Light measuring apparatus

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention is generally not limited to an illuminance (light amount) -frequency conversion type electronic photometric device, but is particularly limited to a photodetector whose output current changes according to the amount of light received, from this photodetector. It relates to a digitized, highly reliable and compact electronic photometric device, except for some elements such as a capacitive load that accumulates the current.

【0002】

[Conventional technology]

As is well known, photodetectors such as photodiodes and phototransistors are used in electronic photometers. For example, the basics of conventional photometric devices with illuminance (light intensity) -frequency conversion method using photodiodes. The circuit configuration is shown in Fig. 5. A photodiode PD as a photodetector is connected in series with a capacitance type load, in this example, a capacitor C, and the current I output from the photodiode PD is proportional to the illuminance or amount of incident light._P Is stored in the capacitor C, and the voltage V_C Convert to. This charging voltage V_C Is detected by the voltage detection unit 21 and compared with a preset reference voltage, and when the charging voltage reaches the reference voltage, the voltage detection unit 21 changes the output signal level. Due to this change in signal level, the electric charge accumulated in the capacitor C is discharged, and the output current I from the photodiode PD is again sent to this capacitor C._P Starts the accumulation of.

【0003】

On the other hand, the arithmetic measurement unit, in this example, the timer counter 22 detects a change in the output signal level of the voltage detection unit 21 and measures the time during which the capacitor C is charged due to the change in the signal level, or for a certain period of time. The number of changes in the signal level inside is measured to detect the magnitude of the output current of the photodiode PD, and the illuminance or the amount of light is obtained.

【0004】

FIG. 6 shows a specific example of the photometric device shown in FIG. 5, in which a photodiode PD, which is a photodetector, and a capacitor C, which is a capacitance type load, are connected in series via an analog switch 23. Current I flowing through the photodiode PD in proportion to the illuminance or amount of incident light_P Is stored in the capacitor C via the analog switch 23, and the voltage V_C Convert to. Voltage V stored in this capacitor C_C Is detected by, for example, a voltage detection unit 21 in which two C-MOS type first and second Schmidt inverters 24 and 25 are connected in series. The first Schmidt inverter 24 has a high level threshold voltage V_THAnd low level threshold voltage V_TLIt has two threshold voltages, and the input voltage is a high level threshold voltage V._THHigher level output voltage V when lower_H Is generated and the input voltage is a high level threshold voltage V_THWhen the output voltage reaches high level V_H From low level V_L Threshold voltage V with a low level input voltage_TLLow level output voltage V until it drops to_L Holds a low level threshold voltage V_TLOutput voltage is low level V when dropped to_L From high level V_H Operates to switch to. Therefore, no light is incident on the photodiode PD, and the current I_P When no charge flows, that is, when no charge is accumulated in the capacitor C, its output voltage is at a high level V._H And also the charging voltage V of the capacitor C_C Is a high level threshold voltage V_THWhen equal to, the output voltage of the Schmidt inverter 24 goes from high level to low level V._L Switch to. Furthermore, the accumulated charge of the capacitor C is discharged, and the low-level threshold voltage V of the Schmidt inverter 24 is generated._TLWhen it drops to, the output voltage of the Schmidt inverter 24 becomes low level V._L From high level V_H Switch to. The second Schmidt inverter 25 also has a high level threshold voltage V._THAnd low level threshold voltage V_TLIt has two threshold voltages and operates in the same way. That is, the high level voltage signal V from the first Schmidt inverter 24_H Low level voltage output V when_L Generates a low level voltage signal V_L High level voltage output V when_H Occurs.

【0005】

On the other hand, the analog switch 23 has two fixed contacts x₀ And x₁ And one movable contact x, the movable contact x is connected to the capacitor C, and the first fixed contact x₀ Is connected to the photodiode PD, and the second fixed contact x₁ Is connected to the discharge resistor R. Further, the movable contact x of the analog switch 23 has a high level output voltage V from the first Schmidt inverter 24 through its control line 24a._H When is applied, the first fixed contact x₀ Connected with, conversely low level output voltage V_L When is applied, the movable contact x is the second fixed contact x₁ It is configured to be connected to.

