JP6917824B2 - Spectral measuring device and spectroscopic measuring method - Google Patents

Description

The present invention relates to a spectroscopic measuring device and a spectroscopic measuring method using an LED as a light source.

There are known spectroscopic measuring devices that measure reflectance and transmittance using at least two wavelength bands, with a light source, a spectroscope, and a detector as main components. Usually, the spectroscopic measuring device monochromaticizes the light obtained from the light source with a spectroscope, and measures the transmitted light or the reflected light of the sample with the monochromatic light (hereinafter referred to as "monochromatic light"). Alternatively, the light obtained from the light source may be applied to the sample, and the reflected light or transmitted light may be spectroscopically analyzed. As the light source, a deuterium discharge tube or a tungsten lamp having a relatively flat spectrum and being continuous is used. A prism or a diffraction grating is used for the spectroscope, and a photomultiplier tube or a photodiode is used for the detector.

For example, Patent Document 1 describes a spectroscopic analyzer (spectral measurement device) that analyzes components based on a spectroscopic spectrum obtained from diffusely reflected light reflected inside a sample such as tomato. In the spectroscopic measuring apparatus described in Patent Document 1, the sample is irradiated with infrared light (continuous spectrum) radiated from a light source via the first optical fiber, and diffused reflected light is emitted through a second optical fiber into a concave diffraction lattice. It is guided to (spectrometer) and the spectroscopic spectrum is obtained by the linear image sensor (detector).

Japanese Unexamined Patent Publication No. 2000-2060337 (Fig. 1)

The spectroscopic measuring apparatus described in Patent Document 1 uses a tungsten-halogen lamp as a light source. Tungsten-halogen lamps require a glass tube and a base, which hinders the miniaturization of spectroscopic measuring devices. On the other hand, if the light source is changed to LED, it seems that the spectroscopic measuring device can be easily miniaturized.

However, LEDs often exhibit a bell-shaped spectrum with a narrow full width at half maximum. An attempt to obtain a light source having flat characteristics in a wide band from such an LED can be realized by preparing a large number of LEDs whose peak wavelengths are slightly deviated from each other. However, trying to miniaturize the device conflicts with preparing a large number of LEDs.

Therefore, if the light source is unavoidably composed of a small number of LEDs having peak wavelengths separated from each other, a band having a weak intensity appears between the peak wavelength of one LED and the peak wavelength of the other LED. In this band with low intensity, the measurement error becomes larger than in the band with high intensity. That is, a light source composed of a small number of LEDs cannot obtain a constant accuracy over the entire band.

Therefore, the present invention has been made in view of the above problems, and a spectroscopic measuring device and a spectroscopic measuring method capable of maintaining a constant accuracy in a wide band even if a light source is composed of a small number of LEDs having peak wavelengths separated from each other. The purpose is to provide.

In order to achieve the above object, the spectroscopic measurement method of the present invention is a spectroscopic measurement method including a light source composed of an infrared emitting type first LED and a second LED having different peak wavelengths and a plurality of filters. Spectroscopic measurement is performed in the bands, one of the two bands is a band around the peak wavelength of the first LED or the second LED, and the other band of the two bands is the first LED. The amount of current supplied to the first LED and the second LED is adjusted in advance so that the peak wavelength of the 1 LED and the peak wavelength of the second LED are the bands and the intensities of the light passing through the plurality of filters are equal. Later, the first measurement step of spectroscopic measurement in the one band and the second measurement in which the current supply amount to the first LED or the second LED is increased from the time of the first measurement step and then spectroscopic measurement is performed in the other band. It has two measurement steps .

In the spectroscopic measurement method of the present invention, the light source includes a first LED and a second LED having different peak wavelengths. Therefore, the intensity is high in the band around the peak wavelengths of the first LED and the second LED, and weak in the band between the peak wavelengths of the first LED and the second LED. Therefore, in the spectroscopic measurement method of the present invention, the transmittance and the reflectance are measured in the first measurement step of measuring the transmittance and the reflectance in the band around the peak wavelength where the irradiation intensity is strong, and in the band which is the valley between the peak wavelengths. Prepare a second measurement step to be measured. In the first measurement step, the first and second LEDs are made to emit light under preset conditions. In the second measurement step, the amount of current supplied to the first or second LED is increased with respect to the above conditions, and the emission intensity of the light source is increased.

