JP2972627B2 - Sensor circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fire alarm system (hereinafter simply referred to as "sensor") which detects a flame, smoke, temperature, or the like when a fire occurs and outputs an alarm signal. ).

[0002]

2. Description of the Related Art FIG. 2 is a schematic block diagram of a conventional fire alarm system. This fire alarm system includes a plurality of sensors 10-1 and 10-2 arranged in a building, a pair of alarm lines 20a and 20b connecting these sensors 10 in common, and the alarm lines 20a and 20b. Connected alarm device 3
0. The sensor 10 has terminals 11 and 12 for connecting to the notification line 20. For example, a sensing unit 13 whose conduction state changes when a fire, smoke, temperature, or the like exceeding a specified value is sensed at the time of a fire occurrence.
Are connected at one end. The other end of the sensing unit 13 is a node N
1 and a resistor 14 is connected between the node N1 and the terminal 12. The input side of the signal processing unit 15 is connected to the node N1. Signal processing unit 15
Is for determining that a normal fire has been detected when the sensing state of the sensing unit 13 has continued for a certain period of time, and its output side is connected to the gate of the thyristor 15. The anode and cathode of the thyristor 15 are connected to the terminals 11 and 12, respectively. The thyristor 15 is for maintaining the fire detection state once detected even after the detection state of the detection unit 13 is cancelled.

[0003] The alarm device 30 is provided with notification lines 20a and 20b.
Are connected to terminals 31 and 32.
1 is connected to one end of a coil 33a of the relay 33. The other end of the coil 33a is connected to the + side of a 24V DC power supply 35 via a push button switch 34. The push button switch 34 is connected to the thyristor 1 in the sensor 10.
6 to return to the off state, and has a contact b that opens when the button is pressed. The terminal 32 is connected to the negative side of the DC power supply 35. A bell 36 for outputting an alarm sound is connected to both ends of the DC power supply 35 via a contact 33b of a relay 33. The contact 33b is an a contact that closes when the relay 33 operates. In such a fire alarm system, when the detector 10 does not detect a fire, the sensing unit 13 is in an off state, and the same voltage as the cathode is applied to the gate of the thyristor 16 from the signal processing unit 15. I have. Therefore, the terminal 11 and 12 of the sensor 10 are turned off, and the coil 3 of the relay 33 is turned off.
No current flows through 3a, and bell 36 does not ring.

When a fire occurs, the sensing unit 13 of the sensor 10
However, when, for example, a flame is sensed, the sensing unit 13 is turned on, and the sensed state is transmitted to the signal processing unit 15.
When the sensing state continues for a certain period of time, the signal processing unit 15 applies the same voltage as the anode to the gate of the thyristor 16. As a result, the thyristor 16 becomes conductive, and the detector 10
Between the terminals 11 and 12 are turned on. Then, current flows from the DC power supply 35 to the coil 33a of the relay 33, the contact 33b closes, and the bell 36 sounds. Here, when the sensing of the flame by the sensing unit 13 is stopped, the voltage applied from the signal processing unit 15 to the gate of the thyristor 16 becomes equal to the voltage of the cathode. However, once the thyristor 15
Maintains its on state regardless of the gate voltage as long as current flows through the anode. For this reason, the terminal 36 between the terminals 11 and 12 of the sensor 10 remains
Keeps ringing. To stop the bell 36 from sounding, the push button switch 34 may be pressed. When the push button switch 34 is depressed, the contact opens and the power supply to the sensor 10 is stopped. As a result, the current flowing through the coil 33a of the relay 33 and the thyristor 15 stops, the contact 33b of the relay 33 opens, and the bell 36 stops sounding. Thereafter, when the push button switch 34 is restored, power supply to the sensor 10 is restarted. At this time, since the thyristor 15 is in the off state,
No current flows through the coil 33a of the relay 33, and the bell 36 remains stopped.

[0005]

However, the conventional fire alarm system has the following problems. In order to stop the bell 36 once sounded, it is necessary to manually operate the push button switch 34. This is necessary as a basic operation of actually confirming the occurrence of a fire or the like and canceling the alarm after taking necessary countermeasures. However, in reality, a problem often occurs that a power switch of an alarm circuit is turned off in a large-scale building fire or the like. This is partly due to the inconvenience of erroneous alarms occurring due to the installation of the detector 10 which is more sensitive than necessary, such as reacting with cigarette smoke, and requiring a reset operation each time. It is thought that it is. The present invention solves the problem of the prior art, detects at regular intervals whether or not the sensing state of the sensor continues, and stops the alarm output when the sensing state is released. Circuit.

