JPH11351968A - Radiometer with high accuracy calibrating function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiometer with a calibrating function for acquiring accurate data necessary to measure when normally measured as well as for acquiring accurate data at the acquisition of a calibration coefficient such as a sensitivity, offset data or the like. SOLUTION: In the radiometer with a high accuracy calibrating function comprising an A-D converter 4 for converting an analog signal from a detector into a digital signal, the converter 4 has higher resolution (N-bits) than a resolution necessary in a normal measurement, and has a means 5 for controlling to switch to output all the N-bit outputs therefrom as calibration data at the time of acquiring calibration data and to output necessary M bits (wherein M<N) of the N-bit outputs therefrom in a normal measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a radiometer, and more particularly to a radiometer capable of obtaining a highly accurate calibration coefficient at the time of calibration.

[0002] In a radiometer for measuring the radiance of a target object, it is one of the product design goals of the apparatus to determine the absolute value of the radiance. In this type of radiometer, the measured output value is converted into luminance information, which is an engineering value, based on the sensitivity measured before shipment of the product and the bias offset calibration coefficient. In an apparatus employing a digital output as the output at this time, the conversion accuracy of an analog / digital (A / D) converter built in the apparatus is one of the factors that determine the measurement accuracy.

[0003] Also, when recalibration of a calibration coefficient for a change over time after product shipment, the A / D conversion characteristics of the apparatus have a great influence on measurement accuracy. As a radiometer, for example, a radiometer having a function of optically calibrating a visible and near-infrared radiometer is proposed in Japanese Patent Application Laid-Open No. Hei 5-296843.

[0004]

As described above, in a radiometer that outputs a digital signal by A / D conversion, obtaining a high-precision calibration coefficient at the time of acquiring a calibration coefficient for sensitivity and offset requires an increase in measurement accuracy and an accurate measurement. It is an important issue to ensure accurate measurement.

Accordingly, the present invention has been made based on the recognition of the above technical problem, and an object of the present invention is to obtain high-precision data at the time of obtaining a calibration coefficient, and to obtain data of the accuracy required for measurement at the time of normal measurement. To provide a radiometer with a calibration function that makes it possible to obtain

[0006]

In order to achieve the above object, the present invention relates to a radiometer having an analog-to-digital converter for converting an analog signal from a detection circuit into a digital signal. Has a resolution (N bits) higher than the resolution (M bits) normally required for measurement, and when the calibration data is acquired, the analog-to-digital conversion performed by the analog-to-digital converter
All the bits are output as calibration data, and at the time of normal measurement, necessary M bits (where M <
(N) is provided as switching data so as to be output as measurement data.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a radiometer for optically measuring the radiance of a target object, which has a higher resolution than that of a normal measurement when acquiring calibration coefficients for sensitivity and offset, and has a higher number of bits. By using a large number of outputs of an A / D (analog-digital) converter, a calibration coefficient can be determined with high accuracy.

Referring to FIG. 1, an embodiment of the present invention will be described. An observation signal input to an optical system (1) is converted into an analog electric signal by a detector (2) and amplified by a preamplifier (3). After that, it is converted into a digital signal by the A / D conversion circuit (4). The output accuracy switching circuit (5)
The output digital signal of the / D conversion circuit (4) is switched so that all bits are selected and output during the normal measurement when the calibration coefficient is obtained, by the number of bits required for the measurement. The selected output signal is edited through the output interface circuit (6) so as to be compatible with the external interface, and output to the outside.

As described above, according to the embodiment of the present invention, it is possible to output high-accuracy data at the time of obtaining a calibration coefficient, and to select and output data of the accuracy required for measurement during normal measurement. it can.

[0010] In another embodiment, the present invention provides a method comprising:
The A / D converter has a resolution (N bits) higher than the resolution (M bits) normally required for measurement, receives the N-bit output of the A / D converter as input, and converts the data having the N-bit width into calibration data. A high-precision calibration output interface circuit to be output, and M bits (M) of the N-bit output of the A / D converter
<N) as input, and a normal measurement output interface circuit for outputting the data having the M-bit width as the measurement data. When the calibration data is obtained, all the N-bit outputs of the A / D converter are high-precision calibration output interfaces. The signal is output from the circuit (7 in FIG. 4) to the outside. During normal measurement, M bits of the N-bit output of the A / D converter are output to the outside from the normal measurement output interface circuit (8 in FIG. 4) as measurement data. May be adopted.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention.

