JP2009281933A - Spectrometer and spectrometry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent spectrometer and a spectrometry for surely performing offsetting without intricacy while performing measurement with such noises removed as arising only when a shutter is open. <P>SOLUTION: A detection element 3 is a linear array sensor wherein a multitude of photoelectric conversion parts 31 and 32 are formed in a line. A spectral element 2 separates light of wavelengths in a specification range from light of wavelengths outside the specification range. The conversion parts each comprise a photoelectric conversion part 31 for the specification range and a photoelectric conversion part 32 for the outside of the specification range. A filter 7 for the offsetting is disposed on an optical path to transmit the light of the wavelengths in the specification range while shutting off the light of the wavelengths outside the specification range. A signal processing part 6 executes signal processing wherein a detected signal obtained in the conversion part 32 is used as an offset value and the offset value is subtracted from a measured value which is a detection signal obtained in the conversion part 31. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a spectroscopic measurement technique.

Spectrometers that measure the light intensity for each wavelength are actively used in various industrial fields. For example, many spectrophotometers are used for composition analysis of samples using absorbance or the like. FIG. 8 is a diagram schematically showing an example of the configuration of a general spectrometer.
The spectrophotometer includes an entrance slit 1, a grating (diffraction grating) 2 as a spectroscopic element on which measurement light that has passed through the entrance slit 1 enters, a detection element 3 on which light split by the grating 2 enters, and an optical system 4, 5 etc. The grating 2 is rotatable about an axis perpendicular to the optical axis, and only the light of an arbitrary wavelength can be incident on the detection element by rotating the grating 2 and selecting an angle with respect to the optical axis. . By detecting the intensity with the detection element 3 while sequentially changing the angle of the grating 2, the spectral irradiance distribution of the light to be measured can be measured.

In such a spectrometer, an offset operation is necessary in order to perform measurement with sufficient accuracy by removing background noise and the like. The offset is an operation in which the light to be measured is not incident on the detection element, an output signal of the detection element in this state is obtained, and this is set as an output of the zero-level detection element. Specifically, the shutter 9 is disposed on the optical path so that the measured light does not enter the detection element 3. In this state, the magnitude of the signal detected by the detection element 3 is set as an offset value. In normal measurement, the offset value is subtracted from the measured value.
JP 2000-55733 A

  Such an offset in the conventional spectrometer is troublesome because it is performed while opening and closing the shutter. A drive mechanism such as a shutter opening / closing mechanism is prone to failure, and if the shutter cannot be opened / closed, offset cannot be performed. In particular, in measurements that require frequent offsets, the complexity becomes significant and the probability of shutter failure increases. For example, in the case of the measurement of spectral irradiance of sunlight that changes every moment, the background noise also changes every moment, so it is necessary to perform offset every time. For this reason, the problems of offset complexity and shutter failure are significant.

  Further, in the conventional offset, there is an aspect that the offset value itself is considered to change between the closed state and the open state of the shutter. For this reason, it is presumed that measurement with high accuracy has become impossible. Hereinafter, this point will be described with reference to FIG. FIG. 8 is an explanatory diagram of the offset value.

  In FIG. 8, the magnitude of the signal detected by the detection element is shown in a bar graph. As shown in FIG. 8, the signal detected by the detection element at the time of measurement includes a signal corresponding to noise in addition to a signal corresponding to the original light to be measured (a value obtained by photoelectrically converting the measurement light). It is included. Noise signals are generated when light other than the light to be measured enters the detection element, or noise generated by the detection element itself (the detection element generates a signal even though no light is incident). Noise).

  A typical noise signal is background noise. As background noise, for example, ambient light is mixed into the housing of the measuring instrument and incident on the detection element. Such background noise often occurs regardless of whether the shutter is opened or closed. For noise that is generated regardless of whether the shutter is open or closed, measurement can be performed with the shutter closed, so that only the noise can be captured. The measurement result from which noise has been removed can be obtained.

  On the other hand, according to the research of the inventors of the present application, there is a noise that occurs only when the shutter is opened as a particular situation in the spectrometer, and such noise disappears when the shutter is closed. Cannot be captured by the detection element, and therefore cannot be included in the offset value. For this reason, it is still included in the measured value in the actual measurement. One type of noise that occurs only when such a shutter is opened is noise due to stray light. The stray light here is stray light generated when the light to be measured travels on the optical path.

Stray light that is a problem often occurs in a spectroscopic element. For example, the surface of each groove of the grating 2 serving as the spectroscopic element cannot be a completely flat surface, and it is considered that slight irregular reflection or scattering occurs. Further, it is estimated that slight irregular reflection and scattering of light occurs at the boundary portion of each groove (the edge portion of the mountain or valley), and these are considered to cause stray light.
For example, when the grating 2 is set to the angle a to measure the light with the wavelength A, only the light with the wavelength A should be selected and enter the detection element. It becomes stray light and is abnormally reflected and enters the detection element. This amount is included in the measurement signal.

  Such noise for stray light disappears when the shutter is closed (it does not enter the detection element). Then, it occurs again when the measurement is performed with the shutter opened, and is included in the measurement signal. That is, as shown in FIG. 8, the offset value in the conventional spectroscopic measuring instrument does not include this stray light noise, and therefore the measurement signal inevitably includes this stray light noise. . That is, in the conventional spectrometer, noise that is not generated when the shutter is closed and is generated only when the shutter is opened is not included in the offset value and cannot be removed from the measurement signal. As will be described later, the noise of the detection element itself is generated only when the shutter is opened, and this noise cannot be removed from the measurement signal.