In order to achieve the above object, the spectroscopic measuring device of the present invention has a light source composed of infrared light emitting type first LED and second LED having peak wavelengths separated from each other, and a first variable constant current connected in series to the first LED and the second LED, respectively. comprising a source and a second variable constant-current source, a control circuit for controlling the current flowing through the first variable constant current source and said second variable constant-current source, and a plurality of filters, wherein the control circuit comprises as the intensity of light through a plurality of filters is equal, the current supply amount is adjusted to advance the first 1LED and second 2LED, the first variable constant-current source in response to said band spectroscopic measurement and the second The current flowing through the variable constant current source is switched .

The spectroscopic measuring device of the present invention includes a light source, a spectroscope, and a detector. The light source includes a first LED and a second LED having peak wavelengths separated from each other, and a first variable constant current source and a second variable constant current source are connected in series to the first LED and the second LED, respectively. The currents flowing through the first variable constant current source and the second variable constant current source are set to different values depending on the measurement band.

The spectroscope may include a plurality of bandpass filters.

The spectroscopic measuring device and the spectroscopic measuring method of the present invention increase the current flowing through the LEDs when acquiring data in the band between the peak wavelengths even if the light source is composed of a small number of LEDs having different peak wavelengths. , The intensity of the light source is increased. As a result, the spectroscopic measuring device and the spectroscopic measuring method of the present invention can maintain a constant accuracy in a wide band.

It is a figure which shows the arrangement relation of the main parts in the spectroscopic measuring apparatus shown as the embodiment of this invention. It is a block diagram of the spectroscopic measuring apparatus shown in FIG. It is a spectrum diagram of the light source included in the spectroscopic measuring apparatus shown in FIG. It is a spectrum diagram of the light source included in the spectroscopic measuring apparatus shown in FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 4. In addition, the matters specifying the invention shown in the claims are described in parentheses.

FIG. 1 is a diagram showing an arrangement relationship of main parts of the spectroscopic measuring device 10 shown as an embodiment of the present invention. As shown in FIG. 1, the spectroscopic measuring device 10 includes a light source 11, a spectroscope 12, and a detector 13 as main components. The spectroscope 12 includes a wheel 12a, a filter 12b (bandpass filter), and a motor 12c. The wheel 12a is a disk, and eight filters 12b are attached in an annular shape. The wheel 12a has an opening for attaching the filter 12b. The shaft of the motor 12c runs through the center of the wheel 12a. The light source 11 is installed on the back surface of the filter 12b together with the detector 13, and the sample 20 is arranged on the front surface side of the wheel 12a.

The light emitted from the light source 11 passes through one filter 12b and irradiates the sample 20. The light that irradiates the sample 20 (hereinafter referred to as “irradiation light”) is reflected by the sample 20. This reflected light (hereinafter referred to as "reflected light") passes through the filter 12b again and is incident on the detector 13.

The eight filters 12b attached to the wheel 12a are bandpass filters having a pass band of 5 to 10 nm, and each pass band is different. For quality evaluation of agricultural products and the like, it is only necessary to know the amount of known substances and the like, so it is often sufficient to measure the reflectance in a specific band. Therefore, as the spectroscope 12, a bandpass filter having a simple structure and capable of increasing the intensity of light rays can be used.

It is necessary that the light emitted from the light source 11 and the reflected light from the sample 20 are vertically incident on the filter 12b as much as possible. At this time, if the reflected light of the filter 12b is incident on the detector 13, the detector 13 may be arranged on the front side (sample 20 side) of the bandpass filter. However, in the following description, the reflection of the filter 12b is ignored, and the light source 11 and the detector 13 are provided side by side on the back side of the filter 12b.

Spectral measurement of reflectance is performed as follows. First, in the spectroscopic measuring device 10, the current to be passed through the light source 11 in advance for each filter 12b so that the intensity of the irradiation light when one filter 12b is selected and the intensity of the irradiation light when the other filter 12b is selected are substantially equal. Decide. That is, the reference plate made of Au or Al and the detector 13 are used, and the current is adjusted so that the light reflected by the reference plate becomes equal for each filter 12b.

Next, the sample 20 and one filter 12b are set, the light source 11 is turned on, and the reflected light in the band determined by the one filter is measured. Subsequently, the wheel 12a is rotated by 45 °, switched to another filter 12b, the light source 11 is turned on, and the reflected light in the band determined by the other filter 12b is measured. As described above, a current determined for each filter 12b is passed through the power supply. This process is carried out for all filters 12b, and the reflected light in the band determined by each filter 12b is measured.

