JPH0962957A - Reception circuit for fire alarm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve detecting resolution by directly detecting a line current without using reception resistance, to suppress the reduction of a supply voltage to the line of a sensor at the time of the alarming of the sensor as little as possible by making a reception circuit low impedance at the same time and to simplify circuit constitution. SOLUTION: A signal line from the plus side of a power source 5 to the sensor line 2 is provided with a first transistor Q1 insert-connecting between an emitter and a collector and directly connecting a base to the collector to make a first current Io corresponding to impedance between the power voltage E and the sensor line flow, and a second transistor Q2 connecting the emitter to the power source through a first resistor R1, connecting between the emitter and the base by a parallel route through a second resistor R2 and furthermore connecting the base to the base of the first transistor Q1 through a third resistor R3 to make a second current IR reduced by a prescribed ratio to the first current Io made to flow by the first transistor Q1 flow through the collector to be a reception output current. An overcurrent limitting circuit is provided between the emitter of the first transistor Q1 and the power source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving circuit of a fire alarm device in which a fire detector is connected to a detector line drawn out to a warning area and a terminating resistor for disconnection monitoring is connected.

[0002]

2. Description of the Related Art Conventionally, as a receiving circuit of a fire alarm device of this type, as shown in FIG. 4, for example, a plurality of fire detectors 3 are connected to a detector line 2 drawn from a receiver 1 to supply a power source + Vcc1. Further, the terminating resistor 4 for detecting disconnection is connected to the end of the sensor line 2. The receiver 1 is provided with a comparator U100 for detecting fire and a comparator U101 for detecting disconnection.

The comparator U100 has a power supply voltage + Vc.
The receiving resistor R100 is inserted from c1 to the line of the sensor line 2, and the resistors R101 to 103 are connected to the receiving resistor R100.
Are connected in series, and the divided voltages V1 and V2 are input to the comparators U100 and 101. As the reference voltage of the comparator U100, the reference voltage Vr1 is set by voltage division by another power source + Vcc2. Similarly, in the comparator U101, the reference voltage Vr2 is set by the voltage division by the resistor.

In the steady monitoring state, since the fire detector 3 is in the non-operating state, there is a high impedance between the lines, and the resistance value of the terminating resistor 4 and the receiving resistor R100.
The line voltage determined by the divided voltage of the comparator U100,
The line voltages V1 and V2 are input to 101. Here, the terminating resistance 4 is about 10 KΩ, while the receiving resistance R100 is set to a sufficiently small value of several hundred Ω.
A line voltage close to the power supply voltage + Vcc1 is obtained.

Since the fire detector 3 has a low impedance when the alarm is issued, the impedance between the lines also becomes low, and the received voltage V1 to the comparator U100 becomes the reference voltage V1.
r1 becomes lower, which causes the comparator U
100 outputs the H level output to the reception control unit 102, and the fire detection signal is output. On the other hand, when the sensor line 2 is disconnected in the steady monitoring state, the terminating resistor 4 is disconnected, so the line voltage is pulled up to the power supply voltage + Vcc1, and the input voltage V2 of the comparator U101 is the reference voltage V2.
When r2 is exceeded and the H level output of the comparator U101 is output, the reception control unit 102 issues a disconnection alarm.

[0006]

However, in such a conventional receiving circuit, a change in the line current is detected as a line voltage determined by the voltage division of the impedance between the receiving resistance and the sensor line, and a comparator is used. There are the following problems because the line voltage is compared and discriminated to monitor fires and disconnections. First, in the steady monitoring state, a weak current of about 3 mA, which is the sum of the current consumed by the fire detector and the current flowing through the terminating resistor 4, flows through the detector line.

On the other hand, when one fire detector is reported, a current of several tens of mA flows, and for example, 60 mA of line current flows through the detector line when one detector is notified. In the conventional receiving circuit shown in FIG. 4, the line current in such a detector line is divided into a value determined by the impedance of the terminating resistor 4 and the fire detector 3 with respect to the receiving resistor R100 when the alarm is issued and when the alarm is not issued. The line voltage is checked by a comparator to detect a fire, and a disconnection is also detected.

However, for example, in monitoring disconnection by the terminating resistor 4, the line current drop when disconnection occurs is very small, for example, about 1 mA, and it is planned that 60 mA will flow when one sensor is issued. Then, in the comparator that monitors the change in the line voltage, if a current change of about 1 mA is converted into a voltage signal, a resolution of 1/60 of the alarm current is required.