As described above, the noise generated only when the shutter is opened cannot be removed by the conventional offset operation, and is included in the measurement result. For this reason, it becomes the cause of reducing the reliability of a measurement result.
The invention of the present application has been made to solve the above-described problem, and it is possible to reliably perform the offset without complications, and to remove noise that occurs only when the shutter is opened. It is an object of the present invention to provide an excellent spectroscopic instrument and spectroscopic measurement method that can be measured.

In order to solve the above-mentioned problem, the invention according to claim 1 of the present application is directed to a spectroscopic element that divides the light to be measured, a detection element to which the light to be measured dispersed by the spectroscopic element is incident, and a detection obtained by the detection element A spectroscopic measuring device including a signal processing unit for obtaining a spectral irradiance of light to be measured from a signal,
The spectroscopic element has a first posture that splits light having a wavelength within a specifiable range, which is a range that can be measured as spectroscopic instrument specifications, and enters the detection element, and is out of the specifiable range. A second posture that splits the light of the wavelength and makes it incident on the detection element,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The signal processing unit uses the detection signal obtained by the detection element when the spectroscopic element is in the second posture as an offset value, and is obtained by the detection element when the spectroscopic element is in the first posture. It has a configuration in which signal processing for subtracting an offset value from a measurement value that is a detection signal is performed.
In order to solve the above problems, the invention described in claim 2 is a spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element is incident, and a detection obtained by the detection element. A spectroscopic measuring device including a signal processing unit for obtaining a spectral irradiance of light to be measured from a signal,
The detection element is a linear array sensor in which a large number of photoelectric conversion units are arranged in a line,
The spectroscopic element can divide light with a wavelength in the specified range, which is the range that can be measured as specs of the spectrophotometer, and can split light with wavelengths outside the range that can be measured as specs And
A number of photoelectric conversion units of the detection element include a photoelectric conversion unit for specification range disposed at a position where light having a wavelength in the specification range is incident according to the attitude of the spectroscopic element, and light having a wavelength outside the specification range according to the attitude of the spectroscopic element. Consists of a photoelectric conversion part for outside the specification range, which is arranged at a position where light can enter,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The signal processing unit performs signal processing for subtracting the offset value from the measurement value that is the detection signal obtained by the photoelectric conversion unit for the specification range, using the detection signal obtained by the photoelectric conversion unit for the outside of the specification range as an offset value. It has a configuration that there is.
In order to solve the above-described problem, the invention according to claim 3 is the configuration according to claim 1 or 2, wherein the offset filter blocks light having a wavelength outside the specification range with a cut wavelength as a boundary. The non-specification range photoelectric conversion unit having the detection signal as an offset value is arranged at a position adjacent to the cut wavelength where light having a wavelength outside the specification range can enter. Have.
In order to solve the above-mentioned problem, the invention according to claim 4 is a spectroscopic element that divides the light to be measured, a detection element that receives the light to be measured dispersed by the spectroscopic element, and a detection obtained by the detection element. A spectroscopic measurement method for performing spectroscopic measurement using a spectrophotometer equipped with a signal processing unit for obtaining spectral irradiance of light under measurement from a signal,
The spectroscopic element has a first posture that splits light having a wavelength within a specifiable range, which is a range that can be measured as spectroscopic instrument specifications, and enters the detection element, and is out of the specifiable range. A second posture that splits the light of the wavelength and makes it incident on the detection element,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The detection signal obtained by the detection element in the state where the spectroscopic element is in the second posture is used as an offset value, and the measurement is the detection signal obtained by the detection element in the state where the spectroscopic element is in the first posture The signal processing unit performs signal processing for subtracting the offset value from the value.
In order to solve the above-mentioned problem, the invention described in claim 5 includes a spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element is incident, and a detection obtained by the detection element. A spectroscopic measurement method for performing spectroscopic measurement using a spectrophotometer equipped with a signal processing unit for obtaining spectral irradiance of light under measurement from a signal,
The detection element is a linear array sensor in which a large number of photoelectric conversion units are arranged in a line,
The spectroscopic element can divide light with a wavelength in the specified range, which is the range that can be measured as specs of the spectrophotometer, and can split light with wavelengths outside the range that can be measured as specs And
A number of photoelectric conversion units of the detection element include a photoelectric conversion unit for specification range disposed at a position where light having a wavelength in the specification range is incident according to the attitude of the spectroscopic element, and light having a wavelength outside the specification range according to the attitude of the spectroscopic element. Consists of a photoelectric conversion part for outside the specification range, which is arranged at a position where light can enter,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
A configuration in which the signal processing unit performs signal processing for subtracting the offset value from the measurement value, which is the detection signal obtained by the detection signal obtained by the photoelectric conversion unit for specification range, using the detection signal obtained by the photoelectric conversion unit for outside the specification range as an offset value. Have.
In order to solve the above problem, the invention according to claim 6 is the configuration according to claim 4 or 5, wherein the offset filter blocks light having a wavelength outside the specification range with a cut wavelength as a boundary. The out-of-specification photoelectric conversion unit using the detection signal as an offset value has a configuration in which light having a wavelength outside the specification range adjacent to the cut wavelength can be incident.

