JPH0827211B2 - Light quantity measuring device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention generally applies to illuminance (light intensity).
The present invention relates to a frequency conversion type electronic photometric device, and more particularly to a highly reliable and compact electronic photometric device having a simple circuit configuration.

[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 housed in a specific light-transmitting cell or flows through the cell, and light is emitted from a light source such as an LED (light emitting diode), and the transmitted light is passed through a photodiode or the like. There is proposed an electronic light quantity measuring device which detects the amount of transmitted light by receiving the light with the light detecting element and determines the degree of contamination or deterioration of the lubricating oil from the detection result. For example, the present applicant has proposed various illuminance (light amount) -frequency conversion type electronic light amount measuring devices using an LED as a light source and a photodiode as a light detecting element, one example of which is shown in FIG. Shown in.

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 DUT 16 is incident on the photodiode PD, and therefore, the current I _P proportional to the illuminance or the light amount of the incident light is the photodiode P.
It flows 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 stored in the capacitor C is reduced to the low level threshold voltage V _TL of the Schmitt inverter 11 by discharging, the output voltage of the Schmitt inverter 11 is switched from the low level _VL 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. 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 accumulated in the capacitor _C and converted into the 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 V _L 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. After that, as a result of the similar 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 becomes the charge / discharge cycle of the capacitor C as shown in FIG. It becomes the pulse waveform of the corresponding frequency.

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 Schmitt 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, the low-level voltage output V _L is generated when the high-level voltage signal V _H is input from the first Schmitt inverter 11, and the high-level voltage output V _L is input when the low-level voltage signal V _L is input. Generate 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 the microcomputer 20 which is a calculation and measurement 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, 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 conventional light quantity measuring device having the above-mentioned configuration, since the continuous pulse output is generated from the illuminance-frequency conversion circuit, the count value differs depending on the timing of capturing by the counter, and the reliability is improved. There was a drawback that it lacked. Further, as the illuminance becomes smaller, the frequency becomes lower, so that there are disadvantages that the count error of the counter becomes large and it is easily affected by external noise. Further, there is a drawback that it is easily affected by ambient light.

Therefore, an object of the present invention is to generate a modulated light of a predetermined cycle from a light source, and to operate the pulse counting means in synchronization with the rising of this modulated light, so that the quantity of light can be accurately controlled with a simple circuit configuration. It is an object of the present invention to provide a high-reliability, small-sized electronic light quantity measuring device capable of measuring light.

[0011]

The above object is achieved by a light quantity measuring device according to the present invention. In summary, the present invention provides a light source for irradiating an object to be measured with light, a modulation means for generating modulated light of a predetermined cycle from the light source, and a transmitted light or a reflected light from the object to be measured and receiving the light. Illuminance (light quantity) -frequency conversion means that includes a photodetector whose output current changes according to the amount, and outputs a frequency signal according to the illuminance (light quantity) of the light from the DUT incident on the photodetector. And an arithmetic control unit that includes a counting unit that counts a frequency signal output from the illuminance (light amount) -frequency conversion unit and that converts the count into an illuminance (light amount). The illuminance (light intensity) is synchronized with the rising-
The light quantity measuring device is characterized in that the conversion operation of the frequency conversion means and the counting operation of the counting means are started to measure the illuminance (light quantity).

[0012]

Embodiments of the present invention will be described in detail below 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 illuminance-frequency conversion circuit 10 is configured with the first Schmitt inverter 11 of the mold.

In the present embodiment, a pulse signal of a predetermined frequency (for example, 270 Hz) is applied from the drive source 30 to the base of the switching transistor 14 connected between the LED 13 and the ground to turn on and off the LED 13, and the LED 13 of FIG. Modulated light with a predetermined period as shown in FIG. 9A is generated, and the transmitted light from the object to be measured is intermittently incident on the photodiode PD. As a result, the illuminance-frequency conversion circuit 10 starts the illuminance (light amount) -frequency conversion operation in synchronization with the rising of the modulated light of the light source, and the illuminance-frequency conversion circuit 10 responds to the modulated light output from the LED 13. The microcomputer 20 generates an intermittent pulse output.
Is supplied to. On the other hand, the counter unit 21 of the microcomputer 20 is operated in synchronization with the rising edge of the modulated light to count the number of input pulses. The counted frequency signal is converted by the arithmetic processing unit 23 into illuminance or light quantity.

