JPH08261932A - Fine grain detecting sensor - Google Patents

Abstract

PURPOSE: To reduce the power consumption of an LD, prolong its life, and expand the dynamic range of a fine grain detecting sensor. CONSTITUTION: An LD light emitting circuit 2 is provided with an analog multiplexer MP having multiple switches and resistors R7 , R8 , R9 , R10 connected to the switches. The resistor R7 is connected at the time of high sensitivity setting to keep the emitted light quantity of an LD1 constant. As sensitivity is reduced, the resistors R8 , R9 , R10 having higher resistance values are connected based on the signal from a control circuit, and the driving current of the LD1 is reduced to reduce the emitted light quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric type particle detection sensor for detecting particles such as smoke generated during a fire or dust contained in the air, and particularly to reduce the drive current of the light source when the alarm level is set to low sensitivity. The present invention relates to a fine particle detection sensor that reduces the power consumption and the life of a light source by reducing the amount of emitted light and expands the dynamic range of the sensor.

[0002]

2. Description of the Related Art Generally, a fine particle detection sensor such as a smoke sensor or a dust monitor with high sensitivity detects a particle by irradiating a detection area with light and receiving scattered light from the particle present in the detection area. are doing. A laser diode (LD), a light emitting diode (LED), a xenon lamp, etc. are generally used as the light source.

In a fine particle detection sensor using, for example, an LD as a light source, in order to detect fine particles with high sensitivity, a high S / N optical system is required, and high resolution (that is, fine particle concentration-sensor output characteristic slope is steep). It is common to choose To realize such high-sensitivity detection, the amount of light emitted from the LD is increased to increase scattered light,
Alternatively, the gain of the amplifier is increased to increase the sensor output (voltage).

However, the alarm level, that is, the set value for increasing the number of particles and the occurrence of a fire is generally changed depending on the installation location of the sensor, and is determined by the environmental conditions. That is, the alarm level is set to high sensitivity in a very clean place, but is set to a lower sensitivity than the above-mentioned sensitivity (high sensitivity) in a place where a certain amount of fine particles constantly flow in.

Generally, when such a sensitivity changing method is performed in a sensor, an alarm judgment is made by comparing a value obtained by amplifying received scattered light with an alarm level, and the sensitivity is changed by changing the alarm level. Had been changed. That is, the sensitivity is changed by changing the reference level of the comparator. Further, even when the sensitivity is changed by a receiving device such as a fire receiver connected to the particle detection sensor, the comparator also makes an alarm judgment when the sensor output is received.

[0006]

As described above, since the conventional fine particle detection sensor is constructed for the purpose of high sensitivity detection, the amount of light emitted from the LD is still sufficiently large even if the sensitivity is changed to low sensitivity. Therefore, there is a problem that the driving current of the LD is large and the life of the LD is shortened. Therefore, the present invention has been made to solve such problems,
The objective is to obtain a particle detection sensor that reduces the power consumption and the life of the light source by reducing the drive current of the light source and reducing the amount of unnecessary light emission without changing the alarm level when low sensitivity is set. . Another object of the present invention is to expand the dynamic range of the sensor.

[0007]

A particle detection sensor according to claim 1 of the present invention comprises at least one light source, a light-emitting circuit electrically connected to the light source, and causing the light source to emit light. Light-receiving means for detecting scattered light of emitted light due to fine particles and generating a sensor output, and electrically connected to the light emitting circuit, the light source of the light source so as to correspond to the sensitivity when changing the sensitivity of the fine particle detection sensor. And a control means for supplying a signal for changing the drive current to change the amount of emitted light to the light emitting circuit.

According to a fourth aspect of the present invention, there is provided a fine particle detection sensor including a means for reducing a driving current of a light source in a light emitting circuit, the driving current reducing means being electrically connected to the light source and receiving a signal from a control means. It comprises a multiplexer for selecting any one of the plurality of switches and a resistor connected to the selected switch.

According to a fifth aspect of the present invention, the fine particle detection sensor uses, as the drive current reducing means, an electronic volume which is electrically connected to the light source and whose resistance value is adjusted by a signal from the control means.

A particle detection sensor according to a sixth aspect uses a laser diode, a light emitting diode or a xenon lamp as a light source.

