JP3248421B2 - Analog-to-digital converter for spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analog / digital converter used for a spectroscope such as a near infrared spectroscope.

[0002]

2. Description of the Related Art Conventionally, a spectroscope employing a Fourier transform type spectroscopy is well known. FIG. 5 is a principle diagram of this type of spectroscope. The light from the light source 1 is divided by the half mirror 2 into two lights, a transmitted light and a reflected light. Each light is reflected by the moving mirror 4 and the fixed mirror 3 placed at a right angle to the optical path, returns to the same optical path again, and returns to the half mirror 2.
Are mixed (combined) again. The light emitted from the half mirror 2 is converted into an electric signal by the light receiver 5. The sample 6 is inserted between the half mirror and the light receiver.

[0003] The portion composed of the half mirror 2 and the two mirrors 3 and 4 is called a Michelson interferometer. In the Fourier transform spectroscopy, one of the Michelson interferometer mirrors is displaced in the optical axis direction. Then, the two emitted lights from the Michelson interferometer have a phase difference corresponding to the displacement of the moving mirror 4. As a result, when the light source 1 has a continuous white spectrum, the amount of light entering the light receiver has a special waveform called an interferogram as shown in FIG.

At the center of the interferogram, the distance from the half mirror 2 to the two mirrors 3 and 4 is equal, the phases match at all wavelengths, and the signal strength is maximized. Except for the center part, the phases of the respective wavelengths cancel each other out, resulting in a signal close to zero. When a Fourier transform is performed on the interferogram having such a waveform, a broad white spectrum as shown in FIG. 6B is obtained. When the sample 6 enters, the absorption spectrum is further included in the white spectrum.

[0005]

By the way, in a spectroscope, an interferogram with and without a sample, that is, an interferogram of a reference beam and a measurement beam can be measured simultaneously, and the measurement is performed at high speed and continuously. It is desirable to be carried out in a targeted manner.

In view of the foregoing, it is an object of the present invention to convert analog signals at two points of an interferogram of a reference light and a measurement light into analog-to-digital converters (hereinafter, analog-to-digital conversions) many times continuously at high speed. AD conversion)
An object of the present invention is to realize an analog-to-digital converter for a spectroscope that can be stored in a memory.

[0007]

In order to achieve the above object, the present invention divides an interferogram obtained from a Michelson interferometer into two, detects one signal as reference light, and detects the other signal as reference light. An analog-to-digital converter for use in a spectroscope configured to detect a signal as a measurement light by transmitting a sample, wherein the data of the measurement light and the reference light are simultaneously sampled by two systems and converted into an analog-digital signal. And collect data by doing
This sampling and conversion operation is performed a number of times so that the peak portion of the interferogram is substantially at the center, and each sampled data is stored in a memory.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an embodiment of the spectroscope according to the present invention. In the figure, reference numeral 11 denotes a white light source such as a halogen lamp, 12 denotes a monochromatic light source such as a He-Ne laser, 13 denotes a lens for converting the light of the light source 11 into parallel light, 1
4 is a beam splitter, 15 is a fixed mirror, and 16 is a movable mirror. Here, a corner cube mirror is used as the fixed mirror 15 and the movable mirror 16.

The movable mirror 16 is reciprocated in the optical axis direction by driving means (not shown). The displacement of the movable mirror 16 is detected by a displacement sensor 17. An electric signal corresponding to the displacement of the movable mirror 16 is output from the displacement sensor 17.

Reference numeral 18 denotes a lens, and the beam splitter 1
A lens for focusing the interference signal of the light source 11 via
9 is a light receiving element for detecting an interference signal of the monochromatic light source 12;
Is an optical fiber receiving the interference light narrowed down by the lens 18;
1 is an optical coupler for dividing the output light of the optical fiber 20 into two,
22 and 24 are optical fibers, 23 is a sample chamber, 25 is a light receiving element for detecting light (measurement light) passing through the sample chamber 23,
Is an optical fiber, and 27 is a light receiving element for detecting output light (reference light) of the optical coupler. Reference numeral 30 denotes an AD converter. The AD converter 30 will be described later in detail.

