JPH095158A - Light intensity measurement device - Google Patents

Abstract

(57) [Abstract] [Purpose] High reliability, simple circuit configuration, small size,
(EN) Provided is a light quantity measuring device having a correction function, which can be easily reduced in price. A light quantity measuring device includes a light emitting section LED for irradiating a measured object with light and a light receiving section PD for receiving light from the measured object.
When a light quantity frequency conversion means 10 for outputting a frequency signal corresponding to the amount of light from the object to be measured which enters the light receiving unit LED (F _0), the frequency signal outputted from the light quantity frequency conversion means 10 (F ₀₎ And a calculation control means 20 for calculating a display value signal (P ₀ ) corresponding to the amount of light. The calculation control means 20 calculates the display value signal (P ₀ ) by the following equation: P ₀ = G (XlogF ₀ −F−Y) + Y where G and F are correction amounts and G is a gain adjustment value. Then, F is calculated based on the offset adjustment value and X and Y are constants determined by the device, and the initial correction of the device is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a light quantity / frequency conversion type electronic photometric device, and more particularly to a highly reliable and compact light quantity measuring device having a correction function, a simple circuit configuration. It is a thing.

[0002]

2. Description of the Related Art For example, when lubricating oil such as automobile engine oil or automatic transmission oil becomes dirty or deteriorates, the light transmittance decreases. For this reason, a part of the lubricating oil is contained in or flows through a specific light-transmissive cell, and L
Light is emitted from a light source such as an ED (light emitting diode), the transmitted light is received by a photodetector such as a photodiode, the amount of transmitted light is detected, and the degree of contamination or deterioration of the lubricating oil is determined from this detection result. It is suggested to do so.

The present inventors have, for example, Japanese Patent Application No. 4-2165.
No. 11 proposed a light quantity measuring device which can be used for such a purpose. As shown schematically in FIG. 5, this light quantity measuring device irradiates a lubricating oil 2 which is an object to be measured, which is held in a measuring cell 1 such as a transparent glass tube, with a light emitting diode LED to irradiate the measuring cell 1 with light. The transmitted light from is received by the photodiode PD. The signal from the photodiode PD is transmitted to the light quantity frequency conversion circuit 10. This light quantity frequency conversion circuit 10 outputs a frequency signal F ₀ according to the light quantity of the light incident on the photodiode PD. The number of pulses of the frequency signal is counted by the microcomputer 20 and is arithmetically processed to calculate the measured deterioration degree of the lubricating oil, and the display value P ₀ is displayed on the display device 30.

[0004]

The light quantity measuring device having the above-described structure has the features of a simple circuit structure, high reliability, and a small size. Photodiode PD which is an element
It is inevitable that the characteristics of each element, such as, will vary from device to device. In addition, variations in the characteristics of the optical system including the light emitting diode LED, the measurement cell 1 and the photodiode PD, or variations in the characteristics of the electronic circuit such as the light quantity frequency conversion circuit may occur due to assembly errors during manufacturing of the device. . The variations in these characteristics will eventually affect the measurement accuracy.

It is extremely complicated and impractical to correct each of these characteristics in order to eliminate variations in these characteristics. Further, it is difficult to provide a correction circuit for performing such a correction in the electronic circuit, and even if it is realized, the circuit configuration becomes very complicated.

Therefore, the object of the present invention is to have high reliability,
An object of the present invention is to provide a light quantity measuring device having a correction function, which has a simple circuit configuration, and can be easily reduced in size and cost.

[0007]

The above object is achieved by a light quantity measuring device according to the present invention. In summary, the present invention provides a light emitting unit that irradiates a DUT with light, a light receiving unit that receives light from the DUT, and a light receiving unit that receives light from the DUT that is incident on the light receiving unit. a light quantity frequency converting means for outputting a frequency signal (F ₀₎ was, it calculates the frequency signal output from the light quantity frequency conversion means (F _0), and outputs a display value signal corresponding to the light quantity (P ₀₎ calculation In the light quantity measuring device having a control means, the calculation control means calculates the display value signal (P ₀ ) by the following equation (1), P ₀ = G (XlogF ₀ −F−Y) + Y (1) Here, G and F are correction amounts, G is a gain adjustment value, F is an offset adjustment value, and X and Y are constants determined by the device, and an initial correction of the device is performed. It is a light quantity measuring device.