As described below, according to the invention described in each claim of the present application, the offset can be reliably performed without complications, and noise that occurs only when the shutter is opened can be removed and measured. .
According to the invention described in claim 2 or 4, in addition to the above effect, measurement can be performed using a multi-channel type measuring instrument using a linear array sensor. At this time, an offset signal, a measurement signal, Can be obtained simultaneously, so that the offset operation is further simplified.
According to the invention of claim 3 or 5, in addition to the above effects, it is possible to suitably obtain a measurement result from which noise caused by the measurement light incident on the detection element is removed.

Next, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described.
FIG. 1 is a diagram showing a schematic configuration of a spectrometer according to an embodiment of the present invention. 1 includes an incident slit 1, a grating 2 as a spectroscopic element on which light to be measured that has passed through the incident slit 1 is incident, a detection element 3 on which light split by the grating 2 is incident, It is composed of first and second optical systems 4 and 5.

The first optical system 4 is for projecting an image of the entrance slit onto the grating 2. The second optical system 5 is for imaging light from the grating 2 on the detection element 3. As the first and second optical systems 4 and 5, an arbitrary system such as a Chelney-Turner type, an Evert type, or a Fastie Evert type can be adopted. Employing the optical system described in Japanese Patent Application Laid-Open No. 2000-55733 is preferable because the aberration is small and the resolution is high.
The spectrometer includes a signal processing unit 6 that processes an output signal (detection signal) from the detection element 3. The signal processing unit 6 performs a calculation process for obtaining the spectral irradiance of the light to be measured from the detection signal.

  This spectrometer includes a filter (hereinafter referred to as an offset filter) 7 used for offsetting. The offset filter 7 is disposed on the optical path on the incident side of the grating 2, and more specifically, is disposed on the optical path between the incident slit 1 and the grating 2.

FIG. 2 is a schematic diagram showing the spectral transmission characteristics of the offset filter 7.
The offset filter 7 in the present embodiment is a filter that transmits light having a wavelength in a range that can be measured as a spec of the spectrophotometer (hereinafter, abbreviated as a spec range) and blocks a wavelength outside the spec range. . A general spectrometer can measure a wide range from the ultraviolet region to the visible region and the infrared region. The offset filter 7 blocks wavelengths outside the range. In this case, the wavelength on the short wavelength side (ultraviolet region) is cut off or the wavelength on the long wavelength side (infrared region) is cut off. In the present embodiment, the former configuration is used as an example.

More specifically, the offset filter 7 is a kind of cut filter, and cuts a wavelength shorter than the cut wavelength λc (sets the transmittance to zero). For example, the cut wavelength λc is set to 300 nm, and a cut filter whose transmittance at a wavelength shorter than 300 nm is zero is used as the offset filter 7.
However, although the transmittance rises steeply at the cut wavelength, it does not rise completely at 90 degrees but rises with a certain inclination. Therefore, there is a transitional wavelength region (hereinafter referred to as a transition region) until the transmittance reaches the maximum. Since the wavelength in the transition region is partially blocked by the offset filter 7, it is usually outside the specification range. Therefore, as shown in FIG. 2, a filter having a characteristic that the wavelength in the specification range is longer than the cut wavelength λc and longer than the transition region is employed as the offset filter 7.

  In the present embodiment, as will be described later, offset is performed using a wavelength outside the specification range. At this time, if the offset is performed including the wavelength of the transition region, the measured light is partially included in the offset wavelength. Therefore, as shown in FIG. The short wavelength side.

  On the other hand, the spectrometer of the present embodiment is a so-called multi-channel type spectrometer and is of a type that can simultaneously measure multi-wavelength irradiance. That is, as the detection element 3, in this embodiment, a linear array sensor in which a large number of photoelectric conversion units are arranged in a line is used. Each photoelectric conversion unit is a photodiode or the like that photoelectrically converts light in each wavelength region. The position of each photoelectric conversion unit is a position where light of each wavelength split by the grating 2 is incident. Therefore, it is not necessary to change the angle of the grating 2, and the irradiance in each wavelength region can be simultaneously measured by a single measurement in a state in which the grating 2 is held at the set angle.

  Such a detection element 3 has a photoelectric conversion unit (hereinafter referred to as a photoelectric conversion unit for specification range) on which light of each wavelength in the specification range is incident, and each wavelength outside the specification range is incident. It also has a photoelectric conversion unit (hereinafter referred to as an out-of-specification photoelectric conversion unit). This point will be described with reference to FIG. FIG. 3 is a diagram illustrating a schematic configuration of the detection element 3 included in the spectrometer according to the embodiment.

As schematically shown in FIG. 3, the detection element 3 has a configuration in which a large number of photoelectric conversion units 31 and 32 made of, for example, photodiodes are arranged in a line. The large number of photoelectric conversion units 31 and 32 include a group of specification range photoelectric conversion units 31 and a group of outside specification range photoelectric conversion units 32 adjacent thereto.
In addition, the grating 2 shown in FIG. 1 is configured to split light in the specification range and enter the photoelectric conversion unit 31 for each specification range, and to split light in the specification range to separate each specification range. The light is incident on the external photoelectric conversion unit 32. In the above-described example, the grating 2 splits light having a wavelength of 300 nm or more to enter the specification range photoelectric conversion unit 31, and splits light having a wavelength shorter than 300 nm into the outside specification range photoelectric conversion unit 32. It is configured as follows.

