JPH0573608B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a smoke detector for a vehicle, and is used to detect cigarette smoke or the like in a vehicle interior and activate an air purifier or the like.

[Conventional technology]

Conventionally, various methods have been used for smoke detection, one of which is to compare the output signal corresponding to the light scattered by smoke with the output of an integrator that obtains the average value of the output signal, and based on the comparison result. Some output detection signals.

[Problem that the invention seeks to solve]

However, this method requires a long time after the power is turned on until the integrator capacitor is charged and the average value is obtained. However, under conditions of use where the power is frequently turned on and off, such as in automobile smoke detectors, there is a problem in that smoke cannot be detected for several minutes after the power is turned on. Therefore, in view of the above problems, the present invention has been made to
The purpose is to obtain an average value immediately after power is turned on.

[Means for solving problems]

Therefore, the present invention is characterized in that it includes a means for immediately charging the capacitor of the integrator with a time constant shorter than the time constant of the integrator, and at the same time making the integrator output match the received light output signal. shall be.

〔Effect of the invention〕

According to the present invention, even if the key switch of the automobile is frequently turned on and off, the average value is maintained at the latest received light output signal each time the key switch is turned on, so that accurate smoke detection can be performed while the key switch is turned on. I can do it.

〔Example〕

In FIG. 1, 6 is a light emitting element, 7 is a switching device, 8 is a pulse oscillator for light emission, 11 is an amplifier,
12 is a sample hold circuit, 4 is an integrating resistor,
3 is an integrating capacitor that forms an integrator with resistor 4;
13 is a differential amplifier, and 14 is a comparator. 5 is a diode for instantaneous charging. FIG. 2 shows an operating time chart of the circuit of FIG. 1 after power is turned on. O indicates the output of the light receiving element 10, output P at point a in FIG. 1 is the output from the sample and hold circuit 12, and R indicates the output at point e in FIG. 1, respectively.

In the above configuration, the light emitting element 6 is pulse-driven by the pulse oscillator 8 and the switching element 7. The light receiving element 10 outputs an output corresponding to the magnitude of the light scattered by the smoke to the point a. This output is amplifier 1
1 and the sample-and-hold circuit 12 convert the received light output signal into a DC power supply voltage and output it to point d. An integrator constituted by a resistor 4 and a capacitor 3 creates an average value of the DC voltage corresponding to the smoke density at point d. By making the time constant of this integrator longer than the increase in smoke concentration due to cigarette smoking, etc.,
An output difference occurs between the outputs at the four points and the average value at point e, making it possible to detect the presence of smoke.

FIG. 2 shows the operation of this circuit when the power is turned on.
The output at point d is the value of P, and if the circuit does not include diode 5, the output at point e of the integrator is the value of P.
However, by providing the diode 5, it is instantly charged and becomes a curve R, which becomes the same as the voltage at point d in a short time. As a result, even when the output O of the light receiving element increases due to smoking, etc. immediately after the power is turned on, the output P at point d is
The output R of the integrator is exceeded, and smoke can be detected. Note that the time constant at this time is determined by the capacitor 3 and resistor 4 since the potential at point d is higher than the potential at point e and no current flows through diode 5, and there is no problem with detectability.

In the above embodiment, the diode 5 was used as a means for rapidly charging the capacitor of the integrator, but other methods may be used. For example, in the example shown in Figure 3, in order to eliminate the forward voltage of the diode,
An operational amplifier 16 is used, and in the example shown in FIG.
and a switch element 18 which is made conductive by its output.
Instant charging is now possible.

Instead of a diode, as in this example,
By using the switch element 18, even if the light receiving output signal at point d drops momentarily due to noise etc. other than when the key switch is turned on, the switch element 18 only operates immediately after the key switch is turned on. The integrator output does not change in response to noise.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram showing one embodiment, FIG. 2 is an operation time chart of the same embodiment, and FIGS. 3 and 4 are electrical wiring diagrams showing modified embodiments. 3... Integrating capacitor, 4... Integrating resistor,
5... Instantaneous charging diode, 10... Light receiving element, 11... Amplifier, 12... Sample hold circuit, 13... Differential amplifier, 14... Comparator, 1
6... operational amplifier, 18... switch element.

Claims (1)

[Scope of Claims] 1. A light-receiving element that generates an output signal corresponding to the magnitude of light scattered by smoke, an integrating means including a capacitor that obtains an average value of this output signal, and each output of the light-receiving element and the integrating means. and a comparison means for outputting a smoke detection signal based on the comparison result, and charging a capacitor of the integrating means with a time constant shorter than a time constant of the integrating means at the same time as the power is turned on, and instantly changing the output of the integrating means to the above. A smoke detector for a vehicle, comprising means for matching a received light output signal.