JPH08122252A - Dust sensor - Google Patents

Abstract

PURPOSE: To measure the concentration of dust with high resolution over a wide range. CONSTITUTION: A light emitting element 1 is intermittently lighted, and a light receiving element 2 is arranged in a position on which direct light from the light emitting element 1 is not made incident. When dust enters a monitoring space in a sensor body, the quantity of receiving light of the light receiving element 2 increases by scattered light. Output voltage of an amplifying circuit 21 increases in a gradient according to the quantity of receiving light in the light receiving element 21 in a lighting period of the light emitting element 1, and decreases in a similar gradient in a lights-out period of the light emitting element 1. A comparator 22 puts output on an H level in a period during which the output voltage of the amplifying circuit 21 exceeds reference voltage, and measures a time width of this H level by a time counter 23, and outputs the output value according to the time width from the time counter 23. Since the quantity of receiving light in the light receiving element 21 is converted into time and is measured by the time counter, the concentration of dust can be detected with high resolution over a wide range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dust sensor for optically detecting fine particles (hereinafter referred to as dust) such as smoke and dust floating in a gas.

[0002]

2. Description of the Related Art Conventionally, as this type of dust sensor,
Dust is contained by the light receiving element that is installed at a position where the light emitting element continuously emits light into the monitoring space through which the gas (generally indoor air) to detect dust passes and does not receive direct light from the light emitting element. There is provided a device for detecting an increase in scattered light when the air to be passed passes through the surveillance space. The output of the light receiving element is converted from analog to digital, and the dust concentration is detected based on the converted digital value.

[0003]

In the above conventional structure, in order to increase the detection accuracy or resolution of dust concentration, it is necessary to use a high resolution converter for performing analog-digital conversion, resulting in a high resolution. When trying to manufacture a dust sensor with high resolution, there has been a problem that the manufacturing cost becomes too high. Further, since the light emitting element is continuously turned on, there is a problem that power consumption is large and it cannot be driven by using a battery power source.

The present invention is intended to solve the above-mentioned problems, and enables the concentration of dust to be measured in a wide range and with high resolution, while suppressing an increase in manufacturing cost and in a battery. An object of the present invention is to provide a dust sensor that consumes low power so that it can be driven.

[0005]

According to a first aspect of the present invention, there is provided a light emitting element for projecting light into a monitoring space in a sensor body through which gas passes, and a light emitting element arranged at a position where direct light from the light emitting element is not received. In the dust sensor that detects the presence of fine particles based on the increase in the amount of light received by the light receiving element when the gas containing fine particles passes through the monitoring space and the light receiving element that receives the light of The light-emission control circuit that causes the light-emitting element to emit light, the amplification circuit that increases the output with a gradient according to the amount of light received by the light-receiving element during the lighting period of the light-emitting element, and reduces the output when the light-emitting element goes out For a period of time exceeding a predetermined threshold, and a time unit for generating an output in multiple stages according to the time when the output of the comparing unit is activated for each light emission of the light emitting element. Characterized by comprising a pointer.

According to a second aspect of the present invention, a light emitting element for projecting light into the monitoring space in the sensor body through which gas passes, and a light receiving element for receiving light from the monitoring space which is arranged at a position where direct light from the light emitting element is not received. Element and a dust sensor that detects the presence of fine particles based on an increase in the amount of light received by the light receiving element when a gas containing fine particles passes through the monitoring space, a light emission control circuit that causes the light emitting element to intermittently emit light for a short time And an amplifier circuit that increases the output with a gradient according to the amount of light received by the light receiving element during the lighting period of the light emitting element and reduces the output when the light emitting element goes out, and the output of the amplifier circuit is a predetermined threshold value. The output of the comparing means is activated during the period exceeding the time, and the time period for generating the output in multiple stages corresponding to the time from the start of light emission to the activation of the output of the comparing means for each light emission of the light emitting element. Characterized by comprising a pointer.

According to a third aspect of the present invention, a gate is provided for passing a pulse signal for driving the light emitting element while the output of the comparison means is inactive, and the light emission of the light emitting element is stopped when the output of the comparison means becomes active. It is characterized by
The invention according to claim 4 is characterized in that the comparison means includes switching means for switching the threshold value in a plurality of steps.