Referring to FIG. 1, in one embodiment of the present invention, an observation signal input to an optical system 1 is converted into an analog electric signal by a detector 2 and amplified by a preamplifier 3. The amplified analog signal is converted by the A / D conversion circuit 4 into an N-bit digital signal. Here, the number of bits for the A / D conversion is selected to be the number of bits necessary for obtaining the calibration coefficient of the radiometer.

The output precision switching circuit 5 outputs the digital signal to the output interface circuit 6 by switching the number of bits between when the calibration coefficient is obtained and when the normal measurement is performed.

When the calibration coefficient is obtained, the A / D converted N
Switching is performed so that all bits are output and only the upper M bits required for measurement are selected and output during normal measurement.

The operation of one embodiment of the present invention will be described. Referring to FIG. 1, during normal measurement, the output accuracy switching signal is on the measurement side, and at this time, M bits (M <N) of the A / D converted N bits are output to the outside. .

On the other hand, at the time of high-accuracy calibration output, the switching signal is on the calibration side, and all the A / D-converted N bits are output.

FIG. 2 shows the output of pixel data from the detector 2 of the radiometer in one embodiment of the present invention. At the time of the high-accuracy calibration output, as shown in FIG. 2A, the output of each pixel is all A / D-converted N bits (for example, 1-1 to 1-N for the first pixel). On the other hand, during normal measurement, as shown in FIG. 2B, only M bits of the A / D converted N bits (for example, the first pixel is 1-1)
To 1-M) are output.

According to one embodiment of the present invention, a radiometer for measuring the radiance of a target object outputs measurement data of a required number of bits at the time of normal measurement and an A / D converter at the time of obtaining a calibration coefficient. By outputting the data of all the bits of the data, the quantization error of the calibration data can be reduced, and the accuracy at the time of measurement can be reduced by the quantization error level of the equipment or the noise of the electric signal, the optical signal from the target object. Noise level can be suppressed. Hereinafter, the principle, operation, and effect of one embodiment of the present invention will be outlined.

The quantization step at the time of A / D conversion at the time of measurement is, assuming that the number of bits of the A / D conversion is M, ＾ {M (one-two-Mth power, symbol ＾ is a power) (Indicating the operation) ... (1)

Therefore, when the dynamic range of measurement by the radiometer is X, the measurement data has the following uncertainty of (X / 2 ＾ M) / 2 (= ΔX) (2) 3).

On the other hand, in the quantization step of A / D conversion at the time of calibration, when the number of bits of A / D conversion is N and the output of the radiometer when the calibration coefficient is obtained is Y, the calibration data is not analyzed. The determinism is (Y / 2 ＾ N) / 2 (= ΔY) (3).

Assuming that the known luminance of the target object at the time of acquiring the calibration data is y, the calibration coefficient is y / Y (4).

The luminance x of the target object obtained from the measured data is as follows: x = X × y / Y (5)

At this time, considering the uncertainty of measurement, x ± Δx = (X ± ΔX) × y / (Y ± ΔY) (6)

Here, if X >> ΔX, Y >> ΔY, x ± Δx = X × y / Y × (1 ± (ΔX / X + ΔY / Y)) (7)

When the left side is transformed into x (1 ± Δx / x), Δx / x = ΔX / X + ΔY / Y (8)

Here, from the definitions of ΔX and ΔY, Δx / x = 1/2 ＾ (M + 1) + 1/2 ＾ (N + 1) (9)

The first term on the right side of the above equation (9) is the uncertainty of the measured data, and the second term is the uncertainty of the calibration data.

Therefore, when N = M, the uncertainty of the measured data and the calibration data is almost the same as the uncertainty of the measured physical quantity.

On the other hand, as in this embodiment, N> M
If the calibration data is acquired with high accuracy such that the following equation, the contribution of the uncertainty at the time of calibration to the uncertainty with respect to the measured physical quantity decreases.

