JPH0431049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a luminance measuring device equipped with a calibration function that automatically performs zero correction and sensitivity correction.

BACKGROUND ART Recently, brightness measuring devices are desired to expand their measurement range and improve their measurement accuracy. Therefore, there is a need for a device that has excellent operability and can perform zero point adjustment and sensitivity correction easily and reliably. below,
A conventional luminance measuring device will be explained.

FIG. 4 shows a configuration diagram of a conventional brightness measuring device, in which 1 is an objective lens, 3 is a light separation means,
4 is a light source for calibration, 5 is a mirror, 6 is a finder lens, 10 is an amplifier circuit, 21 is a lens cap, and 22 is a light receiving element.

In the brightness measuring device configured as described above, the light incident on the objective lens 1 is separated by the light separating means 3 into the light receiving element 22 side and the viewfinder side (mirror 5 side), and the brightness measurement device measures the light on the viewfinder side. Look directly into the field of view. On the other hand, the light on the light receiving element 22 side is
The light receiving element 22 converts it into an electrical signal. As this light separating means, a half mirror, a half prism, or a mirror with an aperture in which only the measurement field of view is hollowed out so that only the light in the measurement field reaches the light receiving element 22 is used.
The photocurrent from the light receiving element 22 is amplified by the amplifier circuit 10, and a luminance signal 20 is output. As the amplifier circuit, a current-voltage conversion circuit using an operational amplifier (OP amplifier 10a) as shown in FIG. 4 is generally used.

In such a brightness measuring device, the light receiving element 2
2 and the amplifier circuit 10, a lens cap 21 is attached to the front of the objective lens 1 to bring the incident light to a zero state, and the offset adjustment potentiometer _R2 of the OP amplifier 10a is manually adjusted. The output of the OP amplifier 10a was set to zero.
In addition, for sensitivity correction, a calibration light source unit with a constant light output is turned on, only that light output is made to enter the light receiving element 22, and photoelectric conversion is performed.
The output value of the amplifier circuit 10 was adjusted to the reference value by manually adjusting the feedback resistor _R1 of the OP amplifier 10a. Furthermore, in the case of using a photomultiplier tube as a light receiving element, a method of adjusting the high voltage applied to the photomultiplier tube was also used for sensitivity correction.

Problems to be Solved by the Invention However, in the above configuration, zero correction and sensitivity correction must be performed manually. Therefore, in order to improve measurement accuracy, it is necessary to perform zero correction and sensitivity correction for each measurement in order to perform accurate calibration, which requires complicated operations and requires a lot of time for calibration. It has been difficult to stabilize the brightness, which has hindered continuous analog brightness measurement.

The present invention solves the above conventional problems by digitizing and automating the calibration system of the brightness measurement system and connecting it to the brightness measurement system, and when measuring brightness, disconnects the automatic calibration system and performs brightness measurement and calibration. The purpose of the present invention is to provide a luminance measurement device that can be used efficiently.

Means for Solving the Problems In order to achieve the above object, the present invention includes an objective lens, a light receiving element that converts incident light from the objective lens into an electrical output, and amplifying and correcting the electrical output of the light receiving element. A brightness measurement system that includes an amplifier circuit, a zero correction circuit, and a sensitivity correction circuit that are connected in series to treat the measured value as an analog quantity; a shutter that shuts off the zero correction value; a zero correction value control circuit that receives the analog output of the zero correction circuit during zero correction operation and digitally outputs the zero correction value; and a digital zero correction value of the zero correction value Kentroll circuit. a zero correction value setting circuit that stores and converts it into an analog value to control the zero correction circuit; a calibration light source section that lights up as a sensitivity correction section so as to be incident on the light receiving element during sensitivity correction operation; A sensitivity correction value control circuit receives an analog output from the sensitivity correction circuit and digitally outputs a sensitivity correction value, and the digital sensitivity correction value of the sensitivity correction value control circuit is stored and converted to an analog value to perform the sensitivity correction. an automatic calibration system consisting of a sensitivity correction value setting circuit that controls the circuit; the shutter is closed during zero correction operation and sensitivity correction operation; the zero correction value setting circuit is operated during zero correction operation; The configuration includes a calibration light source section and a measurement control section that controls the operation of the sensitivity correction value setting circuit.