According to a fifth aspect of the present invention, a light emitting element for projecting light into a monitoring space in the sensor body through which gas passes, and a light receiving element arranged at a position where direct light from the light emitting element is not received and receiving light from the monitoring space. Element and a dust sensor that detects the presence of fine particles based on an increase in the amount of light received by the light receiving element when a gas containing fine particles passes through the monitoring space, a light emission control circuit that causes the light emitting element to intermittently emit light for a short time And an amplifier circuit that increases the output with a gradient according to the amount of light received by the light receiving element from a specified value over time within each fixed time in the lighting period and the extinguishing period of the light emitting element, and the output of the amplifier circuit is a predetermined value. The comparing means that activates the output during the period in which the threshold is exceeded, and the output in multiple stages according to the time when the output of the comparing means is activated during the lighting period and the extinguishing period of the light emitting element, respectively. A time counter for raw, characterized by comprising a time difference calculating means obtains and outputs the difference between the output value of the time counter in the extinction period and the lighting period of the light emitting element.

[0009]

According to the structure of the invention of each claim, since the light emitting element is made to intermittently emit light for a short time, power consumption is greatly reduced as compared with the conventional structure in which the light emitting element is made to continuously emit light. If the light emission period and the light emission interval are appropriately set, the battery can be driven. Also, in the amplifier circuit, it is converted into a time function according to the amount of light received by the light receiving element, and output with a time width according to the amount of light received by the light receiving element according to the magnitude relationship between the output of this amplifier circuit and a predetermined threshold A comparing means for activating the light emitting element is provided, and the time when the output of the comparing means is activated for each light emission of the light emitting element or the time from the start of light emission until the output of the comparing means is activated is measured and a plurality of values are measured. Since the stepwise output is generated and the amount of light received by the light receiving element is converted into time, the concentration of fine particles can be detected without using an analog-digital conversion circuit, and the time measurement is relatively easy. Since it is possible to measure with high accuracy even with an inexpensive circuit configuration, it is possible to measure with high resolution. Further, since the amount of light received by the light receiving element is obtained by measuring the time, it is possible to set the measurement range of the concentration of fine particles in a wide range. In addition, since a digital circuit can be used for the comparison means and the time counter, a one-chip microcomputer can be realized, and the concentration of fine particles can be measured with high accuracy even with a relatively low-accuracy digital circuit.

According to the third aspect of the present invention, the time from the start of light emission of the light emitting element to the activation of the output of the comparison means is measured, and when the output of the comparison means becomes active, the light emission of the light emission element is stopped. Since the light emitting element is stopped, the light emitting period of the light emitting element can be shortened by a necessary and sufficient length, and as a result, the power consumption can be further reduced. According to the structure of the invention of claim 4, the comparison means is provided with the switching means for switching the threshold value in a plurality of steps, whereby the light receiving amount of the light receiving element when the output of the comparison means becomes active can be changed, As a result, the sensitivity can be switched. That is, the fine particle concentration can be detected in a wide range by changing the sensitivity.

According to the fifth aspect of the invention, in the case of detecting the particle concentration based on the amount of scattered light on the particles, it is possible to obtain the difference in the amount of light received between the lighting period and the extinguishing period of the light emitting element. The influence of ambient light incident on the light receiving element can be removed during the light-off period, which leads to improvement in detection accuracy.

[0012]

【Example】

(Embodiment 1) As shown in FIG. 1, the light emitting element 1 is driven by a light emission control circuit 10 so as to emit light intermittently. That is, the light-emission control circuit 10 generates a pulse signal that turns on for 5 milliseconds at 0.5 second intervals.
1 and a drive circuit 12 including a transistor Q,
By inputting a pulse signal to the base of the transistor Q, the light emitting element 1 formed of a light emitting diode connected to the collector of the transistor Q is intermittently turned on.

