JPS5819673Y2 - Noise removal device for memory circuit of airborne foreign object detector - Google Patents

Description

[Detailed description of the invention] A memory circuit that stores voltage in a capacitor is also used in transmitted-light smoke detectors installed in automobile tunnels, etc., and is used to detect dirt on the light-emitting and light-receiving windows in the smoke detection part of the sensor. It is used to ensure that the detector always operates at a predetermined smoke concentration regardless of the smoke concentration.

Figure 1 is a circuit diagram of such a sensor, where L is the receiver Re.
The light source lamp is connected to the terminal atb connected to the power supply E inside, and SB is a solar cell as a photoelectric conversion element that receives the light from the lamp L through the smoke path, through the amplifier side connected to terminals a and b. The obtained output V, is once divided into two resistors R1tP2 connected in series at a point P, and the resistors R1tP2 are connected in series so that this sensor operates at a dimming rate δ corresponding to a predetermined smoke density. The ratio of the resistance values of R1 and R2 is selected as δ/100:(1-δ/100), and the resistance R
The voltage V2 across 2 is stored in the capacitor C2 through a filter made up of a resistor R3 and a capacitor C1 and a diode D1, and is also used as the source voltage of the field effect transistor FET connected between the terminals atb through a load resistor R4. The source voltage of the FET and the output voltage of the solar cell SH are applied to the input side of the operational amplifier OPA, and smoke is generated and the output voltage of the solar cell SH is
0 decreases and becomes equal to the source voltage of the FET, the voltage across the resistor R5 on the output side of the amplifier OPA suddenly rises from zero to a predetermined value, making the Zener diode ZD conductive and increasing the voltage between terminals a and b. By energizing the transistor Tr1 connected through the relay K having a diode Di in parallel, the relay K is operated, its contact k is closed, and the receiving relay N in the receiver Re is operated.

However, if a memory circuit that stores voltage in a capacitor is used in smoke detectors, etc., it may be difficult to detect fluctuations in power supply voltage, induced surge voltage from the power supply line of other equipment such as ventilation fans, or a running car. When the light from the headlights of an emergency vehicle or the revolving lights of an emergency vehicle illuminates a photoelectric conversion element, noise such as voltage changes that occur in the element enters the memory circuit and is stored. There are defects that prevent normal operation.

Such noise is caused by resistor R3 and capacitor C in Figure 1.
Although noise with a frequency below the cutoff frequency of the filter can be removed to some extent by a low-pass filter made of 1 and 1 before entering the storage circuit,
It is rectified by diode D1 and stored in storage capacitor C2, and even if the frequency is higher than the cutoff frequency, the frequency close to the cutoff frequency cannot be sufficiently attenuated by the filter, so it cannot be stored for a long time. If this is necessary, it will gradually accumulate in capacitor C2, causing malfunction.

This idea has a simple structure, and the memory circuit equipped with the memory capacitor of a detector that detects foreign substances in the air such as smoke, such as a smoke detector, which causes a change in the performance of the detection element over time.
The purpose of this invention is to obtain a noise removal device for a memory circuit of an airborne foreign object detector that is capable of storing almost no noise included in the output of a foreign object detection element, and is shown in the drawings below. This invention will be explained with reference to an example shown in FIG.

FIG. 2 is a circuit diagram of an embodiment of this invention. The difference from the circuit in FIG. 1 is that a transistor Tr2 is connected in parallel with the storage capacitor C2 to discharge the charge of C2,
To control the conduction of r2 its base and resistor R1t
A diode D2, a coupling capacitor C3, and a resistor R7 are connected in series between R2 and the connection point P, and R7 and Tr2 are connected in series.
The only point is that a resistor R6 is connected in parallel with the series circuit with the base and emitter of the resistor R6.

To explain its operation, in a transient state at 1, where the DC voltage V2 at point P is constant after the power is turned on, the diode D3, the coupling capacitor C3, the resistor T'L7, the base and emitter of the transistor Tr2 A current flows through the
Tr2 becomes conductive and discharges the charge stored in the storage capacitor C2.

