JP2657445B2 - Light intensity measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic light quantity measuring device for measuring the quantity of light by receiving transmitted light (including scattered light) or reflected light of light emitted from a light source to an object to be measured.

[0002]

2. Description of the Related Art For example, lubricating oils used in engine oils of automobiles and the like are reduced in light transmittance as they become dirty or deteriorate. For this reason, a part of the lubricating oil is accommodated in a specific cell having light transmissivity or is allowed to flow through the cell, and light is irradiated from a light source such as an LED (light emitting diode) to the transmitted light, and the transmitted light is used as a photodiode. There has been proposed an electronic light quantity measuring device in which a light detecting element is used to detect the amount of transmitted light and determine the degree of contamination or deterioration of the lubricating oil based on the detection result. For example, illuminance (light amount) using an LED as a light source and a photodiode as a photodetector
FIG. 4 shows an example of a conventional frequency-converted electronic light quantity measuring device.

This light quantity measuring device comprises a photodiode PD as a light detecting element, a capacitor C as a capacitive load, and diodes D1 and C-MO functioning as switches.
The S-type first Schmitt inverter 11 constitutes an illuminance-frequency conversion circuit 10, and the diode D1 has a polarity opposite to that of the photodiode PD between the output and the input of the first Schmitt inverter 11, and a resistance R1. , And the photodiode PD and the capacitor C are connected in series between a predetermined voltage source and the ground, and their connection point is connected to the input of the first Schmitt inverter 11.

On the other hand, the LED 13 is connected in series with a switching transistor 14 between a predetermined voltage source and the ground. When the transistor 14 is turned on, it emits light and emits light in the light-transmitting cell 15. The object 16 to be measured such as oil is irradiated with light. The light transmitted through the object to be measured 16 is incident on the photodiode PD, therefore, proportional to the illuminance or amount of incident light current I _P photodiode P
Flow to D.

[0005] current I _P flowing through the photodiode PD is accumulated in the capacitor C, it is converted into a voltage V _C. Voltage V _C to be accumulated in the capacitor C is converted into a pulse signal at a first Schmitt inverter 11. The first Schmitt inverter 11 has two threshold voltages, a high-level threshold voltage V _TH and a low-level threshold voltage V _TL , and when the input voltage is lower than the high-level threshold voltage V _TH , the high-level output voltage V _TH
H , and when the input voltage reaches the high level threshold voltage V _TH , the output voltage switches from the high level V _H to the low level _VL , and the input voltage drops to the low level threshold voltage V _TL . until holds the output voltage V _L of the low level, the output voltage when the input voltage drops to a low level threshold voltage V _TL operates to switches from the low level V _L to the high level V _H. Therefore, not incident light to the photodiode PD, when the current I _P does not flow, i.e., when the charge in the capacitor C are not accumulated, the output voltage is a high level V _H, also the charging voltage V of the capacitor C _{When C} becomes equal to the high-level threshold voltage V _TH , the output voltage of the Schmitt inverter 11 switches from the high level to the low level _VL . Further, when the charge accumulated in the capacitor C is decreased to a low level threshold voltage V _TL of the Schmitt inverter 11 by the discharge, the output voltage of the Schmitt inverter 11 is switched from the low level V _L to the high level V _H. Accordingly, the first Schmitt inverter 11 outputs a pulse voltage having a cycle corresponding to the charging and discharging of the capacitor C, and thus the illuminance or the amount of light incident on the photodiode PD is converted into a frequency signal.

In the above structure, the photodiode PD
In the initial state in which no current flows and no charge is stored in the capacitor C, the output voltage of the first Schmitt inverter 11 is at the high level _VH , so that the diode D1 is reversely biased, and the switch D is turned off. Performs the same function. Therefore, no current flows through the resistor R1, and the capacitor C is in a chargeable state. When the measurement of the light quantity is started, the current I _P in the photodiode PD flows, capacitor C is charged. When the charging voltage V _C of the capacitor C reaches a high level threshold voltage V _TH of the first Schmitt inverter 11, the output voltage of the Schmitt inverter 11 is switched from the high level V _H to the low level V _L. This diode D1 is forward biased, since forming the same function as the switch-on, the output current I _P of the charging voltage V _C and the photodiode PD of the capacitor C flows through the resistor R1 and the diode D1, the capacitor C The charging voltage is discharged. When the charging voltage V _C of the capacitor C drops to the low level threshold voltage V _TL of the Schmitt inverter 11 by discharging, the output voltage of the Schmitt inverter 11 switches from the low level _VL to the high level V _H. As a result, the diode D1 is again reverse-biased and turned off, so that a charging current flows through the capacitor C. Hereinafter, as a result of the same operation being repeated, the output voltage of the first Schmitt inverter 11
That is, the output voltage V ₁ from the illuminance-frequency conversion circuit 10
Has a pulse waveform having a frequency corresponding to the charge / discharge cycle of the capacitor C, as shown in FIG.