On the other hand, the light receiving element 2 is composed of a photodiode, and the voltage across the light receiving element 2 is amplified by an amplifier circuit 21 which is composed of a differential amplifier 21a and an integrating circuit 21b having a resistor R and a capacitor C. Therefore, the output voltage of the amplifier circuit 21 increases or decreases with a gradient according to the amount of light received by the light receiving element 2. In other words, during the period when the light receiving element 2 is receiving light, the amplification circuit 2 has a slope according to the amount of received light as time passes.
If the output voltage of 1 increases and then the light reception by the light receiving element 2 is stopped, the output voltage of the amplifier circuit 21 decreases with the passage of time with a similar gradient. The output of the amplifier circuit 21 is input to a comparator 22 as a comparing means and compared with a reference voltage (threshold value) set in advance by the resistors R ₁ and R ₂ . In the comparator 22, the amplifier circuit 21
The output is set to the H level (active) while the output voltage is higher than the reference voltage. The output of the comparator 22 is input to the time counter 23, and the time counter 23 measures the time during the period when the output of the comparator 22 is at H level. Here, the time counter 23 includes a pulse generation circuit 11
The pulse signal output from the light emitting element 1 is input, the time counter 23 is reset each time the light emitting element 1 starts emitting light (that is, when the pulse signal rises), and the output of the comparator 22 is at the H level each time the light emitting element 1 emits light. Is to measure the period. The time counter 23 has a 4-bit output and generates outputs in a plurality of stages according to the measurement result. That is, the time counter 23 can output up to 16 levels. The output of the time counter 23 is output to the outside through an output circuit 24 including a 4-bit buffer. Here, the comparator 22 can be replaced with an analog-digital converter and an appropriate program, and the time counter 23 can be replaced with an appropriate program, so that it can be realized by a digital circuit using a microcomputer. . In this sense, the comparator 22 and the time counter 23 are shown together in FIG. 1 as the arithmetic circuit 20.

By the way, the light emitting element 1 and the light receiving element 2
Are arranged in the sensor body 3 in such a positional relationship that direct light from the light emitting element 1 does not enter the light receiving element 2, as shown in FIG. In the sensor body 3, as shown in FIG.
A vent hole 31 is formed between both side surfaces so that air can pass therethrough, and the vent hole 31 communicates with a monitoring space provided inside the sensor body 3. Here, air flowing in one direction is vented to the vent holes 31 as indicated by an arrow in FIG. The light emitting element 1 projects a substantially parallel light flux 5 into the monitoring space through the light projecting lens 4 as a collimating lens as shown in FIG. 3, and the light receiving element 2 collects scattered light generated when dust enters the monitoring space. It is placed at a position where it can receive light.

When the light emitting element 1 is driven by the pulse signal as shown in FIG. 2A, the voltage at one end of the light receiving element 2 changes as shown in FIG. The output voltage is as shown in FIG. One end of the light receiving element 2 is maintained at a substantially constant voltage even when dust is not present, and when scattered light is received due to the presence of dust in the monitoring space, the amplifier circuit 21 as shown in FIG.
The output voltage of 1 increases gradually with the passage of time during the light emission period of the light emitting element 1 with a gradient according to the amount of light received by the light receiving element 2, and gradually decreases with the passage of time as the light emitting element 1 is turned off. That is, as the dust concentration is high and the scattered light is large (shown at the right end of FIG. 2), the output level of the amplifier circuit 21 is high. Therefore, by setting an appropriate threshold value Vref in the comparator 22, Figure 2
As shown in (d), the period in which the output of the comparator 22 is at the H level can be associated with the dust concentration. More specifically, as shown in FIG. 5, as the dust concentration increases and the peak value of the output of the amplifier circuit 21 increases, the period higher than the threshold value Vref becomes longer, and this time width τ Assuming that the output voltage of the amplifier circuit 21 is V ₂₁ , as shown in FIG. 6, τ = 0.0048681 +0.
It can be expressed by the relationship of log (V ₂₁ −3.0) (here, 3.0 is the output voltage of the amplifier circuit 21 in the absence of dust). The time counter 23 generates a plurality of stages of output according to the ON period of the comparator 22, and here the ON period of the comparator 22 is 0 second, 0.005 milliseconds, and 0.015 milliseconds. The three stages of output corresponding to the case are shown. The output of the time counter 23 is held until the output for the next pulse signal for driving the light emitting element 1 is obtained.

