JPH07286900A - Light-quantity measuring instrument - Google Patents

Abstract

PURPOSE:To provide an electronic light-quantity measuring instrument which can detect a very weak light, is reliable without causing the oscillation frequency to fluctuate due to temperature change, has a simple circuit configuration, and can be miniaturized and less expensive. CONSTITUTION:An illuminance (light quantity) - frequency conversion means 10 outputs a frequency signal corresponding to the illuminance (light quantity) of light from an object to be measured entering a photodiode PD. The illuminance (light quantity) - frequency conversion means 10 is provided with the above photodiode PD, a capacitor C which is charged by the output current from the photodiode PD, a diode D1 which functions as a switch, and a C-MOS type Schmitt inverter 11, and the photodiode PD and the capacitor C are connected in series between a power supply and ground, the input of the Schmitt inverter 11 is connected to the connection point between the photodiode PD and the capacitor C, and the diode D1 having the opposite polarity to that of the photodiode PD is connected between the output and input of the Schmitt inverter 11 via a resistor R.

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, a lubricating oil used for automobile engine oil or the like has a reduced light transmittance as it becomes dirty or deteriorates. 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. It has been proposed to detect the amount of transmitted light by receiving light with the photodetector element and determine the degree of contamination or deterioration of the lubricating oil from the detection result.

There are various possible light amount measuring circuits that can be used for such a purpose.
There is a light amount detection circuit disclosed in Japanese Patent No. 22782. The outline of this light amount detection circuit is shown in FIG.

This light quantity detecting circuit comprises a light emitting element 101 which is a light emitting diode and a light receiving element 102, and an analog-digital converter 103 for outputting a digital quantity proportional to the light output current of the light receiving element 102, Capacitor 104 and unijunction transistor (UJ
It is realized by a UJT oscillator whose main constituent element is T) 105.

That is, when the capacitor 104 is charged by the light output current of the light receiving element 102 and the peak point voltage of the UJT 105 is reached, a pulse is generated. Since this pulse train is proportional to the light output current of the light receiving element 102, the light quantity (analog quantity) is changed to a digital quantity. The signal from the UJT oscillator 103 is transmitted to the reversible counting circuit 107 via the gate circuit 106 and digitally output.

[0006]

However, the UJT having the capacitor 104 and the UJT 105 as main constituent elements is used.
The oscillator 103 has the following drawbacks. That is, the input capacitance of UJT 105 is large, and the capacitor 104
Cannot be made smaller. For this reason, the oscillation frequency cannot be increased, and therefore weak light cannot be detected. The UJT 105 has a large leakage current, which also makes it impossible to detect weak light. The oscillation frequency (f) of the UJT oscillator 103 is f = 1 / RCln {1 / (1-η)} where η is the standoff ratio of UJT, and η is larger due to temperature and voltage. However, the oscillation frequency fluctuates depending on the temperature, resulting in low reliability. There is no discharge resistance of the capacitor 104, that is, the UJT oscillator 103 does not have a resistance component in the circuit, and therefore the voltage accumulated in the capacitor 104 is UJT105.
The discharge waveform is not a rectangular wave, but a trigger pulse. It is difficult to measure such a trigger pulse with a simple counter built in a microcomputer. Therefore, in practice, a waveform shaping circuit or the like is required in the subsequent stage, the circuit configuration becomes complicated, and it is difficult to reduce the size and cost. It has various problems.

Therefore, an object of the present invention is to detect weak light, to have high reliability without fluctuation of the oscillation frequency due to temperature change, to have a simple circuit structure, and to easily reduce the size and cost. An object is to provide an electronic light quantity measuring device.

[0008]

The above object can be achieved by the light quantity measuring device according to the present invention. In summary, the present invention relates to a light source for irradiating an object to be measured with light, a photodiode serving as a light detection element, a capacitor charged by an output current from the photodiode, a diode functioning as a switch, and a C-MOS type. A Schmidt 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 the Schmitt Between the output and the input of the inverter, the photodiode has a polarity opposite to that of the photodiode, and is connected via a resistor. A frequency signal corresponding to the illuminance (light quantity) of the light incident on the photodiode from the DUT is generated. Output illuminance (light quantity) -frequency conversion means and the illuminance (light quantity) -frequency conversion means Includes counting means for counting a frequency signal output, a light amount measuring apparatus comprising: the operation control means for converting the the regimen number illuminance (light intensity), the.