Finally, the reflected light obtained from the sample 20 and the reflected light measured by the reference plate are compared for each filter 12b (corrected by the reflectance of the reference plate to be exact). The reflectance of the band of is obtained.

FIG. 2 is a block diagram of the spectroscopic measuring device 10. Note that FIG. 2 does not show members related to driving the spectroscope 12, such as the motor 12c and the wheel 12a. As shown in FIG. 2, the spectrophotometer 10 includes a light source 11, a spectroscope 12, a detector 13, a control circuit 14, and two variable constant current sources 15 and 16 (first variable constant current source, second). Variable constant current source) and power supply 17 have been added.

The light source 11 is composed of two LEDs 11a and 11b (first LED and second LED). The LEDs 11a and 11b are infrared light emitting LEDs having peak wavelengths of 800 nm and 850 nm, respectively (see FIG. 3), and are connected in series with the variable constant current sources 15 and 16. The variable constant current sources 15 and 16 adjust the current flowing through the LEDs 11a and 11b based on the control signals 15a and 16a output from the control circuit 14. The power supply 17 supplies electric power to the LEDs 11a and 11b.

The light beam L1 emitted from the light source 12 passes through one filter 12b (see FIG. 1) included in the spectroscope 12 and is reflected by the sample 20. The light ray L2 composed of the reflected light passes through the filter 12b again and is incident on the detector 13. The detector 13 is a photodiode, and outputs a current value corresponding to the incident light to the control circuit 14 as measurement data 13a.

When one filter 12b is set as described above, the control circuit 14 sets the variable constant current sources 15 and 16 so that a predetermined current flows through the LEDs 11a and 11b. That is, information is exchanged between the spectroscope 12 and the control circuit 14 via the signal 12d as to which filter 12b is set and which filter 12b is selected.

FIG. 3 is a spectrum diagram showing an emission spectrum 30 (solid line) of the light source 11 included in the spectroscopic measuring instrument 10. As shown in FIG. 3, the emission spectrum 30 of the light source 11 is the sum of the spectrum 31 (broken line) of the LED 11a having a peak near λ = 800 nm and the spectrum 32 (broken line) of the LED 11b having a peak near λ = 850 nm. It is a thing. The emission spectrum 30 has a valley near λ = 820 nm.

FIG. 4 is a spectrum diagram of the light source 11 in which the pass band of the filter 12b (see FIG. 1) is added to the spectrum diagram shown in FIG. In the figure, the code fn (n is an integer) attached to the hatched band indicates that this band is the pass band of the nth filter 12b. Each pass band f1 to f8 has a width of 5 to 10 nm, and is dispersed over 780 to 870 nm in a discrete state as a whole.

As mentioned above, when selecting agricultural products, it is often sufficient to know the amount of known substances. That is, it is only necessary to know the reflectance of the required wavelength band in advance, and the bands to be analyzed may be discrete. As a result, in the spectroscopic measurement device 10, the spectroscope 12 can be configured by the bandpass filter 12b, the optical system can be simplified, and the intensity of the light irradiating the sample 20 (see FIG. 1) can be increased.

Since the reflectance is (intensity of reflected light) / (intensity of irradiation light), in order to make the accuracy of the reflectance uniform between the bands f1 to f2, the irradiation light of each band to be measured is used. It is desirable that the strength is substantially constant. As described above, in the spectroscopic measuring device 10, when switching from the nth filter 12b to the (n + 1) th filter 12b, the current flowing through the variable constant current circuits 15 and 16 is reset. As a result, in the spectroscopic measuring device 10, the intensity of the irradiation light becomes substantially equal for each filter 12b.

As described above, since the spectroscopic measurement device 10 can make the intensity of the light irradiating the sample 20 (see FIG. 1) substantially equal for each filter 12b, the measurement accuracy becomes substantially the same in all measurement bands.

The features of the spectroscopic measurement method in the spectroscopic measurement device 10 are summarized below. The spectroscopic measuring device 10 having the LED 11a (first LED) and the LED 11b (second LED) having peak wavelengths separated from each other performs measurement in at least two bands. One of the two bands is, for example, band f3 (or band f7) around the peak wavelength of LED11a, and the other band is band f4 (or band f4) between the peak wavelength of LED11a and the peak wavelength of LED11b. Or the band f5) (see FIG. 4). Then, the spectroscopic measuring device 10 has a first measurement step of measuring the reflectance in one band, and a second measurement step of increasing the amount of current supplied to the LED 11a or the LED 11b and then measuring the reflectance in the other band. have.