As described above, since the dust concentration is replaced with time, the concentration detection accuracy depends on the time measurement accuracy. Further, the concentration measurement range can be set in any range within the time measurement range, and thus can be set in a wide range. Moreover, as described above, since the time width τ is logarithmically compressed, the change rate of the time width τ is large on the low concentration side, and the change rate of the time width τ is small on the high concentration side. , This increases the dynamic range. Since the light emitting element 1 emits light intermittently, it consumes less power and can be driven by a battery. Light emitting interval of light emitting element 1, light emitting period, time counter 2
The output stage and the like in 3 are not limited to the above-mentioned values, and can be appropriately set according to the response speed, the detection sensitivity, and the like.

(Embodiment 2) In this embodiment, as shown in FIG. 7, a gate 25 is inserted between a comparator 22 and a time counter 23. This gate 25 negates the output of the comparator 22. And a pulse signal for driving the light emitting element 1 are output. Therefore, FIG.
As can be seen by comparing (a), (d), and (e), from the rise of the pulse signal (FIG. 8 (a)) driving the light emitting element 1 to the rise of the output of the comparator 22 (FIG. 8 (d)). The output of the gate 25 (Fig. 8 (e)) is H during the period
Become a level. That is, as shown in FIG. 9, the higher the concentration of dust flowing into the monitoring space (the higher the peak value of the output voltage V ₂₁ of the amplifier circuit 21), the higher the output of the gate 25 becomes.
The period to reach the level becomes shorter. As shown in FIG. 10, when the time width is τ, this relationship is τ = 0.0062791 · (V
₂₁ −3.0) ^-1.1439 . FIG. 8B
Similar to FIGS. 2B and 2C, FIG. 2C shows the potential at one end of the light receiving element 2 and the output voltage of the amplifier circuit 21. Here, the output of the time counter 23 becomes smaller as the period during which the signal intermittently output from the gate 25 is at H level is shorter as shown in FIG. 8 (f). That is,
In FIG. 8, the output of the time counter 23 is set in three stages, and if dust is not present, an output corresponding to 0.016 milliseconds is generated, and 0.0025 milliseconds, 0. The output of each step of 0005 milliseconds is generated.
Other configurations and operations are the same as those of the first embodiment.

(Embodiment 3) In this embodiment, as shown in FIG. 11, a gate 13 is added between the pulse generation circuit 11 and the drive circuit 12 in addition to the structure of the embodiment 2. The gate 13 outputs the logical product of the negation of the comparator 22 and the pulse signal output from the pulse generation circuit 11, and the output of the gate 13 is the gate 25.
Similarly to the output of, the output goes to the H level during the period from the rise of the pulse signal to the rise of the output of the comparator 22. That is, the output of the gate 25 is at the H level only during the period from the start of lighting of the light emitting element 1 to the output of the comparator 22 being at the H level.
Since the light is turned on, as the output of the pulse generation circuit 11 shown in FIG. 12A is compared with the turned on / off state of the light emitting element 1 shown in FIG. 12B, the higher the dust concentration is, the light is emitted. Since the amount of light emitted once from the element 1 is reduced, the dynamic range on the light receiving side can be reduced. 12C to 12G show the terminal voltage of the light receiving element 2, the output voltage of the amplifier circuit 21, the output of the comparator 22, the output of the gate 25, and the output of the time counter 23, respectively. The operation is the same as that of the second embodiment except that the period changes according to the dust concentration.

(Embodiment 4) In the present embodiment, as shown in FIG. 13, with respect to the structure of the embodiment 2, a resistor R _{2 is} used as a switching means for switching the reference voltage of the comparator 22 in two steps.
An example in which a resistor R ₃ is connected in series with and a switch SW is connected in parallel with the resistor R ₃ is shown. The other configuration is the second embodiment.
Is the same as However, the time counter 23 is configured to output an output value corresponding to a longer time as the period during which the input signal is at the H level is shorter. Instead of using the time counter 23 having such a configuration, the gate 25
If omitted, it is possible to use the time counter 23 that operates in the same manner as in the first embodiment.

