JPH0218518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an analog output type smoke detection circuit used in an analog output type scattering type smoke detector or the like.

[Background technology]

Conventional analog output type smoke detection circuits maintain the smoke detection output by using two power supplies and biasing the gate of the FET (field effect transistor) used for peak hold to a negative voltage. However, such a configuration requires positive and negative power supplies, and the ground line cannot be shared between the power supply input and the analog output, making the circuit configuration extremely complicated.

On the other hand, if you want to operate with a single power supply to simplify the circuit configuration, you can use a P-channel enhancement type FET, or use an analog switch that combines these elements into an integrated circuit. However, there were drawbacks such as difficulty in obtaining the elements and high cost.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an analog output type smoke detection circuit that can perform intermittent peak hold of the received light output with a simple circuit configuration using easily available and inexpensive elements.

[Disclosure of the invention]

The analog output type smoke detection circuit of the present invention includes a pulse oscillator that periodically generates pulses, a light emitting element that lights up in response to the output pulse of the pulse oscillator, and a light emitting element that receives light emitted from the light emitting element. A light-receiving element, a light-receiving amplifying section that amplifies the output of the light-receiving element, and a charging/discharging device that quickly charges a charging/discharging capacitor with the output pulse of the pulse oscillating section and slowly discharging the charging/discharging capacitor during a pulse rest period. a peak-hold capacitor that is charged by the output of the light-receiving and amplifying section; and a peak-hold capacitor that is inserted in series between the light-receiving and amplifying section and the peak-hold capacitor and charged and discharged by the output pulse of the pulse oscillation section. a junction type FET that is forward biased via a capacitor and reverse biased by the voltage of the charging/discharging capacitor during the pulse rest period; an impedance conversion section to which a voltage held by the peak hold capacitor is input; and this impedance. and a calculation section that amplifies the output voltage of the conversion section and outputs it as an analog smoke detection signal having a level corresponding to the concentration of smoke.

With this configuration, intermittent peak hold of the received light output can be performed using a single power supply and an inexpensive and easily available junction type FET.

An analog smoke detection circuit according to an embodiment of the present invention will be explained with reference to FIGS. 1 and 2. In FIG. 1, T _IN and T' _IN are power input terminals to which a DC voltage of 5 to 24 V is applied. 1 is a constant voltage section that stabilizes the DC voltage of 5 to 24 V applied to the power input terminal, and is composed of a bipolar transistor Q ₁ , a resistor R ₁ , a Zener diode ZD, and a capacitor C ₁ , and stabilizes the constant voltage of 3 to 12 V. Output. Reference numeral 2 denotes a pulse oscillation section which oscillates pulses at a constant period when the output voltage of the constant voltage section 1 is applied, and includes bipolar transistors Tr ₁ to Tr ₃ , resistors R ₂ to R ₉ , diode D ₁ and capacitors C ₂ and C _{3 .} The pulse period is 100
Outputs a pulse with a pulse width of 100 usc at ~200 msec to periodically turn on the light emitting diode LED intermittently with a large current of about 1 A. SPD has an optical axis other than a straight line (e.g. 90 degrees) with respect to the light emitting diode LED.
A silicon photodiode placed in the sensor receives the scattered light from the light smoke from the light emitting diode LED. Reference numeral 3 denotes a light receiving amplifying section which amplifies and converts the light receiving current output of the silicon photodiode SPD into a voltage, and is composed of bipolar transistors Tr ₄ to _{Tr 7} , resistors R ₁₀ to R ₁₇ and capacitors C ₄ to C ₆ . 4 is a charging/discharging unit synchronized with the oscillation pulse that is quickly charged by the output pulse of the pulse oscillation unit 2 and slowly discharged during the pulse rest period, and the capacitor C ₇ ,
It consists of a discharging resistor R ₁₈ , a charging resistor R ₁₉ , a resistor R ₂₀ and a diode D ₂ . Reference numeral 5 denotes a peak hold unit that holds the output of the light receiving amplifying unit 3 at its peak, and a capacitor _C8 charged by the output of the light receiving amplifying unit 3, and a capacitor C8 that is connected to the output terminal of the light receiving amplifying unit 3 and the capacitor.
Switching is performed by inserting N in series with _C8 .
When the charging/discharging unit 4 is being charged _{, the N-channel junction type FET Tr 8 is turned on, and the voltage of the capacitor C 8 changes according} to the change in the output of the light receiving amplification unit 3. , when the charging/discharging section 4 is discharging, the N-channel junction type FET Tr ₈ is turned off and the capacitor is
C ₈ now retains its previous state. Reference numeral 6 denotes an impedance conversion section that converts the high impedance voltage of the peak hold section 5 into a low impedance voltage, and is composed of a source follower circuit consisting of an N-channel junction type FET Tr ₉ and a resistor R ₂₁ . 7 converts the output of the impedance converter 6 into a necessary voltage or
This is an arithmetic unit that changes points and is composed of an operational amplifier OP and resistors _R22 to _R25 . T _OUT and
T _OUT ′ is an analog output terminal.