FIG. 1 also shows a schematic configuration of the signal processing unit 6 provided in the spectroscopic measuring instrument of the embodiment. As shown in FIG. 1, the signal processing unit 6 includes an amplifier 61 that amplifies the detection signal, an A / D converter 62 that converts the detection signal into a digital signal, and an absolute value of the spectral irradiance from the detection signal. It has an output circuit 65 including a processor 63 that performs operations, a storage unit (memory) 64, an interface for outputting data to the outside, and the like. The output circuit 65 is for connecting a display for displaying the measurement result and a printer for printing the measurement result to the measuring instrument. In some cases, the spectrometer is connected to a computer such as a personal computer. In this case, the output circuit 65 includes an interface for a computer such as a USB.
Note that an input unit (not shown) is provided in the housing of the spectrometer. The input unit can be an operation button, a touch panel, or the like.

A detection signal sent from each photoelectric conversion unit (specification range photoelectric conversion unit 31 and out of specification range photoelectric conversion unit 32) of the detection element 3 is amplified by an amplifier 61 and then converted into a digital signal by an A / D converter 62. And is temporarily stored in the storage unit 64. At this time, the detection signals in the photoelectric conversion units 31 and 32 are sent as serial signals, amplified and photoelectrically converted, and then each wavelength (strictly, each wavelength region defined by the resolution, It is temporarily stored in the storage unit 64 as a detection signal for each wavelength). For convenience of explanation, among the detection signals stored in the storage unit 64, the detection signals for the specification range (λ _{1 to} λ _m ) are S _{1 to} S _m, and are outside the specification range (λ _{m + 1 to} λ _n ). _Let S _{m + 1 to} S _n be the detection signals for. Further, the detection signal S ₁ to S _m is called the measurement signal this because signal underlying the measurements, referred to as a detection signal S _{m + 1} ~S _n is offset signal this because offset signal.

The storage unit 64 of the signal processing unit includes a program for calculating the absolute value of the spectral irradiance from the measurement signal (hereinafter referred to as a measurement program), a reference value for calculating the absolute value (hereinafter referred to as a calibration value), and the like. It is remembered. FIG. 4 is a flowchart showing an outline of the measurement program.
In the spectrometer of the present embodiment, a mode (offset mode) for measuring after offsetting and a mode (normal mode) for measuring without offsetting can be selected. The selection is performed by the input unit, and the selection result is temporarily stored in the storage unit 64 as a control signal.

As shown in FIG. 4, the measurement program is programmed to operate differently depending on whether it is in the offset mode or the normal mode.
First, the case where the normal mode is selected will be described. In the normal mode, the calculation for obtaining the absolute value of the irradiance from each measurement signal S _{1 to} S _m is performed without performing offset. That is, the storage unit 64, the calibration values _C 1 -C _m for specification range lambda ₁ to [lambda] _m is stored. Further, the storage unit 64 stores the offset value Of obtained at the time of the previous offset.

The measurement program subtracts the offset value Of for the measurement signals S _{1 to} S _m , compares it with the calibration value (C _{1 to} C _m ), and calculates the absolute value of the irradiance. That is, (S ₁ -Of) / C ₁ is performed to calculate the absolute value of the irradiance of λ ₁ . Similarly, absolute values are calculated for S ₂ , S ₃ ,... S _m . The offset value Of is a value that is subtracted from the measurement signals S _{1 to} S _m as a constant. When the absolute value of irradiance is calculated for S _{1 to} S _m in this way and the calculated absolute value of each wavelength is temporarily stored in the storage unit 64, the measurement program ends. Each calculated absolute value is output through the output circuit 65 and displayed on a display unit such as a personal computer screen or printed by a printer.

Next, a case where the offset mode is selected will be described. When the offset mode is selected, the measurement program calculates an absolute value after offsetting. That is, it reads the offset signal S _{m + 1} ~S _n of the signal stored in the storage unit 64, calculates the average value for these. The calculated average value is set as a new offset value Of and updated and stored in the storage unit 64.
After that, the absolute value of irradiance is calculated as in the normal mode. That is, the measurement signals S _{1 to} S _m are sequentially called from the storage unit 64, the updated offset value Of is subtracted, and then compared with each calibration value to calculate an absolute value.

  In the spectrometer of the embodiment, an optical fiber may be used for capturing the light to be measured. In this case, an optical fiber is provided on the incident side of the incident slit 1. The spectroscopic measuring instrument is configured to include a casing in which each unit is housed, and the rear end (outgoing end) of the optical fiber is connected to the casing. The tip of the optical fiber is disposed at the position where the light to be measured is taken in.

Next, the operation of the spectrometer according to the above configuration will be described. The following description is also a description of an embodiment of the invention of the spectroscopic measurement method.
If necessary, light to be measured is captured using an optical fiber, and is incident through an entrance slit. The incident light is split by the grating 2, travels in each direction according to the wavelength, and enters the photoelectric conversion units 31 and 32 of the detection element 3. The photoelectric conversion units 313 and 32 perform photoelectric conversion to generate detection signals, which are sent to the signal processing unit 6. Then, signal processing is performed in the signal processing unit 6 as described above, and spectral irradiance within a specified range is obtained.

  In the spectroscopic measuring instrument and the spectroscopic measurement method according to the above-described configuration and operation, offset is performed using the offset filter 7, so that the offset can be reliably performed without complications and the shutter. It is possible to measure by removing noise that occurs only when the is opened. Hereinafter, this point will be described with reference to FIG. FIG. 5 is a schematic diagram illustrating the principle of offset in the spectrometer according to the embodiment.

