JPS583190Y2 - alarm receiver - Google Patents

Description

[Detailed description of the invention] This invention is a fire alarm system equipped with a plurality of terminal devices having capacitive load impedance such as a smoke detector.
This invention relates to an alarm receiver equipped with means for preventing non-fire alarms that are likely to occur when the power is turned on.

A plurality of terminal devices including a capacitive element in the load impedance are connected in parallel to a power feeding/signal line led out from a receiver having a power source, and the above-mentioned power feeding due to the operation of this terminal device, such as a smoke detector or a heat sensor, In an alarm device that detects a change in current in the signal line by a current detector, such as a relay, in the receiver and issues an alarm, the operation of the current detector is performed at a predetermined rate with respect to the monitored current in a steady state. It is well known that what happens when a current exceeding this magnitude flows.

However, as described above, when a large number of terminal devices such as sensors containing large capacitance components such as capacitors of internal voltage stabilizing circuits are connected in parallel between the lines as load impedance, the equivalent This means that the line end is terminated with a large capacitance, and when the power is turned on, the rising part of the step voltage is applied to the capacitance as a transient phenomenon, causing a transient current from the power transmission end to flow much larger than in a steady state.

This is because the thicker the capacitance, the closer it is to a short circuit with respect to the rising edge, and the magnitude and decay time of this transient current are determined by the line resistance and the capacitance, making it a constant time constant. Therefore, the larger the capacity, the longer it will take to decay, which will eventually cause the receiver's current detector to operate, resulting in a non-fire alarm.

Furthermore, for example, in the case where the terminal device is an ionization type smoke detector, a transient current due to the step voltage rising portion when the power is turned on flows between the electrodes forming the inner and outer ion chambers. The voltage division distribution of the capacitance series circuit is controlled by the voltage division ratio based on the capacitance value, and since the intermediate connection point of the series circuit is connected to the gate of the FET as an output amplifying element, this FET is If the operating state is reached before the transient current decays to a predetermined value or less, the FET will be temporarily turned on by the gate voltage at the above-mentioned partial voltage level, and the sensor will issue a non-fire alarm based on its output. Incur consequences.

As a measure to prevent the occurrence of non-fire alarms that are often experienced when the power is turned on, conventional methods include inserting a high resistance in series on the power supply side from the capacitance component of the terminal device to limit the transient current, and the method described above. When the terminal device is an ionization type smoke detector, a time constant is given to the time relationship between the voltage supply to the electrode capacitor section and the voltage supply to the intensifier section, and after the transient state of the electrode capacitor section is saturated, the intensifier section is Although measures have been taken to make the terminal device operable, this not only complicates the internal structure of the terminal device1 and increases the number of component parts, leading to higher costs, but also makes it difficult to operate the terminal device normally. However, there still remain problems such as having to incorporate means that do not contribute anything to the terminal device, unnecessarily complicating its configuration.

This idea was made to fundamentally improve these shortcomings, and the internal structure of terminal equipment such as fire detectors is kept to the minimum necessary to achieve its original purpose, and the power supply is This method is designed to prevent false alarms such as non-fire alarms that may occur when the power is turned on or even when the power is turned off, by installing a button inside the alarm device receiver that contains the power supply. The purpose is to simplify the internal structure of terminal devices such as appliances, solve problems related to turning on and off power centrally within the alarm receiver, and rationalize the entire alarm system.

An embodiment in which the present invention is applied to a fire alarm system equipped with an ionization smoke detector will be described below.

FIG. 1a shows a simplified block diagram of the entire general fire alarm system.

In the figure, 1 is a DC power supply section T, Tj, and a power supply switch S.

This is a fire alarm system receiver including fire indicators I, I...I, etc.

tl, t2...1o is the power supply/power supply leading to each warning area.
t on the signal line.

is a common line, and the TL line has several smoke or heat detectors D1. Dz...JDn is the common line t.

Similarly, several sensors are connected to each line of t2...tn.

Figure 1 shows in more detail the signal circuit of one sensor extracted from the above-mentioned fire alarm system. , a fire indicator ■, the detector is an ionization type smoke detector as an example, and the collecting electrodes of the internal ionization chamber Ch1 and the external ionization chamber Ch2 form capacitances C1 and C2, respectively. They are electrically connected in series and receive a DC voltage.