[0006]

According to a first aspect of the present invention, there is provided a sensor circuit comprising: a sensor for detecting the occurrence of a fire; two terminals to which a DC voltage is applied; A sensor having a holding portion for short-circuiting the two terminals when the sensed amount exceeds a prescribed value and holding the short-circuit state by the short-circuit current; and switch means, detection means and integration means as described below. , Difference voltage output means, differentiating means, switch control means, and output means. The switch means is provided with a control signal having different first and second levels, and when the control signal is at the first level, applies the DC voltage to the sensor, and the control signal is applied to the second signal. When the level is at the level, the application of the DC voltage to the sensor is stopped. The detecting means detects a voltage between two terminals of the sensor and outputs a detection signal when the sensor is in a short-circuit state. The integration means is activated by the detection signal and outputs an output voltage that changes according to an exponential function having a constant time constant.

The difference voltage output means is provided with the output voltage, and outputs a difference voltage between the output voltage and the constant voltage when the output voltage exceeds a certain voltage. An output voltage of the difference voltage output means is provided, and a voltage proportional to a time differential value of the output voltage is output. The switch control means is provided with an output voltage of the differentiating means, outputs the control signal at the first level when the output voltage is equal to or lower than a predetermined voltage, and outputs the control signal when the output voltage exceeds a predetermined voltage. The control signal is output at the second level. The output means outputs an alarm signal when the detection signal is given from the detection means. In the second invention, the first
Detecting means in the invention of the invention having a Zener diode of a Zener voltage lower than the DC voltage, by detecting the presence or absence of a current flowing through this Zener diode,
It is configured to detect a short-circuit state between two terminals of the sensor. Further, the integrating means is constituted by an integrating circuit comprising a resistor and a capacitor having the constant time constant, the difference voltage output means is constituted by a Zener diode having a Zener voltage equal to the constant voltage, and further, a differentiating means is provided. , A differential circuit composed of a resistor and a capacitor.

According to the present invention, since the sensor circuit is configured as described above, the following operation is performed. When the occurrence of a fire is detected and the detector is short-circuited, a detection signal is output from the detection means. This detection signal activates the integration means, and outputs an output voltage that changes according to a constant time constant. When the output voltage of the integration means exceeds a certain voltage, a voltage having a difference between the output voltage and the certain voltage is output from the difference voltage output means. The voltage output from the differential voltage output means is converted into a voltage proportional to the time differential value by the differentiating means, and given to the switch control means. The switch control means stops the supply of the DC voltage from the switch means to the sensor when the voltage supplied from the differentiating means exceeds a predetermined voltage. When the supply of the DC voltage stops, the short-circuit current flowing to the sensor stops, and the short-circuit state of the sensor is released. As the time elapses, when the output voltage of the integrator approaches a constant value, the output voltage of the differentiator also becomes lower than the predetermined voltage. Thereby, the switch control means restarts the supply of the DC voltage from the switch means to the sensor. At this time, if fire detectors continue to detect fire,
The sensor is short-circuited again, and the detecting means detects the fire condition. On the other hand, if the fire detection by the sensor has been eliminated, the detection of the fire state by the detection means is not performed.
The fire condition detected by the detection means is output from the output means as an alarm notification signal.

[0009]

FIG. 1 is a configuration diagram of a sensor circuit showing an embodiment of the present invention. This sensor circuit has a sensor 10 similar to the sensor 10 in the conventional fire alarm system of FIG. The terminals 11 and 12 of the sensor 10 are connected to the node N41 and the reference voltage GND, respectively. The node N41 is a terminal to which a DC voltage is applied to the detector 10 via the switch 41. The switch means 41 includes, for example, a switching NPN transistor Q41, a current limiting resistor R41, and a bias current supplying resistor R42. The collector of the transistor Q41 is connected to the power supply voltage V via a resistor R41.
DD (for example, +24 V), and the emitter is connected to the node N41. The resistor R42 is connected between the power supply voltage VDD and the base of the transistor Q41, and forms a bias circuit. Node N41 and reference voltage G
Detecting means 42 for detecting a fire detection state by the detector 10 is connected to the ND. Detecting means 4
2 is, for example, about 1/2 (= 12 V) of the power supply voltage VDD.
A Zener diode ZD41 having a Zener voltage of
It comprises a voltage dividing circuit by resistors R43 and R44, and an NPN transistor Q42 for outputting a detection signal. The cathode of Zener diode ZD41 is connected to node N41.
The anode is connected to the node N42. Resistors R43 and R4 are connected between node N42 and reference voltage GND.
4 are connected in series, and the divided voltage is applied to the base of the transistor Q42. The emitter of the transistor Q42 is connected to the reference voltage GND, and the collector is connected to the node N43, and the detection signal V43 is output to this node N43.