【0006】

In the above configuration, in the initial state where no current flows through the photodiode PD and therefore no charge is accumulated in the capacitor C, the output of the first Schmidt inverter 24 is at a high level V._H Therefore, the movable contact x of the analog switch 23 is the first fixed contact x.₀ Is connected to. When the measurement of the amount of light is started, the current I in the photodiode PD_P Flows, and the capacitor C is charged. Charging voltage V of capacitor C_C Is the high level threshold voltage V of the Schmidt inverter 24_THWhen the output voltage of this Schmidt inverter 24 is reached, the output voltage of this Schmidt inverter 24 is high level V._H From low level V_L Switch to. As a result, the movable contact x of the analog switch 23 becomes the second fixed contact x.₁ Switching to the side, the charging voltage V of the capacitor C_C Is discharged through the resistor R. Charging voltage V of capacitor C by discharge_C Is the low level threshold voltage V of the Schmidt inverter 24_TLWhen it drops to, the output voltage of the Schmidt inverter 24 becomes low level V._L From high level V_H Switch to. As a result, the movable contact x of the analog switch 23 becomes the first fixed contact x again.₀ It is connected to the charging current flowing through the capacitor C . After that, as a result of repeating the same operation, the output voltage V of the first Schmidt inverter 24₁ The waveform of is shown in Fig. 7.

【0007】

The current I that flows into the capacitor C now_P Is constant, the charging time Δt (that is, the output voltage V) of the capacitor C₁ High level output voltage V_H Duration) Δt = (V_TH-V_TL) C / I_P (1) Will be. Thus, the output current I of the photodiode PD is measured by measuring the charging time Δt with the timer counter 22 or by measuring the number of pulses within a certain time and performing arithmetic processing based on the above relational expression (1)._P The value of can be measured, and therefore the illuminance or amount of light incident on the photodiode PD can be determined.

【0008】

Also, the discharge time Td of the capacitor C (that is, the output voltage V)₁ Low level output voltage V_L (Duration of) can be expressed by the following equation.

【0009】

Td = CRlog_n {(V_TH-I_P R) / (V)_TL-I_P R)} (2) [0010]

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional photometric device, the movable contact x of the analog switch 23 is the fixed contact x.₁ When connected to the side, that is, when the capacitor C is discharged, the current output from the photodiode PD is its junction capacitance C._j And analog switch 23 fixed contact x₀ Terminal capacity C_i Because the movable contact x is the fixed contact x₀ When switching to the side, these capacities C_j And C_i The electric charge accumulated in the capacitor C is discharged to the capacitor C. Therefore, in reality, as shown in Fig. 8, the voltage of the capacitor C is V at the start of charging._TLFrom V_TL'(However, V_TL<V_TL') Has risen, and the charge of capacitor C has this risen voltage V_TLHigh level threshold voltage V starting from '_THIt will be done until it becomes. That is, the time required for charging is shortened. As a result, the characteristics of the illuminance (light amount) -frequency conversion become unstable, the error in the light amount measurement becomes large, and there is a drawback that the reliability is lacking.

【0011】

In addition, analog switches are relatively expensive among the parts used, and require a large occupied area when the entire circuit is made into one LSI, so there is a limit to miniaturization and cost reduction. There was also a drawback that there was. Further, there is a drawback that various errors may occur due to the on-resistance of the analog switch.

【0012】

On the other hand, there are the following restrictions in setting the discharge time Td of the capacitor.

【0013】

(1) In order to lower and lower the detection lower limit of the amount of light, it is necessary to make the capacitance C of the capacitor C as small as possible.

【0014】

(2) In order to raise the upper limit of light intensity detection, it is necessary to make the resistance value R of the resistor R as small as possible.

【0015】

That is, in order to satisfy the above constraint and obtain the required light amount detection range, the discharge time Td of the capacitor must be made very small. If a high-performance frequency counter can be used, there is almost no problem even if the discharge time Td of the capacitor is made very small. However, since the above-mentioned electronic photometer is a fairly inexpensive device, an expensive frequency counter is used. There is a drawback that the cost of the entire device increases significantly if it is used. Therefore, a counter with a certain level of performance, such as a counter built in a microcomputer or a general-purpose counter, is usually used. Therefore, the discharge time Td of the capacitor, and therefore the output voltage V₁ Low level output voltage V_L Has the disadvantage that measurement is not possible if the duration of is very short (high level output voltage V)._H Even if the duration is very short, it becomes impossible to measure), and there is a drawback that the light amount detection range must be limited.

【0016】

Therefore, one object of the present invention is to provide a photometric device capable of stabilizing the characteristics of illuminance (light intensity) -frequency conversion, improving reliability, miniaturization, and cost reduction.

【0017】

Another object of the present invention is to provide a photometric device capable of performing highly accurate measurement by an inexpensive frequency counter.