At the time of disconnection due to such a terminating resistor 4, even if disconnection occurs, only a slight voltage change due to an extremely weak line current can be obtained by the receiving resistor R100,
There is a limit to the accurate detection by the comparator. Furthermore,
Power supply voltage + V supplied from receiver 1 to sensor line 2
cc1 is expected to fluctuate in a considerable range such as several volts, and when the power supply voltage drops, the resolution of the comparator that monitors the line voltage drops, causing a problem of unstable detection performance.

Further, as the receiving resistor R100, the comparator U101 can detect a line voltage change corresponding to a very slight line current change of about 1 mA at the time of disconnection. I have to However, when a plurality of detectors are reported sequentially or simultaneously due to the spread of fire, the voltage drop of the receiving resistor R100 accompanying the increase of the line current greatly reduces the power supply voltage that can be supplied to the detector line, and the connection can be detected. In addition to limiting the number of devices, when multiple lines are connected to the receiver, the number of comparator circuits increases in proportion to the number of lines, resulting in a significant cost increase.

Furthermore, since comparators U100 and U101 are provided for each sensor line and are always operating, the supply voltage for comparator operation and R101 to R10 are provided.
There is a problem that the current consumption increases due to the current flowing through 7. The present invention improves the resolution by detecting the line current itself without using the receiving resistor, and at the same time lowers the impedance of the receiving circuit to reduce the supply voltage to the sensing line as much as possible when the sensor is issued. Further, it is an object of the present invention to provide a receiving circuit of a fire alarm device which is suppressed in operation and has a very simple circuit configuration and which operates reliably at low cost.

[0012]

To achieve this object, the present invention is constructed as follows. The reference numerals in the drawings are also shown. First, the present invention is to connect a fire detector to a detector line drawn out to a warning area to supply power and to connect a terminating resistor to a terminal end, thereby increasing the line current due to the alarm of the fire detector or disconnecting the line current. This is intended for the receiving circuit of a fire alarm device that detects the interruption of the disconnection monitoring current that is determined by the terminating resistance and produces a reception output.

As a receiving circuit of such a fire alarm device, the present invention has a structure in which a signal line from a positive side of a power source to a sensor line is inserted and connected between an emitter and a collector and a base is directly connected to a collector to obtain a power supply voltage. A first transistor Q1 through which a first current Io corresponding to the impedance between the sensor line and the sensor line is connected, the emitter is connected to a power supply via a first resistor R1, and the emitter-base is connected via a second resistor R2. , The base is connected to the first via the third resistor R3
A second current Ir connected to the base of the transistor Q1 and output from the collector as a reception current, a second current Ir reduced at a predetermined ratio with respect to the first current Io flowing in the first transistor Q1.
And a transistor Q2. Here, the overcurrent limiting circuit 6 is provided between the emitter of the first transistor Q1 and the power supply.

The reception current output from the collector of the second transistor Q2 is supplied to the fourth resistor R4 and converted into a voltage signal, and this voltage signal is input to the AD converter.
Further, the received current output from the collector of the second transistor Q2 can be supplied to each of the fire detection circuit and the disconnection detection circuit to detect a fire or disconnection. According to such a receiving circuit of the fire alarm device of the present invention, the line voltage determined by the voltage division of the conventional receiving resistance and the line impedance is not used, and the first condition can be obtained for the monitoring state, the disconnection state, or the reporting state. A reception current is output as a second current Ir from the collector of the second transistor Q2 in accordance with the line current (first current Io) flowing through the transistor Q1 into the sensor line, and this reception current is passed through a resistor for voltage conversion. As a result, a detection voltage that depends only on the line current is obtained.

Therefore, the direct current impedance of the receiver circuit to the sensor line can be lowered, the change of the supply voltage to the sensor line at the time of the alarm can be suppressed to the minimum, and the restriction of the number of connected sensors can be suppressed. Along with
It is possible to guarantee the improvement of resolution and stable operation of the sensor.

[0016]

1 is a circuit diagram of an embodiment of a fire alarm device according to the present invention. In FIG. 1, a detector line 2 also serving as a power supply line is drawn from the receiver 1, a plurality of fire detectors 3 are connected to the detector line 2, and a termination resistor 4 for disconnection detection is connected to the end. There is. A power supply 5 is provided in the receiver 1 and supplies a power supply voltage E to the sensor line 2 via the receiving circuit.