According to a preferred embodiment of the present invention, there are provided first and second oscillating means for varying the output frequencies Fα and Fβ, and the variable frequencies Fα and Fβ and the correction amounts G and F are F = K ₁ · Fα (K ₁ is a constant) and G
= K ₂ · Fβ (K ₂ is a constant), and the output frequency signals Fα and Fβ are adjusted to set the correction amounts F and G in the above equation (1). Perform initial correction. Preferably, the first and second oscillating means form a CR oscillating circuit between an inverter element, a variable resistor connected to a feedback circuit of the inverter element, and an electric resistance value of the variable resistor. To output the frequencies Fα and Fβ, respectively, and operate the variable resistor to output the frequencies Fα and Fβ.
Adjust β.

Further, preferably, the light quantity frequency conversion means has a capacitor charged by an output current from a photodiode constituting the light receiving section, a diode functioning as a switch, and a C-MOS type Schmitt inverter, The photodiode and the capacitor are connected in series between a voltage source and ground, the input of the Schmidt inverter is connected to the connection point between the photodiode and the capacitor, the diode is between the output and the input of the Schmitt inverter. The photodiode has a polarity opposite to that of the photodiode and is connected through a resistor, and outputs a frequency signal according to the amount of light from the DUT incident on the photodiode.

[0010]

EXAMPLES The light quantity measuring device according to the present invention will be described in more detail below with reference to examples.

FIG. 1 shows an embodiment of the light quantity measuring device of the present invention. This light quantity measuring device is arranged facing both sides of the measuring cell 1 in the same manner as described with reference to FIG.
And the light receiving section PD is installed. Lubricating oil 2, which is the object to be measured, held in the measurement cell 1 is irradiated with light from the light emitting section LED, and transmitted light from the measurement cell 1 is received by the light receiving section PD. The signal I _p from the photodiode PD is transmitted to the light quantity frequency conversion circuit 10, and the light quantity frequency conversion circuit 10 outputs a frequency signal F ₀ according to the light quantity incident on the light receiving unit PD. The number of pulses of this frequency signal F ₀ is
The microcomputer 20 which is an arithmetic control unit counts and performs arithmetic processing to calculate the measured deterioration degree of the lubricating oil, and the display value P ₀ thereof is displayed on the display device 30.
Is displayed in.

To explain further with reference to FIGS. 2 and 3, the light quantity measuring device of the present invention is configured such that a photodiode PD which is a light detecting element constituting a light receiving portion and an electrostatic capacitance which is a capacitance type load. Element (capacitor) C, diode D1 functioning as a switch, and inverter element, that is, CM
The light quantity frequency conversion circuit 10 is configured with the OS-type first Schmitt inverter 11, 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 the resistance R1. 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, a light emitting diode (LE
D) 13 has a switching transistor 14 connected in series between a predetermined voltage source and the ground, and emits light when the transistor 14 is on to transmit a light-transmissive cell 15
The object to be measured 16 such as lubricating oil existing inside is irradiated with light. The light transmitted through the DUT 16 is incident on the photodiode PD, and therefore, a current I _P proportional to the illuminance or the light amount of the incident light flows through the photodiode PD.

The current I _P flowing through the photodiode PD is accumulated in the capacitor _C and converted into the 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. Therefore, the first Schmitt inverter 11 outputs a pulse voltage having a cycle corresponding to the charging / discharging of the capacitor C, and thus the light amount (illuminance) of the 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. The measurement of the light quantity is started,
When the light to be measured enters the photodiode PD, a current I _P proportional to the illuminance or the light amount of the incident light flows through the photodiode PD. This current _IP is stored in the capacitor _C and converted to a voltage VC. 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 causes the diode D1 to be forward biased and has the same function as switching on.
Charging voltage V _C and the photodiode PD of the capacitor C
Output current I _P of the capacitor C flows through the resistor R1 and the diode D1, and the charging voltage of the capacitor C 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 reverse-biased again and turned off,
A charging current flows through the capacitor C. Hereinafter, as a result of repeating the same operation, the output voltage of the first Schmitt inverter 11, that is, the output voltage V ₁ from the light quantity frequency conversion circuit 10 corresponds to the charge / discharge cycle of the capacitor C as shown in FIG. It becomes the pulse waveform of the frequency.