The connection point J of the electrodes of both the inner and outer chambers is connected to the gate electrode G of an MO8 type field effect transistor FET 1 whose drain is grounded, and the source electrode of the transistor FET is connected via a source resistor R8 and a drain resistor RD.
are respectively connected to the power supply circuits through which they receive bias voltage.

The output voltage of the FET is supplied to the transistor Tr, gates the thyristor SCR, and has the function of issuing a fire signal and operating the fire indicator (2) via the power supply signal lines, 11, and Lo.

Stabilization of the voltage applied to the collector electrode of the above sensor and the above F
In order to stabilize the operation of the ET button and the transistor Tr, in the illustrated example, the voltage stabilizing circuit VRC is
This voltage stabilizing circuit VRC has the above-mentioned z] i- and t.

A smoothing capacitor cR inserted between the lines is included.

Capacitive components such as voltage stabilizing circuits containing such capacitors or simply capacitors for bypassing AC components are used not only in the case of the above-mentioned ionization type smoke detectors, but also in differential heat detectors and photoelectric type smoke detectors, for example. Most terminal devices, such as smoke detectors, in which it is desired to stabilize the operation of the detection element and its detection signal amplification part, have this capacitive component, and therefore, a large number of terminal devices having these capacitive components are shown in Figure 1a. When connected in parallel to the power supply as shown in the figure, a large capacitor equivalent to the sum of the capacitances of the capacitive components of each terminal device is connected between the lines as a capacitive component in the load impedance of the receiver 1. It will be connected to the song.

Therefore, in this case, the moment the power switch S is closed, a transient current flows through the line through the large-capacity capacitor, and until it is fully charged, the current detector such as the fire indicator ■ will be sufficiently activated. , which leads to the unfavorable result of non-fire alarms.

In this invention, a means is provided in the receiver 1 to enable a slow voltage rise by preventing a step voltage from being applied between the lines when the power is turned on.
The figure shows the 701st embodiment.

In other words, as shown in Figure 2, there is a power switch S inside the receiver 1.
A transistor 2 (MO8POWERFET) constituting a voltage control amplifier is inserted between and the fire indicator 11-In, and its gate electrode is connected to the terminal of the capacitor of the RC series circuit consisting of a resistor 3 and a capacitor 4. The voltage is applied as a control voltage and the button is pressed so that the gradual rise in the terminal voltage of the capacitor 4 of the RC series circuit, which is pressed when the power is turned on, appears directly on the source electrode side of the transistor 2. The voltage change between the line and the TO line when the power is turned on is made slow.

That is, in this circuit, when the DC power supply voltage is Ed, the current flowing through the RC series circuit is 11, and the capacitance of the capacitor 4 is C4, the terminal voltage ec of the capacitor 4 when the power switch S is turned on is e.

--! -f idt, reaches the power supply voltage Ed after a time determined by the RC time constant, and is initially zero.

This gradually increasing voltage e.

is used as the gate voltage of the transistor 2, and therefore the output voltage of the transistor 2 V oidV □ = e
(HVG S(th) (However, ■Gs(th) is the gate-source voltage of the transistor = O, S ~ 2, Ov)
Therefore, the voltage rises slowly in the same way as the change in ec, and its rising speed is also determined by the time constant of the RC series circuit.

After the capacitor 4 is charged, the transistor 2
Since the output voltage VO of , the terminal voltage of capacitor 4 has almost reached the power supply voltage (actually, it is connected to the transistor)
(through a monitoring circuit including each terminal device beyond the source of the transistor 2), the transistor 2 enters the saturation region and becomes conductive (although it is lower by the threshold voltage between the gate and source),
It becomes equal to the power supply voltage.

Therefore, in the alarm device equipped with the receiver shown in FIG. 2, even if a large number of terminal devices including capacitance components are connected as shown in FIG. This can be prevented by appropriately determining the error message, thereby completely preventing false alarms when the power is turned on.

On the other hand, for example, when a sensor as a terminal device includes a thyristor as an output element, the power is cut off when the device is restored after an alarm is issued, but when the power is turned on again after this cutoff, the same applies to non-fire alarms. Especially in this case, it is essential to distinguish the state in which the detector is still operating, that is, the state in which the alarm is still being issued, so the occurrence of such non-fire alarms must be further prevented. Must be.