In such a configuration, an interferogram is obtained according to the same principle as in the prior art, and the signal is divided into two by the optical coupler 21. The two lights are respectively detected by the light receiving elements 25 and 27 as measurement light and reference light, converted into electric signals, and input to the AD converter 30.

On the other hand, an interference signal of a monochromatic light source (in the case of a He-Ne laser, the wavelength is 633 nm) 12 is detected by a light receiving element 19, and its electric signal is also input to an AD converter 30. This interference signal is used as a sample clock of the AD converter. The output of the displacement sensor 17 is also converted to the AD converter 3
0 is input as a phase signal.

The AD converter 30 simultaneously samples and AD converts the measurement light and the reference light. The AD conversion data is sequentially stored in the memory. This sampling, A
D conversion and data storage are repeated a plurality of times for each sample clock.

FIG. 2 is a block diagram of the AD converter. In the figure, 31 is an output signal (measurement light signal) of the light receiving element 25.
An input buffer 32 cuts the DC component of the output signal (reference light signal) of the light receiving element 27. Reference numerals 33 and 34 denote bandpass filters for extracting only necessary frequency components. 35,
Numeral 36 denotes AD converters. One AD converter 35 AD-converts the measurement light signal passed through the band-pass filter 33, and the other AD converter 36 AD-converts the reference light signal passed through the band-pass filter 34. .

Reference numerals 37 and 38 denote serial / parallel conversion circuits for converting the respective serial outputs of the AD converters 35 and 36 into parallel data, respectively. Reference numeral 39 denotes a level converter for converting the level of an interference signal (herein referred to as a zero-cross signal) obtained from the light receiving element 19 into an AD conversion sample clock. It is input to the control circuit 41 and the AD write address control circuit 42. A normal counter is used as the AD write address control circuit 42.

Reference numeral 40 denotes a level converter which takes in an output signal (herein referred to as a phase signal) of the displacement sensor 17 and converts the level thereof. The output signal is input to the AD write address control circuit 42 as a reset signal. The level converter performs a conversion so that a reset signal is generated when the moving mirror 16 changes direction.

The write control circuit 41 includes a serial / parallel conversion circuit 3
7, 38, address selector 43, data selector 44
And each control signal to the memory 45. The address selector 43 selects one of an address at the time of data writing (an output of the AD write address control circuit 42) and an address at the time of data reading (an address given from a microprocessor (not shown)). It is led to 45.

The data selector 44 selects one of data at the time of data writing (output of the serial / parallel conversion circuits 37 and 38) and data at the time of data reading (data output to a microprocessor (not shown)). .

The AD conversion device 30 having such a configuration
3 will be described next with reference to the waveform diagram of FIG. 3 and the time chart of FIG. The sample is sealed in the sample chamber 23, and the movable mirror 16 is reciprocated right and left. The displacement sensor 17 outputs a triangular signal as shown in FIG. The interferogram appears as shown in FIG. 3B, and the point at which the peak appears is from the half mirror 2 to the half mirror 2.
This corresponds to the point in time when the distances to the two mirrors 3 and 4 become equal.

A pulse signal (sample clock) obtained by level-converting the zero-cross signal, that is, the He-Ne interference signal by the level converter 39, is generated as shown in FIG. In the embodiment, the unit displacement of the movable mirror 16 (one displacement in the leftward or rightward direction, here about 60 ms)
Is adjusted so that, for example, 1024 pulses are generated. There is a peak of the interferogram at an intermediate point in this period, and 512 sample data are used as interferogram data before and after the peak.

Next, the operation of each section for each sample clock will be described. The sample clock which is the output of the level converter 39 is a start command signal ((a) in FIG. 4).
Are added to the AD converters 35 and 36 and the write control circuit 41. As a result, the AD converters 35 and 36 simultaneously sample and hold the input signals, start AD conversion of the hold values, and sequentially output 16-bit serial data (FIG. 4B).