However, when the DC voltage v2 at point P reaches a constant value, no transient current flows through the coupling capacitor C3, so the transistor Tr2 is cut off, and the DC voltage v2, which has become almost constant, is stored in the storage capacitor C2. .

Next, when AC noise is superimposed on the DC voltage v2 at point P as shown by the dotted line in Figure 5 a of the characteristic diagram showing the relationship between voltage and time, the first positive half wave of the noise The current flows through the diode D3, the coupling capacitor C2, and the resistor R7 to the base and emitter of the transistor Tr2, making Tr2 conductive, and the current flows from the storage capacitor C2 to the transistor Tr2.
A current that amplifies the base current of Tr2 flows through the collector, emitter, and emitter of Tr2, discharging the electric charge stored in C2, and the voltage Vc2 of C2 temporarily decreases as shown in section 5b, but the voltage Vc2 of C2 decreases temporarily. The charge due to the first positive half-wave of the noise flowing into the diode D3 is discharged through the discharge circuit made of D3 and the resistor R25RB within a certain time which is considerably longer than the expected connection time of the noise due to the diode D3. It accumulates in C3 without finishing, and C3
The voltage Vc3 is stored at a value higher than the initial value, as shown in FIG. 5C.

The discharging time constant γR is much larger than the charging time constant γF, and the capacitance of C3 is C3, and the resistance value of D3 in the opposite direction is γ.
If T, then rR: C35r R, and when high resistance HR is connected in parallel with diode D3 as shown by the dotted line in the figure, if the resistance of HR is expressed by HR, rRf: c
3 (rR/HR).

However, it is assumed that HR and rR are much larger than the resistances R2t and R3.

In other words, after a certain period of time determined by this time constant has elapsed, the noise accumulated in capacitor C3 is
After that, only the original DC voltage v2 remains at C3.

Therefore, a lower positive half-wave following the first positive half-wave of noise will not cause transistor Tr2 to conduct, and Tr2 will conduct only if followed by a higher positive half-wave, and that higher positive half-wave will cause transistor Tr2 to conduct. T r 2 due to the difference between the voltage at
The electric charge in the capacitor C2 is discharged by the current obtained by amplifying the Basemi current by the Tr2.

That is, the charge corresponding to the extra charge stored in the storage capacitor C2 due to the noise voltage is discharged from C2 prior to being charged by the noise voltage.

and the storage capacitor C discharged by the first positive half-wave of noise and the subsequent higher positive half-wave.
2 is the resistance R of the voltage V2 at point P and the noise riding on it.
3 and the capacitor C1, as shown in FIG.
By selecting the amplification factor of the transistor Tr2 and the resistance value of the resistor R7 to appropriate values, the amount of charge of the capacitor C2 discharged through Tr2 due to noise can be set to an appropriate amount, and the charging time constant of the filter can be set to an appropriate value. By selecting a value that is suitable for charging capacitor C2, before C2 is charged to the voltage before discharging, the charging due to the noise on DC voltage v2 that has passed the above filter is completed, and C2 is It is possible to avoid charging to a voltage higher than the voltage before discharging.

In this way, the charging of C2 due to noise reduces the time required for C2 to be charged to the voltage before discharging as shown in Figure 5 (the chain line in the figure shows the amount of noise generated during charging). C2
It is not useful to charge the battery above its previous discharge voltage.

In this embodiment, the noise voltage riding on the DC voltage ■2 at point P does not exceed the sum of the rising voltage (forward voltage drop) of diode D3 and the rising voltage (forward voltage drop) between the base and emitter of transistor Tr2. Although Tr2 and Tr2 are not conductive, the sensitivity to noise can be made more sensitive by moving the diode D3 to the position of the diode rj3 shown by the dotted line in FIG.