At this time, the effect of the integrating filter becomes higher as the number of samplings for obtaining the light quantity is larger, but the output signal of the illuminance-frequency conversion circuit 10 is a frequency output unlike the case of the analog circuit. It is not affected unless noise of a fairly high voltage level is superimposed. Therefore, it is not necessary to increase the sampling frequency. Of course, other means may be used to generate the modulated light of a predetermined cycle from the LED 13.

The function of the illuminance-frequency conversion circuit 10,
Since the operation mode and the like are as described above, further description is omitted here, but as shown in FIG. 2B, the illuminance-frequency conversion circuit 10 is intermittent according to the modulated light output from the LED 13. Pulse output is generated and supplied to the microcomputer 20.

Next, as shown in FIG. 3, consider a case where the amount of light input to the photodiode PD is small and the output frequency of the illuminance-frequency conversion circuit 10 is smaller than the frequency of the modulated light of the light source. In this case, the capacitor C is charged when the modulated light of FIG. 3 (A) becomes high level. But,
The amount of light is small, and as shown in FIG.
Is not fully charged in one high level section.
The charging voltage of the capacitor C is kept constant as long as the modulated light is at a low level, the charging is restarted in the next high level section of the modulated light, and the high level threshold voltage V of the first Schmitt inverter 11 is reached. _When it reaches _TH , the output voltage of the Schmitt inverter 11 switches from the high level V _H to the low level V _L. As a result, the diode D1 is forward-biased and has the same function as switching on, so that the charging voltage of the capacitor C and the output current I _P of the photodiode PD flow through the resistor R1 and the diode D1 and the charging voltage of the capacitor C is increased. Is discharged. The discharge causes the charging voltage V _C of the capacitor C to change to the low level threshold voltage V of the Schmitt inverter 11.
_When it drops to _TL , the output voltage of the Schmitt inverter 11 switches from the low level V _L to the high level V _H. As a result, as shown in FIG. 3C, one output pulse is sent from the illuminance-frequency conversion circuit 10. Thus, it can be seen that the illuminance-frequency conversion circuit 10 of the present embodiment can also generate an output having a frequency lower than that of the modulated light under a weak light amount.

The lower limit of detection in this case depends on the number of times of sampling. In the case of FIG. 3, the number of sampling times required for detection is at least two. Furthermore, if at least 2 bits are required to secure reliability in the arithmetic processing when the value counted by the counter unit 21 of the microcomputer 20 is processed by the arithmetic processing unit 23, the number of sampling times is 4 times. become. In this embodiment, the detection range is 100H as the output frequency of the illuminance-frequency conversion circuit 10.
Since z is set to 100 KHz, the number of samplings is about 10 to satisfy the lower limit.

Therefore, the pulse output supplied to the counter section 21 of the microcomputer 20 is calculated by the arithmetic processing section 23.
Convert to illuminance or light intensity at.

It is needless to say that the use of the modulated light as described above can eliminate the influence of the ambient light, but further, the following advantages occur.

That is, when the modulated light rises, the capacitor C of the illuminance-frequency conversion circuit 10 is charged by the current I _P flowing through the photodiode PD in synchronization with it. Therefore, the pulse output from the illuminance-frequency conversion circuit 10 rises after the time T _{C has} elapsed and is supplied to the counter section 21 of the microcomputer 20, as shown in FIG. On the other hand, since the counter section 21 is operated in synchronization with the rise of the modulated light, a count error does not occur unlike the conventional light amount measuring apparatus of this type, and therefore the reliability is remarkably improved.

If the measurement cycle of the apparatus of this embodiment is, for example, 5 seconds (5000 ms), the current flows through the LED 13 because one high level section of the modulated light is 1.85 ms.
Therefore, the time is 1.85 × 10 = 18.5 ms only. Given that the life of an LED depends on the product of its current and energization time, it can be seen that when the LED current is 10 mA, it corresponds to the next LED current in the case of continuous energization, and the reliability is much improved. .