At this time, the address selector 43 selects the AD
The output ((d) in FIG. 4) of the write control circuit 42 is selected and a write address is given to the memory 45, and the data selector 44 selects the output of the serial / parallel conversion circuit and gives it to the memory 45.

When the A / D conversion operation (16-bit serial data output) by the A / D converter is completed, the A / D end signal (inverted BUSY signal) falls as shown in FIG. Later, FIG.
Memory write signals (memory write S and memory write R) shown in (f) are issued from the write control circuit 41. In addition,
An OR (OR) signal ((j) in FIG. 4) of the memory write S and the memory write R is input to the memory 45 as a write signal.

Note that the write control circuit 41 corresponds to (g) of FIG.
As shown in (5), the serial / parallel conversion circuits 37 and 38 are controlled so that the measurement light data or the reference light data is output onto the data bus 46 before the memory write signal is generated.
The lower address ((h) in FIG. 4) of the addresses supplied to the memory 45 is supplied from the AD write address control circuit 42, and the upper address ((i) in FIG. 4) is supplied from the write control circuit 41. . The upper address is 1 bit here, and is 1 bit when writing the measurement light data and the reference light data.
And 0. As a result, the measurement light data and the reference light data are written in different address groups of the memory 45 separately.

The above operation is repeated every sample clock, and data of a predetermined number of samples can be collected. After the required number of samples have been taken, the microprocessor can specify the address and read the data stored in the memory 45 as appropriate.

It is to be noted that the above description of the present invention has been presented by way of explanation and illustration only of particular preferred embodiments. Thus, it will be apparent to one skilled in the art that the present invention may be modified or modified in many ways without departing from its essentials.

[0027]

As described above, according to the present invention, the measurement light data and the reference light data can be sampled at the same time, and can be continuously sampled many times. In addition, a plurality of data before and after the peak of the interferogram can be collected in the memory, so that even if the center position of the interferogram is shifted due to equipment adjustment, drift, etc., the shift before and after is easy. Can be covered by the memory area.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a spectroscope according to the present invention.

FIG. 2 is a configuration diagram of an AD converter.

FIG. 3 is a waveform chart of each part for explaining the operation.

FIG. 4 is a time chart for explaining the operation.

FIG. 5 is a principle diagram of a Fourier transform type spectrometer.

FIG. 6 is a diagram for explaining a waveform of an interferogram.

[Explanation of symbols]

 Reference Signs List 11 white light source 12 monochromatic light source 13, 18 lens 14 beam splitter 15 fixed mirror 16 moving mirror 17 displacement sensor 19, 25, 27 light receiving element 20, 22, 24, 26 optical fiber 21 optical coupler 23 sample chamber 30 AD conversion device 31, 32 input buffer 33,34 band-pass filter 35,36 AD converter 37,38 serial-parallel conversion circuit 39,40 level converter 41 write control circuit 42 AD write address control circuit 43 address selector 44 data selector 45 memory 46 data bus

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-269032 (JP, A) JP-A-51-92671 (JP, A) JP-A-7-270311 (JP, A) JP-A-4- 269646 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 G01J 3/00-3/52

Claims (2)

(57) [Claims] An interferogram obtained from a Michelson interferometer is bisected, and one of the signals is detected as reference light, and the other signal is transmitted through a sample and detected as measurement light. An analog-to-digital converter for use in a spectroscope, wherein data of the measurement light and reference light are simultaneously sampled by two systems and converted into analog-to-digital data to collect data. An analog / spectrometer analog device characterized in that the interferogram is performed a number of times so that the peak portion is almost at the center, and each sampled data is stored in a memory.
Digital conversion device. 2. The analog-to-digital converter for a spectroscope according to claim 1, wherein said sampling is performed in synchronization with an interference signal obtained by making monochromatic light incident on said Michelson interferometer.