Function The function of the present invention will be explained using the basic configuration diagram shown in FIG. A zero correction circuit 11 and a sensitivity correction circuit 14 are connected in series to the output of the amplifier circuit 10 of the brightness measurement system 18. Further, a light source section 4 for calibrating the shutter 2 for cutting incident light is provided in the optical path in front of the light receiving element 22 of the brightness measurement system 18. The output of the amplifier circuit 10 and the output of the zero correction value setting circuit 12 are input to the zero correction circuit 11 . The sensitivity correction circuit 14 includes a zero correction circuit 11.
and the output of the sensitivity correction value setting circuit 15 are input.

During zero correction, the shutter 2 is closed to make the incident light zero, and a zero correction value control circuit 13 digitally increases or decreases the zero correction value set value according to the analog output level of the zero correction circuit 11. By repeating such operations, the output of the zero correction circuit 11 is controlled to become zero. When correcting the sensitivity, the shutter 2 is closed and the light source in the calibration light source section 4 is turned on to supply a constant amount of light to the light receiving element 22, and in the same way as during zero correction, the analog output of the sensitivity correction circuit 14 is set to the reference value. (calibration value).The sensitivity correction value control circuit controls the sensitivity correction value set as a digital quantity so that the sensitivity correction value becomes (calibration value). In this way, the zero correction value and the sensitivity correction value are digitally set by the feedback operation (repetitive operation), and the calibration zero correction and sensitivity correction of the luminance measurement system are automatically performed.

On the other hand, when measuring brightness, the shutter 2 is opened, the calibration light source section 4 is turned off, and the digital zero correction value in the zero correction value setting circuit 12 and the sensitivity correction value setting circuit 15 determined by the above calibration operation are The digital sensitivity correction value within is converted into an analog value, and this is used to calibrate the brightness value in an analog manner and continuously measure it.

In this way, during calibration, the incident light to the brightness measurement system is cut off and automatic calibration is performed digitally, and during brightness measurement, a part of the automatic calibration system is used as fixed data, and the brightness values are accurately measured in analog form. Measure continuously.

Embodiment FIGS. 2A and 2B show the configuration of a luminance measuring device in an embodiment of the present invention. In these figures, 1 is the objective lens, 2 is the shutter, and 3 is the objective lens.
a is a mirror with an aperture, 4 is a calibration light source, 5
is a mirror, 6 is a finder lens, 8 is a photomultiplier tube, 9 is a high-voltage power supply, 10 is an amplifier circuit, 11 is a zero correction circuit, 12 is a zero correction value setting circuit, 13 is a zero correction value control circuit, and 14 is a Sensitivity correction circuit, 1
5 is a sensitivity correction value setting circuit, 16 is a sensitivity correction value control circuit, and 17 is a measurement control section. Among these, a brightness measurement system 18 is composed of an objective lens 1, a mirror with an aperture 3, a photomultiplier tube 8, a high voltage power supply 9, an amplifier circuit 10, a zero correction circuit 11, and a sensitivity correction circuit 14, a shutter 2, and a light source for calibration. section 4, zero correction value setting circuit 12, zero correction value control circuit 13,
The sensitivity correction value setting circuit 15 and the sensitivity correction value control circuit 16 constitute an automatic calibration system 19, and the mirror 5 and the finder lens 6 constitute a finder system. Further, the calibration light source section 4 is composed of a calibration LED 4a and a constant current power supply 4b, and the zero correction value setting circuit 12 is composed of a D/A converter 12a and a zero correction value memory 12b, and a zero correction value control circuit 13.
is the A/D converter 13a, the reference voltage 13b, the digital comparator 13c, and the AND circuit 13.
d, 13e, the sensitivity correction value setting circuit 15 connects the D/A converter 15a and the sensitivity correction value memory 15.
b, the sensitivity correction value control circuit 16 includes an A/D converter 16a, a reference voltage 16b, a digital comparator 16e, an AND circuit 16d,
16e. In this embodiment, a photomultiplier tube is used as the light receiving element.