The node N43 is connected to an integrating means 43 which is activated by the detection signal V43 and outputs an output voltage which changes according to an exponential function having a constant time constant. The integration means 43 has, for example, resistors R45 and R46 and a capacitor C41 that constitute an integration circuit, and a diode D41 for discharging the charge charged in the capacitor C41 at the time of reset. The resistor R45 is connected between the power supply voltage VDD and the node N43.
Is connected between nodes N43 and N44. Node N
A capacitor C41 is connected between the reference voltage GND and the reference voltage GND, and an output voltage V44 of the integration means 43 is output to the node N44. A diode D4 is connected between the nodes N43 and N44 so that a reverse connection is made during charging.
1 is connected. The cathode of a Zener diode ZD42, which is the differential voltage output means 44, is connected to the node N44, and the anode of the Zener diode ZD42 is connected to a node N45. The Zener diode ZD42 is, for example, about １ ／ of the power supply voltage VDD.
(= 12 V), and when the output voltage V44 of the node N44 rises to be equal to or higher than the Zener voltage, a voltage V of a difference between the output voltage V44 and the Zener voltage is obtained.
45 is an element for outputting 45 to the node N45. For example, a differentiating means 45 including a capacitor C42 and a resistor R47 is connected between the node N45 and the reference voltage GND. Then, the capacitor C42 and the resistor R
A voltage V46 proportional to the time derivative of the voltage V45 at the node N45 is output to a node N46, which is a connection point of the node 47.

The node N46 is connected to, for example, a switch control means 46 comprising an NPN transistor Q43 and a PNP transistor Q44. The base of transistor Q43 is connected to node N46, the emitter is connected to reference voltage GND, and the collector is connected to the base of transistor Q44. And the transistor Q44
Is connected to the reference voltage GND, the emitter is connected to the base of the transistor Q41 of the switch means 41, and the control signal C is supplied to the transistor Q41.
ON is given. On the other hand, detection means 4
The input side of the output means 47 is connected to the node N43 on the output side of No. 2. The output means 47 includes, for example, a switching diode D42, an output control NPN transistor Q45, and a resistor R4 constituting a bias circuit.
8, R49. Diode D42 has a cathode connected to node N43 and an anode connected to the base of transistor Q45. The bias voltage from the power supply voltage VDD and the reference voltage GND is applied to the base of the transistor Q45 via the resistors R48 and R49, respectively. The emitter of the transistor Q45 is connected to the reference voltage GND, and the collector is connected to the load circuit 48.
To the power supply voltage VDD. Then, an alarm notification signal OUT is output to the collector side of the transistor Q45.

FIG. 3 is an operation waveform diagram showing the operation of FIG. Hereinafter, the operation of the sensor circuit of FIG. 1 will be described with reference to FIG. At time t0 in FIG. 3, the power supply voltage VDD is applied to the sensor circuit in FIG.
Shall not operate. When the power supply voltage VDD is turned on, no charge is stored in the capacitors C41 and C42, and the transistors Q43 and Q44 are turned off.
Control signal CON output from switch control means 46
Are at the level “H”. In addition, the power supply voltage VDD
, The power supply voltage VDD is applied to the base of the transistor Q41 via the resistor R42, so that the transistor Q41 is turned on. Since the sensor 10 connected between the node N41 and the reference voltage GND is not operating and is in an off state, 24 V substantially equal to the power supply voltage VDD is output to this node N41.
The voltage of the node N42 in the detection means 42 is about 1 due to a voltage drop due to the Zener voltage of the Zener diode ZD1.
2V. The transistor Q42 is connected to the resistor R4
3 is turned on by a base current supplied through the node N3, and the collector node N4 of the transistor Q42
The detection signal V43 of No. 3 becomes almost 0V. For this reason, the base of the transistor Q45 of the output means 47 is connected to the diode D45.
The voltage is reduced to almost 0 V by the transistor 42, and the transistor Q45 is turned off. Notification signal OUT at this time
Is at the level “H”.

