JP7643956B2 - Light detection system and photon number calculation method - Google Patents

Description

The present invention relates to an optical detection system that detects light such as flames.

Phototube type ultraviolet sensors are sometimes used as optical sensors to detect the presence or absence of flames in combustion furnaces and the like based on the ultraviolet light emitted from the flame light. It has been observed that phototube type ultraviolet sensors can cause irregular discharge phenomena (pseudo discharges) due to noise components other than discharges due to the photoelectric effect.

Patent Document 1 proposes a flame detection system that can calculate the amount of light received from a discharge by controlling the pulse width of a drive pulse applied to an optical sensor, and can determine the lifespan of the optical sensor from the amount of light. However, the actual discharge of an optical sensor includes irregular discharges caused by noise, collectively known as malfunctions, and discharges can occur even when there is no light from a flame, resulting in false detection. In order to eliminate false detection of such discharges, it is necessary to consider the amount of light received with the discharge probability of noise components removed.

Therefore, the flame detection system disclosed in Patent Document 2 proposes a method of calculating the amount of received light that takes into account the probability of irregular discharge of noise components, making it possible to accurately detect the presence or absence of a flame.
Furthermore, in the failure detection device disclosed in Patent Document 3, it is proposed to detect failure due to self-discharge of the optical sensor by providing a shutter mechanism that blocks electromagnetic waves incident on the optical sensor.

The technologies disclosed in Patent Documents 1, 2, and 3 all calculate the amount of light received by the optical sensor. However, because the amount of light received was a relative value for the optical sensor itself, it was difficult to compare the degree of discharge with that of a different optical sensor.

JP 2018-84422 A JP 2018-84423 A Japanese Patent Application Publication No. 05-012581

The present invention has been made to solve the above problems, and aims to provide a light detection system and a method for calculating the number of photons that can compare the degree of discharge with that of a separate solid-state light sensor.

The optical detection system of the present invention includes an optical sensor configured to detect light emitted from a light source, a lens mechanism provided between the light source and the optical sensor and configured to adjust the focal length, an applied voltage generation unit configured to periodically apply a drive pulse voltage to an electrode of the optical sensor, a current detection unit configured to detect a discharge current of the optical sensor, and a discharge determination unit configured to detect a discharge of the optical sensor based on the discharge current detected by the current detection unit, and a number of times the applied voltage generation unit applies the drive pulse voltage and the number of times the discharge occurs during application of the drive pulse voltage for each of a first state in which the focal length of the lens mechanism is a predetermined first value and a second state in which the focal length is a predetermined second value different from the first value. The optical sensor is characterized by comprising a discharge probability calculation unit configured to calculate a discharge probability based on the number of discharges detected by the discharge determination unit, a storage unit configured to store in advance the discharge probability at the time of shipment from the factory of the optical detection system as a known sensitivity parameter of the optical sensor, and a photon number calculation unit configured to calculate a ratio of the number of photons reaching the light receiving surface of the optical sensor at the time of shipment from the factory and after installation at the site based on the sensitivity parameter stored in the storage unit, the discharge probability calculated by the discharge probability calculation unit in the first and second states, a predetermined first ratio between the reference amount of light received by the optical sensor and the amount of light received in the first state, and a predetermined second ratio between the reference amount of light received and the amount of light received in the second state.

Furthermore, in one configuration example of the optical detection system of the present invention, the photon number calculation unit calculates the photon number ratio E/Ere using the discharge probabilities _P1 , _P3 calculated by the discharge probability calculation unit in the first and second states, a predetermined first ratio _r1 between the reference amount of received light and the amount of received light in the first state, a predetermined second ratio _r3 between the reference amount of received light and the amount of received light in the second state, and the discharge probability _Pre at the time of _shipment from the factory stored in the memory unit.

The optical detection system of the present invention includes an optical sensor configured to detect light emitted from a light source, a lens mechanism provided between the light source and the optical sensor and configured to adjust the focal length, an applied voltage generation unit configured to periodically apply a drive pulse voltage to an electrode of the optical sensor, a current detection unit configured to detect a discharge current of the optical sensor, a discharge determination unit configured to detect a discharge of the optical sensor based on the discharge current detected by the current detection unit, and a discharge probability calculation unit configured to calculate a discharge probability based on the number of applications of the drive pulse voltage by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage for each of a first state in which the focal length of the lens mechanism is a predetermined first value and a second state in which the focal length is a predetermined second value different from the first value, and a discharge probability calculation unit configured to calculate a discharge probability based on the number of applications of the drive pulse voltage by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage as known sensitivity parameters of the optical sensor. The optical detection system is characterized in that it has a memory unit configured to store in advance a reference pulse width of the driving pulse voltage, a discharge probability of a first type of irregular discharge caused by a noise component other than a discharge caused by the photoelectric effect of the optical sensor, which occurs depending on the pulse width of the driving pulse voltage and does not depend on the amount of light received by the optical sensor, and a discharge probability of a second type of irregular discharge caused by the noise component, which occurs independent of the pulse width of the driving pulse voltage and the amount of light received by the optical sensor, and a photon number calculation unit configured to calculate a ratio of the number of photons reaching the light receiving surface of the optical sensor when the optical detection system is shipped from the factory and after installation at the site, based on the sensitivity parameters stored in the memory unit, the discharge probability calculated by the discharge probability calculation unit in the first and second states, a predetermined first ratio between the reference amount of light received by the optical sensor and the amount of light received in the first state, a predetermined second ratio between the reference amount of light received and the amount of light received in the second state, and the pulse width of the driving pulse voltage in the first and second states.

Furthermore, in one configuration example of the optical detection system of the present invention, the photon number calculation unit calculates the photon number ratio E/Ere using the discharge probabilities _P1 , _P3 calculated by the discharge probability calculation unit in the first and second states, a predetermined first ratio _r1 between the reference amount of received light and the amount of received light in the first state, a predetermined second ratio _r3 between the reference amount of received light and the amount of received light in the second state, the discharge probability _Pre at the time of shipment from the factory stored in the memory unit, the reference pulse width _T0 of the driving pulse voltage, the discharge probability P _aB of the first type of irregular discharge, the discharge probability _{P bB} of the second type of irregular discharge, and the pulse width T of the driving pulse voltage in the first and second states.
Moreover, one configuration example of the optical detection system of the present invention is characterized in that it further includes a received light amount ratio setting unit configured to control a focal length of the lens mechanism to the first value so that a ratio between the reference received light amount and the amount of received light in the first state becomes the first ratio, thereby putting the optical detection system in the first state, and further control a focal length of the lens mechanism to the second value so that a ratio between the reference received light amount and the amount of received light in the second state becomes the second ratio, thereby putting the optical detection system in the second state.
Furthermore, in one configuration example of the optical detection system of the present invention, the discharge probability calculation unit calculates a discharge probability based on the number of times the drive pulse voltage is applied by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage at the time of shipment from the factory prior to installation at the site of the optical detection system, and stores the calculated discharge probability in the memory unit.
Moreover, one configuration example of the optical detection system of the present invention is characterized in that it further includes a received light amount calculation unit configured to calculate the amount of light received by the optical sensor after the optical detection system is installed at the site, based on the ratio of the numbers of photons calculated by the photon number calculation unit.