[0011]

In the fine particle detection sensor according to the first aspect, the light emitted from the light source is scattered by fine particles such as smoke generated during a fire or dust contained in the air, and the scattered light is received by the light receiving means. Detect the presence of. The control means supplies a signal for changing the drive current of the light source to change the amount of emitted light to the light emitting circuit when the sensitivity of the particle detection sensor is changed. In the particle detection sensor according to the second aspect, when the particle concentration reaches the saturation region at the set sensitivity, the control unit controls the sensitivity to shift to low sensitivity. In the particle detection sensor according to claim 3, the light emitting circuit keeps the amount of light emitted from the light source constant.
In the particle detection sensor according to the fourth aspect, the corresponding resistor is connected to the light emitting circuit by the switch selected by the signal of the control means when the low sensitivity is set, thereby reducing the drive current of the light source. In the fine particle detection sensor according to the fifth aspect, the resistance value of the electronic volume is further increased by the signal from the control means, thereby reducing the drive current of the light source.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the accompanying drawings will be described in detail below. FIG. 1 is a block diagram showing an embodiment of a particle detection sensor according to the present invention. In FIG. 1, 1 is at least one light source, for example, an LD is used, but an LED, a xenon lamp or the like may be used. Reference numeral 2 is a light emitting circuit which is electrically connected to the LD 1 to keep the amount of emitted light constant, for example, an LD light emitting circuit, and 4 is fine particles of light emitted from the LD 1 such as smoke generated during a fire or dust contained in the air. Sensor output photodiode (PD) that receives scattered light from
By being electrically connected to 4 and performing a predetermined process,
A PD light receiving circuit for generating a sensor output, 6 is electrically connected to the PD light receiving circuit 5 and outputs the sensor output as an analog signal.
It is an A / D conversion circuit that performs digital (A / D) conversion. The sensor output PD 4, PD light receiving circuit 5 and A
The / D conversion circuit 6 constitutes a light receiving means. 7 is a control circuit as control means, for example, a one-chip microcomputer, which is a microprocessor (not shown),
LD including ROM and RAM1 to RAM3, etc.
It is electrically connected to the light emitting circuit 2 and the light receiving means, especially to the A / D conversion circuit 6 thereof, and also to a power supply circuit (not shown) and a receiving device such as a fire receiver (not shown). The control circuit 7 controls the LD light emitting circuit 2 as described later in detail. It should be noted that the control circuit 7 is connected to a means for switching the sensitivity of the particle detection sensor, for example, a dip switch (not shown).
The control circuit 7 supplies to the LD light emitting circuit 2 a signal for changing the drive current of the light source to change the amount of emitted light so that it can be set in steps and corresponds to the sensitivity when the sensitivity is changed.

FIG. 2 is a circuit diagram showing a specific example of the LD 1 and the LD light emitting circuit 2 shown in FIG. The LD1 has a built-in PD1a for monitoring the emitted light amount, and a current proportional to the emitted light amount of the LD1 flows through the PD1a for monitoring the emitted light amount.

In FIG. 2, terminals CON ₁ and CON ₂ are connected to a control circuit 7, terminals + V and −V are connected to a + terminal and a − terminal of a power source (not shown), respectively.
The terminal G is connected to the ground. The NPN transistor Q ₁ has its base connected to the terminal CON ₁ via the input resistor R ₁ , connected to the terminal + V via the voltage dividing resistor R ₂ , and to the terminal −V via the voltage dividing resistor R _3. Connected, its emitter is connected to terminal G, and capacitor C is connected between its collector and emitter.
The NPN transistor Q ₂ has its collector directly connected to the collector of the transistor Q ₁ and connected to the terminal + V via the bias resistor R ₄ , and its emitter connected to the terminal −V via the Zener diode Z. . N
The PN transistor Q ₃ has its base directly connected to the collectors of the transistors Q ₁ and Q ₂ , its collector connected to the terminal + V through the resistor R ₅ , and its emitter connected through the LD portion of LD 1 to the terminal. It is connected to G.

Further, the PD1a for monitoring the amount of emitted light incorporated in the LD1 is connected between the terminal G and the base of the transistor Q ₂ . The connection point between the emitted light amount monitoring PD 1a and the base of the transistor Q ₂ is a resistor R ₆ , a plurality of analog multiplexers MP having, for example, four switches as shown, and a resistor corresponding to a closed switch, for example, R ₇ , R _8, R ₉ or R ₁₀ (resistance values of these resistors _{R 7 <R 8 <R 9} < in which a R ₁₀₎ terminals via the -V
Connected to. The switch of the analog multiplexer MP is selected and closed by the signal supplied from the control circuit 7 to the terminal CON ₂ , and the corresponding resistor is connected.