In FIG. 5, the light to be measured L widely includes wavelengths outside the specification range from the specification range (λ _{1 to} λ _n ). Since the measured light L passes through the offset filter 7 and reaches the grating 2, when reaching the grating 2, only the wavelength within the specified range (λ _{1 to} λ _m ) is obtained. Therefore, the grating 2 can disperse wavelengths (λ _{m + 1 to} λ _n ) outside the specification range, and the photoelectric conversion unit 32 outside the specification range is arranged at a position where light of these wavelengths can enter according to the attitude of the grating 2. However, the light of these wavelengths of the light to be measured does not reach the out-of-specification photoelectric conversion unit 32 by design.

Here, as described above, the measurement value includes background noise and noise due to stray light. Among these, first, background noise is considered, and ambient light (hereinafter referred to as “mixed light”) that flows into the housing of the measuring device is considered as background noise.
In FIG. 5A, it is assumed that the wavelength λx in the specification range is split by the grating 2 and enters the specification range photoelectric conversion unit 31x. That is, it is assumed that the specification range photoelectric conversion unit 31x is arranged at a position where light of wavelength λx is incident according to the attitude of the grating 2. In the photoelectric conversion unit 31x for specification range, a detection signal D (λx) that is an original measurement value is generated by the incidence of light of λx.

On the other hand, in FIG. 5 (1), the impregnated light is indicated by Lb. It is assumed that the penetration light Lb is incident on the photoelectric conversion unit 31x for the specification range. In this case, the detection signal Db by the interstitial light Lb is generated in the photoelectric converter for specification range 31x. Therefore, the entire signal sent from the specification range photoelectric conversion unit 31x to the signal processing unit 6 is D (λx) + Db.
It is considered that such interstitial light Lb is incident on the out-of-specification photoelectric conversion unit 32 with a probability similar to the probability of being incident on the specification-range photoelectric conversion unit 31. In other words, if the detection signal Db ′ is generated in the photoelectric conversion unit 32 outside the specification range due to the incident light Lb entering the photoelectric conversion unit 32 outside the specification range, the magnitude of the photoelectric conversion unit for the specification range is It is considered that the magnitude is almost the same as the detection signal Db for the mixed light generated in the part 31x.

  As described above, since the wavelengths (λm + 1 to λn) to be incident on the outside-specification photoelectric conversion unit 32 in the light to be measured are blocked by the offset filter 7, the detection signal generated in the outside-specification photoelectric conversion unit 32. Does not include the amount of light to be measured. Therefore, if any detection signal is obtained from the out-of-specification photoelectric conversion unit 32, it can be assumed that the detection signal is due to the above-described interstitial light Lb. Therefore, by subtracting the value from the detection signal in the specification range photoelectric conversion unit 31 as an offset value, a measurement result from which the amount of the interfering light Lb is removed can be obtained.

Next, consider noise caused by stray light. The above-mentioned immersive light is also considered to be stray light in a broad sense. However, here, stray light is considered to be narrow, and light that enters the photoelectric conversion unit that should not be incident is defined as stray light.
As described above, the main stray light source in the spectroscopic measuring instrument is a spectroscopic element such as a grating. The light that is abnormally reflected by the edge of the groove of the grating is incident on the photoelectric conversion element that should not be incident and becomes noise. In FIG. 5 (2), let us consider λx and λy, which are wavelengths within the specification range. The specification range photoelectric conversion unit 31x is arranged at a position where light of wavelength λx is incident when the light to be measured is correctly split, and a position where light of wavelength λx is incident when the light to be measured is correctly split It is assumed that the photoelectric conversion unit 31y for specification range is arranged in FIG.

Now, it is assumed that light of wavelength λx is abnormally reflected by the grating 2 and becomes stray light M. It is assumed that the stray light M has entered the photoelectric conversion unit 31y although it originally has to enter the photoelectric conversion unit 31x. In this case, the photoelectric conversion unit 31y, in addition to the minute detection signal D of correctly spectral wavelength [lambda] y ([lambda] y), the detection signal D _M of the stray light component is generated.

Here, it can be considered that the probability that the light of wavelength λx becomes stray light M and enters the photoelectric converter for specification range 31y is almost the same as the probability of incident on any of the photoelectric converters for outside specification range 32. . That is, as shown in FIG. 5 (2), it is considered that the light of wavelength λ (x) becomes stray light M ′ with almost the same probability as that of stray light M and enters the photoelectric converter 32 for outside the specification range. Therefore, if the detection signal D _M ′ is generated in the out-of-specification photoelectric conversion unit 32 and is caused by the stray light component, the specification-range photoelectric conversion unit 31 has the same magnitude as the average value. It can be assumed that a detection signal due to stray light is generated. Therefore, if the average value of the detection signal in the out-of-specification photoelectric conversion unit 32 is set as an offset value and subtracted from the detection signal (measurement signal) in each of the specification-range photoelectric conversion units 31, the measurement with the stray light component removed is performed. The result can be obtained.