In this example, the output voltage V ₁ of the first Schmitt inverter 11 is supplied to a second Schmitt inverter 12 of the same C-MOS type as the first Schmitt inverter 11. This second Schmidt inverter 1
2 also has two threshold voltages, a high level threshold voltage V _TH and a low level threshold voltage V _TL , and operates similarly. That is, when a high-level voltage signal _VH is input from the first Schmitt inverter 11, a low-level voltage output _VL is generated, and when a low-level voltage signal _VL is input, a high-level voltage output _VL is generated. It generates an output V _H. Therefore, the second Schmitt inverter 12 generates an output voltage of the same frequency F ₀ in which the pulse waveform of the first Schmitt inverter 11 is inverted,
It is supplied to a microcomputer 20 which is an arithmetic measuring unit.

The microcomputer 20 counts the number of pulses of the frequency signal F ₀ input from the illuminance-frequency conversion circuit 10 through the second Schmitt inverter 12, and the input / output characteristics of the photodiode PD and the conversion circuit. ROM storing arithmetic processing program
(Read-only memory) and the number of pulses within a certain time counted by the counter 21
Photodiode PD according to program in storage unit 22
And an arithmetic processing unit 23 for detecting the magnitude of the output current and calculating the illuminance or the amount of light. Thus, the illuminance or the amount of light incident on the photodiode PD can be obtained.

[0009]

However, in the light quantity measuring device having the above configuration, the illuminance-frequency conversion circuit 1
The input / output characteristics of FIG.
The input / output range (range) is 5-6.
Over the digits, the frequency increases as the illuminance increases,
Above a certain area, nonlinearity appears in the input / output characteristics,
Eventually, the oscillation stops. (The illuminance at which oscillation stops is determined by the constants of the elements constituting the illuminance-frequency conversion circuit.) On the other hand, when the illuminance decreases, the frequency decreases, so that the counting error by the counter increases and the influence of the external noise increases. Furthermore, for example, when the use environment temperature is about 100 ° C.,
Due to the temperature dependency of the illuminance-frequency conversion circuit, if the illuminance is made smaller than a certain illuminance value, a saturation phenomenon of the input / output characteristics that the output hardly changes occurs as shown by a dotted line in FIG.

Therefore, in one light quantity measuring device, the upper limit value FH and the lower limit value F of the output frequency under actual use conditions.
There is a serious drawback that only a change in illuminance (light amount) of about three digits during L can be measured.

Further, in the analog light quantity measuring device using the conventional illuminance-voltage conversion circuit 30 shown in FIG. 7, the input / output characteristics are as shown in FIG. 8, and the illuminance-frequency conversion circuit 10 is used. The oscillation stop state does not occur as in the case described above. However, as shown in the characteristic of FIG.
When the illuminance and the output voltage are made to correspond to each other so that the output voltage becomes 1 V when the value is 0, the illuminance is reduced by five orders of magnitude to 0.001.
In this case, the output voltage becomes as very small as 10 μV. For this reason, errors due to extraneous noise and environmental temperature changes increase, and if the measurement range (range) is widened, the reliability is lacking.
Under actual conditions of use, there is a disadvantage that the change in illuminance (light amount) can be measured at most by about three digits.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly reliable and small-sized electronic light quantity measuring device capable of measuring the light quantity with high accuracy over a wide measuring range with a simple circuit configuration by automatically controlling the light quantity of a light source. It is to provide a device.