In the present embodiment, the output voltage V ₁ of the first Schmitt inverter 11 is supplied to the same C-MOS type second Schmitt inverter 12 as the first Schmitt inverter 11. The second Schmitt inverter 12 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 which is the inverted pulse waveform of the first Schmitt inverter 11 and supplies the output voltage to the microcomputer 20 which is the arithmetic control means.

The microcomputer 20 counts the number of pulses of the frequency signal F ₀ input from the light quantity frequency conversion circuit 10 through the second Schmitt inverter 12, and calculates the input / output characteristics of the photodiode PD and the conversion circuit. ROM that stores processing programs
(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 that calculates the illuminance or the light amount, and thus obtains the illuminance or the light amount of the light incident on the photodiode PD.
The deterioration degree display value P ₀ of the lubricating oil is output and displayed on the display device 30.

Further, according to the present invention, the microcomputer 20 is provided with a correction function, and the correction amounts Fα and Fβ are input from the correction circuit 50 to the microcomputer 20. Correction circuit 5 for outputting the correction amounts Fα and Fβ
Details of 0 will be described later.

Now, assuming that the light intensity (irradiance) of the light emitting diode LED is L ₀ and the intensity of light incident on the photodiode (light receiving illuminance) is L, the absorbance by the lubricating oil 2 held in the measuring cell 1 Is defined as: absorbance = log (L / L ₀ ) = − kcd (1). Here, k is an extinction coefficient, c is a deterioration degree of oil, and d is a distance in the measurement cell 1 in a light path from the light emitting section LED to the light receiving section PD, that is, an optical path length.

If the output current I _p flows through the photodiode PD at this time, logL = AlogI _p + B (2), where A and B are constants.

Further, the relationship between the frequency F ₀ output from the light quantity frequency conversion circuit 10 and the current I _p is expressed by logI _p = ClogF ₀ + D (3), where C and D are constants.

Therefore, from the above equations (1), (2) and (3), it can be seen that c = αlogF ₀ + β (4) holds between the oil deterioration degree c and the output frequency F ₀ . Here, α = −AC / kd β = (logL ₀ −AD−B) / kd.

In the above equations, the constants A and B define the characteristics of the light receiving element PD and vary from element to element. Further, the constants C and D define the characteristics of the light quantity frequency conversion circuit 10, and similarly, are different for each circuit. Further, L ₀ defines the characteristics of the light emitting element LED, k and d define the characteristics of the optical system, and these values also vary.

Since it is actually extremely difficult to correct the variations in the above constants, the constants α and β in the equation (4) are collectively corrected.

That is, assuming that the variations are Δα and Δβ and the correction amounts are Δαc and Δβc, the deterioration degree c and the output frequency F ₀
The relation with is c = (α + Δα-Δαc) logF ₀ + (β + Δβ-Δβc) (5).

Therefore, when the correction amounts Δαc and Δβc are adjusted so that Δαc = Δα Δβc = Δβ, the above equation (5) becomes equal to the equation (4), and there is no variation in characteristics. can get. The present invention is based on this principle.

However, in reality, it is difficult to provide such a correction circuit in the light quantity frequency conversion circuit 10. Even if it were realized, the circuit configuration would be very complicated.

The present inventors investigated the relationship between the degree of deterioration of the lubricating oil and the absorbance when the light quantity measuring device having the above-mentioned structure of the present invention was used as a device for detecting the deterioration of the lubricating oil. The result is shown in FIG.

As can be seen from FIG. 4, for example, when the light emitting diode LED has a wavelength in the range of 400 to 570 nm and the optical path length d of the measuring cell 5 is 1 to 5 mm, the optical system is used. For example, the absorbance is 0.5
It was found that a linear relationship is substantially established between the absorbance and the deterioration degree in the range of up to 2.5.