Note that it is impossible to determine whether the detection signal in each of the out-of-specification photoelectric conversion units 32 is due to the stray light Lb or the stray light M ′. However, it is not necessary to discriminate them, and it is sufficient to remove them as noises from the measurement signal.
In addition, the light having the wavelength λ (x) has been described as stray light. However, the fact that the light has become stray light means that the light has not been correctly dispersed, and a specific wavelength λ (x) is selected and becomes stray light. The light does not enter the photoelectric conversion unit 32 outside the range. However, it can be assumed that the average amount of stray light incident on each specification range photoelectric conversion unit 32 and the average amount of stray light incident on each specification range photoelectric conversion unit 31 are the same, With respect to the point that the stray light portion can be included in the offset value, the wavelength of the stray light need not be particularly problematic.

Next, according to the inventor's research, according to the configuration of the offset in the embodiment, it is possible to remove noise caused by the fact that the light to be measured enters the detection element 3 itself. Hereinafter, this point will be described.
According to the inventor's research, it has been confirmed that the detection element 3 currently on the market has a problem that the offset value changes due to the incident light itself. FIG. 6 is a diagram showing an experiment confirming this problem.

In this experiment, the detection element 3 was partially masked and light was incident. That is, as shown in FIG. 6A, all the photoelectric conversion units 34 other than the photoelectric conversion unit 33 near the left and right end portions of the detection element 3 are covered with the light shielding cover 8 and light is incident thereon. I let you. The incident light is light that has not been split, and the optical system was adjusted so that the light was uniformly incident on the detection element 3.
FIG. 6B shows detection signals obtained by the photoelectric conversion units 33 and 34 of the detection element 3. In FIG. 6B, the vertical axis indicates the magnitude of the detection signal, and the horizontal axis indicates the position on the detection element 3 (which photoelectric conversion unit is the signal obtained).

  As shown in FIG. 6B, a large detection signal corresponding to the incident light is confirmed in the photoelectric conversion unit 33 that is not masked by the light shielding cover 8. On the other hand, in the photoelectric conversion unit 34 masked by the light shielding cover 8, the detection signal is almost zero, but there is a slight detection signal in the peripheral portion. The detection signal gradually increases as it goes to the periphery. Even the impression that the detection signal leaks and spreads from the photoelectric conversion unit 33 not masked by the light shielding cover 8 is received.

It is impossible that the detection signal is generated in the photoelectric conversion unit 34 masked by the light shielding cover. Although it is conceivable that the light shielding by the light shielding cover 8 is not complete, and light sneaks into and enters, but a detection signal is similarly generated even in a state where the light is sufficiently shielded and it is considered that there is no wraparound. From this, it is presumed that wraparound is not the cause.
It is conceivable that a detection signal is generated due to an internal factor of the detection element 3. When strong light enters an adjacent photoelectric conversion unit, a weak photocurrent may flow through the photoelectric conversion unit for some reason, or a weak photovoltaic power may be generated.

  In any case, the detection signal is generated when light enters the adjacent photoelectric conversion unit. The generation of the detection signal corresponding to the detection signal also occurs when the light is incident on the photoelectric conversion unit itself. It is thought that it has occurred. In other words, the detection signal generated when light is incident on a certain photoelectric conversion unit includes not only the amount of light converted into an electric signal but also the amount generated by the detection element itself due to light incidence. it is conceivable that. Such noise (hereinafter referred to as light incidence-induced noise) is not generally known, but is considered to be included in a considerable amount in the measured value.

In the conventional measuring instrument, light is blocked by a shutter and offset is performed. Therefore, the offset value does not include noise due to light incidence. Therefore, even if subtracted by the offset value, noise due to light incidence cannot be removed from the measured value.
On the other hand, according to the spectrometer of the embodiment, it is possible to remove this noise caused by light incidence by appropriately performing signal processing. Hereinafter, this point will be described.

FIG. 7 is a schematic diagram showing an offset for performing measurement with removal of noise caused by light incidence. FIG. 7 shows a result of performing spectroscopic measurement of a light to be measured using the spectroscopic measuring instrument of the embodiment.
FIG. 7 shows a spectral irradiance distribution of certain measurement light. In the offset wavelength region below the cut wavelength λc, the offset filter 7 may cut the value, and the value is not confirmed on a normal scale. However, as shown in an enlarged view in FIG. 7, when the scale is made finer, it can be confirmed that there is a value even below the cut wavelength.
At this time, as shown in an enlarged manner in FIG. 7, it can be confirmed that the value increases in the vicinity of the cut wavelength λc in the offset wavelength region. At a position away from the cut wavelength λc, the value converges almost constant.

  Since the small value that converges uniformly in the offset wavelength region has no wavelength dependence, it can be estimated that it is the amount of noise caused by the background noise and stray light described above. On the other hand, it is estimated that the noise (indicated by hatching in FIG. 7) that increases in the portion near the cut wavelength λc is the above-described noise due to light incidence. That is, it is presumed that a detection signal is generated for some reason because light of a certain intensity is incident on the photoelectric conversion unit in charge of the long wavelength side portion of the cut wavelength λc.

  In this case, as shown in FIG. 7, it is conceivable that a value in a very narrow wavelength region (indicated by Δλ in FIG. 7) adjacent to the cut wavelength λc in the offset wavelength region is taken as an offset value. In the case of a signal extending over a plurality of photoelectric conversion units, the average value thereof is set as an offset value. In this way, it is possible to obtain a measurement result in which noise due to light incidence is removed in addition to background noise and noise due to stray light.

