JPH05758B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a transmitter circuit for a fire alarm.

<Prior art> Figure 5 is a circuit diagram of a conventional fire alarm system. When the fire detector DT is activated due to a fire, the district relay N of the receiver CP is activated, its contact n1 is closed, and the operation is automatically activated. Retained. Also, other contacts
2 is closed and fire alarm relay F is activated.

Meanwhile, the person who discovered the fire should call the nearest transmitter.
When pushbutton switch PB of MB is pressed, district relay N and relay F operate in the same way as when fire detector DT operates. Furthermore, the other contacts of the pushbutton switch PB are also closed, and the contact f of the relay F
is closed, relay M operates and its contacts m
1 and m2 are closed and the relay M is self-maintained.
By closing this contact m2, and assuming that the line between the transmitter MB and the receiver CP is short and the line resistance Pl is approximately zero ohm, the power supply voltage E will be applied to the response indicator La. If the power supply voltage is 24V and an incandescent lamp with a rated voltage of 24V and a rated current of 30mA is used as the response indicator La, each response indicator
A current of 30mA flows through the lamp, for a total of 60mA, and it lights up brightly.

<Problems with the prior art> Originally, the response indicator La of the transmitter MB described above was equipped with two incandescent lamps in parallel so that it would operate normally even if one incandescent lamp was disconnected. If the contact becomes poor or if both wires are disconnected without being noticed, the relay M will not operate, and the fire hydrant pump etc. that operate through the contact will not be activated in an emergency.

For this purpose, as shown in Figure 6, the response indicator light La
It is also possible to connect a resistor R′ in parallel with
Considering the current of the relay M, the resistance value of the resistor R' must be kept to about 240Ω. In this case as well, if we use a lamp with the same rating as in the example in Figure 5 above and assume that the line between the receiver CP and the transmitter MB is short and the line resistance is approximately zero ohm, then the closing of contact m2 of relay M As a result, a power supply voltage of 24V is applied to the 240Ω resistor R' and the incandescent lamp as the response indicator La, so 100mA is applied to the resistor R' and 100mA to the response indicator La.
A current of 30mA, a total of 130mA, flows and lights two incandescent lamps.
Approximately twice as much current will flow as compared to a case in which each device is connected in parallel.

Furthermore, it is conceivable to use light-emitting diodes (LEDs) instead of incandescent lamps, which have an inherently long life. However, when using a light emitting diode LED, the current flowing therein is generally limited to 10 to 20 mA, and as shown in Figure 7, a limiting resistor R1' and a diode D to prevent reverse connection are used.
However, it is difficult to operate the relay M directly through this series circuit in terms of the applied current. Therefore, as in the case of Fig. 6, a resistor is connected in parallel.
R', which had the disadvantage of increasing the current consumption after the transmitter was operated.

<Means for Solving the Problems> In view of the above points, the present invention aims to obtain a transmitter circuit for a fire alarm using a long-life light emitting diode, which suppresses current consumption to less than the conventional one. The push button switch of the transmitter, the current limiting resistor, the light emitting diode, and the diode for preventing reverse connection are connected in series with the relay that detects the operation of the transmitter, and the current limiting resistor and the light emitting diode are connected in series. A constant current load circuit is provided in parallel with the series circuit to flow a predetermined current greater than the current value of the relay.

<Operation> Since this invention is configured as described above,
The relay operates reliably by being supplied with a predetermined current greater than the current value through the constant current load circuit. Further, due to this operation, a predetermined current flows through the current limiting resistor to the light emitting diode as a response indicator directly connected to the power source, and the light is brightly lit.

<Embodiment> An embodiment of a transmitter circuit for a fire alarm according to the present invention will be described below with reference to FIGS. 1 to 4. The drawing shows the circuitry of the transmitter section, and these transmitters are connected to the conventional transmitter shown in FIG.

FIG. 1 is a diagram showing the principle of the transmitter circuit. One of the pair of contacts of the transmitter's push button switch PB is connected to the power source through terminals C and L and the district relay N of the transmitter CP. Other contacts are terminals C and A.
A current limiting resistor R1, a light emitting diode LED as a response indicator, a reverse connection prevention diode D _B , a transmitter diode, and a relay M are connected in series between them.
and is connected to the power supply through contact f of relay F. In addition, the current limiting resistor R1 and the light emitting diode
A constant current load circuit S is connected in parallel to the series circuit of the LEDs.

In the embodiment shown in FIG. 2, the constant current load circuit S includes two transistors Q1, Q2 and a resistor R2,
In the embodiment shown in FIG. 3, it consists of a single transistor Q, diodes D1 and D2, and a resistor R.
In the embodiment shown in FIG. 4, a light emitting diode LED is used as a reference voltage element, a limiting resistor R1 is used as a resistor, and the resistor is also composed of a transistor Q and a resistor R2.