The photon number calculation method of the present invention includes a first step of periodically applying a drive pulse voltage to an electrode of the optical sensor when the focal length of a lens mechanism provided between a light source and an optical sensor is a predetermined first value, a second step of detecting a discharge current of the optical sensor in the first state, a third step of detecting a discharge of the optical sensor based on the discharge current in the first state, a fourth step of calculating a discharge probability in the first state based on the number of applications of the drive pulse voltage by the first step and the number of discharges detected in the third step during application of this drive pulse voltage, a fifth step of periodically applying a drive pulse voltage to the electrode of the optical sensor when the focal length of the lens mechanism is a predetermined second value different from the first value, a sixth step of detecting a discharge current of the optical sensor in the second state, and a sixth step of calculating a discharge probability in the second state based on the number of applications of the drive pulse voltage by the first step and the number of discharges detected in the third step during application of this drive pulse voltage. a seventh step of detecting the discharge of the optical sensor based on the discharge current; an eighth step of calculating the discharge probability in the second state based on the number of applications of the drive pulse voltage in the fifth step and the number of discharges detected in the seventh step during the application of the drive pulse voltage; and a ninth step of referring to a storage unit that pre-stores the discharge probability at the time of shipment from the factory of the optical detection system as a known sensitivity parameter of the optical sensor, and calculating the ratio of the number of photons reaching the light receiving surface of the optical detection system at the time of shipment from the factory and after installation at the site based on the sensitivity parameter stored in the storage unit, the discharge probability calculated in the fourth and eighth steps in the first and second states, a predetermined first ratio between the reference amount of light received by the optical sensor and the amount of light received in the first state, and a predetermined second ratio between the reference amount of light received and the amount of light received in the second state.

The photon number calculation method of the present invention includes a first step of periodically applying a drive pulse voltage to an electrode of the optical sensor when the focal length of a lens mechanism provided between a light source and an optical sensor is a first predetermined value, a second step of detecting a discharge current of the optical sensor when the optical sensor is in the first state, a third step of detecting a discharge of the optical sensor based on the discharge current when the optical sensor is in the first state, and a third step of detecting a discharge of the optical sensor based on the number of applications of the drive pulse voltage in the first step and the number of discharges detected in the third step during application of the drive pulse voltage. a fourth step of calculating a probability of discharge when the focal length of the lens mechanism is in a second state in which the focal length is a predetermined second value different from the first value; a fifth step of periodically applying a drive pulse voltage to an electrode of the optical sensor when the focal length of the lens mechanism is in a second state in which the focal length is a predetermined second value different from the first value; a sixth step of detecting a discharge current of the optical sensor when in the second state; a seventh step of detecting a discharge of the optical sensor based on the discharge current when in the second state; an eighth step of calculating a discharge probability in the second state by calculating a discharge probability in the second state based on the reference pulse width of the drive pulse voltage; and storing in advance, as known sensitivity parameters of the optical sensor, a discharge probability at the time of shipment from a factory of the optical detection system, a reference pulse width of the drive pulse voltage, a discharge probability of a first type of irregular discharge caused by a noise component other than a discharge caused by a photoelectric effect of the optical sensor, which occurs depending on the pulse width of the drive pulse voltage and occurs independently of the amount of light received by the optical sensor, and a discharge probability of a second type of irregular discharge caused by the noise component, which occurs independently of the pulse width of the drive pulse voltage and the amount of light received by the optical sensor. The method further includes a ninth step of calculating a ratio of the number of photons that reach the light receiving surface of the optical sensor when the optical detection system is shipped from the factory and after installation on site, based on the sensitivity parameters stored in the storage unit, the discharge probability calculated in the fourth and eighth steps when the optical sensor is in the first and second states, a predetermined first ratio between the reference amount of light received by the optical sensor and the amount of light received in the first state, a predetermined second ratio between the reference amount of light received and the amount of light received in the second state, and the pulse width of the drive pulse voltage when the optical detection system is in the first and second states.

Furthermore, one configuration example of the photon number calculation method of the present invention is characterized in that it further includes a tenth step of controlling the focal length of the lens mechanism to the first value so that the ratio between the reference amount of received light and the amount of received light in the first state becomes the first ratio, thereby putting the light detection system in the first state, and an eleventh step of controlling the focal length of the lens mechanism to the second value so that the ratio between the reference amount of received light and the amount of received light in the second state becomes the second ratio, thereby putting the light detection system in the second state.
Furthermore, one configuration example of the photon number calculation method of the present invention is characterized in that it further includes a twelfth step of periodically applying a drive pulse voltage to an electrode of the optical sensor at the time of shipping the optical detection system from a factory prior to installation on site, a thirteenth step of detecting a discharge current of the optical sensor, a fourteenth step of detecting a discharge of the optical sensor based on the discharge current, and a fifteenth step of calculating a discharge probability based on the number of applications of the drive pulse voltage by the twelfth step and the number of discharges detected in the fourteenth step during the application of this drive pulse voltage, and storing the calculated discharge probability in the memory unit.

According to the present invention, it is possible to calculate the ratio of the number of photons when the optical detection system is shipped from the factory to that after installation in the field. In the present invention, by calculating the ratio of the number of photons, it is possible to compare the degree of discharge with that of a separate solid-state optical sensor. Since the amount of received light determined by conventional technology is affected by the variation of the optical sensor, there is a possibility that the life of the optical sensor will be erroneously determined if the life of the optical sensor is determined based on the amount of received light. On the other hand, in the present invention, the influence of the variation of the optical sensor can be eliminated by calculating the ratio of the number of photons, so that the possibility of erroneously determining the life of the optical sensor can be reduced by determining the life of the optical sensor based on the ratio of the number of photons.

FIG. 1 is a diagram for explaining the ratio of the amount of received light when the amount of received light on the electrode surface of the optical sensor is changed by a lens mechanism. FIG. 2 is a block diagram showing the configuration of a light detection system according to a first embodiment of the present invention. FIG. 3 is a waveform diagram showing a drive pulse applied to the optical sensor and a detection voltage detected in the current detection circuit in the first embodiment of the present invention. FIG. 4 is a diagram for explaining the ratio of the amount of received light when the amount of received light on the electrode surface of the optical sensor is changed by the lens mechanism. FIG. 5 is a flow chart for explaining the operation of the light detection system according to the first embodiment of the present invention at the time of shipment from the factory. FIG. 6 is a front view of the revolver-type lens mechanism according to the first embodiment of the present invention, as viewed from the light source side. FIG. 7 is a flow chart for explaining the operation of the light detection system according to the first embodiment of the present invention after installation at the site. FIG. 8 is a block diagram showing an example of the configuration of a computer that realizes the light detection systems according to the first and second embodiments of the present invention.

[Principle of the Invention]
In the present invention, an optical sensor with known sensitivity parameters and a lens mechanism with a variable focal length are provided, and the discharge probability when the amount of light received is varied for the wavelength to which the optical sensor is sensitive is used to determine the number of photons relative to the number at the time of shipment from the factory of the optical detection system. An example of a lens mechanism with a variable focal length is a revolver-type lens mechanism with multiple lenses that varies the focal length and relativizes the amount of light received.

In this invention, the ratio of the number of photons in the optical sensor is calculated. In the technology disclosed in Patent Document 1, the amount of light received by the optical sensor is calculated and the lifespan of the optical sensor is determined from the amount of light received. However, since the amount of light received was a relative value for the optical sensor itself, it was difficult to compare the amount of light received with that of another solid-state optical sensor. In this invention, the ratio of the number of photons in the optical sensor is calculated, making it possible to compare the degree of discharge of another solid-state optical sensor.

[First embodiment]
Below, we will explain how to calculate the number of photons when the amount of light received by the optical sensor is variable. In the first embodiment of the present invention, we will explain an example in which only the normal discharge of the optical sensor is considered. An optical sensor that uses the photoelectric effect is a phototube that is electrified when photons hit the electrode. The electrification progresses under the following conditions.

