JPH0670588B2 - Photometric 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 capable of canceling an error due to variations in characteristics of circuit elements.

[0002]

2. Description of the Related Art As is well known, photodetectors such as photodiodes and phototransistors are used in electronic photometers. For example, the conventional illuminance (light quantity) -frequency conversion method using photodiodes is used. An example of this photometric device is shown in FIG. This photometric device includes a photodiode PD which is a light detecting element and a capacitor C which is a capacitance type load.
And the analog switch 23 and the first C-MOS type Schmitt inverter 24 constitute a light quantity-frequency conversion circuit 30, and the photodiode PD and the capacitor C are connected in series via the analog switch 23 and are incident. The current I _P flowing through the photodiode PD in proportion to the illuminance or the amount of light is accumulated in the capacitor C via the analog switch 23 and converted into the voltage V _C. The voltage V _C accumulated in the capacitor C is converted into a pulse signal by the first Schmitt inverter 24 of C-MOS type. The first Schmitt inverter 24 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 the light is not incident on the photodiode PD and the current I _P does not flow, that is, when the charge is not accumulated in the capacitor C, the output voltage is the high level V _H , and
When the charging voltage V _C of the capacitor C is equal to the high-level threshold voltage V _TH, the Schmitt inverter 24
The output voltage of the switch from the high level to the low level V _L. Further, when the charge accumulated in the capacitor C is reduced to the low level threshold voltage V _TL of the Schmitt inverter 24 by discharging, the output voltage of the Schmitt inverter 24 is switched from the low level _VL to the high level V _H. Therefore,
The first Schmitt inverter 24 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.

On the other hand, the analog switch 23 has two fixed contacts x ₀ and x ₁ and one movable contact x, the movable contact x is connected to the capacitor C, and the first fixed contact x ₀ is connected to the photodiode PD. Connected, and the second fixed contact x ₁ is connected to the discharge resistor R. The movable contact x of the analog switch 23 has a first fixed contact x ₀ when a high level output voltage V _H is applied from the first Schmitt inverter 24 through the control line 24a.
When the low-level output voltage V _L is applied, the movable contact x is connected to the second fixed contact x ₁ .

In the above structure, the photodiode PD
In the initial state in which no current flows through the capacitor C and thus no charge is stored in the capacitor C, the output of the first Schmitt inverter 24 is at the high level V _H , so the movable contact x of the analog switch 23 is the first fixed contact x. Connected with ₀ . When the measurement of the amount of light is started, the photodiode P
A current I _P flows through D, and the capacitor C is charged. When the charging voltage V _C of the capacitor C reaches the high level threshold voltage V _TH of the first Schmitt inverter 24,
The output voltage of the Schmitt inverter 24 is high level V
_Switch from _H to low level V _L. As a result, the movable contact x of the analog switch 23 is switched to the second fixed contact x ₁ side, and the charging voltage V _C of the capacitor _C is discharged via the resistor R. Charging voltage V _{C of} capacitor C due to discharge
Falls to the low level threshold voltage V _TL of the first Schmitt inverter 24, the output voltage of the Schmitt inverter 24 changes from the low level V _L to the high level V _H.
Switch to. As a result, the movable contact x of the analog switch 23 is again connected to the first fixed contact x _0, and the charging current flows through the capacitor C. Hereinafter, as a result of repeating the same operation, the output voltage of the first Schmitt inverter 24, that is, the output voltage V from the light quantity-frequency conversion circuit 30.
_As shown in FIG. 3, ₁ has a pulse waveform having a frequency corresponding to the charge / discharge cycle of the capacitor C.

In the present example, the output voltage V ₁ of the first Schmitt inverter 24 is supplied to the same C-MOS type second Schmitt inverter 25 as the first Schmitt inverter 24. This second Schmitt inverter 2
5 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 24, 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 25 generates an output voltage having the same frequency as the pulse waveform of the first Schmitt inverter 24, and supplies the output voltage to the microcomputer 22 which is a calculation and measurement unit.

The microcomputer 22 counts the number of pulses of the frequency signal F ₀ input from the light quantity-frequency conversion circuit 30 through the second Schmidt inverter 25, the photodiode PD, and the input / output characteristics of the conversion circuit. RO storing arithmetic processing program
Storage unit 22b including M (read only memory)
And an arithmetic processing unit 22c that detects the magnitude of the output current of the photodiode PD according to the program of the storage unit 22b from the number of pulses within a certain time counted by the counter unit 22a and calculates the illuminance or the light amount. ing.