The operation of the brightness measuring device of this embodiment configured as described above will be described below.

The light incident on the objective lens 1 is separated into optical paths by a mirror 3 with an aperture, and is used for brightness measurement and a finder. The apertured mirror 3 is a type of mirror that has the function of transmitting only light within the measurement range and reflecting light outside the measurement range. The light reflected by the apertured mirror 3 is guided to the finder system,
It is reflected by the mirror 5 and forms a finder image by the finder lens 6. On the other hand, the light transmitted through the apertured mirror 3 is guided to the photomultiplier tube 8 via the shutter 2. The photomultiplier tube 8 is a high voltage power supply 9
The photoelectric conversion operation is performed by receiving a negative high voltage from the The photocurrent from the photomultiplier tube 8 is transmitted to the amplifier circuit 1
Convert to voltage signal with 0. In the embodiment, amplifier circuit 1
This is a current-voltage conversion circuit using an OP amplifier 10a as the zero. The amplifier circuit 10 outputs a voltage obtained by multiplying the photocurrent by the resistor R ₃ . Note that _R4 in the amplifier circuit 10 is a potentiometer for offset adjustment.

First, the automatic calibration operation will be explained. The automatic calibration operation is divided into a zero correction operation and a sensitivity correction operation. In the zero correction operation, the shutter 2 is closed in response to a command from the measurement control section 17 to cut off light incident on the photomultiplier tube 8 from the measurement field of view. Further, the effect correction LED 4a in the effect correction light source section 4 is turned off, and the incident light to the photomultiplier tube 8 becomes zero.
Therefore, the output voltage value from the amplifier circuit 10 is the sum of the voltage value obtained by amplifying the dark current of the photomultiplier tube 8 and the offset voltage value of the OP amplifier 10a. Next, the output of the amplifier circuit 10 is supplied to a zero correction circuit 11. The output of the zero correction value setting circuit 12 is also input to the zero correction circuit 11, and the zero correction circuit 11 inputs the output of the OP amplifier 1.
1a is used to configure an adder circuit for these two input signals. The output of the zero correction circuit 11 is supplied to a sensitivity correction circuit 14 and a zero correction value control circuit 13. In the zero correction value control circuit 13, the A/D
It is converted into a digital signal by the converter 13a,
Reference voltage 13b and digital comparator 13c
are compared. The reference voltage 13b outputs the upper and lower limits of the output voltage of the zero correction circuit 11,
Each is compared with the A/D converter 13a output,
It is determined whether the value is above the upper limit, within the upper and lower limits, or below the lower limit. Here, when the output of the A/D converter 13a, that is, the output of the zero correction circuit 11, is above the upper limit value or below the lower limit value, the digital comparator 13c outputs a control signal to each, Zero correction value memory 12
Rewrite the data in b as a digital value. The data in the zero correction value memory 12b is supplied to the D/A converter 12a, converted into an analog value, and added to the output signal of the amplifier circuit 10 in the zero correction circuit 11.