【0018】

[Means for solving problems]

The above object is achieved by the photometric device according to the present invention. In summary, on the one hand, the present invention includes a light detection element whose output current changes according to the amount of light received, a capacitance type load charged by the output current from the light detection element, and the load. A voltage detector that compares the charged voltage charged in the battery with a preset reference voltage and changes the output signal level when the charge voltage reaches the reference voltage, and a change in the output signal level from the voltage detector. A switch means for forming a discharge path for the capacitance type load is provided, and an output from the light detection element to the capacitance of the light detection element or the switch means when the capacitance type load is discharged. It is a photometric device characterized in that electric charges are not accumulated by an electric current.

【0019】

Further, in other aspects, the present invention includes a light detection element whose output current changes according to the amount of received light, a capacitance type load charged by the output current from the light detection element, and the load. The charged charging voltage is compared with a preset reference voltage, and the light is generated by a voltage detection unit that generates a pulse signal each time the charging voltage reaches the reference voltage and a pulse output signal from the voltage detection unit. A calculation and measurement unit that calculates the amount of light received incident on the detection element and a voltage level time width corresponding to the discharge time of the capacitance type load of the generated pulse signal provided in the voltage detection unit are required. It is a photometric device characterized by having a waveform shaping circuit extending to a length.

【0020】

[Example]

Hereinafter, examples of the present invention will be described in detail with reference to the accompanying drawings.

【0021】

FIG. 1 is a circuit diagram showing a main part of the first embodiment of the photometric device according to the present invention. In this embodiment, a photodiode PD is used as a photodetector, a capacitance type load is connected in series with this photodiode PD, and a capacitor C is connected in this embodiment, in proportion to the illuminance or amount of incident light. Current I output from photodiode PD_P Is stored in the capacitor C, and the voltage V_C Convert to. Voltage V stored in this capacitor C_C Is input to, for example, a C-MOS type first Schmidt inverter 24. Since the functions, operation modes, etc. of the Schmidt inverter 24 are as described above, they will be omitted here.

【0022】

In this embodiment, one fixed contact x is used as an analog switch 30.₀Using an on / off switch with one movable contact x, connect the movable contact x to the connection between the photodiode PD and the capacitor C, and fix the fixed contact x.₀ Is connected to the discharge resistor R. Further, this analog switch 30 has a high level output voltage V from the first Schmidt inverter 24 through the control line 24a._H When is applied, the movable contact x becomes the fixed contact x₀ It is in the off state shown in the figure that is not connected to, and conversely the low level output voltage V_L When is applied, the movable contact x becomes the fixed contact x₀ It is configured to be in the on state connected to.

【0023】

In the above configuration, in the initial state where no current flows through the photodiode PD and therefore no charge is accumulated in the capacitor C, the output of the first Schmidt inverter 24 is at a high level V._H The analog switch 30 is off and the capacitor C is rechargeable. When the measurement of the amount of light is started, the current I in the photodiode PD_P Flows, and the capacitor C is charged. Charging voltage V of capacitor C_C Is the high level threshold voltage V of the Schmidt inverter 24_THWhen the output voltage of this Schmidt inverter 24 is reached, the output voltage of this Schmidt inverter 24 is high level V._H From low level V_LSwitch to. As a result, the movable contact x of the analog switch 30 becomes the fixed contact x.₀Since it is connected to and turned on, the charging voltage V of the capacitor C_C Is discharged through the resistor R. Charging voltage V of capacitor C by discharge_C Is the low level threshold voltage V of the Schmidt inverter 24_TLWhen it drops to, the output voltage of the Schmidt inverter 24 becomes low level V._L From high level V_H Switch to. As a result, the analog switch 30 is turned off again, and the charging current flows through the capacitor C. Hereinafter, as a result of repeating the same operation, the output voltage V of the first Schmidt inverter 24₁ The waveform of is shown in FIG. 7 described above.

【0024】

As described above, in this embodiment, an on / off switch 30 having a simple structure is used, the switch 30 is turned on when the capacitor C is discharged, and the output current I from the photodiode PD is used._P By its junction capacity C_j And the terminal capacity C of the movable contact or fixed contact of the analog switch 30_i The charging start voltage of capacitor C is always V because_TLTherefore, the time required for charging will not be shortened. Therefore, the characteristics of illuminance (light intensity) -frequency conversion are stable, and the reliability is further improved, so that the measurement accuracy is improved. Further, since it is an analog switch having a simple structure, it is relatively inexpensive and occupies a small area, so that it is possible to reduce the size and cost.