At time t1, the sensing unit 1 of the sensor 10
When the flame 3 detects the flame, the detection unit 13 is turned on, and the detection state is transmitted to the signal processing unit 15. When the sensing state continues for a certain time until time t2, the same voltage as that of the anode is applied to the gate of the thyristor 16 from the signal processing unit 15. As a result, the thyristor 16 conducts, and the terminals 11 and 12 of the sensor 10 are short-circuited.
The voltage at node N41 drops to almost 0V. Therefore, the Zener diode ZD41 is turned off, the current i42 at the node N42 does not flow, and the transistor Q4
2 is turned off. When the transistor Q42 is turned off, the detection signal V43 at the node N43 increases to a voltage obtained by dividing the power supply voltage VDD by the resistors R45 and R46, and the diode D42 is turned off. And
The transistor Q45 is supplied with a base current from a bias circuit formed by the resistors R48 and R49, and the transistor Q45 changes to the ON state, so that the notification signal OUT becomes the level “L”.

On the other hand, the integration circuit including the resistors R45 and R46 and the capacitor C41 starts operating, the capacitor C41 is charged, and the voltage V44 at the node N44 rises with time according to an exponential curve as shown in FIG. . At time t3, the voltage between the nodes N44 and N45 becomes the Zener voltage (= 12) of the Zener diode ZD42.
When the voltage reaches V), the Zener diode ZD42 is turned on. Thus, the differentiating means 45 including the capacitor C42 and the resistor R47 is connected to the node N45, and the voltage V4 of the output node N46 of the differentiating means 45 is connected.
6 changes according to the rate of change of the voltage V45, as shown in FIG. At time t4, transistor Q43 is turned on by an increase in voltage V46 applied to the base of transistor Q43. When the transistor Q43 is turned on, the transistor Q4 connected to the transistor Q43 is turned on.
4 is also turned on at the same time, and the control signal CON becomes "L". As a result, the transistor Q41 is turned off, the supply of the DC voltage to the sensor 10 is stopped, and the thyristor 16 in the sensor 10 is restored and turned off. The detection signal V43 at the node N43 is substantially equal to the power supply voltage V
DD, the diode D42 remains off, and the transistor Q45 remains on. This state continues as shown in FIG. 3 until the voltage V46 of the node N46 of the differentiating means 45 rises, then gradually falls, and becomes lower than the threshold voltage (for example, 0.7 V) of the transistor Q43.

At time t5, when the voltage V46 becomes the threshold voltage of the transistor Q43, this transistor Q4
3 is turned off. When the transistor Q43 is turned off, the transistor Q44 connected thereto is also turned off at the same time, and the control signal CON becomes "H". As a result, the transistor Q41 is turned on, the supply of the DC voltage to the sensor 10 is restarted, and the power supply voltage VDD is applied to the node N41. The current i42 flows through the node N42 via the Zener diode ZD41, and the transistor Q42 is turned on. Transistor Q42
Is turned on, the detection signal V43 of the node N43
Is substantially equal to the reference voltage GND, and the capacitor C4
1, the electric charge stored in C42 is discharged via the diode D41. At time t5, if the sensing unit 13 has not recovered and is in the ON state, the sensing state is transmitted to the signal processing unit 15. Then, when the sensing state continues for a predetermined time until time t6, the signal processing unit 15
Applies the same voltage as the anode to the gate of the thyristor 16. As a result, the thyristor 16 is turned on again, and the terminals 11 and 12 of the sensor 10 are turned on similarly to the state at the time t2.
The current is substantially short-circuited, the current i42 at the node N42 becomes 0, the transistor Q42 is turned off, and the transistor Q45 is turned on. The voltage V44 increases according to an exponential function.

At time t7, nodes N44 and N45
When the voltage between them reaches the Zener voltage of the Zener diode ZD42, as in the state at the time t3, the node N4
The voltage V46 of 6 starts changing according to the rate of change of the voltage V45. At time t8, when the transistor Q43 is turned on, the base of the transistor Q41 is almost pulled down to the ground voltage GND and turned off, and the supply of the DC voltage to the sensor 10 is stopped, as in the state at time t4. Is done. And the thyristor 16 in the sensor 10
Is restored and turned off. At time t9, the voltage V4
When the voltage of the transistor 6 becomes equal to or lower than the threshold voltage of the transistor Q43, the base of the transistor Q41 is almost raised to the power supply voltage VDD as in the state at the time t5. This allows
The transistor Q41 is turned on, and the supply of the DC voltage to the sensor 10 is restarted. At this time t9,
If the sensing unit 13 recovers and is in the off state, the thyristor 16 remains in the off state, no current flows through the sensor 10, and the voltage of the node N41 becomes substantially equal to the power supply voltage VDD. As a result, similarly to the state at the time t0, the transistor Q42 is supplied with the base current to be turned on, the voltage of the node N43 becomes substantially equal to the ground potential GND, the transistor Q45 is turned off, and the capacitor C41 is turned off. , C42 are discharged and restored to the same state as at time t0.