[0013]

The above object is achieved by a light quantity measuring device according to the present invention. In summary, the present invention includes a light source that irradiates light to the device under test, and a photodetector that receives transmitted light or reflected light from the device under test and changes the output current according to the amount of received light, An illuminance (light amount) -frequency converter for outputting a frequency signal corresponding to an illuminance (light amount) of light from the device to be incident on the light detecting element; and an output from the illuminance (light amount) -frequency converter. An arithmetic control unit for measuring illuminance (light amount) from a frequency signal, wherein the illuminance (light amount) -frequency conversion unit is a capacitor charged by an output current from the photodetector, and the capacitor is charged In the light quantity measuring device that is a pulse oscillation circuit that compares the set charging voltage with a preset reference voltage and changes the output signal level each time the charging voltage reaches the reference voltage to generate a pulse signal, The light And a voltage source for driving the light source, a plurality of resistors having different resistance values are connected via switching means, respectively, and the arithmetic and control means is configured to detect light incident on the photodetector from the device under test. When measuring the illuminance (light amount), the switching means is sequentially operated to sequentially switch and connect the resistors to change the light output from the light source in a stepwise manner. Is controlled so that the output frequency from the light falls within the range of the upper limit value and the lower limit value of the output frequency from the illuminance (light amount) -frequency conversion means, and the illuminance (light amount) of the light from the DUT is 5 to 6 digits. A light quantity measuring device characterized in that measurement is performed over the range of available power. The range of the upper limit value and the lower limit value of the output frequency from the illuminance (light amount) -frequency converting means is the illuminance (light amount) of the light from the DUT incident on the photodetector and the illuminance (light amount). The relationship with the output frequency from the frequency conversion means is a range showing linearity.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of a light quantity measuring device according to the present invention. In the light amount measuring apparatus of this embodiment, the LED 13 is used as a light source, the photodiode PD is used as a light detecting element, and the photodiode PD and a capacitor C which is a capacitance type load are used.
And diode D1 and C-MOS functioning as a switch
The case where the illuminance-frequency conversion circuit 10 is configured with the first Schmitt inverter 11 of the type will be described, but the present invention is not limited to this, and other elements and circuit configurations may be used. Needless to say.

In this embodiment, the LED 13 and the LED 1
3 and a plurality of resistors R11 to R14 having different resistance values are connected to the switching means SW1 to SW4 respectively.
SW4 is connected in series, and when measuring the illuminance (light amount) of the light incident on the photodiode PD, the microcomputer 20 operates the switching means sequentially to sequentially switch and connect these resistances, and the LED 13 emits light. The illuminance (light amount) is measured by gradually adjusting the intensity of the light to be emitted.

The switching means SW1 to SW4 are connected to a control signal S from a control port 24 of the microcomputer 20.
The state is switched from the off state to the on state by application of 1 to S4, and a resistor having a predetermined resistance value is selectively connected between the LED 13 and the voltage source. Thereby, the illuminance-frequency conversion circuit 10
The input / output characteristics can be switched and set stepwise. Needless to say, the switching connection of the resistors R11 to R14 may be automatically performed by means other than the microcomputer. Although transistors are used as the switching means SW1 to SW4 in this embodiment, it is needless to say that various switching means such as an electronic switch and an analog switch known in this technical field can be used. In addition, since the function, operation mode, and the like of the illuminance-frequency conversion circuit 10 are as described above, the description is omitted here.

In the above configuration, four resistors R11
When the resistance value of ~R14 is R11>R12>R13> assumed to be R14, the current I ₁ ~I flowing to LED13 when each switching means SW1~SW4 are turned on
₄ becomes I ₁ <I ₂ <I ₃ <I ₄ . These currents I _1-
The light emitted when I ₄ flows to the LED 13 is the cell 1
5, the relationship between the degree of absorption by the DUT 16, that is, the relationship between the absorbance and the output frequency from the illuminance-frequency conversion circuit 10, is shown by the dotted line in FIG. 2. When the resistor R11 is selectively connected and the current I1 is flowing through the LED ₁₃ ,
The characteristic (range I ₁ ) indicated by A in FIG.
Are selectively connected and the current I ₂ flows through the LED 13, the characteristic shown by B in FIG. 2 (range I ₂ ) is obtained. When the resistor R 13 is selectively connected and the current I ₃ flows through the LED 13, FIG. the characteristic indicated by C (range I ₃₎ next, and resistance R14 is selected connected, when in the current I ₄ flows in LED13 is a characteristic (range I ₄₎ shown in D in FIG.