Further, instead of the analog multiplexer MP and the resistors R _{7 to} R ₁₀ , the electronic volume EV shown in FIG.
By using, it is possible to make finer drive current settings.

The LD 1 and the LD light emitting circuit 2 are configured as described above, and are connected from the control circuit 7 to the terminal CON.
_{When a} high potential signal is supplied to ₁ , the high potential signal is supplied to the base, so that the transistor Q ₁ is turned on.
N, and its collector is at a low potential of approximately the ground potential. Since this low potential is applied to the base, the transistor Q ₃ is OFF, and therefore no drive current flows through the LD 1, so that the LD 1 does not emit light.

However, when the signal supplied from the control circuit 7 to the terminal CON ₁ becomes a low potential signal, this low potential signal is supplied to the base, so that the transistor Q
₁ is turned off, its collector has a voltage drop across resistor R ₄ ,
The potential becomes a high potential divided by the collector-emitter voltage V _{CE of the} transistor Q ₂ and the voltage of the Zener diode Z. This high potential is applied to the base of transistor Q ₃ , but at this time transistor Q ₃ is set to operate in the active region rather than in the switching state, so transistor Q ₃ does not saturate V _CE. A driving current defined by the V _CE and the resistance R ₅ is made to flow, and the LD 1 emits light by this driving current. As described above, the control circuit 7 repeatedly supplies the high-potential and low-potential signals to the terminal CON ₁ , so that the LD 1 intermittently emits light.

[0019] The LD1 emits light, the current proportional to the amount of emitted light is generated in the light emission amount monitoring PD1a, this current resistor R _6, in the analog multiplexer MP,
A signal from the control circuit 7 causes a current to flow to the terminal -V through, for example, the leftmost switch (for high sensitivity setting) currently selected and the resistor R ₇ having a small resistance value connected to this switch, and the transistor Q ₂ Generate the base potential of. When the light emission amount of the LD1 is large, the generated current amount of emitted light monitoring PD1a be therefore increased transistor Q ₂
Since the base potential is high, V _CE of the transistor Q ₂ is decreased, the base potential of the collector potential clogging transistor Q ₃ of the transistor Q ₂ is decreased, V _CE of the transistor Q ₃ are increased, the drive current of LD1 is reduced As a result, the amount of emitted light also decreases. On the contrary, when the amount of emitted light is reduced in this way, the generated current of the emitted light amount monitoring PD 1a is also small, and the base potential of the transistor Q ₂ is also low. Therefore, V _{CE of the} transistor Q ₂ is large and the base potential of the transistor Q ₃ is large. Rises, the driving current of the LD1 increases, and the amount of emitted light also increases. The LD light emitting circuit 2 is thus L
It operates so as to keep the amount of light emitted from D1 constant.

Since the amount of emitted light versus the LD monitor current value is individually specified for each LD, the PD current for the emitted light amount monitor at the required amount of emitted light can be specified, and the current value allows the resistors R ₆ and R ₇ to be controlled. Determine the resistance value.

FIG. 4 is a diagram showing a sensor output / conversion data table stored in the ROM of the control circuit 7, where Va represents an alarm level. In FIG. 4, the sensor output characteristic with respect to the amount of smoke, that is, the amount of fine particles is
It shows a state that changes depending on B, C, and D. By making this relation table in the ROM as a comparison table, it is possible to know which fine particle amount the sensor output at a certain emitted light amount corresponds to. Smoke can be detected accurately even when changes occur. The data table A is the resistance R _{7 of} FIG.
Represents the state of high sensitivity setting connected to the light emitting circuit 2,
When the particle concentration reaches S1, the sensor output reaches the alarm level Va. However, in the data table B representing the state when the medium sensitivity is set, to which the resistor R ₈ is connected, the alarm level Va is not reached until the particle concentration reaches S2. Similarly, in the data table C showing the state at the time of low sensitivity setting with the resistor R ₉ connected, the alarm level Va is not reached until the particle concentration reaches S3, and the low level low sensitivity with the resistor R ₁₀ connected is set. In the data table D representing the state, the warning level Va is not reached even when the particle concentration exceeds S3 considerably.