The above embodiment is an example of a transmitted light type smoke detector installed in a car tunnel, etc., but the memory circuit noise removal device according to this invention is a scattered light type smoke detector installed in a general building. For detectors, ionization smoke detectors, etc.
When a memory circuit is provided to eliminate changes in sensitivity due to dust, it can also be used as a noise removal device for the memory circuit.

FIG. 3 shows an embodiment of a scattered light type smoke detector, in which, compared to the embodiment shown in FIG. A photoconductive element CdS, which serves as a photoelectric conversion element that receives scattered light from smoke that is pressed inside the smoke chamber, is connected between terminals a and b through a resistor R8, and a transistor Tr whose base is connected to the mutual connection point of CdS and R8 is connected. The embodiment is the same as the embodiment shown in FIG. 2 except that the resistors R1 and R2 are connected in series between terminals a and b.

Generally, in a scattered light type smoke sensor, when dust floating in the air enters the smoke chamber, it causes scattered light.

Therefore, if a diffused light smoke detector is installed in a room where people are constantly coming in and out, such as a waiting room at a clinic, or in a place where there is a large amount of dust and the amount fluctuates over time, such as a factory, it will cause light scattering due to dust. Since light constantly enters the photoelectric conversion element, the sensitivity of the sensor changes, and the sensor cannot always operate at a predetermined smoke density. By providing the device as in this embodiment, the scattered light type smoke detector is not hindered by dust as described above, and can always operate at a predetermined smoke density as in the case of Fig. 2. At the same time, it is possible to prevent the memory circuit from being adversely affected by noise such as fluctuations in power supply voltage or induced surge voltage from electrical circuits of other devices installed in the same building.

Figure 4 shows an example of an ionization type smoke detector.
Compared to the embodiment shown in the figure, the lamp L and the photoconductive element CdS
, an open external ion chamber CHo where smoke enters instead of
A sealed internal ion chamber CHi is placed at the position of the resistor Ro.
The embodiment is the same as the embodiment shown in FIG. 3, except that a field effect transistor FET-o is used in place of the transistor TrO.

In general, in ionization type smoke detectors, when airborne dust adheres to and accumulates on the radiation source in the external ionization chamber, the amount of α-ray radiation gradually decreases, so it is treated as if smoke had entered the external ionization chamber. As a result, the sensitivity of the sensor changes,
Although it is not possible to always operate at a predetermined smoke density, by providing a memory circuit and its noise removal device similar to those in the embodiment of FIG. 2 as in this embodiment, the ionization type smoke detector can be The radiation source in the ion chamber is not hindered by the accumulation of dust on the radiation source, and can always operate at a predetermined smoke concentration, as in the case of Figure 2, and is also free from fluctuations in power supply voltage and interference from other equipment. The memory circuit can be prevented from being affected by noise such as induced surge voltage from the electric circuit.

As described above, the noise removal device for the memory circuit of an airborne foreign object detector according to this invention has a simple structure, and can be used to eliminate noise in the memory circuit of an airborne foreign object detector, which causes aging deterioration in the performance of the detection element such as a smoke detector. This has the effect that almost no noise contained in the output of the foreign object detection element to be stored in the storage circuit including the capacitor can be stored.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional transmitted light type smoke detector, Figures 2 to 4 are circuit diagrams of three embodiments of this invention, and Figures 5 a, b, and c.
, are characteristic line circuits of the embodiment shown in FIG. SB, CdS, CH...Smoke detection element, C2...
...Capacitor that stores the output of smoke detection elements, etc.
Tr: Transistor for discharging the charge of C2, C3: Coupling capacitor in the input circuit of Tr2, D3: Discharging time constant of C3 during charging. A diode to make it much larger than the constant.

Claims (1)

[Scope of utility model registration request] In a memory circuit equipped with a capacitor that stores the output of an airborne foreign object detection element, a transistor is connected in parallel with the above capacitor, and the noise in the above output is added to the input side of the above transistor through the coupling capacitor. At the same time, this is a noise removal device for a memory circuit of an airborne foreign object detector in which the discharging time constant of the coupling capacitor is much larger than the charging time constant.