Next, the operation of this analog output type smoke detection circuit will be explained with reference to FIGS. 2A to 2E.

When a DC voltage of 5 to 24 V is applied between the power input terminals T _IN and T _IN ', the constant voltage section 1 operates and
Outputs a stable constant voltage of 12V. The output of the constant voltage section 2 activates the pulse oscillation section 2, which periodically oscillates pulses, causing the light emitting diode LED to generate a pulse of about 1A with a pulse period of 100 to 200 msec and a pulse width of 100 usc, as shown in Figure 2A. A pulse current is passed periodically to cause the light emitting diode LED to emit light intermittently.

The light from the light emitting diode LED is received by the silicon photodiode SPD, and from the light receiving amplification section 3, the light from the light emitting diode LED is received as shown in FIG. 2B.
When the LED is turned on and there is no smoke, it outputs a voltage of, for example, about 50 mV, and as the smoke concentration increases, it outputs a voltage that increases sequentially to 100 mV, 150 mV, and 200 mV. In addition, light emitting diode
The minute waves that exist during the LED off period (pulse rest period) are due to noise.

On the other hand, for example, output from the pulse oscillator 2
The 8V pulse rapidly charges capacitor C 7 through capacitor C ₇ , diode D ₂ and charging resistor R ₁₉ , and during pulse pauses capacitor _{C 7 is} slowly discharged through discharge resistor R ₁₈ . The resistance value of the resistor _R19 is approximately several kilohms, and the capacitor _C7 is fully charged in a short period of time during the 100-usec pulse width, and when the charging is completed and the pulse reaches 0V (at the beginning of the pulse rest period), the capacitor C7 is completely charged. ₇ voltage (e.g. -8V)
The gate of _the N-channel junction _type FET Tr ₈ is reverse biased as shown in FIG. The resistance value of the resistor _R18 is several MΩ, and the capacitor _C7 is slowly discharged to, for example, about -4V in a period of 100 to 200 msec, and the N-channel junction type FET _Tr8 maintains the pinch-off state during this period.

When the 8V pulse is generated again from the pulse oscillator 2, the N-channel junction type FET Tr ₈
As shown in Fig. 2C, the voltage at the gate of the circuit instantly rises to +4V and becomes a forward bias state, and the N-channel junction type FET Tr ₈ turns on, and the light receiving amplifier section 3 and the capacitor C ₈ become conductive. The capacitor C ₈ is charged by the output of the light receiving and amplifying section 3 .

In this way, the charging/discharging section 4 periodically turns on and off the N-channel junction type FET Tr ₈ , so that the voltage of the capacitor _C8 changes as shown in FIG. The peak of the output voltage is maintained.

The voltage of this capacitor C ₈ is then applied to the calculation unit 7 via the impedance conversion unit 6.
As shown in Figure 2 E from the calculation unit 7, when there is no smoke, the voltage is 0V, and when there is smoke, the voltage is determined according to the concentration.
It will be output as 1.0V, 1.5V, and 2.0V.
Note that the arithmetic unit 7 of this embodiment sets the voltage output from the light receiving amplification unit to a threshold value of, for example, 70 mV, and sets it to 0 V if it is lower than 70 mV, and sets it to 10 mV if it is higher than that.
The output is now doubled in amplification.