In FIG. 4, A, B, C and D are shown by straight lines rising to the right, but in reality, when the sensor output reaches a certain particle concentration (saturation region), it does not rise any further. If the sensitivity remains high, it is not possible to accurately measure the concentration of very high concentration of fine particles.

As is clear from these data tables A to D, if the particle concentration is the same, for example, S1,
It can be seen that the sensor output and hence the amount of light emitted from the LD1 can be reduced as the sensitivity decreases. Therefore, in the present invention, when the sensitivity is set low (for example, the data table A is changed to the data table B), the control circuit 7 outputs a signal and replaces the switch in the analog multiplexer MP to which the resistor R ₇ is connected. Then, the switch to which the resistance R ₈ having a larger resistance value than the resistance R ₇ is connected is selected and closed (naturally, the switch to which the resistance R ₇ is connected is opened). Since the resistance value has increased in this way, if the same current that has flowed in the resistor R ₇ flows in the resistor R ₈ , the voltage drop across it becomes large, and as a result, the transistor Q
The base potential of ₂ rises, and as a result of the above-described feedback operation, the drive current of LD1 and hence the amount of emitted light is reduced, and thus the power consumption and the life of LD1 are reduced. The sensitivity becomes lower (data table C,
D), and the resistor R ₉ instead of the resistor R ₈ , and further the resistor R
_The resistor R ₁₀ is selected and connected instead of ₉ , so that the drive current is further reduced and the amount of emitted light is reduced.

In the LD light emitting circuit 2 shown in FIG. 2, the corresponding resistor is connected in the circuit by closing the switch by the signal from the control circuit 7, but the corresponding resistor is connected by opening the switch. However, such an example is shown in FIG. According to the LD light emission circuit 2, the switches connected to the resistor R ₈ to R ₁₀ by a signal supplied from the terminal CON ₂ as sensitivity decreases are sequentially opened. It is not necessary to close the switch connected to the resistor R ₇ when the sensitivity is reduced. In the LD light emitting circuit 2 of FIG. 2 and the LD light emitting circuit 2A of FIG. 5, the amount of emitted light decreases each time the sensitivity is switched to the lower one, as described above. In addition to this, the high sensitivity data table A is saturated between the particle concentrations S1 and S2, but when it exceeds S1, it is switched to the data table B, and then S2 and S3.
Data tables C and D with low sensitivity at each stage
If the control circuit 7 controls the data table D so that the data table D is saturated, the data table D will be saturated only after S3 has been exceeded, so that the dynamic range can be expanded.

FIG. 6 is a flowchart for explaining the operation of the particle detection sensor shown in FIG. In step S1, the ROM and the like are initialized by a predetermined process of the microprocessor in the control circuit 7. Next, in step S2, the set alarm level Va, that is, the sensitivity or the measurement full scale is read and stored in the RAM 1.

In step S3, a sensor output (and emitted light amount) / fine particle concentration conversion data table is selected based on the data read from the RAM 1. For example, when the high sensitivity is set, the data table A is selected to set the emitted light amount of the LD 1 to be large, but when the low sensitivity is set, the data table C is selected to set the emitted light amount to be small, and the set emitted light amount value is stored in the RAM 2. .

[0027] In step S4, based on the RAM2 value, a predetermined resistance is connected by a signal supplied from the control circuit 7 to the LD light emission circuit 2 or 2A terminal CON ₂ of the signal that is then supplied to the CON ₁ LD1 Is emitted at the set emission light amount value.

In step S5, the sensor output PD4 first receives the light emitted from the LD1 and scattered by fine particles such as dust contained in the air or smoke generated during a fire, and then the output is received by the PD light receiving circuit. A sensor output is generated by performing processing such as peak hold, sample hold, etc., as necessary. After the sensor output is digitized by the A / D conversion circuit 6, the data is stored in the RAM 3.

In step S6, the data in RAM3 is converted into voltage / voltage based on the data table selected in step S3.
After density conversion, it is returned to RAM3. In step S7,
The control circuit 7 transmits the data in the RAM 3 to the receiving device. Finally, in step S8, the value of the data table is waited for, the process returns to step S4, and the detection of fine particles is continued again. Needless to say, no waiting time is required. After step S8, the control circuit 7 may determine whether the sensor output has reached the saturation region, and if so, the sensitivity may be lowered by one step.