As described above, by switching the reference voltage of the comparator 22 between the two stages Vref ₁ and Vref ₂ (Vref ₁ > Vref ₂ , for example, Vref ₁ = 3.6V and Vref ₂ 3.2V), FIG. It can be operated as shown in. That is, when the switch SW is turned off, the higher reference voltage Vref ₁ is set, so the output of the comparator 22 does not become the H level unless the output voltage of the amplifier circuit 21 is high, and the dust concentration with respect to the dust concentration is increased. Becomes less sensitive. That is, the terminal voltage of the light receiving element 2 and the amplifier circuit 22 when the light emitting element 1 emits light as shown in FIG.
The output voltage of each is as shown in FIGS. 14 (b) and (c).
Although it depends only on the dust concentration regardless of whether the switch SW is turned on or off, when the switch SW is turned on, the lower reference voltage Vref ₂ is selected as shown in FIG. 14C. In other words, if the dust concentrations are equal, turning on the switch SW causes the output of the comparator 22 to be at the H level for a longer period as shown in FIG. 14D, so that the sensitivity is set to be substantially high. become. FIG.
In the example shown in FIG. 4 (e), the output of the time counter 23 is 0.0 when the switch SW is off for the same dust concentration.
The output value corresponds to 05 milliseconds, and when the switch SW is on, the output value corresponds to 0.0125 milliseconds.
That is, as shown in FIG. 15, even if the peak value of the output voltage of the amplifier circuit 21 is the same (that is, even if the dust concentration is the same), if the reference voltages Vref ₁ and Vref ₂ change, the output of the comparator 22 The time width τ at which the H level changes to H changes, the time width becomes long at high sensitivity and becomes short at low sensitivity. The relationship between the output voltage of the amplifier circuit 21 and the time width τ is as shown in FIG. 16, and τ = 0.0091235 +0.0141 at high sensitivity.
366 log (V ₂₁ -3.0), τ = 0.00079059 + 0 at low sensitivity.
Can be expressed as _{018745 · log (V 21 -3.0)} .

With such a structure, it is possible to set the sensitivity to low in the initial state and switch to high sensitivity when the presence of dust is not detected at the low sensitivity. Especially,
If a suitable switching element is provided as the switch SW and ON / OFF of the switching element is determined according to the output of the output circuit 24, switching between low sensitivity and high sensitivity is automated,
A wide range of dust concentration can be detected with auto range. It is also possible to replace the switch SW for switching the sensitivity with a port of a microcomputer and control it with an appropriate program.

The gates shown in Examples 2 to 4 may be implemented by appropriate programs. (Embodiment 5) In this embodiment, in order to eliminate the influence of the internal reflection of the sensor body 3 and the disturbance light incident through the ventilation hole 31, the amount of light received by the light receiving element 2 in the light-off period of the light emitting element 1 is adjusted. The difference between the time width and the time width corresponding to the amount of light received by the light receiving element 2 in the lighting period of the light emitting element 1 is output.

That is, as shown in FIG. 17, the JK of the integrated circuit is provided between the pulse generating circuit 11 and the driving circuit 12.
Flip-flop 1 constructed using flip-flops
4 and two AND circuits 15 for outputting a logical product of each output of the flip-flop 14 and the output of the pulse generation circuit 11.
a and 15b are provided, and the output of one AND circuit 15a is given to the drive circuit 12. The output of the flip-flop 14 is inverted every cycle of the pulse signal, and the AND circuits 15a and 15b output the logical product of each output of the flip-flop 14 and the pulse signal. As a result, each AND circuit 15a. , 15b alternately set the output to the H level for each cycle of the pulse signal. The period in which the outputs of the AND circuits 15a and 15b are at the H level matches the period in which the pulse signal is at the H level. Therefore, by inputting the output of the AND circuit 15a to the drive circuit 12, the light emitting element 1 is set to 1 every two cycles of the pulse signal.
It will light up at the rate of once. Here, in the present embodiment, the pulse generation circuit 11 will be described as outputting a pulse signal having a duty ratio of approximately 50% (see FIG. 18).
(C) shows an output of an inversion circuit 21c described later, which is a signal obtained by inverting a pulse signal.) As in each of the above-described embodiments, the light emitting element 1 is lit for 5 milliseconds at a 0.5 second cycle. If the pulse signal is set to 5
The signal may be an H level only for milliseconds.