[Operation of the optical sensor]
When a voltage is applied between a pair of electrodes of an optical sensor, if a photon hits one of the electrodes, there is a certain probability that a photoelectron will be emitted, causing an electron avalanche and causing electricity to flow (a discharge current flows between the electrodes).
The optical sensor continues to conduct electricity while a voltage is applied between the electrodes. Alternatively, the conduction of electricity is stopped by immediately lowering the voltage once the conduction of electricity is confirmed. In this way, the optical sensor stops conducting electricity when the voltage between the electrodes is lowered.

Let _P1 be the probability that the optical sensor discharges when one photon hits the optical sensor electrode. Let _P2 be the probability that the optical sensor discharges when two photons hit the optical sensor electrode. Since _P2 is the inverse of the probability that the optical sensor does not discharge when hit by either the first or second photon, the relationship between _P2 and _P1 is expressed as in formula (1).

In general, if the probability that the optical sensor discharges when n photons hit the optical sensor electrode is _Pn and the probability that the optical sensor discharges when m photons hit the optical sensor electrode is _Pm (n and m are natural numbers), then equations (2) and (3) hold, just like equation (1).

From the formulas (2) and (3), the formula (4) can be derived as the relationship between _Pn and _Pm .

Consider the case where light is detected through a lens whose focal length can be changed. If the number of photons that fly to the electrodes of the optical sensor per unit area and unit time is E, the area of the lens is S _l , and the time during which a voltage equal to or greater than the discharge start voltage of the optical sensor is applied between the electrodes (hereinafter referred to as pulse width) is T _i , the number of photons that collide with the electrodes per voltage application is expressed as ET _i S _l . Therefore, when the same optical sensor is operated under a certain condition A and another condition B, the relationship between the number of photons E, the area S, the pulse width T, and the discharge probability P is as shown in formula (5). Here, if the reference number of photons is defined as E ₀ , and Q _A =E _A /E ₀ and Q _B =E _B /E ₀ , formula (6) is obtained. Here, Q _i is called the amount of received light.

As shown in FIGS. 1A and 1B, when the amount of light received on the electrode surface of the optical sensor 1 is set to 100% by the lens mechanism ₂₁ with a variable focal length, the ratio _rb of the amount of light received when the amount of light received is set to Qb (Qa ≠ Qb) can be expressed by equation (7).

[Configuration and operation of the optical detection system]
2 is a block diagram showing the configuration of a light detection system according to a first embodiment of the present invention. The light detection system drives a light sensor and calculates the ratio of the number of photons and the amount of received light from the drive result of the light sensor. This light detection system includes a light sensor 1 that detects light (ultraviolet rays) generated from a light source 100 such as a flame, an LED, or a lamp, an external power source 2, a computing device 3 to which the light sensor 1 and the external power source 2 are connected, and a lens mechanism 21 provided between the light source 100 and the light sensor 1.

The optical sensor 1 is composed of a phototube equipped with a cylindrical enclosure with both ends closed, two electrode pins penetrating both ends of the enclosure, and two electrodes supported parallel to each other by the electrode pins inside the enclosure. In such an optical sensor 1, when a predetermined voltage is applied between the electrodes via the electrode support pins and ultraviolet light is irradiated onto one of the electrodes arranged opposite the light source 100, electrons are emitted from the electrode due to the photoelectric effect, and a discharge current flows between the electrodes.

The external power source 2 is, for example, an AC commercial power source having a voltage of 100 V or 200 V.

The arithmetic unit 3 includes a power supply circuit 11 connected to the external power supply 2, an applied voltage generating circuit 12 and a trigger circuit 13 connected to the power supply circuit 11, a voltage dividing resistor 14 consisting of resistors R1 and R2 connected in series between the downstream terminal 1b of the optical sensor 1 and the ground line GND, a current detection circuit 15 that detects the voltage (reference voltage) Va generated at the connection point Pa between the resistors R1 and R2 of the voltage dividing resistor 14 as the current I flowing through the optical sensor 1, and a processing circuit 16 to which the applied voltage generating circuit 12, the trigger circuit 13, and the current detection circuit 15 are connected.

The power supply circuit 11 supplies AC power input from the external power supply 2 to the applied voltage generating circuit 12 and the trigger circuit 13. In addition, power for driving the arithmetic device 3 is obtained from the power supply circuit 11. However, it can also be configured to obtain power for driving from a separate power supply, regardless of whether it is AC or DC.

The applied voltage generating circuit 12 (applied voltage generating section) boosts the AC voltage applied by the power supply circuit 11 to a predetermined value and applies it to the optical sensor 1. In this embodiment, a pulsed voltage of 200 [V] (a voltage equal to or greater than the discharge start voltage _VST of the optical sensor 1) synchronized with the rectangular pulse PS from the processing circuit 16 is generated as the driving pulse voltage PM, and this generated driving pulse voltage PM is applied to the optical sensor 1. FIG. 3 shows the driving pulse voltage PM applied to the optical sensor 1. The driving pulse voltage PM is synchronized with the rectangular pulse PS from the processing circuit 16, and its pulse width T is equal to the pulse width of the rectangular pulse PS. The rectangular pulse PS from the processing circuit 16 will be described later.

The trigger circuit 13 detects a predetermined value point of the AC voltage applied by the power supply circuit 11 and inputs this detection result to the processing circuit 16. In this embodiment, the trigger circuit 13 detects the minimum value point where the voltage value is at a minimum as the predetermined value point (trigger time point). By detecting the predetermined value point of the AC voltage in this way, it becomes possible to detect one period of the AC voltage.

The voltage divider resistor 14 generates a reference voltage Va as a divided voltage between resistors R1 and R2, and inputs it to the current detection circuit 15. Here, the voltage value of the drive pulse PM applied to the upstream terminal 1a of the optical sensor 1 is a high voltage of 200 [V] as described above, so if the voltage generated at the downstream terminal 1b when a current flows between the electrodes of the optical sensor 1 is input directly to the current detection circuit 15, a large load will be placed on the current detection circuit 15. For this reason, in this embodiment, a reference voltage Va with a low voltage value is generated by the voltage divider resistor 14, and this is input to the current detection circuit 15.

The current detection circuit 15 (current detection section) detects the reference voltage Va input from the voltage dividing resistor 14 as the discharge current I of the optical sensor 1, and inputs the detected reference voltage Va to the processing circuit 16 as a detected voltage Vpv.
The processing circuit 16 includes a rectangular pulse generating section 17 , an A/D converting section 18 , a sensitivity parameter storing section 19 , and a central processing section 20 .

The rectangular pulse generating unit 17 generates a rectangular pulse PS with a pulse width T every time the trigger circuit 13 detects a trigger time point, that is, every period of the AC voltage applied from the power supply circuit 11 to the trigger circuit 13. The rectangular pulse PS generated by the rectangular pulse generating unit 17 is sent to the applied voltage generating circuit 12. The rectangular pulse generating unit 17 and the applied voltage generating circuit 12 can adjust the pulse width of the drive pulse voltage PM. That is, the rectangular pulse generating unit 17 sets the pulse width of the rectangular pulse PS to a desired value, so that a drive pulse voltage PM with a pulse width equal to that of the rectangular pulse PS is output from the applied voltage generating circuit 12.
The A/D conversion unit 18 A/D converts the detected voltage Vpv from the current detection circuit 15 and sends it to the central processing unit 20 .

The central processing unit 20 is realized by hardware consisting of a processor and a storage device, and a program that cooperates with this hardware to realize various functions, and functions as a discharge determination unit 201, a discharge probability calculation unit 202, a pulse application number accumulation unit 203, an application number determination unit 204, a photon number calculation unit 205, a received light amount calculation unit 206, a received light amount determination unit 207, and a received light amount ratio setting unit 208.