According to a preferred embodiment of the present invention, a digital-analog converter for converting a digital signal corresponding to the illuminance (light quantity) from the arithmetic control means into an analog signal is provided.

[0010]

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.

The light quantity measuring device of the present invention comprises a photodiode PD which is a light detecting element, a capacitor C which is a capacitance type load, and diodes D1 and C which function as switches.
The illuminance-frequency conversion circuit 10 is configured by the first MOS type Schmitt inverter 11 and the diode D1.
Is connected between the output and the input of the first Schmitt inverter 11 via the resistor R1 with a polarity opposite to that of the photodiode PD, and the photodiode PD and the capacitor C.
Are connected in series between a predetermined voltage source and ground, and their connection point is connected to the input of the first Schmitt inverter 11.

On the other hand, the LED 13 as a light source is connected via a switching transistor 14 in series between a predetermined voltage source and the ground. When the transistor 14 is on, the LED 13 emits light to enter a light transmissive cell 15. The object 16 to be measured such as existing lubricating oil is irradiated with light. This DUT 1
The light transmitted through 6 is incident on the photodiode PD, and therefore a current I _P proportional to the illuminance or the amount of light 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. The voltage V _C stored in the capacitor C is converted into a pulse signal by the 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 a high-level output voltage V _TH when the input voltage is lower than the high-level threshold voltage V _TH.
H is generated, 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 V _L , and the input voltage drops to the low level threshold voltage V _TL . The low level output voltage V _L is maintained until the input voltage drops to the low level threshold voltage V _TL , and the output voltage switches from the low level V _L to the high level V _H. Therefore, when light is not incident on the photodiode PD and the current I _P does not flow, that is, when the electric charge is not accumulated in the capacitor C, the output voltage is the high level V _H , and the charging voltage V of the capacitor C is V _{H. 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 V _L. 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. 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 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 in the capacitor C, and thus the charge is not accumulated in the capacitor C, the output voltage of the first Schmitt inverter 11 is at the high level V _H , so that the diode D1 is reverse-biased and switched off. Do 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 the high level threshold voltage V _TH of the first Schmitt inverter 11, the output voltage of the Schmitt inverter 11 switches 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 due to 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 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, 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 which is the inverted pulse waveform of the first Schmitt inverter 11 and supplies the output voltage 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 photodiode PD, and the input / output characteristics of the conversion circuit. ROM storing arithmetic processing program
From the storage unit 22 including (read only memory) and the number of pulses within a certain time counted by the counter unit 21,
According to the program of the storage unit 22, the photodiode PD
And an arithmetic processing unit 23 for calculating the illuminance or the light amount, and thus, the illuminance or the light amount of the light incident on the photodiode PD can be obtained.

In this embodiment, the polarity of the photodiode PD is opposite to that of the photodiode PD between the output and the input of the first Schmitt inverter 11 of the illuminance (light quantity) -frequency conversion circuit 10, and the resistance R1.
The diode D1 is connected via
Functioning as a switch, it is possible to use an analog switch instead of the diode D1.
Since the analog switch has a terminal capacitance, the illuminance-frequency conversion characteristics may become 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 (3) by a digital-analog converter having a simple circuit configuration as shown in FIG. In FIG. 3, 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. 4 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).

[0021]

As described above, the light quantity measuring device according to the present invention includes a photodiode which is a photodetector, a capacitor charged by an output current from the photodiode, a diode which functions as a switch, and a C-.
It has a MOS type Schmidt 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, 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. An illuminance (light quantity) -frequency conversion means for outputting a signal is provided, and a frequency signal output from the illuminance (light quantity) -frequency conversion means is counted by the arithmetic control means and converted into illuminance (light quantity). Since it is possible to detect weak light, the oscillation frequency does not fluctuate due to temperature changes, it is highly reliable, and the circuit configuration is simple. , There is a reduction in size, many remarkable effect equal cost reduction is easy.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing a voltage output of a Schmitt inverter used in the light quantity measuring device of FIG.

FIG. 3 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.

FIG. 4 is a waveform diagram showing a voltage output in each part of the digital-analog converter of FIG.

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

[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 unit 22 Storage unit 23 Processing unit PD Photodiode C Capacitor D1 diode R1 resistance

Claims (2)

[Claims] 1. A light source for irradiating an object to be measured with light, a photodiode serving as a light detection element, a capacitor charged by an output current from the photodiode, 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,
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) And a light quantity measuring device. 2. 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.