  As will be understood from the above description, the spectroscopic measuring instrument according to the embodiment has an out-of-specification photoelectric conversion unit 32 arranged at a position where light having a wavelength out of the specification range can be incident according to the attitude of the grating 2, and is out of this use range. The light having the wavelength is blocked by the offset filter 7, and the detection signal of the out-of-specification photoelectric conversion unit 32 obtained in this state is set and updated as an offset value. Therefore, unlike the conventional spectrometer, it is not necessary to block the measured light with the shutter. For this reason, there is no problem that offset cannot be performed due to malfunction of the shutter. Further, even when the offset is performed for each measurement, the shutter opening / closing operation is not necessary, and there is no complication.

In addition, light that becomes noise (if it exists) is incident on the photoelectric conversion unit 32 outside the specification range, and only the offset value is updated by processing the detection signal from the photoelectric conversion unit 32 outside the specification range. It is. That is, in the case of performing offset, only signal processing in the signal processing unit 6 is added. Since the signal processing calculates the average and updates the offset value, it ends immediately. Therefore, also in this respect, the spectroscopic measuring instrument of the present embodiment is excellent in that the effort required for offset is simplified.
As described above, the spectroscopic measurement device according to the embodiment does not need to open and close the shutter for offsetting, but of course may include a shutter and its driving mechanism. In order to prevent inadvertent incidence of light into the casing, a shutter and its driving mechanism are often provided.

In the above embodiment, the wavelength range outside the specification range for offset is set on the short wavelength side than the specification range, but may be set on the long wavelength side. When the specification range is a range from the visible range to the infrared range, for example, the offset wavelength range is set in the infrared range having a longer wavelength.
Further, although the offset filter 7 is disposed between the entrance slit 1 and the grating 2, this is not an essential condition. Any position on the optical path until it enters the detection element 3 may be used.

  In the spectroscopic measuring instrument of the above embodiment, the detection element 3 is a linear array sensor and is of a type that performs spectroscopic measurement with the grating fixed, but the detection element 3 as described in the related art. However, the present invention can be implemented in the same manner even if it is of a type (hereinafter referred to as a mono-channel type) in which measurement is performed while sequentially changing the angle of the grating. Hereinafter, this point will be described.

Even in the case of a monochannel type spectrometer, an offset filter having the same configuration as that of the above embodiment is arranged on the optical path. First, the offset value is updated prior to measurement. That is, by operating the grating, light of wavelengths (λm _{+1 to} λ _n ) outside the specification range is sequentially incident on the detection element, and the detection signals obtained at this time are sent to the signal processing unit and sequentially stored in the storage unit. . Since the light to be measured is incident through the offset filter, the light corresponding to the light to be measured that has been correctly dispersed does not enter the detection element, but a detection signal is generated when there is a stray light or stray light as described above. . When the detection signals are stored for all wavelengths (λm _{+1 to} λ _n ) outside the specification range, they are read out, an average value is calculated, and the value is updated as a new offset value.

Next, a normal measurement operation is performed. That is, the grating is operated so that light having a wavelength within the specified range (λ _{1 to} λ _m ) is sequentially incident on the detection element. Then, the detection signals obtained by the detection elements are sequentially sent to the signal processing unit, and signal processing is performed to calculate the absolute value of the spectral irradiance. At this time, the absolute value is calculated by subtracting the offset value from the detection signal of each wavelength and comparing it with the calibration value. As a result, a measurement result obtained by removing background noise, noise due to stray light, noise due to light incidence, and the like can be obtained.
Although the wavelength in the specification range is described as λ ₁ to λ _m and the wavelength for obtaining the offset value is described as λ _{m + 1} to λ _n , there is a transition region between the two as shown in FIG. Therefore, λ _m and λ _{m + 1} may not be continuous. In other words, the wavelength in the transition region is not used as a measured value and may not be used as an offset signal. This is the same in the case of the embodiment of the multi-channel type spectrometer.

  As understood from the above description, in the monochannel type spectrometer, it is necessary to perform an operation for obtaining an offset signal separately from a normal measurement operation (operation for obtaining a measurement signal). In the above-described multi-channel type, the operation for obtaining the offset signal is performed simultaneously with the normal measurement operation. In this respect, the multi-channel type makes the offset operation easier. As can be seen from the above description, the multi-channel type spectrometer uses a detection element made of a linear array sensor, so the light receiving surface of the detection element is larger (longer) than the mono-channel type, and stray light is captured. easy. Therefore, the superiority of the present invention that can remove stray light is more remarkable in the multi-channel type.

  In the case of a monochannel type spectrometer, the offset signal may be obtained with only a single wavelength. That is, the offset value may be updated by adjusting the attitude of the spectroscopic element so that light having a single wavelength outside the specification range is incident on the detection element. From the same meaning, the present invention can be implemented even with the multi-channel type described above even if there is only one photoelectric conversion element outside the specification range for offset. However, the reliability of the offset value becomes higher when the signals for offset of a plurality of wavelengths are obtained and averaged. In the case of an offset value having a single wavelength, it is preferable to obtain an offset value at a wavelength adjacent to the cut wavelength λc in terms of removing noise caused by light incidence as described above.

As the spectroscopic element, elements other than the grating may be used. In principle, the present invention can be implemented even when a spectroscopic element such as a prism is used.
In the above description, it has been described that “spectral irradiance” is measured. However, only the irradiance of a specific wavelength or wavelength range may be measured, or the spectral irradiance distribution (spectral irradiance) in a wide wavelength range may be measured. Distribution) may be obtained as a measurement result.