In the central processing unit 20, the discharge determination unit 201 detects the discharge of the optical sensor 1 based on the discharge current of the optical sensor 1 detected by the current detection circuit 15. Specifically, each time the drive pulse voltage PM is applied to the optical sensor 1 (each time the rectangular pulse PS is generated), the discharge determination unit 201 compares the detection voltage Vpv input from the A/D conversion unit 18 with a predetermined threshold voltage Vth (see FIG. 3), and when the detection voltage Vpv exceeds the threshold voltage Vth, it determines that the optical sensor 1 has discharged and increments the number of discharges n by 1.

When the number of times N of application of the drive pulse voltage PM applied to the light sensor 1 exceeds a predetermined number (when the number of pulses of the rectangular pulse PS exceeds a predetermined number), the discharge probability calculation unit 202 calculates the discharge probability P of the light sensor 1 from the number of times n of discharge detected by the discharge determination unit 201 and the number of times N of application of the drive pulse voltage PM.

This discharge probability P is output as a frame signal. It is assumed that the discharge probability _P0 at certain operating conditions, the amount of received light _Q0 ( _Q0 ≠ 0), and the pulse width _T0 is known. For example, in a shipping inspection of a light detection system, there is a method of measuring the discharge probability P at a set amount of received light and pulse width. In this case, the relationship between the amount of received light Q, the pulse width T, and the discharge probability P is given by equation (8). However, P=0 is treated as Q=0. In the present invention, the cases when P=0 and P=1 are excluded from the calculation process of the amount of received light Q.

Now, _Q0 , _T0 , and _P0 are known, and T is also known because it is the pulse width controlled by the light detection system. By applying the driving pulse voltage PM multiple times to the light sensor 1, measuring the number of discharges n, and calculating the discharge probability P, the unknown quantity of received light Q can be calculated from equation (8).

From equation (8), it is assumed that the discharge probability P _aA under certain operating conditions, the amount of received light Q ₀ , and the pulse width T ₀ are known, and the relationship between the amount of received light Q, the pulse width T, and the discharge probability P is given by equation (9).

[Method of calculating the number of photons when using lenses with different focal lengths]
When the focal length of the lens mechanism 21 is changed as shown in Figures 4(A) to 4(C), the discharge probability in three different focal length states is _Pi (i = 1 to 3) _, and the amount of received light is _Qi . Here, it is assumed that _Q1 = _r1Q2 , _Q3 = _r3Q2 ( _{r1 ≠ r3} ), the ratios _r1 and _r3 are known, and the number E of photons per unit electrode area that reach the electrode of the optical sensor 1 in the state of Figure 4(B) is unknown.

Equation (10) is obtained by substituting the probability of discharge _P1 and the amount of received light _Q1 when measured in the state of Figure 4(A) after the optical detection system is installed at the site into equation (9), and equation (11) is obtained by substituting the probability of discharge _P3 and the amount of received light _Q3 when measured in the state of Figure 4(C) into equation (9).

Dividing equation (10) by (11) gives equation (12).

Furthermore, it is assumed that when the light detection system is shipped from the factory, the focal length of the lens mechanism 21 is set to an arbitrary value, the amount of received light _Qre when the discharge probability is _Pre is calculated, and the discharge probability _Pre and the amount of received light _Qre are known. The discharge probability _Pre and the amount of received light _Qre are substituted into equation (9) and the equation is transformed to obtain equation (13).

Substituting equation (12) into equation (13) and transforming it gives equation (14).

Substituting Q ₁ =r ₁ Q ₂ and Q ₃ =r ₂ Q ₂ into equation (14), we obtain equation (15).

By substituting Q ₂ =(ES _l )/(E ₀ S _l ) and Q _re =(E _re S _l )/(E ₀ S _l ) into equation (15), E/E _re can be obtained as in equation (16).

Therefore, it is possible to calculate the ratio E _/ Ere of the number of photons at the time of shipment from the factory to the number of photons after installation at the site using the known values _P1 , _P3 , _r1 , and _r2 after installation at the site and the known values _Pre and _Qre at the time of shipment from the factory.

The operation of the light detection system of this embodiment will be described in more detail below. Fig. 5 is a flow chart for explaining the operation of the light detection system of this embodiment at the time of shipment from the factory.
For example, during an inspection stage prior to shipment from a factory, the focal length of the lens mechanism 21 is manually set to an arbitrary value (step S100).

Figure 6 is a front view of the revolver-type lens mechanism 21 as seen from the light source 100 side. The revolver-type lens mechanism 21 has multiple lenses 210-212 with different focal lengths fixed to a revolver 213. By rotating the revolver 213, the lenses 210-212 inserted between the light source 100 and the light sensor 1 can be changed, thereby changing the focal length.

The lens mechanism 21 is not limited to a revolver type, and may be one in which the focal length can be changed by moving the lens along the optical axis direction.
Furthermore, the lens mechanism 21 may be configured to include a driving mechanism such as a motor. In this case, the light receiving amount ratio setting unit 208 can control the focal length of the lens mechanism 21.

The discharge probability calculation unit 202 instructs the rectangular pulse generation unit 17 to start applying the drive pulse voltage PM. In response to the instruction from the discharge probability calculation unit 202, the rectangular pulse generation unit 17 sets the pulse width of the rectangular pulse PS to a predetermined value T. With this pulse width setting, the applied voltage generation circuit 12 applies the drive pulse voltage PM with the pulse width T between the pair of terminals 1a, 1b of the optical sensor 1 (step S101). Note that the pulse width T may be the same as the reference pulse width _T0 .

The discharge determination unit 201 compares the detection voltage Vpv from the current detection circuit 15 with a predetermined threshold voltage Vth, and determines that the optical sensor 1 has discharged when the detection voltage Vpv exceeds the threshold voltage Vth. When the discharge determination unit 201 determines that the optical sensor 1 has discharged, it counts this as one discharge and counts the number of discharges n (step S102). The initial values of the number of discharges n and the number of applications N of the drive pulse voltage PM are both 0. In this manner, the processes of steps S101 and S102 are repeatedly executed.

The pulse application number accumulator 203 counts the number of rectangular pulses PS output from the rectangular pulse generator 17 to count the number of times N the driving pulse voltage PM is applied.
The application number determination unit 204 compares the number of times N that the driving pulse voltage PM is applied with a predetermined number Nth.

When the application number determination unit 204 determines that the number of applications N of the drive pulse voltage PM from the start of application of the drive pulse voltage PM with the pulse width T in step S101 exceeds a predetermined number Nth (YES in step S103), the discharge probability calculation unit 202 calculates the discharge probability P _re using equation (17) based on the number of applications N of the drive pulse voltage PM at this time and the number of discharges n detected by the discharge determination unit 201 (step S104).
P _re =n/N (17)

The sensitivity parameter storage unit 19 pre-stores, as known sensitivity parameters of the optical sensor 1, the amount of light received by the optical sensor 1 _Q0 , the reference pulse width _T0 of the drive pulse voltage PM, the discharge probability P _aA of a normal discharge when the pulse width of the drive pulse voltage PM is the reference pulse width T0 and the amount of light received by the optical sensor _{1 Q0} , and the light-receiving area S ₂ of the electrode surface of the optical sensor 1 when the reference amount of light received _Q2 in the state of FIG. 4B is obtained.

When the discharge probability P _re calculated by the discharge probability calculation unit 202 is greater than 0 and less than 1 (YES in step S105), the received light amount calculation unit 206 calculates the received light amount Q=Q _re by equation (9) based on the discharge probability P _re , the pulse width T of the drive pulse voltage PM when the discharge probability P _re was calculated, and the parameters Q ₀ , T ₀ , and P _aA stored in the sensitivity parameter storage unit 19 (step S106). In this calculation, P _re is substituted for P in equation (9).