To explain with a specific example, first, assume that the output of the zero correction value setting circuit 12 is zero and the output of the amplifier circuit 10 is a voltage V shifted in the positive direction. The output of the zero correction circuit 11 is a voltage of V ₁ =-R ₇ /R ₅ ·V. Voltage V ₁ is digitally converted by A/D converter 13a, and digital comparator 1
3c, it is compared with the reference voltage 13b. If the value obtained by digitally converting the voltage V ₁ is less than the lower limit of the reference voltage 13b, the digital comparator 1
The output of D/A converter 12a is subtracted from the data in zero correction value memory 12b through AND circuit 13d, thereby lowering the output voltage of D/A converter 12a. The output of the D/A converter 12a is added to the output of the amplifier circuit 10 in the zero correction circuit 11, so the zero correction circuit output _V1 is _V3 = ( _-R7 / _R5・V)+(- _R7 / _R6・
V ₂ ). Here, V ₂ is D/A converter 12
The output voltage value of a is a negative voltage, and V ₃ <V ₁ , so the output voltage of the zero correction circuit 11 approaches zero. Next, the output voltage _V3 of the zero correction circuit 11 is again applied to the A/D converter 13a in the zero correction value control circuit 13.
The same operation as above is repeated until the output voltage of the zero correction circuit 11 falls within the upper and lower limits of the reference voltage 13b. On the other hand, amplifier circuit 1
When the output of 0 is shifted in the negative direction, the data in the zero correction value memory 12b is added via the AND circuit 13e to increase the output voltage of the D/A converter 12a, and the zero correction is performed in the same manner as above. Do this. Note that the AND circuits 13d and 13e are in charge of subtraction commands and addition commands to the zero correction value memory 12b, respectively.
It becomes operational only during zero correction during automatic calibration.

Next, the sensitivity correction operation will be explained. In the sensitivity correction operation, the calibration LED 4a is lit at a constant current by the constant current power supply 4b in the calibration light source section 4, and a stable light with a constant amount of light is incident on the photomultiplier tube 8, so that the output of the sensitivity compensation circuit 14 is adjusted to the sensitivity. Correction value control circuit 1
The data in the sensitivity correction value memory 15b in the sensitivity correction value setting circuit 15 is increased or decreased so that the reference voltage 16b falls within the upper and lower limits (calibration level) of the reference voltage 16b. In this way, the sensitivity correction operation is basically the same as the zero correction operation. The difference from the zero correction operation is the method of supplying sensitivity correction data to the sensitivity correction circuit 14. The data in the sensitivity correction value memory 15b is D/A
It is converted into an analog value by the converter 15a.
Turn on LEDD ₁ . The light from LEDD ₁ is fed back to the OP amplifier 14a in the sensitivity correction circuit 14.
Optically coupled to _R9 . i.e. resistance
_R9 is a photoconductive element such as Cds whose resistance value changes depending on incident light. For this reason,
The amplification degree of the sensitivity correction circuit 14 is adjusted by changing the value of the resistor R ₉ according to the light intensity level from the LEDD ₁ .

In this way, in the automatic calibration operation, the zero correction value memory 12b is changed digitally, and the output 20 of the brightness measurement system 18 becomes zero.
The sensitivity correction value memory 15b is changed digitally, and the output 20 of the brightness measurement system 18 is adjusted by repeating the operation so that it becomes equal to the calibration value.

Next, the luminance measurement operation will be explained. When measuring brightness, the shutter 2 is opened and the calibration LED is turned off in response to a command from the measurement control section 17. Further, the AND circuits 13d and 13e in the zero correction value control circuit 13 are turned off, and the electrical connection between the zero correction value control circuit 13 and the zero correction value setting circuit 12 is disconnected. Similarly, the AND circuits 16d and 16e in the sensitivity correction value control circuit 16 are turned off, and the electrical connection between the sensitivity correction value control circuit 16 and the sensitivity correction value setting circuit 15 is disconnected. As a result, the brightness measurement system consists only of an analog signal processing system, and the brightness values measured by the brightness measurement system are subjected to zero correction by the analog output of the zero correction value setting circuit 12 and analog signal processing by the sensitivity correction value setting circuit 15. Sensitivity correction based on output is automatically performed, allowing continuous analog measurement of brightness values. Note that the zero correction value and the sensitivity correction value are digitally set by an automatic calibration operation, and stable brightness measurement can be performed.

Among the above-mentioned operations, the automatic calibration function can be efficiently implemented by using a program operation of a microcomputer.

As described above, according to this embodiment, the luminance measurement system is provided with a shutter that blocks incident light, a zero correction circuit and a sensitivity correction circuit that digitally set values, and a zero correction value and a sensitivity correction value during calibration. is automatically set as a digital value through repeated operations, and when measuring brightness, the digitally set zero correction value and sensitivity correction value are used to perform analog conversion and then correct the measured value. Efficient automatic calibration through operation and highly accurate analog continuous brightness measurement can be performed.