[0030] Thus, in this embodiment, as shown in FIG. 4, in the light amount measurement device with the above structure, the display value in absorbance 0.8 (P ₀₎ 130, the display value in absorbance 1.7 (P ₀₎ 20
It was set to display 0.

However, as described above, due to various factors, the characteristic curve showing the relationship between the absorbance and the deterioration degree is
The inclination differs from device to device. Therefore, in the present embodiment, the characteristic curve of each device is, as described above, the display value (P ₀ ) 130 at the absorbance of 0.8 and the display value (P ₀ at the absorbance of 1.7).
₀ ) It is necessary to adjust the inclination so as to pass through 200.

Therefore, according to the present invention, the frequency signal F ₀
The display value P ₀ indicating the degree of deterioration of the lubricating oil displayed on the display device 30 after being counted and calculated by the microcomputer 20 is corrected by the following calculation.

P ₀ = G (XlogF ₀ −F−Y) + Y (6) Here, X and Y are constants determined by the type of the device to be used, and this example measures the degree of deterioration of the lubricating oil. In the light quantity measuring device of No. 2, X was set to 40 and Y was set to 130. That is,
Expression (6) is expressed as follows.

P ₀ = G (40logF ₀ −F−130) +130 (7) Further, G and F are correction amounts, G is a gain adjustment value, and F is an offset adjustment value.

That is, when making a correction, first, a standard oil having a lower absorbance, for example, an oil having an absorbance of 0.8 is introduced into the measuring cell 1, and the display value P ₀ of the LCD display device 30 becomes 130. Thus, the correction amount F is set. Thereby, for example, the characteristic curve 1 in FIG. 4 is moved in parallel like the characteristic curve 2 (offset adjustment).

Next, a standard oil having a higher absorbance, for example, an oil having an absorbance of 1.7 is introduced into the measuring cell 1, and the correction amount G is adjusted so that the display value P ₀ of the LCD display device 30 becomes 200. Set. Thereby, for example, the characteristic curve 2 of FIG. 4 is rotated like the characteristic curve 3 (gain adjustment).

By repeating such an operation several times, the first characteristic curve 1 becomes a desired characteristic curve, that is, the display value 130 at the absorbance 0.8 and the display value at the absorbance 1.7. It can be calibrated to display 200.

According to the present invention, in order to perform such correction, a correction circuit 50 is provided as shown in FIG.

In this embodiment, the correction circuit 50 is the oscillator circuit 50.
It consists of A and 50B. The oscillating circuits 50A and 50B have the same configuration and include inverter elements 51A and 51B such as C-MOS Schmitt inverters, and variable resistors (volumes) 52A and 52B connected to the feedback circuits of the inverter elements 51A and 51B. , This variable resistor 5
It is composed of capacitors 53A and 53B forming a CR time constant circuit, that is, a CR oscillation circuit with the electric resistance values of 2A and 52B, and outputs frequencies Fα and Fβ, respectively. The operations of the CR oscillation circuits 50A and 50B are similar to those of the light quantity frequency conversion circuit 10 described above. Frequency Fα, Fβ
Can be variously changed by the volumes 52A and 52B. The output signals Fα and Fβ are input to the above equation (6) of the arithmetic unit of the microcomputer 20, that is, the equation (7) in this embodiment. Here, F = K ₁ · Fα G = K ₂ · Fβ is set. K ₁ and K ₂ are constants.

That is, in the present invention, the offset adjustment and the gain adjustment at the start of the measurement are performed by simply alternately operating the two volumes 52A and 52B of the correction circuit 50, and each element used in the light quantity measuring device is adjusted. ,
It is possible to correct variations caused by electronic circuits and the like, and to detect with high accuracy, for example, the degree of deterioration of lubricating oil.

In the above embodiment, the light quantity measuring device according to the present invention is applied to the measurement of the dirt or deterioration of the lubricating oil such as the engine oil of the automobile or the oil for the automatic transmission, but the light from the light source is transmitted. The present invention can be applied to the case of measuring dirt or deterioration of various oils, and dirt or deterioration of liquids, gases, etc. through which light other than oil can pass, and the measured object that reflects light from a light source. The present invention can also be applied to the case of measuring the amount of reflected light from an object.