Furthermore, if the discharge probability P _re calculated by the discharge probability calculation unit 202 is 0 or 1 (NO in step S105), the received light amount calculation unit 206 returns to step S101. In this manner, the processes of steps S101 to S105 are repeated until the discharge probability P _re is greater than 0 and less than 1, and the process ends when the received light amount Q _re can be calculated. The discharge probability calculation unit 202 stores the value of the discharge probability P _re that is greater than 0 and less than 1 in the sensitivity parameter storage unit 19.

Next, the operation of the light detection system after installation at the site will be described with reference to Fig. 7. After the light detection system is installed at the site, the light reception ratio setting unit 208 initializes the light reception ratio and the discharge probability number i to 1 (step S200). The light reception ratio setting unit 208 controls the focal length of the lens mechanism 21 to a predetermined first value (step S201) so that the amount of light reception becomes _Q1 in the state of Fig. _4A compared to the reference amount of light reception _Q2 in the state of Fig. _4B , and _Q1 = r1Q2 is established.

The discharge probability calculation unit 202 instructs the rectangular pulse generation unit 17 to start applying the drive pulse voltage PM. In response to the instruction from the discharge probability calculation unit 202, the rectangular pulse generation unit 17 sets the pulse width of the rectangular pulse PS to a predetermined value T. With this pulse width setting, the applied voltage generation circuit 12 applies the drive pulse voltage PM with the pulse width T between a pair of terminals 1a, 1b of the optical sensor 1 (step S202). Note that the pulse width T after installation at the site may be a different value from the pulse width T at the time of shipment from the factory.

Similarly to the above, when the detection voltage Vpv from the current detection circuit 15 exceeds the threshold voltage Vth, the discharge determination unit 201 determines that the optical sensor 1 has discharged, and increments the number of discharges n _i =n ₁ by 1 (step S203). The initial values of the number of discharges n ₁ and the number of applications N ₁ of the drive pulse voltage PM are both 0. In this manner, the processes of steps S202 and S203 are repeatedly executed.

The discharge probability calculation unit 202 calculates the number of times N the drive pulse voltage PM is applied from the start of application of the drive pulse voltage PM with a pulse width T in step S202._i= N₁When the application number determination unit 204 determines that the application number N of the driving pulse voltage PM at this time exceeds the predetermined number Nth (YES in step S204),_i= N₁and the number of discharges n detected by the discharge determination unit 201_i= n₁Based on this, the discharge probability P_i=P₁(step S205).
P₁= n₁/N₁ ...(18)

If the discharge probability _P1 is 0 or 1 (NO in step S206), the discharge probability calculation unit 202 returns to step S202. In this manner, the processes in steps S202 to S206 are repeated until the discharge probability _P1 is greater than 0 and less than 1.

If the calculated discharge probability _P1 is greater than 0 and less than 1 (YES in step S206), the discharge probability calculation unit 202 increments the number i by 2 (step S207). If the number i is smaller than 5 (YES in step S208), the discharge probability calculation unit 202 returns to step S201.

When the discharge probability _P1 is greater than 0 and less than 1, and the number i is smaller than 5, the light receiving amount ratio setting unit 208 controls the focal length of the lens mechanism ₂₁ to a predetermined second value so that the amount of light received becomes _Q3 in the state of FIG. 4C relative to the reference amount of light received _Q2 in the state of FIG. 4B, and _Q3 = _r3Q2 is established (step S201).

Either one of the received light amounts _Q1 and _Q3 may be the same as the received light amount _Q2 . That is, either one of the received light amount ratios _r1 and _r3 ( _r1 ≠ _r3 ) may be 1.

The discharge probability calculation unit 202 instructs the rectangular pulse generation unit 17 to start applying the drive pulse voltage PM. In response to the instruction from the discharge probability calculation unit 202, the rectangular pulse generation unit 17 temporarily stops outputting the rectangular pulse PS, and then sets the pulse width of the rectangular pulse PS to a predetermined value T. By setting this pulse width, the applied voltage generation circuit 12 applies the drive pulse voltage PM with the pulse width T between the pair of terminals 1a, 1b of the optical sensor 1 (step S202).

Similarly to the above, when the detection voltage Vpv from the current detection circuit 15 exceeds the threshold voltage Vth, the discharge determination unit 201 determines that the optical sensor 1 has discharged, and increments the number of discharges n _i =n ₃ by 1 (step S203). The initial values of the number of discharges n ₃ and the number of applications N ₃ of the drive pulse voltage PM are both 0. In this manner, the processes of steps S202 and S203 are repeatedly executed.

The discharge probability calculation unit 202 calculates the number of times N the drive pulse voltage PM is applied from the start of application of the drive pulse voltage PM with a pulse width T in step S202._i= N₃When the application number determination unit 204 determines that the application number N of the driving pulse voltage PM at this time exceeds the predetermined number Nth (YES in step S204),_i= N₃and the number of discharges n detected by the discharge determination unit 201_i= n₃Based on this, the discharge probability P_i=P₃(step S205).
P₃= n₃/N₃ ...(19)

If the discharge probability _P3 is 0 or 1 (NO in step S206), the discharge probability calculation unit 202 returns to step S202. In this manner, the processes in steps S202 to S206 are repeated until the discharge probability _P3 is greater than 0 and less than 1.

When the calculated discharge probability P ₃ is greater than 0 and less than 1 (YES in step S206), the discharge probability calculation unit 202 increments the number i by 2 (step S207).
When the number i reaches 5 (NO in step S208), the photon number calculation unit 205 calculates the ratio E/Ere of the number of photons at the time of factory shipment to the number of photons after installation on site using equation (16) based on the discharge probabilities _P1 , _P3 calculated by the discharge probability calculation unit ₂₀₂ , the light receiving amount ratios _r1 , _r3 set by the light receiving amount _ratio setting unit 208, and the discharge probability Pre at the time of factory shipment stored in the sensitivity parameter memory unit 19 (step S209).

The received light amount calculation unit 206 calculates the received light amount _Q by equation (20) based on the photon number ratio E/E calculated by the photon number calculation unit ₂₀₅ and the light receiving area S stored in the sensitivity parameter storage unit 19 (step S210).
Q=(E/ _Ere ) _S2 ...(20)

The light-receiving amount determination unit 207 compares the amount of light received Q calculated by the light-receiving amount calculation unit 206 with a predetermined light-receiving amount threshold Qth (step S211), and if the amount of light received Q exceeds the light-receiving amount threshold Qth (YES in step S211), it determines that there is a flame (step S212). If the amount of light received Q is equal to or less than the light-receiving amount threshold Qth (NO in step S211), the light-receiving amount determination unit 207 determines that there is no flame (step S213).

As described above, in this embodiment, it is possible to calculate the ratio E/ _Ere of the number of photons of the optical sensor 1. In this embodiment, by calculating the ratio E/ _Ere of the number of photons, it is possible to compare the degree of discharge with that of another solid-state optical sensor.

[Second embodiment]
Next, a second embodiment of the present invention will be described. In this embodiment, an example will be described in which irregular discharge phenomena (pseudo discharges) caused by noise components other than discharges caused by the photoelectric effect are also taken into consideration. In this embodiment, the configuration of the light detection system is the same as in the first embodiment, so the symbols in FIG. 2 will be used for the description.