The power source 5 inputs a commercial AC power source AC100V into a power source circuit (not shown) and outputs a DC voltage E. The power source voltage E is, for example, 12V at a rating. Considering the case of switching, it varies in the range of 9 to 15V, for example. The receiving circuit includes a first transistor Q1 and a second transistor Q2. The transistor Q1 is connected to the signal line from the positive side of the power source 5 to the sensor line 2 by inserting and connecting the emitter and collector and directly connecting the base to the collector, and the impedance between the line output voltage Vo and the sensor line 2 is set. A corresponding line current (first current) Io flows. The transistor Q1 is always on in the monitoring state and can be regarded as equivalent to a diode.

The second transistor Q2 has its emitter connected to the power source 5 via the resistor R1 (first resistor), has its emitter and base connected in parallel with the resistor R2 (second resistor), and has its base connected to the resistor R2. The second current, which is connected to the base of the transistor Q1 via R3 (third resistor) and reduced at a predetermined ratio with respect to the line current Io flowing through the first transistor Q1, is output from the collector as a reception current Ir. In this embodiment, a resistor (fourth resistor) is connected to the collector of the transistor Q2.
R4 is connected to convert the reception current Ir into the reception voltage Vr.

Further, the emitter of the transistor Q1 and the power source 5
An overcurrent limiting circuit 6 is provided between and. The overcurrent limiting circuit 6 is composed of transistors Q3 and Q4 and resistors R5 and R6. The transistor Q3 is on in the steady monitoring state, and the transistor Q4 is off. Further, for example, when the sensor line is short-circuited and the line current Io increases, the transistor Q4 receives a base bias to shift to the ON state, and when the specified current is exceeded, the base current to the transistor Q3 increases via the resistor R5. Hold down
Finally, the load is limited so as not to supply more than the current limited by the resistor R6 to the load.

Here, the emitter of the transistor Q2 is connected to the power source 5 side of the overcurrent limiting circuit 6 via the resistor R1, and therefore the bias voltage corresponding to the voltage drop depending on the impedance of the overcurrent limiting circuit 6 is applied. Is transistor Q2
The resistors R1, R2 and R3 are added to the emitter and the base of. The reception operation will be described together with the operation using the transistors Q1 and Q2. This reception operation consists of monitoring, disconnection, and alarm.
Divided into two states. First, since the bias of the transistor Q2 is determined by the voltage drop of the overcurrent limiting circuit 6, this will be described. First, the number n of fire detectors is n ≦ 12, and the resistance value of the terminating resistor 4 is Re = 4.7KΩ.
The power supply voltage E of the receiver 1 is set to 12V.

Therefore, assuming that the average monitoring current for each of the fire detectors 3 during steady monitoring (when no alarm is issued) is Is, for example, Is = 50 μA. The output voltage Vo between the LC and the sensor line 2 at this time is Vce3 as the collector-emitter voltage of the transistor Q3, Vbe4 as the base-emitter voltage of the transistor Q4 and Veb1 as the emitter-base voltage of the transistor Q1. Then, it is given by the following equation.

Vo = E− (Vce3 + Vbe4 + Veb1) = E− {Vce3 + (Io × R6) + Veb1} (1) A specific example of the formula (1) is, for example, Vo = 12V− {0.7V + (2. 8mA × 47Ω) + 0.6V} = 12V− (0.7V + 0.13V + 0.6V) = 10.6V.

Assuming a short circuit between L and C of the sensor line 2, the current flowing through the resistor R6 of the overcurrent limiting circuit 6 increases, and the base-emitter voltage Vce4 of the transistor Q4 is about 0. When it reaches 6V, transistor Q4
Turns on, suppresses an increase in the base current of the transistor Q3, and does not supply more than the current limited by the resistor R6 to the load.

Next, the output currents Ioa, Iob, Ioc at the time of monitoring, disconnection, and alarming will be obtained. For example, since the monitoring current Is of the sensor line is 50 μA, the number of sensors n = 12, and the terminating resistance Re = 4.7 KΩ, the line current Ioa during monitoring is
Is given by the following equation. Ioa = Is + n (Vo / Re) = 50 μA × 12 units + (10.6 V / 4.7 KΩ) = 600 μA + 2.2 mA = 2.8 mA (2) When the wire is disconnected, the resistance value Re of the terminating resistor 4 is disconnected. Therefore, the line current Iob at the time of disconnection is given by the following equation.