In the above embodiment, one LD is used,
Although the drive current is reduced to reduce the amount of emitted light when the low sensitivity is set, a plurality of light sources may be used and the number of emitted light may be reduced when the low sensitivity is set. Instead of constantly sending the sensor output to the receiving device, the particle detection sensor may be provided with a discrimination circuit and the discrimination result may be transmitted when necessary. Further, the sensor output or the determination result may be sent by a polling signal from the receiving device. Furthermore, a switch for setting the sensitivity may be provided on the receiving device side.

In the embodiment, the case where the sensitivity is first set to high sensitivity and the sensitivity is changed stepwise is described. However, the sensitivity is set to low first and then set to high sensitivity later. Of course, it is possible to switch. Further, by providing a light receiving element for monitoring the amount of light emitted from the light source, it is possible to confirm whether or not the sensitivity of the sensor has really changed when the sensitivity was switched. In the past, it was not possible to confirm on the sensor side whether the sensitivity was actually switched.

[0032]

As described in detail above, the particle detection sensor according to claim 1 of the present invention comprises at least one light source, a light emitting circuit for causing the light source to emit light, and light emitted from the light source. A light receiving unit that detects scattered light by the fine particles to generate a sensor output, and a signal for changing the amount of emitted light by changing the drive current of the light source so as to correspond to the sensitivity when changing the sensitivity of the fine particle detection sensor. When the sensitivity is switched to a low sensitivity, the reference value such as the threshold value is left unchanged to reduce the amount of light emitted from the light source, thereby reducing the power consumption of the light source. Not only can the life be extended, but the dynamic range of the sensor can be expanded.

According to the second aspect of the invention, when the fine particle concentration reaches the saturation region at the set sensitivity, the control means controls the sensitivity to shift to a low sensitivity, so that the fine particle concentration is saturated even if it increases. Without a warning (fire)
Even after that, the effect that the density can be displayed on the receiving device side and the increase can be seen. According to the invention of claim 3, since the light emitting circuit keeps the amount of light emitted from the light source constant, a stable sensor output can be obtained. Furthermore, the invention of claim 4 or 5 has an effect of extending the life of the light source and expanding the dynamic range by reducing the drive current of the light source stepwise or linearly when the low sensitivity is set.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a particle detection sensor according to the present invention.

FIG. 2 is a circuit diagram showing an example of the LD light emitting circuit shown in the block diagram of FIG.

3 is a diagram showing an electronic volume used in place of the analog multiplexer and the plurality of resistors in FIG.

FIG. 4 is a diagram showing a conversion data table.

FIG. 5 is a circuit diagram showing another example of an LD light emitting circuit.

FIG. 6 is a flowchart for explaining the operation of the embodiment of the present invention.

[Explanation of symbols]

1 LD 2, 2A LD light emitting circuit 4 sensor output PD 5 PD light receiving circuit 6 A / D conversion circuit 7 control circuit MP analog multiplexer R _{7 to} R ₁₀ resistance EV electronic volume

Claims (6)

[Claims] 1. A fine particle detection sensor for detecting fine particles such as smoke generated during a fire or dust contained in air, comprising at least one light source, electrically connected to the light source, and emitting light from the light source. A light emitting circuit, a light receiving means for detecting scattered light of the fine particles of light emitted from the light source to generate a sensor output, electrically connected to the light emitting circuit, and a sensitivity when changing the sensitivity of the fine particle detection sensor. The control means for supplying a signal for changing the drive current of the light source to change the amount of emitted light to the light emitting circuit so as to correspond to the above. 2. The particle detection sensor according to claim 1, wherein the control means controls the sensitivity to a low sensitivity when the particle concentration reaches a saturation region at the set sensitivity. 3. The light emitting circuit is a circuit for keeping a constant amount of light emitted from the light source.
Particle detection sensor. 4. The light emitting circuit includes means for reducing the drive current according to a signal supplied from the control means, the drive current reduction means being electrically connected to the light source and provided by the control means. 4. The particulate matter detection sensor according to claim 1, comprising a multiplexer for selecting any one of a plurality of switches according to a signal and a resistor connected to the selected switch. 5. Another drive current reducing means, which is an electronic volume, is electrically connected to the light source and has a resistance value adjusted by a signal from the control means, in place of the drive current reducing means of claim 4. 4. The particle detection sensor according to claim 1, wherein: 6. The particle detection sensor according to claim 1, wherein the light source is a laser diode, a light emitting diode or a xenon lamp.