small is amplified by feeding back from point b divided by resistors R1 and R2, and the differential The characteristic that the output of amplifier 4 does not become completely zero V output is improved by increasing the potential at point a = I x R + a (where I is the ion current and R is the resistance value of resistor 2). It is.

In other words, in general, the output does not completely drop to 0V, but remains at 1V.
Approximately 2V remains.

Therefore, if the potential at point a is I×R, it cannot be balanced in a stable state, so the potential at point a is I×R+a
If the value is set a little higher, the output V1=(R1+2R)/
It becomes R2×a and becomes stable.

In addition, in order to change the amplitude of the output by several volts without increasing the value R of resistor 2 too much, if we feed back through resistor 2 from point b divided by resistors R1 and R2, the output will be (I × R) × (R1
+R2)/R2.

The amplifier circuit for the ionization type smoke detector according to the present invention constitutes an inverting amplifier in which feedback is applied to the negative input with high resistance from the output, and an ion chamber is connected to the negative input terminal of the inverting amplifier. and amplifying the ion current in the ion chamber, and applying a voltage corresponding to the product of the ion current and the high resistance by dividing the power supply voltage to the positive input terminal of the inverting amplifier. Since the output increases in proportion to the amount of signal, that is, the amount of smoke, subsequent signal processing can be easily performed, and since it operates with only positive voltage, the power supply section can be configured easily. Of course, it also has features such as excellent utilization of power supply voltage.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing a first embodiment of an amplification circuit for an ionization smoke detector according to the present invention, FIG. 2 is an output characteristic diagram of the electric circuit of FIG. 1, and FIG. FIG. 4 is an electric circuit diagram showing the second embodiment; FIG. 4 is an output characteristic diagram in the electric circuit in FIG. 3; FIG. 5 is an electric circuit diagram of a conventional circuit corresponding to the circuit of the present invention; FIG. 6 is an output in the electric circuit in FIG. Characteristic diagram. 1 is a single power supply operated inverting amplifier, 2 is a resistor, 3 is an ion chamber,
4 is an inverting amplifier, 5 and 6 are resistors, and 9 is a switching circuit composed of a constant voltage diode 7 and a thyristor 8.

Claims (1)

[Claims] 1 Configure an inverting amplifier in which feedback is applied to the negative input with high resistance from the output, connect an ion chamber to the negative input terminal of the inverting amplifier, and amplify the ion current in the ion chamber, and an amplifier circuit for an ionization type smoke detector, characterized in that a voltage corresponding to the product of the ion current and the high resistance is applied by dividing the power supply voltage to the positive input terminal of the inverting amplifier. .