[Operation of the optical detection system taking noise into account]
The relationship between the discharge of the optical sensor 1 and time can be considered to be one of the following two cases.
(a) Discharge that occurs with a uniform probability during application of the driving pulse voltage PM (Equation (9)).
(b) Discharge occurring at the rising or falling edge of the driving pulse voltage PM.

Next, the relationship between the discharge of the optical sensor 1 and the amount of received light can be considered in the following two cases.
(A) Discharge that appears according to the relationship between the amount of received light and equation (9).
(B) Discharge that appears regardless of the amount of light received.

As shown in the matrix of Table 1, the noise discharge of the optical sensor 1 can be categorized into combinations of (a), (b) and (A), (B). In the present invention, it is considered that the combination of (a) and (A) (aA), the combination of (a) and (B) (aB), the combination of (b) and (A) (bA), and the combination of (b) and (B) (bB) are most likely to be reliably observed.

The discharge in combination aA is a normal discharge called "sensitivity" (already incorporated into equation (9)). The discharge in combination aB is a discharge that is unrelated to the amount of ultraviolet light triggered by thermoelectrons, etc. The discharge in combination bA is a discharge that occurs in a limited manner due to inrush current or residual ions when the drive pulse voltage rises or falls, and is dependent on the amount of light. The discharge in combination bB is a discharge that occurs in a limited manner due to inrush current or residual ions when the drive pulse voltage rises or falls, and is independent of the amount of light.

Note that the types listed in Table 1 do not cover all UV (ultraviolet) failure modes. For example, there are failure modes not included in Table 1, such as discharge not being cut off or different sensitivity wavelengths.

The above aA discharge and the three types of aB, bA, and bB noise discharges can be expressed in the form of equation (21).

In equation (21), P _aB is the discharge probability of aB at the amount of received light Q and pulse width T, P _bA is the discharge probability of bA at the amount of received light Q and pulse width T, and P _bB is the discharge probability of bB at the amount of received light Q and pulse width T.

[Method of calculating the number of photons when using lenses with different focal lengths]
In equation (21), it is assumed that the discharge probabilities P _aB and P _bB are known. When the focal length of the lens mechanism 21 is changed as shown in Figures 4(A) to 4(C), the discharge probability in three different focal length states is _Pi (i = 1 to 3 ₎ , and the amount of received light is _Qi . Here, it is assumed that _Q1 = _r1Q2 , _Q3 = _r3Q2 ( _r1 ≠ _{r3 )} , the ratios _r1 and _r3 are known, and the number E of photons per unit electrode area that reach the electrode of the optical sensor 1 in the state of Figure 4(B) is unknown.

Equation (22) is obtained by substituting the discharge probability _P1 and the amount of light received _Q1 when measured in the state of Figure 4(A) after the optical detection system is installed at the site into equation (21), and equation (23) is obtained by substituting the discharge probability _P3 and the amount of light received _Q3 when measured in the state of Figure 4(C) into equation (21).

Dividing equation (22) by (23) gives equation (24).

Furthermore, assume that when the light detection system is shipped from the factory, the focal length of the lens mechanism 21 is set to an arbitrary value, the amount of received light _Qre when the discharge probability is P _re is calculated, and the discharge probability P _re and the amount of received light Q _re are known. Since the discharge probabilities P _aB and P _bB are known, equation (21) when the discharge probability is P _re and the amount of received light is Q _re can be modified to obtain equation (25).

Substituting equation (24) into equation (25) and transforming it gives equation (26).

Substituting Q ₁ =r ₁ Q ₂ and Q ₃ =r ₂ Q ₂ into equation (26), we obtain equation (27).

By substituting Q ₂ =(ES _l )/(E ₀ S _l ) and Q _re =(E _re S _l )/(E ₀ S _l ) into equation (27), E/E _re can be obtained as shown in equation (28).

Therefore, it is possible to calculate the ratio E/Ere of the number of photons at the time of factory shipment to the number of photons after installation at the site using the known values _P1 , _P3 , _r1 , and _r3 after the optical detection system has been installed at the site and the known values _PaB , _PbB , _T0 , _{Pre ,} and _Qre at the time of shipment from the factory.

The operation of the photodetection system of this embodiment will be described in more detail below. In this embodiment, the flow of the operation of the photodetection system at the time of shipment from the factory is similar to that of the first embodiment, so the operation at the time of shipment from the factory will be described with reference to FIG.
For example, at the inspection stage before shipping from the factory, the focal length of the lens mechanism 21 is set to an arbitrary value manually or under the control of the light receiving amount ratio setting unit 208, as in the first embodiment (step S100).

The applied voltage generating circuit 12 applies a driving pulse voltage PM having a pulse width T between a pair of terminals 1a and 1b of the optical sensor 1 (step S101).
The discharge determination unit 201 determines that the optical sensor 1 has discharged when the detected voltage Vpv from the current detection circuit 15 exceeds the threshold voltage Vth, and increments the number of discharges n by 1 (step S102).

When the number of times N of applications of the drive pulse voltage PM from the start of application of the drive pulse voltage PM with a pulse width T in step S101 exceeds a predetermined number Nth (YES in step S103), the discharge probability calculation unit 202 calculates the discharge probability P _re using equation (17) based on the number of times N of applications of the drive pulse voltage PM at this time and the number of discharges n detected by the discharge determination unit 201 (step S104).

If the discharge probability P _re calculated by the discharge probability calculation unit 202 is greater than 0 and less than 1 (YES in step S105), the received light amount calculation unit 206 calculates the received light amount Q = Q re using equation (9) based on the discharge probability P _re , the pulse width T of the driving pulse voltage PM when the discharge probability _{P re} was calculated, and the parameters Q ₀ , T ₀ , and P _aA stored in the sensitivity parameter memory unit 19 (step S106).

When the discharge probability P _re is 0 or 1, the processes of steps S101 to S105 are repeated until the discharge probability P _re becomes greater than 0 and less than 1, and the process ends when the amount of received light Q _re is calculated. The discharge probability calculation unit 202 stores the value of the discharge probability P _re that is greater than 0 and less than 1 in the sensitivity parameter storage unit 19.

Next, the operation of the light detection system after installation at the site will be described with reference to Fig. 7. After the light detection system is installed at the site, the light reception amount ratio setting unit 208 initializes the number i to 1 (step S200). The light reception amount ratio setting unit 208 controls the focal length of the lens mechanism ₂₁ to a predetermined first value (step S201) so that the amount of light reception becomes _Q1 in the state of Fig. 4A compared to the reference amount of light reception Q2 in the state of Fig. 4B, _{and Q1} = _r1Q2 is established.

The applied voltage generating circuit 12 applies the drive pulse voltage PM having a pulse width T between the pair of terminals 1a, 1b of the optical sensor 1 (step S202).
The discharge determination unit 201 determines that the optical sensor 1 has discharged when the detected voltage Vpv from the current detection circuit 15 exceeds the threshold voltage Vth, and increments the number of discharges n _i =n ₁ by 1 (step S203).

When the number of applications N _i =N ₁ of the driving pulse voltage PM from the start of application of the driving pulse voltage PM with the pulse width T in step S202 exceeds a predetermined number Nth (YES in step S204), the discharge probability calculation unit 202 calculates the discharge probability P _i =P ₁ by equation (18) based on the number of applications N _i = _{N 1} of the driving pulse voltage PM at this time and the number of discharges n i =n ₁ detected by the discharge determination unit 201 (step S205). When the calculated discharge probability P ₁ is greater than 0 and less than 1 (YES in step S206), the discharge probability calculation unit 202 increments the number i by 2 (step S207).