Iob = Is × n = 50 μA × 12 units = 600 μA (3) Further, the alarm current Ioc when one arbitrary sensor alarms is:
Assuming that the current required for lighting the LED for alarm display provided in the fire detector 3 is I _LED = 9.4 mA, it is given by the following equation.

Ioc = I _LED + (Vo / Re) + (Is × n) = 9.4 mA + 2.2 mA + 600 μA = 12.2 mA (4) In the equation (1), the output voltage between L and C in the monitoring state is The output voltage between L and C at the time of disconnection, alarm and short circuit is as follows. In any case, it is detected from the path of power supply voltage E, R1, R2 // be2, R3. An electric current flows on the side of the instrument line 2. Here, R2 // Vbe2 means a parallel path of the resistors R2 and Vbe2.

Output voltage between L and C at disconnection Vo = 10.8V Output voltage between L and C at alarm output Vo = 10.23V Output voltage between L and C at short circuit between L and C Vo = 0V Now R1 = 1 KΩ R2 = 22 KΩ R3 = 22 KΩ R4 = 10 KΩ Ib = base current of transistor Q2 h _fe = DC amplification factor of transistor Q2 The following relational expression holds.

E = R1 {Ib + hfeIb + (Vbe2 / R2)} + Vbe2 + R3 {Ib + (Vbe2 / R2)} + Vo (5) If this is rearranged with respect to the base current Ib, the following equation is obtained. Ib = [E-Vbe2-Vo- {R1 (Vbe2 / R2)}-Vbe2] / {R1 + R3 + (R1 * _hfe )} (6) Therefore, the transistor Q2 at the time of monitoring, disconnection, and alarm is issued.
The reception voltage Vr of the resistor R4 due to the current Ir output from the collector of is obtained. Here, there is the following relationship between the base current Ib of the transistor Q2 and the reception voltage Vr which is the collector output voltage.

Vr = Ib × h _fe × R4 (7) First, the base current Ib of the transistor Q2 at the time of monitoring is Ib = 1 μA from the equation (6). Therefore, the reception voltage Vra which is the collector output voltage of the transistor is substituted into the equation (7) and becomes Vra = Ib × h _fe × R4 = 1 μA × 150 × 10 kΩ = 1.5V. Similarly, the base current Ib at the time of disconnection becomes Ib = 0.42 μA, and when the reception voltage Vrb is obtained, Vrb = Ib × h _fe × R4 = 0.42 μA × 150 × 10 kΩ = 0.63 V. Further, the base current Ib at the time of reporting is Ib = 3.1 μA, and when the received voltage Vrc is obtained, Vrc = Ib × h _fe × R4 = 3.1 μA × 150 × 10 kΩ = 4.7 V.

Further, since the base current Ib at the time of short circuit becomes large as Ib = 62 μA, the transistor Q2 is turned on in the saturated state, so that the reception voltage Vrd becomes about Vrd = E (= 12 V).

Next, when the fluctuation of the reception voltage Vr of the transistor Q2 with respect to the fluctuation of the power supply voltage E of the receiver 1 was actually measured, the following result was obtained. Note that the measured values do not necessarily match the calculation results because hfe and Vbe of the transistors used are different from those used in the above theoretical calculation formula.

[0032]

[Table 1]

As can be seen from Table 1, the power supply voltage E is 9.
It fluctuates in the range of 0 to 15.0V, and the wire breakage accompanying it
It can be seen that even if the monitoring and reporting voltages fluctuate, the fluctuation ranges do not overlap each other, so that erroneous detection of the three states can be reliably prevented, and high detection resolution can be obtained. FIG. 2 shows the reception voltage V obtained by the reception circuit of FIG.
In this embodiment, r is input to the A / D converter 9 built in the MPU 8. The A / D converter 9 normally has 0 to 5
Since it has an input range of V, the value of the resistor R4 may be determined so that the maximum value of the line current to be detected is 5V.

