JP3484781B2 - Dust sensor - Google Patents

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, and the output of the amplification circuit There comparing means to activate the output period exceeding a predetermined threshold, or the emission start to the light emission for each of the light emitting element
And a time counter for generating outputs in a plurality of stages according to the time until the output of the comparing means becomes active.

[0006]

According to a second 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 comparing means is inactive, and the light emission of the light emitting element is stopped when the output of the comparing means becomes active. It is characterized by The invention according to claim 3 is characterized in that the comparing means includes a switching means for switching the threshold value in a plurality of steps.

According to a fourth 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 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 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 first aspect of the present invention, since the light emitting element is made to intermittently emit light for a short period of time, the 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 value. the provided comparing means to activate, it is to generate an output of a plurality of stages in which the output of the comparator means from emitting light beginning each emission corresponding to the measured value by measuring the time until the active light emitting element, the light receiving Since the amount of light received by the device is converted into time, the concentration of fine particles can be detected without using an analog-digital conversion circuit, and time measurement can be performed with high accuracy even with a relatively inexpensive circuit configuration. Therefore, high resolution measurement becomes possible. 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 second aspect of the present invention, in the method for measuring the time from the start of light emission of the light emitting element to the activation of the output of the comparison means, when the output of the comparison means becomes active, the light emission of the light emission element is turned on. 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. Claim
According to the configuration of the invention of Item 3 , since the comparison means is provided with the switching means for switching the threshold value in a plurality of stages, it is possible to change the amount of light received by the light receiving element when the output of the comparison means becomes active. The sensitivity can be switched selectively. That is, the fine particle concentration can be detected in a wide range by changing the sensitivity.

According to the structure of the fourth aspect of the invention, in the case of detecting the particle concentration based on the scattered light amount of the particles, the difference in the amount of light received between the lighting period and the extinguishing period of the light emitting element can be obtained. 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]

EXAMPLES ( Reference Example ) As shown in FIG. 1, a 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 includes a pulse generation circuit 11 that generates a pulse signal that is turned on for 5 milliseconds at a cycle of 0.5 seconds, and a drive circuit 12 that includes a transistor Q, and the pulse signal is provided at the base of the transistor Q. By inputting, the light emitting element 1 including 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 emits 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 1 ) 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, as can be seen by comparing FIGS. 8A, 8D, and 8E, the output of the comparator 22 (FIG. 8D) changes from the rise of the pulse signal (FIG. 8A) that drives the light emitting element 1. 8), the output of the gate 25 (FIG. 8E) becomes H 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 shorter the period in which the output of the gate 25 is at the H level. As shown in FIG. 10, when the time width is τ, this relationship is τ = 0.0062791 · (V ₂₁ −3.0)
It can be expressed as ^-1.1439 . Figure 8 (b)
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 similar to those of the reference example .

[0018] (Example 2) This example, as shown in FIG. 11, the configuration of the first embodiment has a configuration obtained by adding a gate 13 between the pulse generating circuit 11 and the driving circuit 12. The gate 13 outputs a logical product of the negation of the comparator 22 and the pulse signal output from the pulse generation circuit 11. The output of the gate 13 is similar to the output of the gate 25 from the rising edge of the pulse signal. The H level is reached during the period until the output of the comparator 22 rises. 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 and the light emitting element 1 is illuminated during this period.
The output of the pulse generation circuit 11 shown in FIG.
As can be seen by comparing the light-on / off state of the light-emitting element 1 shown in (4), the higher the dust concentration is, the smaller the light emission amount of the light-emitting element 1 at one time is. It can be reduced. Figure 1
2 (c) to (g) are terminal voltages of the light receiving element 2,
Same as the first embodiment , except for 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, and the light emitting period of the light emitting element 1 changes according to the concentration of dust. It works.

( Third Embodiment ) As shown in FIG. 13, in the present embodiment, with respect to the configuration of the first embodiment , a resistor R ₃ is connected in series with a resistor R ₂ as a switching unit that switches the reference voltage of the comparator 22 in two stages. An example in which a switch SW is connected in parallel to the resistor R ₃ is shown. Other configurations are similar to those of the first embodiment . 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. Omitting the gate 25 instead of using the time counter 23 having such a configuration, reference
It is also possible to use the time counter 23 which operates similarly to the example .

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. That is, if the dust concentrations are equal, turning on the switch SW causes a longer period in which the output of the comparator 22 is at the H level as shown in FIG. 14D, and therefore the sensitivity is set to be substantially high. become. Figure 1
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 the first to third embodiments may be realized by appropriate programs. ( Example 4 ) In this example, in order to remove 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 during the extinguishing period of the light emitting element 1 was used. 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 similar to those of the reference example . As shown in FIG. 18A, the light emitting element 1 is intermittently turned on, and as shown in FIG. The 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 first aspect of the present invention, the light emitting element is made to intermittently emit light for a short period of time, so that the power consumption is greatly increased as compared with 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. the provided comparing means to activate, it is to generate an output of a plurality of stages in which the output of the comparator means from emitting light beginning each emission corresponding to the measured value by measuring the time until the active light emitting element, the light receiving Since the amount of light received by the element is converted into time, without using an analog-digital conversion circuit,
Since the concentration of fine particles can be detected, and time measurement can be performed with high accuracy even with a relatively inexpensive circuit configuration, there is an advantage that high resolution measurement is possible. Furthermore, 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 the 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 a second 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 a third aspect of the present invention, the comparison means includes a switching means for switching the threshold value in a plurality of steps.
The amount of light received by the light receiving element when the output of the comparison means becomes active can be changed, and as a result, the sensitivity can be switched. 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 4 , in which the concentration of 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 reference example .

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 reference example .

FIG. 4 is an external perspective view of a reference example .

FIG. 5 is an operation explanatory diagram showing an input / output relationship of a comparator in the reference example .

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 reference example .

FIG. 7 is a circuit diagram showing a first 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 the input / output relationship of the comparator in the first 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 second 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 third 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 third 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 third embodiment .

FIG. 17 is a circuit diagram showing a fourth 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 generation 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

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 PATOLIS

Claims (4)

(57) [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. comparison means to activate the output of the comparator means from the emission start for each emission of the light emitting device I activated
A dust sensor, comprising: a time counter that generates a plurality of stages of output according to the time until the dust sensor reaches . 2. The output of the comparing means is in the inactive period.
A gate that passes the pulse signal for driving the light emitting element
When the output of the comparison means becomes active,
The dust sensor according to claim 1, wherein light emission is stopped . 3. The comparing means switches the threshold value in a plurality of steps.
2. The dust sensor according to claim 1, further comprising a switching means for adjusting the dust sensor. 4. A monitoring space within the sensor body through which gas passes.
The light-emitting element that emits light to the
A light receiving element that is placed in a position that does not receive light from the monitoring space
Of the child and the gas when the gas containing fine particles passes through the monitoring space.
Detection of the presence of fine particles based on the increase in the amount of light received by the optical element
In the dust sensor, the light emitting element is intermittently
Light emission control circuit for selectively emitting light, and the lighting period of the light emitting element
Amount of light received by the light receiving element within each fixed time during the off period
The output increases with time from the specified value with a gradient according to
The amplification circuit to increase and the output of the amplification circuit is a predetermined threshold
Comparison means that activates the output for a period exceeding
The comparison means is output during the lighting period and the extinguishing period of the optical element.
Output in multiple stages depending on the time when the force is activated
Occurrence time counter, light emitting element lighting period and extinguishing period
Output by calculating the difference between each output value of the time counter between and
Dasutosen service, characterized by comprising a time difference calculating means for.