JPH0727612A - Method for monitoring interferogram of ftir - Google Patents

Abstract

PURPOSE:To make it possible to (perform) monitoring in high accuracy at the time of display by using a spline function and performing the complementary operation for the data in the vicinity of ZPD of stored data. CONSTITUTION:The interferogram in analog time series obtained by an analyzing part l is inputted into a data processing part 2. The raw data are sampled in an A/D converter circuit 15 and once stored into a memory circuit 16 as the discrete data. For the T adjustment of a mirror 7 in an interferometer 8, the complementary operation of the data in the vicinity of ZPD of the stored data is performed by using. a spline function when the stored interferogram is monitored. The operation is monitored and displayed. The display has the value very close to the raw data. Therefore, when the maximum value of the complementary data is used as the intensity of the central burst and the mirror 7 of the interferometer 8 is adjusted, the adjustment can be performed accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an FTIR (Fourier transform) in which an interferogram output from an analysis unit is discretely sampled by a sampling pulse, temporarily stored as AD-converted data, and then displayed. Infrared spectrophotometer) interferogram monitoring method (hereinafter, simply referred to as monitoring method).

[0002]

2. Description of the Related Art The FTIR is constructed, for example, as shown in FIG. That is, in this figure, 1 is an analysis unit, and 2 is a data processing unit for processing the interferogram output from the analysis unit 1. The analysis unit 1 includes an infrared light source 3 configured to emit parallel infrared light (indicated by a solid line in the figure), a beam splitter 4, a fixed mirror 5, and a drive mechanism (not shown) that causes a double-headed arrow 6 to move. An interferometer 8 composed of a movable mirror 7 that moves parallel to the direction and scans, a cell 9 that houses a measurement sample and the like, and is irradiated with infrared light from the infrared light source 3 through the interferometer 8, and semiconductor detection Vessel 10
It comprises a laser light source 11 and a semiconductor detector 12 for detecting a laser light (shown by a two-dot chain line in the figure) emitted from the laser light source 11 and taking a path similar to the infrared light. In addition, 13 is a fixed mirror.

The data processing section 2 is composed of, for example, a computer, and generates a sampling pulse [see FIG. 5 (B)] based on the interference signal of the laser beam output from the semiconductor detector 12. 14 and an interferogram output from the semiconductor detector 10 (see FIG. 9A) are input, and the interferogram is discretely (temporally) triggered by the sampling pulse from the sampling pulse generation circuit 14. AD conversion circuit 15 that performs AD conversion at equal intervals), storage circuit 16 that stores the AD-converted data, and the interferograms are averaged, and the average output is subjected to fast Fourier transform, and further, As an arithmetic circuit that performs spectrum calculation for the measurement target component based on the Fourier transform output Consisting of Metropolitan CPU17. Note that FIG.
In, the dotted line indicates the flow of electric signals.

In the FTIR configured as described above, quantitative analysis or qualitative analysis can be performed as follows. That is, the comparative sample or the measurement sample is housed in the cell 9, respectively, and the infrared light from the infrared light source 3 is applied to the cell 9, and the interferograms of the comparative sample and the measurement sample are measured. The data processing unit 2 performs FFT on each of these interferograms to obtain a power spectrum, then obtains the ratio of the power spectrum of the measurement sample to the power spectrum of the comparative sample, and converts this into an absorbance scale to obtain an absorption spectrum. Then, the absorption spectrum is applied to Lambert-Beer's law to quantitatively or qualitatively analyze the components (single component or multicomponent) contained in the measurement sample.

By the way, in the FTIR, it is necessary to accurately adjust the position and inclination of the fixed mirror 5 in the interferometer 8 and so on. Generally, as shown in FIG. The intensity of the interferogram after AD conversion is displayed on the monitor, and the adjustment is performed while watching this.

However, when the interferogram is sampled discretely, as shown in FIGS. 5A and 5B, the peak position P in the interferogram is shown.
If the sampling point and the sampling point are displaced from each other, the same figure (C)
As shown in, even though the actual peak is shown by a virtual line in the figure, this is not displayed and only a value lower than the actual intensity is obtained. Therefore, it is difficult to make an accurate adjustment even if the above-mentioned adjustment is performed while observing the monitor strength displayed in this way.

[0007]

In the prior art, therefore, an electric circuit has been used to adjust the sampling point to the peak position or to narrow the sampling interval to improve the accuracy. However, in both cases, a special sampling circuit is used. And has the drawback that the configuration becomes complicated,
In particular, the latter means has a drawback in that the spectral region is widened, so that a significant digit loss occurs at the time of fast Fourier transform, resulting in a decrease in S / N.

The present invention has been made in consideration of the above matters, and an object thereof is to provide a monitoring method capable of accurately monitoring the intensity of an interferogram with a simple configuration.

[0009]

In order to achieve the above object, the monitor method of the present invention is such that, at the time of display, data in the vicinity of ZPD in the stored data is complemented using a spline function. Is characterized by.

[0010]

The interferogram is sampled and stored in the memory circuit as digital data. ZPD (Zero Path Difference;
Data near the point where the optical path difference in the interferometer is zero) is complemented by using a spline function. By displaying the maximum value of the complementary data a obtained by this calculation, it is possible to display a value extremely close to the original interferogram shown in FIG.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

The monitoring method of the present invention can be applied to the FTIR shown in FIG. 3 described above, and is largely different from the conventional method in that when displaying, the data in the vicinity of ZPD in the stored data is subjected to the spline function. The point is that the complementary calculation is performed by using this.

FIG. 1 is a flow chart showing an example of the procedure of the monitoring method of the present invention. An analog time series interferogram obtained by the analysis unit 1 is input to the data processing unit 2. This interferogram is, so to speak, raw data having a waveform as shown in FIG.

The raw data is AD conversion circuit 15 triggered by a sampling pulse as shown in FIG.
Are sampled at (step S1) and temporarily stored as discrete data in the memory circuit 16 (step S2).

When monitoring the stored interferogram for the adjustment of the mirror in the interferometer 8, the data in the vicinity of ZPD of the stored data is complemented using a spline function (step S3). ), The complementary data as indicated by the symbol a in FIG. 2C can be obtained, and the complementary data is displayed on the monitor (step S4). This monitor display is
The value is extremely close to the raw data.

Therefore, if the mirror of the interferometer 8 is adjusted while monitoring the maximum value of the complementary data as the center burst intensity, the adjustment can be performed accurately.

[0017]

As described above, according to the present invention,
Even if the peak position in the interferogram deviates from the sampling point, the center burst intensity can be accurately displayed. As a result, the mirror adjustment of the interferometer can be performed with high accuracy. The method of the present invention does not require a complicated circuit, and the S /
It does not lower N.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of a monitoring method according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the monitoring method.

FIG. 3 is a diagram schematically showing a configuration of a general FTIR.

FIG. 4 is a flowchart showing a conventional monitoring method.

FIG. 5 is a waveform diagram for explaining the operation of the conventional monitoring method.

[Explanation of symbols]

 1 ... Analytical department.

Claims (1)

[Claims] 1. An interferogram monitoring method of FTIR, wherein an interferogram output from an analysis unit is discretely sampled by a sampling pulse, temporarily stored as AD converted data, and then displayed. An FTIR interferogram monitoring method, characterized in that, in displaying, data in the vicinity of ZPD in stored data is complemented using a spline function.