By the way, the input / output characteristics of the photodiode PD, that is, the relationship between the illuminance E and the output current I _P is expressed by the following equation.

LogE = AlogI _P + B (1) Here, A and B are constants that differ depending on each photodiode used.

Since the input / output characteristics of the circuit of the photometric device are determined by the capacitance C of the capacitor C, the resistance value R of the discharging resistor R, the high level threshold voltage V _TH and the low level threshold voltage V _{TL of} the Schmitt inverter, the above equation is used. (1) is expressed by the following function G.

I _P = G (C, R, V _TH , V _TL ) (2) Therefore, the overall input / output characteristics can be expressed by the following function F.

E = F ( _IP , A, B, C, R, V _TH , V _TL ) (3)

[0012]

In order to obtain the illuminance E with the conventional photometric device shown in FIG. 2, the program of the function F is stored in the ROM of the storage unit 22b of the microcomputer 22 in advance, and is stored at the time of the arithmetic processing. It suffices to read the program from the ROM and execute it. However, the constants A, B, C, R, V _TH, and V _TL of the function F vary depending on the circuit element used in each device,
It is necessary to change the contents of the program of the function F according to each constant of each device. This requires a lot of complicated work, and has the drawback that the contents of the program must be changed again when some elements are replaced. Further, when the program of the function F is not changed, there is a drawback that an error occurs due to the variation of the constants.

Therefore, an object of the present invention is to provide a highly reliable photometric device which is provided with means for canceling variations in the characteristics of circuit elements and which eliminates the need to change the contents of the program for each device.

[0014]

The above object is achieved by the photometric device according to the present invention. In summary, the present invention is
A photodetector element whose output current changes according to the amount of received light, and a capacitance type load which is connected to the photodetector element through first and second switch means and is charged by the output current from the photodetector element. And comparing the charging voltage charged in the load with a preset reference voltage and changing the output signal level each time the charging voltage reaches the reference voltage; A variable impedance element connected between the outputs via the second switch means,
A counter unit that counts the number of pulses of the supplied frequency signal, a storage unit that stores a calculation processing program, and a photodetector element according to the program of the storage unit from the number of pulses within a certain time counted by the counter unit. An arithmetic processing unit for calculating an illuminance or a light amount of incident light, and an arithmetic and measurement unit including a control unit for switching and controlling the second switch unit are provided, and the first switch unit is provided from the voltage detection unit. Is selectively switched and connected so as to form a discharge path of the capacitance type load according to a change in the output signal level of the second type, and the second switch means connects the capacitance type load to the first switch means. When connected to, the illuminance (light amount) -frequency conversion circuit is configured to generate a frequency signal according to the illuminance or light amount of light incident on the photodetector, and the second signal is generated. When the switch means connects the load of the electrostatic capacitance type in the variable impedance element,
A comparison frequency generation circuit for generating a frequency-variable comparison frequency signal is configured, and a storage unit of the calculation / measurement unit stores at least an arithmetic processing program of input / output characteristics of the photodetector and the conversion circuit and correction of characteristics by comparison frequency. The arithmetic processing program is stored, and the arithmetic value corresponding to the comparison frequency is introduced into the arithmetic expression for performing the arithmetic processing of the input / output characteristics,
It is characterized in that an arithmetic value corresponding to the comparison frequency is adjusted by an arithmetic processing program for characteristic correction by the comparison frequency so as to cancel an error caused by the arithmetic processing of the input / output characteristic based on the arithmetic expression. It is a photometric device.

[0015]

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 the photometric device according to the present invention. In the photometric device of this embodiment, the illuminance (light quantity) is composed of a photodiode PD which is a photodetector, a capacitor C which is a capacitance type load, an analog switch 23 and a first C-MOS type Schmitt inverter 24.
A frequency conversion circuit is configured, and a second analog switch 35 having the same configuration as the first analog switch 23 is connected between the first analog switch 23 and the capacitor C, and the second analog switch 35 is used. A variable resistance VR which is a variable impedance element is connected between the input and output of the first Schmitt inverter 24, and when the second analog switch 35 connects the capacitor C to the variable resistance VR, a variable frequency comparison frequency generator is configured. It is something that is done. That is, the capacitor C and the first Schmitt inverter 24 are shared by the light amount-frequency conversion circuit and the comparison frequency generation circuit.