The outputs of the AND circuits 15a and 15b are input as clock signals to the latch circuits 26a and 26b formed by using D flip-flops, respectively. The latch circuits 26a and 26b latch the output of the time counter 23 at the falling edge of the clock signal. Further, the outputs of both latch circuits 26a and 26b are input to the subtraction circuit 27 at appropriate timings (every time the outputs of the time counter 23 are latched by the respective latch circuits 26a and 26b) and latched from the output value of the latch circuit 26a. The output value of the circuit 26b is subtracted, and this output value is output to the outside through the output circuit 24. Since the time counter 23 is reset each time the pulse signal from the pulse generation circuit 11 rises, the output value of the time counter 23 corresponding to the lighting period of the light emitting element 1 is latched in the latch circuit 26a.
In b, a time counter 2 corresponding to the extinguishing period of the light emitting element 1
The output value of 3 will be latched. That is, the output of the subtraction circuit 27 is the time counter 2 of the lighting period of the light emitting element 1.
From the output value of 3, the time counter 2 of the extinguishing period of the light emitting element 1
It becomes a value obtained by subtracting the output value of 3 from the latch circuit 26a, 2
The time difference calculating means is composed of 6b and the subtraction circuit 27.

In the amplifier circuit 21, the capacitor C of the integrating circuit 21b is connected to the transistor Q ₁ as a switching element.
The collector - the series circuit of the emitter and the DC power source are connected in parallel, the transistor Q ₁ is the pulse generating circuit 1
It is driven by the output of the inverting circuit 21c which inverts the output of 1. Therefore, the transistor Q ₁ is turned on when the time counter 23 is reset, and the terminal voltage of the capacitor C is set to the power source voltage of the DC power source DC.
When the time counter 23 is reset, the output value of the amplifier circuit 21 is set to a constant value (that is, the dust is not present),
The arithmetic circuit 20 including the comparator 22 and the time counter 23 is always operated under the same condition to improve the measurement accuracy. Further, since the transistor Q ₁ is turned on while the pulse signal is at the L level, the comparator 22
The time width τ of the output of 1 corresponds to only the charging time of the capacitor C.

Other configurations and operations are the same as those of the first embodiment. As shown in FIG. 18A, the light emitting element 1 is intermittently turned on, and the light receiving element 2 is turned on as shown in FIG. 18B. The terminal voltage is constant if dust is not present in the monitoring space in the sensor body 3, and increases if dust is present in accordance with its concentration. FIG. 18C shows the output of the inverting circuit 28, which inverts the pulse signal output from the pulse generating circuit 11, and the capacitor C provided in the amplifier circuit 21 is reset at each rising edge of the pulse signal. Become. Now, due to ambient light and signal leakage inside the circuit, the amplifier circuit 21
18D, the output voltage of the amplifier circuit 21 may exceed the reference voltage Vref set in the comparator 22 even when the light emitting element 1 is turned off. That is, the output of the comparator 22 is as shown in FIG.
As shown in (e), the light emitting element 1 is generated every time a pulse signal is generated.
In the lighting period and the extinguishing period, pulses having a time width of a period in which the output voltage of the amplifier circuit 21 exceeds the reference voltage Vref are alternately output. The time counter 23 measures the time width in which the output of the comparator 23 is at the H level each time a pulse signal is generated, and generates an output value according to the measured value. That is, the output value of the time width according to each of the light emission period and the light extinction period of the light emitting element 1 is generated. Here, the time counter 23 is configured to generate a larger output value as the time width of the pulse output from the comparator 22 is longer.