For this purpose, as shown in FIG. 3, in the case of manual recovery, the manual recovery switch 5a is provided with an interlocking contact 5b that opens and closes symmetrically, and this contact 5b is used to switch the recovery switch. 5a is opened and the power supply is cut off, a discharge path for discharging the charge in the capacitor 4 is formed via a resistor 3' having a relatively small value,
Alternatively, in the case of automatic recovery, when the switched automatic recovery contact 6 and one contact 7a of the district relay (fire indicator) are closed, the lines are short-circuited and the automatic recovery operation is performed. Similarly, the capacitor 4 is connected to the capacitor 4 through a resistor 3' having a relatively small value, without directly dropping the base of the transistor 20 to the negative power supply side, by the contact 9 of another relay 8, which is activated by the other contact 7b of the relay (2). These problems can be addressed by forming a discharge path.

Further, in FIG. 4, the transistor 2 constituting the voltage control amplifier of FIG. 3 is composed of a first field effect transistor 2a and a second transistor 2b, and the voltage applied to the source of the first transistor 2a is is set to an appropriate bias voltage value so that the point at which conduction of the second transistor 2b starts can be appropriately selected with respect to the time constant formed by the capacitor 4 and the resistor 3, and as shown in FIG. The change in the gate voltage of the transistor 2a when the transistor 2a is turned on gradually decreases from the power supply voltage to zero due to the change in the charging current to the capacitor 4, and when the gate potential drops to a potential determined by the source bias of the transistor 2a, the voltage of the transistor 2a decreases.
becomes conductive, and the base current of the second transistor 2b gradually increases due to its drain current, and the output voltage V.

will also gradually increase.

Upon recovery, the electric charge in the capacitor 4 is transferred to the resistor 3 by opening the contact 9 of the relay 8 or the switch 5a and closing the switch 5b.
It is gradually discharged in accordance with the time constant of ', and returns to the initial state as in FIG. 3 described above.

Therefore, even if the button shown in FIG. 4 is pressed, it is possible to deal with the problem when the power is turned on again in the same way as in FIG. 3, and it is also possible to apply the button to a large current load.

As described above, according to this invention, when the power is turned on or when the terminal device is turned on again after recovery, the DC voltage applied between the lines always increases gradually with a predetermined time constant.
Since a step voltage is not applied, even if a large number of terminal devices including capacitive components are connected in parallel between the lines, a large amount of transient current due to these capacitive components will flow when voltage is applied between the lines. This effectively prevents false alarms as it does not cause the current detector to operate.Also, even if an ionization type smoke detector is connected between lines as a terminal device, the step voltage of the voltage distribution of both the inner and outer ion beams is The initial unbalance caused by the rising edge can be negated by applying a voltage that gradually increases with a time constant much larger than the charging time constant of both chambers, and is further limited by the upper limit of the allowable magnitude of the transient current. Many practical effects can be achieved, such as the number of connected terminal devices that have previously been connected can be increased in accordance with the CR time constant for voltage control.

[Brief explanation of drawings]

Figure 1a is a block diagram showing a configuration example of a general alarm device, Figure 1 is a circuit diagram detailing one line segment in Figure 1a, and Figure 2 is an embodiment of this invention. FIG. 3 is a circuit diagram of a receiver showing another embodiment, and FIG. 4 is a circuit diagram of a receiver showing still another embodiment. 1...Receiver, 2.2a, 2b...Transistor,
3...Resistor, 4...Capacitor.

Claims (1)

[Scope of utility model registration request] A plurality of terminal devices are connected to a receiver including a DC power source and a current detector via power supply/signal lines, and the current detector detects changes in the current flowing through the lines due to the operation of the terminal devices. A capacitive component included in the terminal device is connected in parallel between a line that is configured to issue an alarm and that passes through the current detector among the lines, and a line that forms a pair with this line regarding the power supply. Press the button on the receiver to connect the alarm device that will be used, connect the transistor constituting the voltage control amplifier into the power supply circuit including the current detector, and connect the control electrode of the transistor to the power supply circuit that includes the current detector. An alarm receiver characterized in that the transistor is connected to a constant circuit so that the change in the line-to-line voltage when the power is turned on or off is slowed down based on the time constant of the time constant circuit.