Further, in this embodiment, the photodiode P
D and the ROM of the storage unit 34b of the microcomputer 34, which stores the arithmetic processing program of the input / output characteristics of the light quantity-frequency conversion circuit, further stores the “arithmetic processing program of characteristic correction by comparison frequency”, and A control port 34d for switching and controlling the second analog switch 35 is provided in the microcomputer 34, and a control signal is supplied from this control port 34d to set the second analog switch 35 to the first analog switch 23 side and the variable resistor V.
Switching connection is made with the R side.

In the above structure, when the movable contact x of the second analog switch 35 is connected to the fixed contact x ₀ on the variable resistance side as shown in the figure, the variable resistance VR, the capacitor C and the first Schmitt inverter 24 are connected. The comparison frequency generation circuit is constituted by the comparison frequency generation circuit, and the comparison frequency output Fr from this comparison frequency generation circuit is the second Schmitt inverter 2
The microcomputer 34, which is a calculation and measurement unit, through
Is supplied to. Further, the movable contact x of the second analog switch 35 is the fixed contact x on the side of the first analog switch 23.
_When connected to ₁ , the photodiode PD, the first analog switch 23, the discharging resistor R, the capacitor C, and the first Schmitt inverter 24 constitute a light quantity-frequency conversion circuit. From this light quantity-frequency conversion circuit, Of the frequency output F ₀ corresponding to the illuminance or the light amount of the microcomputer 34 via the second Schmitt inverter 25.
Will be supplied to. In the microcomputer 34, the counter unit 3 calculates the number of pulses of each frequency signal supplied.
4a counts the number of pulses within a certain period of time respectively, and from the measured comparison frequency output Fr and the frequency output F ₀ corresponding to the illuminance or the light amount, R is calculated by the arithmetic processing unit 34c.
The illuminance or the light amount is calculated by performing arithmetic processing according to the program stored in the OM.

The input / output characteristics of the light quantity-frequency conversion circuit having the above configuration can be approximated by the following equation.

[0020] _{logF 0 = logI P + C ···} (4) where, F ₀ is light intensity - frequency output of the frequency conversion circuit, C
Is a constant determined by C, R, V _TH and V _TL of the circuit. The above formula (4) is as follows when the input / output characteristics of the photodiode PD are taken into consideration.

LogE = AlogF ₀ + (B−AC) (5) Here, the calculated value D (F∝D) corresponding to the comparison frequency Fr.
When the above is introduced, the above arithmetic expression (5) becomes as follows.

LogE = AlogF ₀ + (B−AC) −D (6) The reference values of the constants A, B, C, and D are A ₀ , B ₀ , C ₀ , D _0.
Assuming that the value of D ₀ is determined so that (B ₀ −A ₀ C ₀ ) = D ₀ , the arithmetic processing regarding the input / output characteristics is performed according to the following equation.

LogE = A ₀ logF ₀ (7) When the photodiodes of the same type are limited, the reference value A ₀ can be regarded as substantially constant, so the constants B and C are the reference values B ₀ and C _0. Can be considered to vary. Therefore, the actual input / output characteristics in this case are logE = A ₀ logF ₀ + Δ {(B−A ₀ C) −D ₀ } (8), and the arithmetic processing unit 34 c of the microcomputer 34.
In the above equation (7), that is, logE = A ₀ logF
_{When the} arithmetic processing is performed according to _0, an error of Δ {(B−A ₀ C) −D ₀ } will occur.

Therefore, in this embodiment, the value of the operation value D corresponding to the comparison frequency is changed according to the comparison frequency Fr by the "operation processing program for characteristic correction by the comparison frequency" stored in the storage section 34b, and -A ₀ C) -D = 0
The error Δ {(B−A ₀ C) −D
₀ } is canceled.

As described above, in this embodiment, the storage unit 3 of the microcomputer 34 which stores the arithmetic processing program of the input / output characteristics of the photodiode PD and the conversion circuit.
An arithmetic expression (logE = A ₀ logF ₀₎ in which a “computation processing program for characteristic correction by comparison frequency” is further stored in 4b and a calculation value D corresponding to the comparison frequency Fr is introduced.
+ (B-AC) -D), the calculation value D is adjusted so as to cancel the error generated when the calculation processing is performed only according to the calculation processing program of the input / output characteristics. It is not necessary to change the input / output characteristic arithmetic processing program stored in the storage unit 34b of the ROM 34 for each device. Therefore, workability is further improved and reliability is increased.