For example, if N = M = 8 bits Where N = 10 and M = 8

If N = 12 and M = 8, Becomes

Therefore, at the time of calibration, the uncertainty of the measured value is increased to about 62% by taking two bits more data from the output of the A / D converter, and to about 54% by increasing four bits.
Can be reduced to

Next, another embodiment of the present invention will be described. FIG. 4 is a block diagram showing the configuration of the second embodiment of the present invention. Referring to FIG. 4, in the second embodiment of the present invention, instead of providing the output accuracy switching circuit 5 of the above embodiment, two outputs of a high-precision calibration output interface circuit 7 and a normal measurement output interface circuit 8 are provided. It has an interface circuit, and uses the output of the high-precision calibration output interface circuit 7 when acquiring the calibration coefficient, and uses the output of the normal measurement output interface circuit 8 during measurement.

In this embodiment, when the output circuit can be selected externally, or the interface of the output data with the outside can be easily switched.

The present invention is not limited to the calibration of the above embodiment, but can be applied to a radiation thermometer for optically measuring the temperature of a target object.

[0037]

As described above, according to the present invention,
By reducing the quantization error of the calibration data, the accuracy at the time of measurement can be suppressed to the level of the quantization error of the device, the noise of the electric signal, and the noise level of the fluctuation of the optical signal from the target object. Play.

The reason is that, in the present invention, a radiometer for measuring the radiance of a target object outputs measurement data of a required number of bits at the time of normal measurement, and outputs an A / D converter at the time of obtaining a calibration coefficient. This is because the data of all the bit numbers of is output.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating an output of an A / D converter according to one embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation principle of one embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical system 2 Detector 3 Preamplifier 4 A / D converter 5 Output precision switching circuit 6 Output interface circuit 7 High precision calibration output interface circuit 8 Normal measurement output interface circuit

Claims (3)

[Claims] 1. A radiometer having an analog-to-digital converter for converting an analog signal from a detection circuit into a digital signal, wherein the analog-to-digital converter has a higher resolution (N) than a resolution normally required for measurement. When the calibration data is obtained, all the N-bit outputs that have been converted from analog to digital by the analog-to-digital converter are output as calibration data. During normal measurement, the analog-to-digital converter Required M out of digitally converted N-bit output
A radiometer comprising means for selecting a bit (where M <N) and performing switching control to output the selected data as measurement data. 2. A radiometer for optically measuring a radiance signal of a target object, wherein an analog signal from a detection circuit for detecting an optical signal from an optical system and converting the signal into an electric signal is converted into a digital signal. In a radiometer provided with an analog-to-digital converter, the analog-to-digital converter has a higher resolution (N bits) than a resolution normally required for measurement, and receives an output of the analog-to-digital converter. An output accuracy switching circuit, which receives an output accuracy switching signal set from the outside and outputs the analog-digital converter when the output accuracy switching signal indicates calibration data acquisition. When the output accuracy switching signal indicates normal measurement, all of the N bits thus output are output as calibration data to the output interface circuit.
A switch control is performed so that necessary M bits (where M <N) are selected from N bits output from the analog / digital converter and the M bits are output to the output interface circuit as measurement data. And radiometer. 3. A radiometer for optically measuring a radiance signal of a target object, wherein an analog signal from a detection circuit for detecting an optical signal from an optical system and converting the signal into an electric signal is converted into a digital signal. In a radiometer provided with an analog-to-digital converter, the analog-to-digital converter has a higher resolution (N bits) than the resolution (M bits) normally required for measurement, A calibration output interface circuit for inputting an N-bit output and outputting the N-bit width data as calibration data; and a M out of the N-bit output of the analog / digital converter.
A measurement output interface circuit that receives a bit (M <N) as input and outputs data of the M-bit width as measurement data;
When the calibration data is obtained, all the N bits output from the analog-to-digital converter are output from the calibration output interface circuit. At the time of normal measurement, of the N bits output from the analog-to-digital converter A radiometer, wherein M bits are output as measurement data from the measurement output interface circuit.