When the discharge probability _P1 is greater than 0 and less than 1, and the number i is smaller than 5, similarly to the first embodiment, the light receiving amount ratio setting unit 208 controls the focal length of the lens mechanism ₂₁ to a predetermined second value so that the amount of light received becomes _Q3 in the state of FIG. 4C relative to the reference amount of light received _Q2 in the state of FIG. 4B, and _Q3 = _r3Q2 is established (step S201).

The applied voltage generating circuit 12 applies the drive pulse voltage PM having a pulse width T between the pair of terminals 1a, 1b of the optical sensor 1 (step S202).
The discharge determination unit 201 determines that the optical sensor 1 has discharged when the detected voltage Vpv from the current detection circuit 15 exceeds the threshold voltage Vth, and increments the number of discharges n _i =n ₃ by 1 (step S203).

When the number of applications N _i =N ₃ of the driving pulse voltage PM from the start of application of the driving pulse voltage PM with the pulse width T in step S202 exceeds a predetermined number Nth (YES in step S204), the discharge probability calculation unit 202 calculates the discharge probability P _i =P ₃ by equation (19) based on the number of applications N _i = _{N 3} of the driving pulse voltage PM at this time and the number of discharges n i =n ₃ detected by the discharge determination unit 201 (step S205). When the calculated discharge probability P ₃ is greater than 0 and less than 1 (YES in step S206), the discharge probability calculation unit 202 increments the number i by 2 (step S207).

In the sensitivity parameter memory unit 19 of this embodiment, in addition to the discharge probability P _re and light-receiving area S _re at the time of shipment from the factory, the amount of light received by the light sensor 1 Q ₀ , the reference pulse width T ₀ of the driving pulse voltage PM, the light-receiving area S ₂ , and the discharge probabilities P _aB and P _bB of irregular discharges are pre-stored as known sensitivity parameters of the light sensor 1.

The discharge probability P _aB is the probability of discharge due to noise components other than discharge due to the photoelectric effect of the optical sensor 1, which occurs depending on the pulse width of the drive pulse voltage PM and independent of the amount of light received by the optical sensor 1 as described above. The discharge probability P _bB is the probability of discharge due to noise components other than discharge due to the photoelectric effect of the optical sensor 1, which occurs independent of the pulse width of the drive pulse voltage PM and the amount of light received by the optical sensor 1 as described above.

When the number i reaches 5 (NO in step S208), the photon number calculation unit 205 in this embodiment calculates the ratio E/ _Ere of the number of photons at the time of factory shipment to the number of photons after installation on the field using equation (28) based on the discharge probabilities _P1 , _P3 calculated by the discharge probability calculation unit 202, the light receiving amount _{ratios r1} , _r3 set by the light receiving amount ratio setting unit 208, the pulse width _T of the driving pulse voltage PM when the discharge probabilities P1, _P3 were determined, and the discharge probability Pre at the time of factory shipment, the reference pulse width T0, and the discharge probabilities P _aB , P _bB of irregular _discharges stored in the sensitivity parameter memory unit 19 (step S209).

The received light amount calculation unit 206 calculates the received light amount _Q by equation (20) based on the photon number ratio E/E calculated by the photon number calculation unit ₂₀₅ and the light receiving area S stored in the sensitivity parameter storage unit 19 (step S210).

The light receiving amount determination unit 207 compares the light receiving amount Q calculated by the light receiving amount calculation unit 206 with the light receiving amount threshold Qth (step S211), and if the light receiving amount Q exceeds the light receiving amount threshold Qth (YES in step S211), it determines that there is a flame (step S212). Also, if the light receiving amount Q is equal to or less than the light receiving amount threshold Qth (NO in step S211), the light receiving amount determination unit 207 determines that there is no flame (step S213).

In this way, in this embodiment, it is possible to obtain the same effect as in the first embodiment. Also, in this embodiment, it is possible to calculate the ratio E/ _E of the number of photons excluding noise components other than the normal discharge of the optical sensor 1.

In the first and second embodiments, the light source 100 is a flame, but the light detection system of the present invention can also be applied to light sources 100 other than a flame.

The sensitivity parameter storage unit 19 and central processing unit 20 described in the first and second embodiments can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources.

An example of the configuration of this computer is shown in FIG. 8. The computer comprises a CPU 300, a storage device 301, and an interface device (I/F) 302. The applied voltage generating circuit 12, the rectangular pulse generating unit 17, the A/D conversion unit 18, and the like are connected to the I/F 302. In such a computer, a program for implementing the photon number calculation method of the present invention is stored in the storage device 301. The CPU 300 executes the processing described in the first and second embodiments according to the program stored in the storage device 301.

The present invention can be applied to flame detection systems. The present invention can also be applied to the detection of light other than flames.

1...optical sensor, 2...external power supply, 3...arithmetic unit, 11...power supply circuit, 12...applied voltage generation circuit, 13...trigger circuit, 14...voltage dividing resistor, 15...current detection circuit, 16...processing circuit, 17...rectangular pulse generation unit, 18...A/D conversion unit, 19...sensitivity parameter storage unit, 20...central processing unit, 21...lens mechanism, 201...discharge determination unit, 202...discharge probability calculation unit, 203...pulse application number accumulation unit, 204...application number determination unit, 205...photon number calculation unit, 206...received light amount calculation unit, 207...received light amount determination unit, 208...received light amount ratio setting unit.

Claims (11)

a light sensor configured to detect light emitted from the light source;
a lens mechanism provided between the light source and the optical sensor and configured to adjust a focal length;
an applied voltage generating unit configured to periodically apply a driving pulse voltage to an electrode of the optical sensor;
a current detection unit configured to detect a discharge current of the optical sensor;
a discharge determination unit configured to detect a discharge of the optical sensor based on the discharge current detected by the current detection unit;
a discharge probability calculation unit configured to calculate a discharge probability for each of a first state in which a focal length of the lens mechanism is a predetermined first value and a second state in which the focal length is a predetermined second value different from the first value, based on the number of applications of the drive pulse voltage by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage;
A storage unit configured to store a discharge probability of the light detection system at the time of shipment from the factory as a known sensitivity parameter of the light sensor in advance;
and a photon number calculation unit configured to calculate a ratio of the number of photons reaching the light receiving surface of the optical sensor when the optical detection system is shipped from a factory and after installation on site, based on the sensitivity parameters stored in the memory unit, the discharge probability calculated by the discharge probability calculation unit in the first and second states, a predetermined first ratio between a reference amount of received light of the optical sensor and the amount of received light in the first state, and a predetermined second ratio between the reference amount of received light and the amount of received light in the second state. 2. The optical detection system of claim 1,
The photon number calculation unit calculates, when the ratio of the number of photons at the time of shipment from the factory to the number of photons after installation at the site is E/E _re , the discharge probabilities calculated by the discharge probability calculation unit in the first and second states are P ₁ and P ₃ , a predetermined first ratio between the reference amount of received light and the amount of received light in the first state is r ₁ , a predetermined second ratio between the reference amount of received light and the amount of received light in the second state is r ₃ , and the discharge probability at the time of shipment from the factory stored in the memory unit is P _re ,