That is, in the first measurement step, the third filter 12b is used to measure the reflectance in the band f3 around the peak wavelength, and in the second measurement step, the fourth filter 12b is used to supply current to the LEDs 11a and 11b. After increasing the amount, the reflectance is measured in the band f4 between the peak wavelengths. In a band (for example, the f6 band) in which the spectrum of the light source 11 is intermediate between the wavelength indicating the peak and the wavelength indicating the valley, the currents intermediate between the current flowing in the first step and the current flowing in the second step are the LEDs 11a and 11b. (Bands f2 and f8 also increase the current).

The spectroscope 12 included in the spectroscopic measuring device 10 was composed of a plurality of bandpass filters 12b. In the spectroscopic measuring apparatus of the present invention, the spectroscope is not limited to the one including a plurality of bandpass filters 12b. For example, the spectroscope may be a well-known prism or diffraction grating. However, compared to these spectroscopes, a spectroscope composed of a plurality of bandpass filters may have a lower degree of parallelization of light rays and can have a stronger irradiation intensity.

When the spectroscope 12 is a diffraction grating or a prism, the measurement band is continuous. Even in this case, the spectroscopic measuring device 10 measures the reflectance in at least two steps in which the currents supplied to the light source 11 are different. That is, the spectroscopic measurement device 10 has a first measurement step of measuring in a band around the peak wavelength and a second measurement step of measuring in a band between peak wavelengths (a band forming a valley). In the first step, a predetermined current is passed through the LEDs 11a and 11b. In the second step, the supply amount is increased more than the current.

If a measurement band wider than the band shown in FIG. 3 is required, a third LED having a peak wavelength different from that of the LEDs 11a and 11b may be added. Although the spectroscopic measuring device 10 has measured the reflected light from the sample 20 (see FIG. 1), the transmitted light may be measured. Since the LEDs 11a and 11b used for the light source 11 have temperature characteristics, it is preferable that the control circuit 14 has a temperature compensation function.

10 ... Spectroscopic measuring device,
11 ... Light source,
11a, 11b ... LEDs (first LED, second LED),
12 ... Spectrometer,
12a ... Wheel,
12b ... Filter (bandpass filter),
12c ... Motor,
13 ... Detector,
13a ... Measurement data,
14 ... Control circuit,
15, 16 ... Variable constant current source (first variable constant current source, second variable constant current source),
15a, 16a ... Control signal,
17 ... Power supply,
20 ... Sample,
L1, L2 ... Rays.

Claims (5)

In a spectroscopic measurement method including a light source composed of an infrared emitting type first LED and a second LED having different peak wavelengths and a plurality of filters.
Take spectroscopic measurements in at least two bands
One of the two bands is a band around the peak wavelength of the first LED or the second LED.
The other band of the two bands is a band between the peak wavelength of the first LED and the peak wavelength of the second LED.
After adjusting the amount of current supplied to the first LED and the second LED in advance so that the intensities of the light passing through the plurality of filters are equal,
The first measurement step of spectroscopic measurement in one of the bands and
A spectroscopic measurement method comprising a second measurement step in which a current supply amount to the first LED or the second LED is increased from the time of the first measurement step and then spectroscopic measurement is performed in the other band. The first LED has an emission spectrum having a peak wavelength of 800 nm, the second LED has an emission spectrum having a peak wavelength of 850 nm, and the relative intensities of the combined emission spectra of the first LED and the second LED are equal. The spectroscopic measurement method according to. One of the two bands is a band around a wavelength of 800 nm or 850 nm, the other is a band around a wavelength of 820 nm, and the other band has a relative intensity of emission spectrum of 30 with respect to the one band. The spectroscopic measurement method according to claim 1, which is% or more. A light source consisting of an infrared emitting type first LED and a second LED having peak wavelengths separated from each other,
A first variable constant current source and a second variable constant current source connected in series to the first LED and the second LED, respectively.
A control circuit that controls the current value flowing through the first variable constant current source and the second variable constant current source, and
With multiple filters,
In the control circuit, the amount of current supplied to the first LED and the second LED is adjusted in advance so that the intensities of the light passing through the plurality of filters are equal.
Spectroscopic said first variable constant-current source in response to the band to be measured and the second variable constant-current source spectrometer which current is switched to flow in. The plurality of filters are composed of a plurality of bandpass filters having different bands, and are arranged within a half-value width range of 50% with respect to the relative intensity of the emission spectra of the peak wavelengths of the first LED and the second LED. The spectroscopic measuring apparatus according to claim 4.

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