In the embodiment, the calibration light source section 4 uses an LED lit at a constant current, but it may also be an incandescent light bulb lit at a constant voltage. Further, although the zero correction value control circuit 13 uses a digital comparison operation, a similar function can be obtained by using an analog comparison operation as shown in FIG. FIG. 3 shows how the output of the zero correction circuit 11 is connected to the voltage comparator 13.
If the comparison result is less than the lower limit of the reference voltage 13h, the output of the clock generator 13i is transferred to the AND circuit 13.
It is supplied to the zero correction value setting circuit 12 as a subtraction signal through j and 13k, and if it is greater than the upper limit value, it is supplied as an addition signal through AND circuits 13l and 13m to control the zero correction value. It goes without saying that the sensitivity correction value control circuit 16 can also have the configuration shown in FIG. 3.

Further, in the embodiment, the zero correction circuit 11 and the sensitivity correction circuit 14 are connected in this order, but the same function can be obtained even in the reverse order. Furthermore, the zero correction circuit 11 and the sensitivity correction circuit 14 may be integrated into one OP amplifier, and the zero correction value may be added at the input stage during the zero correction operation, and the feedback resistance may be changed during the sensitivity correction operation.

Effects of the Invention The brightness measurement device of the present invention has a brightness measurement system including a shutter, a light source for calibration, a zero correction section consisting of a zero correction circuit, a zero correction value setting circuit, a zero correction value control circuit, a sensitivity correction circuit, and a sensitivity correction circuit. A sensitivity correction section consisting of a correction value setting circuit and a sensitivity correction value control circuit is provided, and the zero correction value and sensitivity correction value are set and stored as digital values, and during calibration, these correction values are converted to analog values and repeated. By comparing it with the photoelectric output, and by converting the zero correction value and sensitivity correction value stored as calibration results during measurement into analog and constantly correcting the photoelectric output, efficient automatic calibration function and accuracy can be achieved. It is possible to achieve both a high luminance measurement function, and its practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a brightness measuring device of the present invention, FIGS. 2A and 2B are block diagrams showing the configuration of a brightness measuring device in an embodiment of the present invention, and FIG. 3 is a block diagram showing the configuration of a brightness measuring device in an embodiment of the present invention. FIG. 4 is a block diagram showing a second embodiment of the value control circuit, and FIG. 4 is a block diagram showing the configuration of a conventional luminance measuring device.

Claims (1)

[Scope of Claims] 1. An objective lens, a light-receiving element that converts incident light from the objective lens into an electrical output, an amplifier circuit connected in series to amplify and correct the electrical output of the light-receiving element, and a zero correction. a brightness measurement system that handles measured values as analog quantities; a shutter that blocks incident light to the light receiving element during zero correction operation and sensitivity correction operation; A zero correction value control circuit that receives the analog output of the zero correction circuit and outputs the zero correction value digitally; and a zero correction value control circuit that stores the digital zero correction value of the zero correction value control circuit and converts it to an analog value to perform the zero correction. A zero correction value setting circuit that controls the circuit, a calibration light source section that lights up as a sensitivity correction section so as to be incident on the light receiving element during sensitivity correction operation, and a sensitivity correction value that receives the analog output of the sensitivity correction circuit during sensitivity correction operation. Automatic calibration consisting of a sensitivity correction value control circuit that outputs digitally, and a sensitivity correction value setting circuit that stores the digital sensitivity correction value of the sensitivity correction value control circuit, converts it to an analog value, and controls the sensitivity correction circuit. and closing the shutter during zero correction operation and sensitivity correction operation, operating the zero correction value setting circuit during zero correction operation, and operating the calibration light source section and the sensitivity correction value setting circuit during sensitivity correction operation. A brightness measurement device comprising: a measurement control unit that controls the brightness to 2. The luminance measuring device according to claim 1, wherein the zero correction circuit and the sensitivity correction circuit are integrated.