Then, each latch circuit 26a, 26b
Respectively latch the values as shown in FIGS. 18F and 18G, and the value latched by the latch circuit 26b becomes the output value of the time counter 23 when the light emitting element 1 is turned off.
Therefore, if the output value of the latch circuit 26b is subtracted from the output value of the latch circuit 26a in the subtraction circuit 27, the result shown in FIG.
As shown in (h), it is possible to obtain the output value from which the noise component is removed during the extinguishing period of the light emitting element 1. As a result, it is possible to increase the degree of coincidence between the dust concentration and the output value by removing the effects of ambient light and signal leakage from internal circuits.

In this embodiment, the output values of the time counter 23 are temporarily held by the latch circuits 26a and 26b for both the lighting period and the extinguishing period of the light emitting element 1, but only one of them is latched. Alternatively, the subtraction circuit 27 may obtain the difference between the value latched in the latch circuit and the output value of the time counter 23 each time the other is obtained by the time counter 23.

[0029]

As described above, according to the inventions of the claims, since the light emitting element is made to intermittently emit light for a short time, the power consumption is much larger than that of the conventional configuration in which the light emitting element is made to continuously emit light. It has an advantage that it can be reduced to a certain level, and has an effect that it can be driven by a battery by appropriately setting the light emitting period and the light emitting interval. Also, in the amplifier circuit, it is converted into a time function according to the amount of light received by the light receiving element, and output with a time width according to the amount of light received by the light receiving element according to the magnitude relationship between the output of this amplifier circuit and a predetermined threshold value. A comparing means for activating the light emitting element is provided, and the time when the output of the comparing means is activated for each light emission of the light emitting element or the time from the start of light emission until the output of the comparing means is activated is measured and a plurality of values are measured. Since the stepwise output is generated and the amount of light received by the light receiving element is converted into time, the concentration of fine particles can be detected without using an analog-digital conversion circuit, and the time measurement is relatively easy. Since the measurement can be performed with high accuracy even with an inexpensive circuit configuration, there is an advantage that high-resolution measurement can be performed. Further, since the amount of light received by the light receiving element is obtained by measuring the time, there is also an advantage that the measurement range of the concentration of fine particles can be set in a wide range. In addition, since a digital circuit can be used for the comparison means and the time counter, it is possible to realize a one-chip microcomputer, and moreover, it is possible to measure the concentration of fine particles with high accuracy even with a relatively low-accuracy digital circuit. There is.

According to the third aspect of the present invention, in measuring the time from the start of light emission of the light emitting element until the output of the comparison means becomes active, the light emission of the light emitting element is stopped when the output of the comparison means becomes active. This has an advantage that the light emitting period of the light emitting element can be shortened by a necessary and sufficient length, and as a result, the power consumption can be further reduced.

According to the invention of claim 4, the comparison means is provided with the switching means for switching the threshold value in a plurality of steps, whereby the light receiving amount of the light receiving element when the output of the comparison means becomes active can be changed. The sensitivity can be switched selectively. That is, there is an advantage that the particle concentration can be detected in a wide range by changing the sensitivity. According to the invention of claim 5, in which the concentration of the fine particles is detected based on the amount of scattered light in the fine particles, the difference in the amount of received light between the lighting period and the extinguishing period of the light emitting element can be obtained. There is an advantage that the influence of incident ambient light can be removed and the detection accuracy can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment.

FIG. 2 is an operation explanatory diagram showing signals of respective parts of the circuit shown in FIG.

FIG. 3 is a schematic configuration diagram of a first embodiment.

FIG. 4 is an external perspective view of the first embodiment.

FIG. 5 is an operation explanatory diagram showing an input / output relationship of the comparator in the first embodiment.

FIG. 6 is an operation explanatory diagram showing the relationship between the output voltage of the amplifier circuit and the output of the comparator in the first embodiment.

FIG. 7 is a circuit diagram showing a second embodiment.

8 is an operation explanatory diagram showing signals of respective parts of the circuit shown in FIG. 7. FIG.

FIG. 9 is an operation explanatory diagram showing an input / output relationship of a comparator in the second embodiment.

FIG. 10 is an operation explanatory diagram showing the relationship between the output voltage of the amplifier circuit and the output of the comparator in the first embodiment.