As described above, the sensor circuit of this embodiment is
There are the following advantages (1) to (4). (1) According to a certain sequence by the integrating means 43, the differential voltage output means 44, and the differentiating means 45, the sensor 10
Switch control stage 4 for controlling the supply of DC voltage to
2 and the switch means 41, the reset operation of the sensor 10 can be performed without manual intervention. (2) Since the components are configured using individual components such as transistors Q41,..., Resistors R41,..., Capacitors C41,. VDD can be supported. (3) Integrating means 41 with resistor R46 and capacitor C4
1 and the voltage V4 charged in the capacitor C41.
4 is supplied to the differentiating means 45 through the differential voltage output means 44. Therefore, the operation time of the differentiating means 45 is continued until the voltage V44 charged in the capacitor C41 substantially reaches the power supply voltage VDD. Therefore, a long time constant can be obtained with the capacitor C41 having a relatively small capacitance. (4) Since the integrating means 41 is provided with the discharging diode D41, the electric charges charged in the capacitors C41 and C42 can be rapidly discharged when the detecting means 42 is restarted, and a reliable operation can be achieved. Will be possible.

The present invention is not limited to the above embodiment, but can be variously modified. For example, there are the following modifications (a) to (c). (A) Although only one sensor 10 is connected, a plurality of sensors 10 can be connected in parallel. Thereby, fine fire detection by the plurality of sensors 10 becomes possible. (B) The circuit configuration of each means such as the switch means 41 is not limited to the circuit configuration of FIG. 1 and may be any circuit configuration as long as each function is achieved. (C) The power supply voltage VDD is not limited to 24 V, and can be adjusted to the standard voltage of the sensor 10. The Zener voltage of the Zener diodes ZD41 and ZD42 is
The value is not limited to VDD / 2, and an appropriate value can be used according to another circuit constant.

[0019]

As described above in detail, according to the first aspect, the switch control for controlling the supply of the DC voltage to the sensor in accordance with a fixed sequence by the integrating means, the differential voltage output means, and the differentiating means. Since the sensor and the switch are provided, the reset operation of the sensor can be performed without manual operation. According to the second invention, in addition to having the same function as the first invention, the detection means, the integration means, the difference voltage output means, and the differentiation means are constituted by a Zener diode, a resistor, and a capacitor. The circuit is simple, the number of parts is small, and a reliable circuit configuration can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a sensor circuit showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional fire alarm system.

FIG. 3 is an operation waveform diagram of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Detector 41 Switch means 42 Detecting means 43 Integrating means 44 Differential voltage output means 45 Differentiating means 46 Switch control means 47 Output means

Claims (2)

(57) [Claims] 1. A sensing unit for sensing the occurrence of a fire, two terminals to which a DC voltage is applied, and a short circuit between the two terminals when the sensing amount of the sensing unit exceeds a predetermined value. A fire detector having a holding unit for holding the short-circuit state by a short-circuit current; and a control signal having different first and second levels are provided. When the control signal is at the first level, the fire detector is Switch means for applying the DC voltage, stopping the application of the DC voltage to the fire detector when the control signal is at the second level, and detecting a voltage between two terminals of the fire detector; Detection means for outputting a detection signal when the fire detector is in a short-circuit state; integration means for outputting an output voltage activated by the detection signal and changing according to an exponential function having a constant time constant; And a difference voltage output means for outputting a difference voltage between the output voltage and the constant voltage when the output voltage exceeds a certain voltage. A differentiating means for outputting a voltage proportional to the time differential value of the voltage, an output voltage of the differentiating means being provided, and when the output voltage is equal to or lower than a predetermined voltage, the control signal is set to the first level and output; A switch control unit for setting the control signal to the second level when the output voltage exceeds a predetermined voltage and outputting the control signal; and outputting an alarm notification signal when the detection signal is given from the detection unit. An output means for outputting, a sensor circuit. 2. The fire detecting device according to claim 1, wherein said detecting means has a Zener diode having a Zener voltage lower than said DC voltage, and detects the presence or absence of a current flowing through said Zener diode to short-circuit between two terminals of said fire detector. Wherein the integrating means comprises an integrating circuit comprising a resistor and a capacitor having the constant time constant, and the differential voltage output means comprises a Zener diode having a Zener voltage equal to the constant voltage. 2. The sensor circuit according to claim 1, wherein said differentiating means comprises a differentiating circuit including a resistor and a capacitor.