The photon number ratio E/ _E is calculated by the above method. a light sensor configured to detect light emitted from the light source;
a lens mechanism provided between the light source and the optical sensor and configured to adjust a focal length;
an applied voltage generating unit configured to periodically apply a driving pulse voltage to an electrode of the optical sensor;
a current detection unit configured to detect a discharge current of the optical sensor;
a discharge determination unit configured to detect a discharge of the optical sensor based on the discharge current detected by the current detection unit;
a discharge probability calculation unit configured to calculate a discharge probability for each of a first state in which a focal length of the lens mechanism is a predetermined first value and a second state in which the focal length is a predetermined second value different from the first value, based on the number of applications of the drive pulse voltage by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage;
a storage unit configured to store in advance, as known sensitivity parameters of the optical sensor, a discharge probability at the time of shipment from a factory of the optical detection system, a reference pulse width of the drive pulse voltage, a discharge probability of a first type of irregular discharge caused by a noise component other than a discharge caused by a photoelectric effect of the optical sensor, which occurs depending on the pulse width of the drive pulse voltage and occurs independently of the amount of light received by the optical sensor, and a discharge probability of a second type of irregular discharge caused by the noise component, which occurs independently of the pulse width of the drive pulse voltage and the amount of light received by the optical sensor;
and a photon number calculation unit configured to calculate a ratio of the number of photons reaching a light receiving surface of the optical sensor when the optical detection system is shipped from a factory and after installation on site, based on the sensitivity parameters stored in the memory unit, the discharge probability calculated by the discharge probability calculation unit when the optical sensor is in the first and second states, a predetermined first ratio between a reference amount of received light of the optical sensor and the amount of received light when the optical sensor is in the first state, a predetermined second ratio between the reference amount of received light and the amount of received light when the optical sensor is in the second state, and a pulse width of the drive pulse voltage when the optical detection system is in the first and second states. 4. The optical detection system of claim 3,
the photon number calculation unit determines the ratio of the number of photons at the time of shipment from the factory to the number of photons after installation at the site as E/E _re , the discharge probabilities calculated by the discharge probability calculation unit in the first and second states as P ₁ and P ₃ , a predetermined first ratio between the reference amount of received light and the amount of received light in the first state as r ₁ , a predetermined second ratio between the reference amount of received light and the amount of received light in the second state as r ₃ , a discharge probability at the time of shipment from the factory stored in the memory unit as P _re , a reference pulse width of the drive pulse voltage as T ₀ , a discharge probability of the first type of irregular discharge as P _aB , a discharge probability of the second type of irregular discharge as P _bB , and a pulse width of the drive pulse voltage in the first and second states as T,

The photon number ratio E/ _E is calculated by the above method. 5. The optical detection system according to claim 1,
a light receiving amount ratio setting unit configured to control a focal length of the lens mechanism to the first value so that a ratio between the reference amount of received light and the amount of received light in the first state becomes the first ratio, thereby putting the light detection system in the first state, and to control a focal length of the lens mechanism to the second value so that a ratio between the reference amount of received light and the amount of received light in the second state becomes the second ratio, thereby putting the light detection system in the second state. 6. The optical detection system according to claim 1 ,
the discharge probability calculation unit calculates a discharge probability based on the number of times the drive pulse voltage is applied by the applied voltage generation unit and the number of discharges detected by the discharge determination unit during the application of the drive pulse voltage, at the time of shipment from the factory prior to installation at the site of the optical detection system, and stores the calculated discharge probability in the memory unit. 7. The optical detection system according to claim 1,
The optical detection system further comprises a light receiving amount calculation unit configured to calculate an amount of light received by the optical sensor after the optical detection system is installed at a site, based on the ratio of the number of photons calculated by the photon number calculation unit. a first step of periodically applying a driving pulse voltage to an electrode of the optical sensor when the focal length of a lens mechanism provided between a light source and the optical sensor is a first predetermined value;
a second step of detecting a discharge current of the optical sensor in the first state;
a third step of detecting a discharge of the optical sensor based on the discharge current in the first state;
a fourth step of calculating a discharge probability in the first state based on the number of times the driving pulse voltage is applied in the first step and the number of times the discharge is detected in the third step during application of the driving pulse voltage;
a fifth step of periodically applying a driving pulse voltage to an electrode of the optical sensor when the focal length of the lens mechanism is in a second state where the focal length is a second predetermined value different from the first value;
a sixth step of detecting a discharge current of the optical sensor in the second state;
a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state;
an eighth step of calculating a discharge probability in the second state based on the number of times the driving pulse voltage is applied in the fifth step and the number of times the discharge is detected in the seventh step during the application of the driving pulse voltage;
a ninth step of referring to a memory unit that pre-stores a discharge probability of the optical detection system at the time of shipment from a factory as a known sensitivity parameter of the optical sensor, and calculating a ratio of the number of photons reaching the light receiving surface of the optical sensor between the time of shipment from a factory and after installation on site, based on the sensitivity parameter stored in the memory unit, the discharge probability calculated in the fourth and eighth steps when the optical sensor is in the first and second states, a predetermined first ratio between a reference amount of received light of the optical sensor and the amount of received light in the first state, and a predetermined second ratio between the reference amount of received light and the amount of received light in the second state. a first step of periodically applying a driving pulse voltage to an electrode of the optical sensor when the focal length of a lens mechanism provided between a light source and the optical sensor is a first predetermined value;
a second step of detecting a discharge current of the optical sensor in the first state;
a third step of detecting a discharge of the optical sensor based on the discharge current in the first state;
a fourth step of calculating a discharge probability in the first state based on the number of times the driving pulse voltage is applied in the first step and the number of times the discharge is detected in the third step during application of the driving pulse voltage;
a fifth step of periodically applying a driving pulse voltage to an electrode of the optical sensor when the focal length of the lens mechanism is in a second state where the focal length is a second predetermined value different from the first value;
a sixth step of detecting a discharge current of the optical sensor in the second state;
a seventh step of detecting a discharge of the optical sensor based on the discharge current in the second state;
an eighth step of calculating a discharge probability in the second state based on the number of times the driving pulse voltage is applied in the fifth step and the number of times the discharge is detected in the seventh step during the application of the driving pulse voltage;
A storage unit is referred to which stores in advance, as known sensitivity parameters of the optical sensor, a discharge probability at the time of shipment from the photodetection system, a reference pulse width of the drive pulse voltage, a discharge probability of a first type of irregular discharge caused by a noise component other than a discharge caused by a photoelectric effect of the optical sensor, which occurs depending on the pulse width of the drive pulse voltage and does not depend on the amount of light received by the optical sensor, and a discharge probability of a second type of irregular discharge caused by the noise component, which occurs independent of the pulse width of the drive pulse voltage and the amount of light received by the optical sensor, and the discharge probability stored in the storage unit is and a ninth step of calculating a ratio of the number of photons reaching the light receiving surface of the optical sensor when the optical detection system is shipped from a factory to after installation on site, based on the sensitivity parameters calculated in the fourth and eighth steps when the optical sensor is in the first and second states, a predetermined first ratio between a reference amount of received light of the optical sensor and the amount of received light in the first state, a predetermined second ratio between the reference amount of received light and the amount of received light in the second state, and a pulse width of the drive pulse voltage when the optical detection system is in the first and second states. 10. The photon number calculation method according to claim 8,
a tenth step of controlling a focal length of the lens mechanism to the first value so that a ratio between the reference amount of received light and an amount of received light in the first state becomes the first ratio, thereby putting the light detection system in the first state;
and an eleventh step of controlling a focal length of the lens mechanism to the second value so that a ratio between the reference amount of received light and the amount of received light in the second state becomes the second ratio, thereby putting the light detection system in the second state. The photon number calculation method according to any one of claims 8 to 10,
A twelfth step of periodically applying a driving pulse voltage to an electrode of the optical sensor at the time of shipment from a factory before installation on site of the optical detection system;
a thirteenth step of detecting a discharge current of the optical sensor;
a fourteenth step of detecting a discharge of the optical sensor based on the discharge current;
a fifteenth step of calculating a discharge probability based on the number of applications of the drive pulse voltage in the twelfth step and the number of discharges detected in the fourteenth step during the application of the drive pulse voltage, and storing the calculated discharge probability in the memory unit.

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