FIG. 11 is a circuit diagram showing a third embodiment.

12 is an operation explanatory diagram showing signals of respective parts of the circuit shown in FIG. 11. FIG.

FIG. 13 is a circuit diagram showing a fourth embodiment.

FIG. 14 is an operation explanatory diagram showing signals of respective parts of the circuit shown in FIG. 13;

FIG. 15 is an operation explanatory diagram showing an input / output relationship of a comparator in the fourth embodiment.

FIG. 16 is an operation explanatory diagram showing the relationship between the output voltage of the amplifier circuit and the output of the comparator in the fourth embodiment.

FIG. 17 is a circuit diagram showing a fifth embodiment.

FIG. 18 is an operation explanatory diagram showing signals of respective parts of the circuit shown in FIG. 17;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 light emitting element 2 light receiving element 10 light emission control circuit 11 pulse generating circuit 12 drive circuit 13 gate 14 flip-flop 15a AND circuit 15b AND circuit 20 arithmetic circuit 21 amplifier circuit 22 comparator 23 time counter 24 output circuit 25 gate 26a latch circuit 26b latch circuit 27 Subtraction circuit R ₁ resistance R ₂ resistance R ₃ resistance SW switch

Claims (5)

[Claims] 1. A light emitting element for projecting light into a monitoring space in a sensor body through which gas passes, a light receiving element for receiving light from the monitoring space which is arranged at a position where direct light from the light emitting element is not received, and a monitoring space. In a dust sensor that detects the presence of fine particles based on an increase in the amount of light received by the light receiving element when a gas containing fine particles passes through, a light emission control circuit that causes the light emitting element to emit light intermittently for a short time, and An amplifier circuit that increases the output with a slope according to the amount of light received by the light receiving element during the lighting period and reduces the output when the light emitting element goes out, and outputs during the period when the output of the amplifier circuit exceeds a predetermined threshold value. And a time counter for generating an output of a plurality of stages according to the time when the output of the comparison means is activated for each light emission of the light emitting element. Dust sensor. 2. A light emitting element for projecting light into a monitoring space in a sensor body through which gas passes, a light receiving element for receiving light from the monitoring space which is arranged at a position where direct light from the light emitting element is not received, and a monitoring space. In a dust sensor that detects the presence of fine particles based on an increase in the amount of light received by the light receiving element when a gas containing fine particles passes through, a light emission control circuit that causes the light emitting element to emit light intermittently for a short time, and An amplifier circuit that increases the output with a gradient according to the amount of light received by the light receiving element during the lighting period and reduces the output when the light emitting element goes out, and outputs during the period when the output of the amplifier circuit exceeds a predetermined threshold value. And a time counter for generating a plurality of stages of output corresponding to the time from the start of light emission to the activation of the output of the comparison means for each light emission of the light emitting element. A dust sensor characterized in that. 3. A gate for passing a pulse signal for driving the light emitting element is provided while the output of the comparison means is inactive, and the light emission of the light emitting element is stopped when the output of the comparison means becomes active. The dust sensor according to claim 2. 4. The dust sensor according to claim 1, wherein the comparison means includes switching means for switching the threshold value in a plurality of steps. 5. A light emitting element for projecting light into a monitoring space inside a sensor body through which gas passes, a light receiving element for receiving light from the monitoring space which is arranged at a position where direct light from the light emitting element is not received, and a monitoring space. In a dust sensor that detects the presence of fine particles based on an increase in the amount of light received by the light receiving element when a gas containing fine particles passes through, a light emission control circuit that causes the light emitting element to emit light intermittently for a short time, and An amplifier circuit that increases the output with a slope according to the amount of light received by the light receiving element from a specified value over time within each fixed time in the lighting period and the extinguishing period, and the output of the amplifier circuit exceeds a predetermined threshold value. The comparison means that activates the output during the period, and the time counter that generates the output in a plurality of stages according to the time when the output of the comparison means is activated during the lighting period and the extinguishing period of the light emitting element, respectively. And a time difference calculating means for calculating and outputting a difference between respective output values of the time counter in the lighting period and the extinguishing period of the light emitting element.