It is the figure which showed schematic structure of the spectrometer which concerns on embodiment of this invention. It is the schematic shown about the spectral transmission characteristic of the filter 7 for offsets. It is the figure shown about schematic structure of the detection element 3 with which the spectrometer of embodiment is equipped. It is the flowchart which showed the outline of the measurement program. It is the schematic shown about the principle of the offset in the spectroscopic measuring device of embodiment. It is the figure shown about the experiment which confirmed the problem that an offset value changes with light incidence itself. It is the schematic shown about the offset for performing the measurement which removed light incidence origin noise. It is the figure which showed typically an example of the structure of the general spectrometer. It is explanatory drawing about an offset value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Entrance slit 2 Grating 3 Detection element 4 1st optical system 5 2nd optical system 6 Signal processing part 7 Filter for offset

Claims (6)

A spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element enters, and a signal processing unit that obtains the spectral irradiance of the light to be measured from the detection signal obtained by the detection element A spectroscopic measuring instrument,
The spectroscopic element has a first posture that splits light having a wavelength within a specifiable range, which is a range that can be measured as spectroscopic instrument specifications, and enters the detection element, and is out of the specifiable range. A second posture that splits the light of the wavelength and makes it incident on the detection element,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The signal processing unit uses the detection signal obtained by the detection element when the spectroscopic element is in the second posture as an offset value, and is obtained by the detection element when the spectroscopic element is in the first posture. A spectrophotometer for performing signal processing for subtracting an offset value from a measurement value which is a detection signal. A spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element enters, and a signal processing unit that obtains the spectral irradiance of the light to be measured from the detection signal obtained by the detection element A spectroscopic measuring instrument,
The detection element is a linear array sensor in which a large number of photoelectric conversion units are arranged in a line,
The spectroscopic element can divide light with a wavelength in the specified range, which is the range that can be measured as specs of the spectrophotometer, and can split light with wavelengths outside the range that can be measured as specs And
A number of photoelectric conversion units of the detection element include a photoelectric conversion unit for specification range disposed at a position where light having a wavelength in the specification range is incident according to the attitude of the spectroscopic element, and light having a wavelength outside the specification range according to the attitude of the spectroscopic element. Consists of a photoelectric conversion part for outside the specification range, which is arranged at a position where light can enter,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The signal processing unit performs signal processing for subtracting the offset value from the measurement value that is the detection signal obtained by the photoelectric conversion unit for the specification range, using the detection signal obtained by the photoelectric conversion unit for the outside of the specification range as an offset value. A spectrophotometer characterized by being. The offset filter blocks light having a wavelength outside the specification range with a cut wavelength as a boundary, and the out-of-specification photoelectric conversion unit having the detection signal as an offset value is adjacent to the cut wavelength. 3. The spectrophotometer according to claim 1, wherein the spectrophotometer is disposed at a position where light having a wavelength outside the specification range can enter. A spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element enters, and a signal processing unit that obtains the spectral irradiance of the light to be measured from the detection signal obtained by the detection element A spectroscopic measurement method for performing spectroscopic measurement using a spectroscopic instrument,
The spectroscopic element has a first posture that splits light having a wavelength within a specifiable range, which is a range that can be measured as spectroscopic instrument specifications, and enters the detection element, and is out of the specifiable range. A second posture that splits the light of the wavelength and makes it incident on the detection element,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The detection signal obtained by the detection element in the state where the spectroscopic element is in the second posture is used as an offset value, and the measurement is the detection signal obtained by the detection element in the state where the spectroscopic element is in the first posture A spectroscopic measurement method characterized in that signal processing for subtracting an offset value from a value is performed by a signal processing unit. A spectroscopic element that divides the light to be measured, a detection element on which the light to be measured dispersed by the spectroscopic element enters, and a signal processing unit that obtains the spectral irradiance of the light to be measured from the detection signal obtained by the detection element A spectroscopic measurement method for performing spectroscopic measurement using a spectroscopic instrument,
The detection element is a linear array sensor in which a large number of photoelectric conversion units are arranged in a line,
The spectroscopic element can divide light with a wavelength in the specified range, which is the range that can be measured as specs of the spectrophotometer, and can split light with wavelengths outside the range that can be measured as specs And
A number of photoelectric conversion units of the detection element include a photoelectric conversion unit for specification range disposed at a position where light having a wavelength in the specification range is incident according to the attitude of the spectroscopic element, and light having a wavelength outside the specification range according to the attitude of the spectroscopic element. Consists of a photoelectric conversion part for outside the specification range, which is arranged at a position where light can enter,
An offset filter that transmits light with a wavelength in the specified range and blocks light with a wavelength outside the specified range is arranged on the optical path.
The signal processing unit performs signal processing for subtracting the offset value from the measurement value, which is a detection signal obtained by the photoelectric conversion unit for the specification range, using the detection signal obtained by the photoelectric conversion unit for the outside of the specification range as an offset value. Spectroscopic measurement method. The offset filter blocks light having a wavelength outside the specification range with a cut wavelength as a boundary, and the out-of-specification photoelectric conversion unit having the detection signal as an offset value is adjacent to the cut wavelength. 6. The spectroscopic measurement method according to claim 4, wherein the spectroscopic measurement method is arranged at a position where light having a wavelength outside the specification range can enter.

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