10 mA × (18.5 / 5000) = 0.037 mA In this embodiment, the polarity of the photodiode PD is opposite between the output and the input of the first Schmitt inverter 11 of the illuminance (light amount) -frequency conversion circuit 10. Then, although the diode D1 is connected via the resistor R1 and this diode D1 is made to function 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 the diode switch from the viewpoint of reliability.

On the other hand, when it is desired to output the illuminance or the light quantity in an analog manner, the illuminance (light quantity) output from the arithmetic processing unit 23.
It can be realized by converting the digital signal corresponding to (4) by a digital-analog converter having a simple circuit configuration as shown in FIG. In FIG. 4, the signal STR is a strobe signal having the same period as the modulated light, and the signal P ₀ is a pulse output supplied from the arithmetic processing unit 23. FIG. 5 shows the waveforms of these signals STR and P ₀ , the operation modes of the switches (electronic switches in this example) SW1 and SW2, and the signal waveforms at each part of the digital-analog converter. The analog signal Vc2 thus converted is amplified to an appropriate size by an amplifier circuit and supplied to, for example, an indicator (not shown), and the measurement result is displayed.

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

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.

[0027]

As described above, in the light quantity measuring device according to the present invention, the light source outputs modulated light of a predetermined cycle, so that the light quantity of the light source becomes constant and the influence of ambient light is eliminated. be able to. Further, when the modulated light rises, the conversion operation of the illuminance-frequency conversion means is started in synchronization therewith, so that the frequency output rises with a certain delay, while the frequency count is synchronized with the rise of the modulated light. Since the operation is started, no counting error occurs, and thus reliability is significantly improved.
Further, it is possible to measure even a weak light quantity with high accuracy, downsizing and cost reduction are possible, and many remarkable effects such as the frequency output can be converted into an analog signal by the digital-analog converting means having a simple circuit configuration. There is.

[Brief description of 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 waveform diagram for explaining how a pulse output is generated in the light quantity measuring device of the present invention shown in FIG.

FIG. 3 is a waveform chart for explaining another generation mode of pulse output in the light quantity measuring device of the present invention shown in FIG.

FIG. 4 is a circuit diagram showing an example of a digital-analog converter that can be used in the light quantity measuring device of the present invention shown in FIG.

5 is a waveform diagram showing a voltage output in each part of the digital-analog converter of FIG.

FIG. 6 is a circuit configuration diagram showing an example of a light quantity measuring device proposed by the present applicant.

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

[Explanation of symbols]

 10 Illuminance (Light Amount) -Frequency Conversion Circuit 11, 12 Schmidt 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 Section 30 Driving Source PD Photo Diode C capacitor

Claims (3)

[Claims] 1. A light source for irradiating an object to be measured with light, a modulation means for generating modulated light of a predetermined cycle from the light source, a photodiode serving as a photodetector, and an output current from the photodiode. Capacitor, a diode that functions 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, and the Schmidt is provided at a connection point between the photodiode and the capacitor. The input of the inverter is connected and the diode is
Between the output and the input of the Schmitt inverter, the photodiode has a reverse polarity and is configured to be connected via a resistor, and has a frequency corresponding to the illuminance (light quantity) of light from the DUT incident on the photodiode. Illuminance (light quantity) -frequency conversion means for outputting a signal, and counting means for counting the frequency signal output from the illuminance (light quantity) -frequency conversion means, and operation control means for converting the count into illuminance (light quantity) The illuminance (light quantity) is measured by synchronizing the rising of modulated light from the light source and starting the conversion operation of the illuminance (light quantity) -frequency conversion means and the counting operation of the counting means. And a light quantity measuring device. 2. The light source is an LED, and the modulation means has a switching transistor connected between the LED and the ground, and a drive source for applying a pulse signal of a predetermined frequency to the base of the switching transistor. The light quantity measuring device according to claim 1. 3. The light quantity measuring device according to claim 1, further comprising a digital-analog converter for converting a digital signal corresponding to the illuminance (light quantity) from the arithmetic control means into an analog signal.