[0042]

As described above, the light quantity measuring apparatus according to the present invention emits light to the object to be measured, a light receiving section for receiving light from the object to be measured, and the light receiving section. A frequency signal (F) corresponding to the amount of light from the object to be measured.
₀ ) for outputting the light quantity frequency converting means and a frequency signal (F ₀ ) outputted from the light quantity frequency converting means,
A light quantity measuring device comprising: a calculation control means for outputting a display value signal (P ₀ ) corresponding to a light quantity; and particularly, the calculation control means calculates the display value signal (P ₀ ) by the following formula ( 1), P ₀ = G (XlogF ₀ −F−Y) + Y (1) where G and F are correction amounts, G is a gain adjustment value, F is an offset adjustment value, and X and Y are devices. Since the calculation is performed based on a constant determined by the above, and the initial correction of the device is performed, it has the features of high reliability, simple circuit configuration, and easy size reduction and cost reduction.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a light quantity measuring device according to the present invention.

FIG. 2 is a circuit configuration diagram of an embodiment used in the light quantity measuring device according to the present invention.

FIG. 3 is a waveform diagram showing a voltage output of a Schmitt inverter used in the light quantity measuring device of FIG.

FIG. 4 is a diagram for explaining a correction operation performed by the light quantity measuring device of the present invention.

FIG. 5 is a configuration diagram showing an example of a conventional light amount measuring device.

[Explanation of symbols]

1 Measuring Cell 2 Object to be Measured (Lubricating Oil) 10 Light Quantity Frequency Conversion Circuit 11, 12 Schmitt Inverter 13 LED (Light Emitting Diode) 14 Switching Transistor 15 Light Transmissive Cell 16 Object to be Measured 20 Microcomputer 21 Counter Section 22 Memory Section 23 Operation Processing unit 30 Display device 50 Correction circuit 50A, 50B CR oscillation circuit 51A, 51B Inverter element (C-MOS Schmitt inverter) 52A, 52B Variable resistor (volume) 53A, 53B Capacitor

Claims (4)

[Claims] 1. A light emitting unit for irradiating a DUT with light, a light receiving unit for receiving light from the DUT, and a frequency signal according to the amount of light from the DUT incident on the light receiving unit. (F
₀ ) for outputting the light quantity frequency converting means and a frequency signal (F ₀ ) outputted from the light quantity frequency converting means,
In a light quantity measuring device having a calculation control means for outputting a display value signal (P ₀ ) corresponding to a light quantity, the calculation control means calculates the display value signal (P ₀ ) by the following equation (1), P ₀ = G (XlogF ₀ −F−Y) + Y (1) where G and F are correction amounts, G is a gain adjustment value, F is an offset adjustment value, and X and Y are constants determined by the device. A light amount measuring device characterized by performing calculation based on the above, and performing initial correction of the device. 2. The first and second oscillating means for varying the output frequencies Fα and Fβ are provided, and the variable frequency F
α and Fβ and the correction amounts G and F are F = K ₁ · Fα
(K ₁ is a constant) and G = K ₂ · Fβ (K ₂ is a constant), and the output frequency signals Fα and Fβ are adjusted to adjust the correction amount F in the above equation (1). 2. The light quantity measuring device according to claim 1, wherein G and G are set to perform initial correction of the device. 3. The CR oscillating circuit between the first and second oscillating means between an inverter element, a variable resistor connected to a feedback circuit of the inverter element, and an electric resistance value of the variable resistor. 3. The light quantity measuring device according to claim 2, further comprising: a capacitance element that forms an output, outputs the frequencies Fα and Fβ, respectively, and adjusts the frequencies Fα and Fβ by operating the variable resistor. 4. The light quantity frequency conversion means includes a capacitor charged by an output current from a photodiode constituting the light receiving section, a diode functioning as a switch, and a C-MOS type Schmitt inverter, and the photodiode. And the capacitor are connected in series between a voltage source and ground, the input of the Schmitt inverter is connected to the connection point between the photodiode and the capacitor, and the diode is the photodiode between the output and the input of the Schmitt inverter. 3. A frequency signal according to the amount of light of the light from the DUT incident on the photodiode, which has a polarity opposite to that of and is connected via a resistor, is output. 3 light quantity measuring device.