FIG. 3 shows another embodiment for detecting fire and disconnection from the received current of the transistor Q2 obtained by the receiving circuit of FIG. In FIG. 4, the received current from the collector of the transistor Q2 is input to the fire detection circuit 10 and the disconnection detection circuit 11. The fire detection circuit 10 is composed of a transistor Q6 and resistors R7, R8, R9. That is, the base-emitter voltage of the transistor Q6 is about 0.6 due to the reception current Ir at the time of the alarm by the resistors R7 and R8.
The resistance value is decided so that it becomes V, and the transistor Q
When 6 is turned on, a fire detection signal is output to the MPU 8.

The disconnection detection circuit 11 comprises a transistor Q7 and resistors R10, R11 and R12. That is, the resistors R10 and R11 turn on by setting the base-emitter voltage of the transistor Q7 to about 0.6 V by the reception current Ir during monitoring, and the disconnection detection turns off the base-emitter voltage of the transistor Q7. Is set to.
Therefore, when the disconnection is detected, the transistor Q7 is turned off to output the disconnection detection signal to the MPU 8.

The values of the resistors R1 to R4 of the receiving circuit described in the above embodiment are appropriately determined according to the number of connected sensors n, the monitoring current per sensor and the alarm current, etc. Therefore, the numerical values shown in the embodiment are not limited. Further, in the above embodiment, the receiving circuit is provided in the receiver, but it may be provided in a repeater or the like.

[0037]

As described above, according to the present invention, the base current of the second transistor is controlled according to the line current flowing through the first transistor according to the monitoring, disconnection or alarm state of the sensor line. By converting it into a receiving current and finally flowing it through a resistor to convert it into a voltage, the impedance of the receiving circuit can be reduced, and the drop in the line voltage when the sensor is triggered can be minimized. Operation can be stabilized and reliability can be improved.

Further, since the impedance of the receiving circuit is lowered, the line voltage is not lowered at the time of issuing a sensor, and the restriction on the number of connected sensors can be relaxed. Further, the range of the detection voltage is determined so that the detection ranges of the monitoring, the wire breakage, and the alarm are not overlapped with respect to the fluctuation of the power supply, so that the resolution and the detection accuracy can be improved. Furthermore, the receiver circuit can be configured with an extremely simple circuit configuration, and the current consumption in the steady monitoring state can be suppressed sufficiently low.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of an embodiment for supplying a reception voltage to an A / D converter of MPU.

FIG. 3 is a circuit diagram of another embodiment including a fire detection circuit and a disconnection detection circuit.

FIG. 4 is an explanatory diagram of a conventional example in which a line voltage determined by a receiving resistance and a line impedance is determined by a comparator.

[Explanation of symbols]

 1: Receiver 2: Detector line 3: Fire detector 4: Termination resistor 5: Power supply 6: Overcurrent limiting circuit 7: Reception output terminal 8: MPU 9: A / D converter 10: Fire detection circuit 11: Disconnection detection Circuit Q1: First transistor Q2: Second transistor R1 to R4: First to fourth resistance

Claims (4)

[Claims] 1. A fire detector is connected to a detector line drawn out to a warning area to supply power and a terminating resistor is connected to the end of the detector line to increase the line current due to the alarm of the fire detector or to disconnect the line current. In the receiver circuit of the fire alarm system that detects the disconnection of the disconnection monitoring current determined by the terminating resistance and generates a reception output, insert the emitter-collector connection and connect the base to the signal line from the positive side of the power supply to the detector line. The first transistor, which is directly connected to the collector and through which the first current flows according to the impedance between the power supply voltage and the sensor line, and the emitter is connected to the power supply via the first resistor, and the emitter-base is connected via the second resistor. And the base is connected to the base of the first transistor via a third resistor to reduce the first current flowing through the first transistor at a predetermined ratio. Receiving circuit of a fire alarm system to a second transistor, comprising the outputs from the collectors of the second current as a reception current was. 2. The receiver circuit of the fire alarm device according to claim 1, wherein an overcurrent limiting circuit is provided between the emitter of the first transistor and the power supply. . 3. The fire alarm device receiving circuit according to claim 1, wherein the receiving current output from the collector of the second transistor is supplied to a fourth resistor and converted into a voltage signal, and the voltage is converted into a voltage signal. A receiving circuit of a fire alarm device, characterized in that a signal is inputted to an AD converter. 4. The fire alarm device according to any one of claims 1 to 3, wherein the received current output from the collector of the second transistor is supplied to each of the fire detection circuit and the disconnection detection circuit. Alternatively, a fire alarm device receiving circuit characterized by detecting a disconnection.