Accordingly, when the upper limit value and the lower limit value of the output frequency from the light quantity-frequency conversion circuit 10 are FH and FL, the absorbance in the range of 0 to a1 can be measured when the LED current = I ₁ . If the LED current = I _2, 0 to
can measure the absorbance in the range of a3, when the LED current = I _3, perform the measurement of absorbance in a range of A2 to A5, when the LED current = I _4, the measurement of absorbance in the range of a4~a6 You can do it. Therefore, for example, if the microcomputer 20 controls the switching means SW1 to SW4 according to the absorbance of the DUT 16 or the illuminance (light amount) of the light transmitted through the DUT 16 to switch the current flowing through the LED 13, It is possible to measure the absorbance over a wide range from 0 to a6, and therefore, the illuminance (light amount) of light incident on the photodiode PD with high accuracy over a wide range.

Thus, according to this embodiment, the current flowing through the LED can be switched with a simple configuration, so that the lower limit of the absorbance that can be accurately measured is lower and the upper limit of the absorbance that can be accurately measured is higher. Therefore, it always has a wide measurement range, and it is possible to measure from a small absorbance to a large absorbance with high accuracy. further,
Since characteristics suitable for the absorbance to be measured can be set by switching the range, not only the absorbance range in which accurate measurement can be performed is widened, but also the measurement accuracy is further increased, and there is an advantage that reliability is further improved.

FIG. 3 is a flowchart showing an example of an algorithm when the microcomputer 20 automatically controls the operation mode of the above-described light quantity measuring device of the present embodiment. First, at the start, in step S1, the LED
Automatically setting the current flowing through the 13 lowest range I _1, the illuminance in step S2 - detecting the output frequency F ₀ from data input corresponding to the amount of light incident on the photodiode PD of the frequency conversion circuit 10, step the output frequency F _0, it is determined whether or not lower than the lower limit frequency FL in S3, if it is lower than the lower limit frequency FL (YES) to range I ₂ by one step increases the current LED13 in step S4. This range I ₂ is in the measurement range measurement of the output frequency F ₀ in (NO at step S5) The range I ₂ is performed in step S2 again, the output frequency F ₀ in step S3 is the lower limit frequency FL It is determined whether the frequency is lower than the lower limit frequency FL (YES).
The third current is one step increased to range I ₃ in. Thereafter, the output frequency F ₀ is measured in the same manner. If the output frequency F ₀ is lower than the lower limit frequency FL even in the range I ₄ , it is determined that the output frequency is out of the measurement range (NO) in step S 5, and an error is output in step S 6. Is generated, and the measurement operation ends.

On the other hand, in step S3, the output frequency F
_When it is determined that ₀ is higher than the lower limit frequency FL (NO)
Processing in step S7 is performed, the amount of light corresponding to the detected output frequency F ₀ is calculated, the amount of the value calculated in step S8 is outputted to end the measuring operation.

In this embodiment, a diode D1 is connected between the output and the input of the first Schmitt inverter 11 of the illuminance (light amount) -frequency conversion circuit 10 with a polarity opposite to that of the photodiode PD via a resistor R1. Although the diode D1 functions as a switch, an analog switch may be used instead of the diode D1. However, since the analog switch has the terminal capacitance, the characteristics of the illuminance-frequency conversion may be unstable. Therefore, it is preferable to use a diode switch from the viewpoint of reliability.

In the above embodiment, a waveform shaping circuit having a simple circuit configuration (for example, a diode is connected in series, and a CR parallel circuit is connected between the output side of the diode and the ground) is connected to the output side of the second Schmitt inverter 12. Connected configuration)
Is connected, and the output voltage V ₁ is shaped into a waveform.
_Since the duration of the low-level output voltage _VL of ₁ , that is, the discharge time of the capacitor C can be lengthened, the output waveform can be reduced by an inexpensive counter having a certain level of performance, such as a general-purpose counter or a microcomputer built-in counter. There is an advantage that measurement can be performed with sufficient accuracy.

Further, in the above embodiment, the light quantity measuring device according to the present invention is applied to the measurement of dirt or deterioration of lubricating oil such as engine oil of an automobile, but various dirt of oil transmitting light from a light source is measured. Alternatively, the present invention can be applied to measurement of deterioration or deterioration of liquid or gas which can transmit light other than oil, or reflected light from an object to be measured which reflects light from a light source. The present invention can be applied to the case of measuring the illuminance (light amount) of the image.