Therefore, the transmitter circuit shown in FIG. 2 will be explained using specific values. When the transmitter's relay M has a current value of 14.5 mA, a margin of 10% is taken to ensure that a current of 16 mA or more flows through it to ensure reliable operation. In Figure 5, the resistance value of the district relay N is 430Ω, the resistance value of the relay M is 950Ω, the line resistance Rl is maximum 25Ω, and the power supply voltage E is E = 24V.
Assuming that it fluctuates by ±15%, and considering the worst case case of a power supply voltage of 20.4V, the current I _L flowing through the district relay N is I _L = 20.4/430 + 2 x 25 = 0.0425A = 42.5mA. . In addition, a current of 58.5 mA including 16 mA flowing through relay M flows through terminal C, and if the voltage drop between terminals C and C is △V and the voltage drop between terminals A and A is △V _A , then ΔV _C =Rl×0.0585≒
1.5V, ΔV _A = Rl x 0.016 = 0.4V, and the fifth
In the figure, if the voltage across the diode connected between the relay M and the transmitter MB is 0.7V, the maximum allowable voltage value △V _MB applied to the constant current load circuit S is:
△V _MB =20.4−(950×0.016+0.7+1.5+0.4)=
It becomes 2.6V.

In this range, each transistor Q1, Q2
Base-emitter voltage and diode D _B
The design is such that the voltage across the resistor R2 is 0.7V, and a current of 16mA flows through the resistor R2. In other words, relay M
Find the resistance values of resistors R2 and R3 that can supply a current of 16 mA or more. Voltage across resistor R3
Assuming V _R3 , R2=0.7/0.016≒44Ω, and V _R3 ≦2.6−(V _DB +V _BE(Q1) +V _BE(Q2) ) becomes V _R3 ≦0.5V, so R3≦0.5/0.016×〓≒ It becomes 3KΩ. Therefore, when the resistor R3 is set to 3KΩ, the current I _R3 flowing through the resistor R3 becomes I _R3 =0.5[V]/3[KΩ]=0.17mA. _hFE ＞10
In the case of 0, this current flows as the collector current of the transistor Q1 and the base current of the transistor Q2, and a total of 16.17 mA of current is supplied to the relay M to ensure reliable operation. Note that the base current of Q1 is very small and can be ignored.

In addition, when the relay M operates and its contacts m1 and m2 are closed, and the power supply voltage of 24V is applied to the transmitter, the voltage V _LED across the light emitting diode LED is 2V.
The value of the resistor R1 to allow a current of 15 mA to flow is, in order to simplify the comparison with the conventional device, assuming that the line between the receiver CP and the transmitter MB is short and the line resistance Rl is zero ohm, as in the conventional example. , R1=24−(V _DB + V _LED )/0.015=1420Ω≒1.4KΩ. Further, the current I _R3 flowing through the resistor R3 in this state is I _R3 =24-(V _DB +V _BE(Q1) +V _BE(Q2)) /R ₃ =0.0073A. Therefore, the current I _MB flowing through the entire transmitter is I _MB = 15 + 16 + 7.3 = 38.3 mA,
Compared to the conventional method, which consumed 60 mA, the current consumption is significantly lower.

In addition, under similar conditions, the embodiment shown in FIG. 3 and the embodiment shown in FIG.
When considering the embodiments shown in the figures, the one in Figure 3 has a value equivalent to that in Figure 2, and the one in Figure 4 has a current of only 31 mA flowing when the light emitting diode LED is turned on.

<Effects> Since the present invention is configured and operates as described above, it uses light emitting diodes that are almost unbreakable, can transmit a necessary and sufficient signal current even if the light emitting diodes are broken, and can prevent fires with low current consumption. This has the effect of providing a transmitter circuit for an alarm.

[Brief explanation of the drawing]

Figure 1 is a principle diagram of the transmitter circuit of this invention, Figure 2
4 to 4 show different embodiments of transmitter circuits, FIG. 5 is a circuit diagram of a fire alarm equipped with a conventional transmitter circuit, and FIGS. 6 and 7 are explanatory circuit diagrams. M...relay, MB...transmitter, PB...push button switch, R1...current limiting resistor, LED...light emitting diode, S...constant current load circuit, D _B ...diode.

Claims (1)

[Claims] 1 Connect the push button switch of the transmitter, the current limiting resistor, the light emitting diode, and the diode for preventing reverse connection in series with the relay that detects the operation of the transmitter, and form a series circuit of the current limiting resistor and the light emitting diode. A transmitter circuit for a fire alarm, characterized in that a constant current load circuit is provided in parallel to flow a predetermined current greater than the current value of the relay.