JPS5914762Y2 - Smoke detectors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a smoke detector, and more particularly to a smoke detector equipped with an operation switch that temporarily disables sensing operation.

First, a conventional example will be explained based on FIG.

This embodiment relates to an ionization type smoke detector.

That is, when smoke enters the external ion chamber 2, the ionic current decreases, and in relation to the fact that the ionic current in the internal ionic chamber is constant, the potential at the connection point A of both ion chambers increases,
This increase is transmitted to the sliding resistor 4 via the gate and source of the FET 3.

When the potential at the sliding point B of this resistor 4 exceeds a certain value, the Zener diode 5 becomes conductive, 5CR7 is activated, the alarm 8 sounds, and an alarm is issued.

Note that 10 is a dry battery that constitutes a power source.

If the alarm 8 is a so-called contact buzzer that self-oscillates, it will stop when the smoke in the external ion chamber 1 disappears.

Generally, when the cause of the alarm is determined, the stop switch 9, which is normally closed, is operated (opened) to prevent energization and stop the alarm.

At present, such measures are indispensable when checking operation and also as a so-called non-fire alarm countermeasure.

The problem here is that if you use a momentary type switch that responds only when pressed in the previous example, the alarm will continue to emit if you do not continue to press it for a while.
Also, if you use a knife type switch, you may forget to turn it on again.

More importantly, the supply current for monitoring this type of smoke detector is an extremely small current of several to tens of microamperes, and inserting a switch that turns on and off such a small current in series with the sensing circuit is A switch having a special specification contact must be used, which not only inevitably increases cost, but also reduces circuit reliability.

Therefore, an object of the present invention is to provide a smoke detector that is easy to operate and has excellent reliability while avoiding an increase in cost.

2 and 3 show an embodiment, and parts equivalent to those in FIG. 1 are given the same reference numerals.

In FIG. 2, a capacitor 11 is connected in parallel to sandwich the inner and outer ion chambers 1 and 2.

Furthermore, a stop switch 9 (normally open) is also connected in parallel, and a resistor 12 is inserted in series with the capacitor 11 (therefore both ion chambers 1 and 2) with respect to the power supply line.

That is, in a normal state, the capacitor 11 is charged and saturated, so that the sensor performs normal monitoring.

Now, when the stop switch 9 is pressed, its contact closes and the charge stored in the capacitor 11 is discharged, and the voltage across it becomes almost zero, so the potential at the connection point A also decreases, and the alarm is activated. The contact buzzer at point 8 stops ringing.

Note that if the alarm device 8 is of a type driven by current, such as a lamp or an electronic buzzer, a power transistor is used instead of the SCR 7 since the self-holding characteristic of the SCR is insufficient.

After the capacitor 11 has been discharged in this way, when the stop switch 9 is released from the suppression, it will last for several tens of seconds or several minutes depending on the resistance value of the resistor 12 and the capacitance of the capacitor 12.
The capacitor 11 is charged via the resistor 12 and the sensor returns to its normal monitoring state.

FIG. 3 shows another embodiment.

In this embodiment, a bridge circuit is constructed by both ion chambers 1 and 2 and resistors 13 and 4, and the electric potential between the rain intermediate connection points A and B is compared by the FET input comparator 14 to issue an alarm. This is what I did.

Then, the newly installed resistor 13 and parallel capacitor 11
and a stop switch 9 are arranged.

That is, when the stop switch 9 is pressed, the charge in the capacitor 11 is discharged and the voltage across the capacitor 11 becomes almost zero, so the voltage at the terminals of the resistor 4 on the capacitor 11 side becomes almost the power supply voltage, and the voltage at one intermediate point B becomes almost zero. The potential also rises, and the output from the comparator 14 becomes ineffective.

When the stop switch 9 is released from the press, the capacitor 11 is charged via the resistor 4, and after a few seconds to a few minutes, the sensor returns to its normal monitoring state as in the previous embodiment.

In both of the above embodiments, since the equivalent impedance of the ion chambers 1 and 2 is extremely high, the resistance values of the resistor 12 and furthermore the resistor 4 can be made large, so that the delay time of several seconds to several minutes can be easily achieved. You can take it.

As described above, in the present invention, the operation switch does not turn on and off the power supply to the smoke detection circuit.
Since the smoke detection circuit is provided to discharge the electric charge of the capacitor in parallel, it is possible to ensure that the input current capacity is above a certain level, and therefore, a commonly used switch can be used, making it inexpensive. Moreover, even with the addition of this operation switch, a highly reliable smoke detector with almost no decrease in reliability can be obtained.

Furthermore, the sensor automatically returns to the monitoring state after a predetermined period of time has elapsed after the operation is released, eliminating problems such as failure of alarm due to forgetting to turn on the sensor again.

[Brief explanation of drawings]

FIG. 1 shows a conventional example, and FIGS. 2 and 3 show an embodiment of the present invention. 1.2...Ion chamber, 3...FET,
4...Sliding resistance, 8...Contact buzzer,
9...Stop switch, 11...Capacitor, 12.13...Resistor.

Claims (1)

[Scope of utility model registration request] In an ion type smoke detector in which a comparator circuit detects changes in the impedance of the ion chamber due to intrusion of smoke, a resistor forming the comparator circuit or a capacitor forming a delay circuit is connected in parallel with the ion chamber. A smoke detector characterized in that an operation switch for stopping an alarm, which is normally open, is connected in parallel with this capacitor.