The electronic photometric device according to the present invention does not only measure the illuminance (light amount) but also stains or deterioration of various oils or stains such as liquids and gases that allow light other than oil to pass through. Deterioration can be measured. For example, it is useful when applied to a device for detecting dirt or deterioration of lubricating oil such as automobile engine oil.

Further, the above embodiments are merely examples of the present invention, and the circuit configuration, the elements to be used, etc. can be arbitrarily changed as required. For example, an inverter other than the C-MOS Schmidt inverter or another circuit element can be used, and a photodetection element other than a photodiode or an element other than a microcomputer, or an electronic switch or the like instead of an analog switch. Of course, the switch means may be used. Further, the frequency output generated from the light quantity-frequency conversion circuit or the comparison frequency generation circuit may be a pulse other than the square wave pulse.

[0028]

As described above, the photometric device according to the present invention generates a variable frequency comparison frequency output from the comparison frequency generation circuit and causes the storage section of the calculation and measurement section to calculate "correction of characteristics by comparison frequency". "Processing program" is stored, and the value D corresponding to the comparison frequency is adjusted during arithmetic processing to cancel the error that occurs when arithmetic processing is performed only according to the arithmetic processing program of the input / output characteristics.
There is no need to change the arithmetic processing program of the input / output characteristics stored in the storage unit of the arithmetic measurement unit for each device.
Therefore, the workability is further improved and the reliability is increased, so that the illuminance or the light amount can be measured with high accuracy.
There are many remarkable effects such as cost reduction.

[Brief description of drawings]

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

FIG. 2 is a circuit configuration diagram showing a specific example of a conventional photometric device.

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

[Explanation of symbols]

 23, 35 Analog switch 24, 25 Schmidt inverter 34 Microcomputer PD Photodiode C Capacitor R resistance VR Variable resistance

Claims (2)

[Claims] 1. A photodetector element whose output current changes according to the amount of received light, and a static charge connected to the photodetector element through first and second switch means and charged by the output current from the photodetector element. A capacitance type load, a voltage detection unit that compares the charging voltage charged in the load with a preset reference voltage, and changes the output signal level each time the charging voltage reaches the reference voltage; A variable impedance element connected between the input and output of the voltage detection means via the second switch means, a counter section for counting the number of pulses of the frequency signal supplied, a storage section for storing an arithmetic processing program, An arithmetic processing unit that calculates the illuminance or the amount of light incident on the photodetection element according to the program of the storage unit from the number of pulses counted by the counter unit within a fixed time, and the second switch. And a calculation and measurement section having a control section for switching and controlling the switch means, wherein the first switch means forms the discharge path of the capacitance type load by the change of the output signal level from the voltage detection means. When the second switch means connects the capacitance type load to the first switch means, an illuminance (light quantity) -frequency conversion circuit is configured to form the illuminance (light quantity) -frequency conversion circuit. A frequency signal is generated according to the illuminance or the amount of light incident on the light detection element, and when the second switch means connects the capacitance type load to the variable impedance element, a frequency variable A comparison frequency generation circuit that generates a comparison frequency signal is configured, and in the storage unit of the calculation and measurement unit,
At least an arithmetic processing program for input / output characteristics of the photodetector and the conversion circuit and an arithmetic processing program for characteristic correction by a comparison frequency are stored, and an arithmetic expression corresponding to the comparison frequency is stored in an arithmetic expression for performing the arithmetic processing of the input / output characteristics. A value is introduced, and a calculation value corresponding to the comparison frequency is adjusted by a calculation processing program for characteristic correction by the comparison frequency so as to cancel an error caused by the calculation processing of the input / output characteristic based on the calculation formula. A photometric device characterized in that 2. The arithmetic processing of the arithmetic and measurement unit is such that the illuminance is E, the frequency output of the illuminance (light quantity) -frequency conversion circuit is F ₀ , a substantially constant constant is A for the same type of photodetector, and each light is The constant that varies depending on the detection element is B, the constant that varies depending on the circuit element constant is C, and the calculated value corresponding to the comparison frequency is D.
Then, the comparison frequency of the comparison frequency generating circuit is adjusted so that (B-AC) -D = 0 holds according to the following arithmetic expression logE = AlogF ₀ + (B-AC) -D. The photometric device according to claim 1, wherein