Thus, this embodiment is a light emitting diode
The capacitor C 7 of the charging _{/discharging section 4 is rapidly charged by the output pulse of the pulse oscillating section 2 that lights the LED intermittently, and the capacitor C 7 of} the charging/discharging section 4 is slowly discharged during the pulse rest period. When charging, forward bias is applied to N-channel FET Tr ₈ through capacitor C ₇ by the output pulse of pulse oscillator 2, and when charging/discharging section 4 is discharging, the voltage of capacitor C ₇ applies forward bias to N-channel FET Tr 8. ₈
Since reverse bias is added to the
By turning on and off the channel type FET Tr ₈ , the peak of the intermittent light receiving output of the light receiving amplifying section 3 can be held and output as an analog smoke detection signal having a level corresponding to the smoke density. Also, regarding the impedance conversion section 6, N
Since this is done using the channel type FET Tr ₉ , this circuit can also be realized at low cost.

Furthermore, since the voltage held by the peak hold capacitor _C8 is amplified by being applied to the calculation unit 7 via the impedance conversion unit 6, the analog smoke detection signal is sent to the next processing circuit, such as a smoke level indicator. , can be input to fire alarm circuits, etc. at an appropriate level. Therefore, variations in the voltage across the resistor _R21 of the impedance conversion section 6 due to variations in the characteristics of the parts of the circuit elements are eliminated,
Analog smoke detection signals with optimal characteristics can be input to the next stage processing circuit.

〔Effect of the invention〕

The analog output type smoke detection circuit of the present invention is provided with a charging/discharging section that quickly charges a charging/discharging capacitor by the output pulse of the pulse oscillation section and slowly discharges the charging/discharging capacitor during the pulse pause period. The junction type FET inserted in series with the peak hold capacitor is forward biased via the charge/discharge capacitor by the output pulse of the pulse oscillator, and reverse biased by the voltage of the charge/discharge capacitor during the pulse rest period. Therefore, using an easily available and inexpensive junction type FET, a simple circuit configuration with a single power supply can hold the intermittent received light output to a peak level that corresponds to the smoke density. Can be output as an analog smoke detection signal.

Furthermore, since the voltage held by the peak hold capacitor is amplified by being applied to the arithmetic unit via the impedance conversion unit, the analog smoke detection signal can be input to the next stage processing circuit at an appropriate level. Therefore, it is possible to eliminate variations in the output of the impedance converter due to variations in characteristics of parts of circuit elements, and input the analog smoke detection signal to the next stage processing circuit with optimal characteristics.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIGS. 2A to 2E are waveform diagrams of various parts thereof. 2... Pulse oscillation section, 3... Light receiving amplification section, 4...
...Charge/discharge section, 5...Peak hold section, LED...
...Light emitting diode, SPD...Silicon photodiode, _C7 ...Capacitor, _R18 , _R19 ...Resistor,
Tr ₈ ...N-channel juncture type FET, C ₈
...Capacitor.

Claims (1)

[Claims] 1 a pulse oscillator that periodically generates pulses;
A light emitting element that lights up in response to the output pulse of this pulse oscillation section, a light receiving element that receives light emitted from this light emitting element, a light receiving amplification section that amplifies the output of this light receiving element, and an output of the pulse oscillating section. a charging/discharging unit that rapidly charges a charging/discharging capacitor with a pulse and slowly discharging the charging/discharging capacitor during a pulse pause period; a peak hold capacitor that is charged by the output of the light receiving amplifying unit; and a peak holding capacitor that is charged by the output of the light receiving amplifying unit; and the peak hold capacitor, and is forward biased by the output pulse of the pulse oscillator via the charging/discharging capacitor, and reversely biased by the voltage of the charging/discharging capacitor during the pulse rest period. An analog smoke detection device having a biased junction type field effect transistor, an impedance conversion section into which the voltage held by the peak hold capacitor is input, and an output voltage of the impedance conversion section which is amplified to have a level corresponding to the concentration of smoke. An analog output type smoke detection circuit equipped with a calculation section that outputs as a signal.