【0025】

FIG. 2 is a circuit diagram showing a main part of a second embodiment of the photometric device according to the present invention. In this embodiment as well, a photodiode PD is used as a photodetector, a capacitance type load capacitor C is connected in series with the photodiode PD, and the photodiode PD is proportional to the illuminance or amount of incident light. Current output from I_P Is stored in the capacitor C, and the voltage V stored in this capacitor C_C Is input to the first Schmidt inverter 24 of the C-MOS type, and the circuit configuration is the same as that of the first embodiment. Therefore, the description of the operation is omitted here.

【0026】

In this embodiment, a diode D1 is used instead of the analog switch, and this diode D1 is connected between the output and the input of the first Schmidt inverter 24 via a resistor R1 having the opposite polarity to the photodiode PD. is there.

【0027】

In the above configuration, in the initial state where no current flows through the photodiode PD and therefore no charge is accumulated in the capacitor C, the output voltage of the first Schmidt inverter 24 is at a high level V._H The diode D1 is biased in the opposite direction and has the same function as switch-off. Therefore, no current flows through the resistor R1, and the capacitor C is in a rechargeable state. When the measurement of the amount of light is started, the current I in the photodiode PD_P Flows, and the capacitor C is charged. Charging voltage V of capacitor C_C Is the high level threshold voltage V of the Schmidt inverter 24_THWhen the output voltage of this Schmidt inverter 24 is reached, the output voltage of this Schmidt inverter 24 is high level V._H From low level V_L Switch to. This biases the diode D1 in the forward direction and performs the same function as switching on, so the charging voltage V of the capacitor C_C And the output current of the photodiode PD I_P Flows through the resistor R1 and the diode D1, and the charging voltage of the capacitor C is discharged. Charging voltage V of capacitor C by discharge_C Is the low level threshold voltage V of the Schmidt inverter 24_TLWhen it drops to, the output voltage of the Schmidt inverter 24 becomes low level V._L From high level V_H Switch to. As a result, the diode D1 is reverse-biased again and turned off, so that a charging current flows through the capacitor C. After that, as a result of repeating the same operation, the output voltage V of the first Schmidt inverter 24₁ The waveform of is shown in FIG. 7 described above in the same manner as in the first embodiment.

【0028】

As described above, in this embodiment, the diode D1 is used instead of the analog switch, and when the capacitor C is discharged, the diode D1 is biased in the forward direction to turn it on, the charging voltage of the capacitor C is discharged, and the photo is taken. Output current from diode PD I_P Was made to flow through the diode D1, so the junction capacitance C of the photodiode PD_j Is no longer charged, and the charging start voltage of capacitor C is always V_TLWill be. Therefore, the time required for charging is not shortened, the characteristics of illuminance (light amount) -frequency conversion are stabilized, and the reliability is further improved, so that the measurement accuracy is improved. In addition, since an analog switch is not used, the cost is low and the occupied area is considerably reduced, so that the size and cost can be reduced. Furthermore, the drawback that various errors can occur due to the on-resistance of the analog switch is eliminated.

【0029】

FIG. 3 is a circuit diagram showing a main part of a third embodiment of the photometric device according to the present invention. In this embodiment, a simple waveform shaping circuit is connected to the output side of the first Schmidt inverter 24, and the output voltage is V.₁ Waveform shaping and output voltage V₁ Low level output voltage V_L That is, the discharge time Td of the capacitor C is lengthened so that the output waveform can be measured with sufficient accuracy by an inexpensive counter such as a general-purpose counter or a counter built in a microcomputer.

【0030】

In the above waveform shaping circuit, a third Schmidt inverter 31 and a diode D2 and a second Schmidt inverter 25 are connected in series with the output side of the first Schmidt inverter 24, and a resistor R2 and a resistor R2 and ground are connected between the output side of the diode D2 and the ground. It has a configuration in which capacitors C2 are connected in parallel, and an output signal whose waveform is shaped by this waveform shaping circuit is supplied to the input of the second Schmidt inverter 25.