The above embodiment is merely an example of the present invention, and the circuit configuration, elements used, and the like can be arbitrarily changed as necessary. For example, an inverter other than a C-MOS Schmitt inverter or another circuit element may be used, a light source other than an LED, a photodetector other than a photodiode, or a microcomputer may be used. Of course, other arithmetic control means may be used. Further, the frequency output generated from the illuminance (light quantity) -frequency conversion circuit may be a frequency output other than a pulse.

[0027]

As described above, the light quantity measuring device according to the present invention can automatically switch the intensity of the light output radiated from the light source with a simple structure, and therefore, can convert the illuminance (light quantity) to frequency. The lower limit of the amount of transmitted light (including scattered light) or reflected light from the object that can be accurately measured by the circuit can be reduced, and the upper limit of the amount of light that can be accurately measured can be increased. Therefore, a wide measurement range is always provided, and it is possible to measure from a small light amount to a large light amount with high accuracy. Furthermore, since the characteristic suitable for the light quantity to be measured can be set by switching the range, not only the light quantity range that can be accurately measured is widened, but also the measurement accuracy is further increased, and the remarkable effect that reliability is further improved. There is.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a light quantity measuring device according to the present invention.

FIG. 2 is a characteristic diagram showing a relationship between the absorbance of an object to be measured and the output frequency of an illuminance-frequency conversion circuit in the light quantity measuring device of the present invention shown in FIG.

FIG. 3 is a flowchart for explaining an operation mode of the light quantity measuring device of the present invention shown in FIG. 1;

FIG. 4 is a circuit configuration diagram showing an example of a conventional light quantity measuring device.

5 is a waveform diagram showing a voltage output of a Schmitt inverter used in the light quantity measuring device of FIG.

6 is a diagram showing typical input / output characteristics of the light quantity measuring device of FIG.

FIG. 7 is a circuit configuration diagram showing another example of a conventional light quantity measuring device.

8 is a diagram showing typical input / output characteristics of the light quantity measuring device of FIG.

[Explanation of symbols]

 Reference Signs List 10 illuminance (light quantity) -frequency conversion circuit 11, 12 Schmitt inverter 13 LED (light emitting diode) 14 switching transistor 15 light transmissive cell 16 DUT 20 microcomputer 21 counter unit 22 storage unit 23 arithmetic processing unit 24 control port PD photo Diode SW1 to SW4 Switching means R11 to R14 Resistor C Capacitor

Claims (2)

(57) [Claims] A light source for irradiating the object with light; and a light detecting element for receiving transmitted light or reflected light from the object and changing an output current according to an amount of received light. An illuminance (light amount) -frequency conversion unit that outputs a frequency signal corresponding to the illuminance (light amount) of the light from the DUT incident on the element, and a frequency signal output from the illuminance (light amount) -frequency conversion unit. An illuminance (light quantity) calculating control means for measuring the illuminance (light quantity), wherein the illuminance (light quantity) -frequency conversion means comprises a capacitance element charged by an output current from the light detection element, and a charge charged to the capacitance element A light quantity measuring device, which is a pulse oscillation circuit that compares a voltage with a preset reference voltage, and changes the output signal level each time the charging voltage reaches the reference voltage to generate a pulse signal, comprises: this A plurality of resistors having different resistance values are connected to a voltage source for driving the power source via switching means, respectively, and the arithmetic control means controls the illuminance of light from the device under test incident on the photodetector ( When measuring the amount of light, the switching means is sequentially operated to sequentially switch and connect the resistors to change the light output from the light source in a stepwise manner. The output frequency is controlled so as to fall within the range of the upper limit value and the lower limit value of the output frequency from the illuminance (light amount) -frequency conversion means, and the illuminance (light amount) of the light from the DUT is input by 5 to 6 digits. A light quantity measuring device characterized in that measurement is performed over an output range. 2. An upper limit value and a lower limit value of an output frequency from the illuminance (light amount) -frequency conversion means are defined by the illuminance (light amount) of light from the DUT incident on the photodetector and the light intensity (light amount). 2. The light quantity measuring device according to claim 1, wherein the relationship between the illuminance (light quantity) and the output frequency from the frequency conversion means is a range showing linearity.