【0031】

Next, the operation of the waveform shaping circuit will be briefly described. Output voltage V of the first Schmidt inverter 24₁ Is inverted by the third Schmidt inverter 31, and its output voltage waveform is as shown in (A) of FIG. In this output waveform, the high level part, that is, the part corresponding to the discharge time Td of the capacitor C charges the capacitor C2 through the diode D2, and the low level part, that is, the part corresponding to the charging time Δt of the capacitor C is It is blocked because the diode D2 has a reverse bias. Therefore, when the output waveform of the third Schmidt inverter 31 goes from high level to low level, the voltage charged in the capacitor C2 becomes the time constant τ = C.₂ R₂ (However, C₂ Is the capacitance of capacitor C2, R₂ Is gradually discharged through the resistor R2 according to the resistance value of the resistor R2), so that the voltage waveform supplied to the input of the second Schmidt inverter 25 is as shown in FIG. 4 (B). As a result, the output voltage waveform of the second Schmidt inverter 25 is as shown in FIG. 4 (C), and a required time width Td'longer than the discharge time Td of the capacitor C can be obtained. This time width Td'is the value C of the capacitor C2 and the resistor R2 of the waveform shaping circuit.₂ , R₂ Since it can be set to any desired value by setting appropriately, it is easy to have a time width Td'that can be reliably measured by an inexpensive counter having a certain level of performance such as a general-purpose counter or a counter built in a microcomputer. Can be set to.

【0032】

As described above, according to the present embodiment, when the discharge time Td of the capacitor C is made very short in order to lower and widen the lower limit of the detection range of the amount of light and to raise and widen the upper limit of the detection range. In addition, since this extremely short discharge time Td is extended to the required length of time by the waveform shaping circuit, the waveform can be accurately generated by an inexpensive counter with a certain level of performance, such as a counter built into a microcomputer or a general-purpose counter. Can be measured. Therefore, there is an advantage that the detection range of the amount of light can be widened by using an inexpensive counter, and there is an advantage that a large cost can be reduced because it is not necessary to use a high-performance frequency counter.

【0033】

Furthermore, it is clear that by combining the first embodiment or the second embodiment with the third embodiment, an electronic photometric device that effectively incorporates the advantages of both embodiments can be configured.

【0034】

The electronic photometric device according to the present invention not only measures the illuminance (light intensity), but also measures the dirt or deterioration of various oils and the dirt or deterioration of liquids, gases, etc. through which light other than oil can pass. it can. For example, it is useful when applied to a device for detecting contamination or deterioration of lubricating oil such as automobile engine oil.

【0035】

Further, the above embodiment is merely an example of the present invention, and the circuit configuration, the elements to be used, and the like can be arbitrarily changed as needed. For example, an inverter other than the C-MOS Schmidt inverter or another circuit element may be used, or a photodetector element other than the photodiode or an element other than the microcomputer may be used. Further, the oscillation circuit may generate a pulse other than the square wave pulse.

【0036】

[Effect of the invention]

As described above, the photometric device according to the present invention has the junction capacitance and the terminal capacitance of the movable contact or fixed contact of the analog switch depending on the output current from the photodetector element when the charged capacitance type load is discharged. Since the charging is not performed, the charging start voltage of the capacitance type load is always a low constant voltage, and the time required for charging is not shortened. Therefore, the characteristics of illuminance (light intensity) -frequency conversion become stable, and the reliability becomes higher, so that highly accurate measurement can be performed. In addition, since the occupied area is reduced, miniaturization becomes possible. Furthermore, when the discharge time of the capacitance type load is made very short and the detection range of the amount of light is widened, this very short discharge time is extended to the required length by the waveform shaping circuit. Therefore, it is possible to measure the waveform with high accuracy with an inexpensive counter having a certain level of performance, such as a counter built in a microcomputer or a general-purpose counter. Therefore, since it is not necessary to use a high-performance frequency counter, there are many remarkable effects such as a significant cost reduction.

[Simple explanation of drawings]

[Figure 1]

It is a circuit diagram which shows the main part of the 1st Example of the light measuring apparatus by this invention.

[Figure 2]

It is a circuit diagram which shows the main part of the 2nd Example of the light measuring apparatus by this invention.

[Fig. 3]

It is a circuit diagram which shows the main part of the 3rd Example of the light measuring apparatus according to this invention.

[Fig. 4]

It is a waveform diagram which shows the voltage output in each part of the 3rd Example shown in FIG.

[Fig. 5]

It is a block diagram which shows the basic circuit structure of the conventional photometric device.

[Fig. 6]

It is a circuit diagram which shows a specific example of the conventional photometric apparatus shown in FIG.

[Fig. 7]

It is a waveform diagram which shows the voltage output of the Schmidt inverter used in the photometric device.

[Fig. 8]

It is a waveform diagram which shows the actual charge / discharge characteristics of the capacitor used in the light measuring device shown in FIG.

[Explanation of symbols]

24, 25, 31 Schmidt inverter 30 analog switch PD photodiode C, C1, C2 capacitors R, R1, R2 resistors D, D1, D2 diodes