JPS60135730A - Double beam spectrophotometer - Google Patents

Abstract

PURPOSE:To remove influence of absorption, etc. due to atmospheric components and to make a high speed wavelength scanning possible by integrating respective optical signals of a control and sample to obtain the ratio, and obtaining the ratio, of both signals from the obtained ratio at front and rear ends of the integral interval in the midway thereof by interpolating method. CONSTITUTION:Each luminous flux R, S of the control and the sample from a light source L are intermitted at frequencies f1, f2 by choppers 1, 2, mixed by a beam mixer 3, made incident to a spectroscope M, detected by a detector D and discriminated by selective amplifiers Sr, Ss. Said lights are integrated by integrators Ir, Is and taken into a CPU. Scanning and data processings of the spectroscope M are performed by wave number unit, integer times of wave number is taken as an integral interval, outputs of the amplifiers Sr, Ss are integrated to obtain the ratio i.e. a transmissivity, and the transmissivity is obtained at every wave number by interpolating method from values of front and rear ends of the integral interval in the midway thereof. Thus, the influence of absorption, etc. of atmospheric components can be eliminated.

Description

Detailed Description of the Invention A. Field of Industrial Application The present invention relates to a north-light type double-beam spectrophotometer that measures the ratio of both side optical signals of a photometric signal for a measurement sample and a photometric signal for a reference sample.

A method for calculating the ratio of the photometric signals of the sample light and reference light using a double-beam spectrophotometer is to control the gain of the photometric circuit and the sensitivity of the detector so that the photometric signal of the reference light shows a constant value. There is a negative feedback method, such as controlling the slit width of the optical system, and a direct method, which directly divides the photometric output of the sample light and the reference target. The sample light beam and the reference light beam are chopped alternately or at different cycles and made incident on one photodetector, and each photometric signal of the sample light and the reference light is discriminated by processing on the circuit.

- Prior Art When the above-mentioned double-beam spectrophotometer is affected by the absorption of atmospheric components, there is a problem that the S/N ratio decreases when wavelength scanning is performed at high speed. Problems like these are especially noticeable in infrared spectroscopy, where the chirping period cannot be shortened.

□ Explain this point in detail. When a double-beam spectrophotometer uses the same photodetector to receive the reference light and the sample light, each light beam is chopped and sent to the photodetector at different times in order to identify both lights, as described above. I am trying to make it incident. For this reason, the photometric values of the control light and the sample light are sampled at different times. Assume that the absorption spectrum of a currently popular ingredient is as shown in Figure 1. The effect of this absorption appears in exactly the same way in both the reference and sample light fluxes, so if the wavelength scanning speed is slow and the reference and sample light photometric values can be considered to have been sampled at the same wavelength position, compare them. This eliminates the effect of absorption (this is the effect of using a double beam), but as wavelength scanning becomes faster, the wavelength change between the time difference Δt between the sampling points of the reference light and the sample light becomes large. However, the absorption at each timing is significantly different, and even division does not eliminate the influence of absorption of atmospheric components, resulting in measurement errors. This problem can be avoided by increasing the chopping frequency according to high-speed scanning, but
In the case of infrared spectroscopy, it is not possible to increase the chopping frequency because a photodetector with a fast response speed cannot be obtained. Therefore, in order to avoid the above problem, there was no choice but to keep the wavelength scanning speed low. The purpose is to make it possible.

D. Configuration The double-beam spectrophotometer of the present invention integrates the reference optical signal and the sample optical signal over a range wider than the wavelength width of the absorption spectrum that causes the above-mentioned error, and calculates the ratio between the integrated values. At the same time, since the ratio is not perfect for each integral interval, the ratio between the sample optical signal and the reference optical signal is calculated by interpolation in the middle of the integral interval.

E. Embodiment FIG. 2 shows an embodiment of the present invention. L is a light source, mirrors mr, m5 (y, so that a control light flux R and a sample light flux S are taken out; Cr is a control sample; Cs is a measurement sample; 1.
A chopper 2 cuts off the reference light flux R at a frequency fl and the sample light flux at a frequency f2. 3 is a beam mixer that mixes the reference light and the sample light and makes them enter the seven spectrometer M. D is a detector that receives the light emitted from the spectrometer M. The output of the detector is amplified by a preamplifier PA and then sent to selection amplifiers Sr and Ss.
The signal is separated into a frequency f1 component and a frequency f2 component.

The component at frequency f1 is a reference light photometric signal, and the component at frequency f2 is a sample light photometric signal. Both signals are integrated by integral fractions r and s. The time during which the integration is performed is calculated by the computer CP.
It is controlled by the timing of a reset signal issued from U, and the integration results for a certain period of time are A/D converted and fed into the CPU.

Wavelength scanning of a spectrometer and data processing of photometric signals are performed in wavenumber units. The wave number scanning of the spectrometer M is driven by a pulse motor in steps of wave numbers ΔW.

The wave number width of the integration interval is set to an integral number N times ΔW. Now let Sr be the output of the selective amplifier Sr, which is the photometric signal of the reference light, and Ss be the output of the selective amplifier SS, which is the photometric signal of the sample light, and assume that the integration is performed between the wavelengths W1 and W 2 = W 1 + NΔW, respectively. , the integral 1 value at that time is expressed as kr and s, respectively.
shall be. In other words, the transmittance Tw2 of the sample at the wave number W'l+NΔW is
Tw2-1B/Engr・・・・・・・・・・A・・
......(2). In this configuration, when the wave number scanning of the spectrometer has progressed to W2=W1+NΔW, the transmittance T, 72, at wave number W2 becomes complete.

With the above configuration, the transmittance is obtained at wave numbers NΔW jumps, so the transmittances between them are calculated and displayed at ΔW jumps by interpolation εl[. This interpolation calculation is performed as follows.

Twl : Transmittance at wave number Wl Tw2: Transmittance at wave number W2 W 2 = W 1 +NΔW T w x : Wave number W 1 +X ΔV/or l as an integer
~N-N -1T□X The interpolation calculation between is performed while the wave number scanning of the spectrometer progresses from W2 to W3.Therefore, in the display device 4, the wave number position of the spectrometer M is !llNΔW.
Displays the transmittance corresponding to the wave number delayed by .

FIG. 3 is a flowchart of the operation of the CPU.

If the wave number at the starting point of the wave number scan of the spectrometer is Wo, then the integer N
is selected such that NΔW sufficiently includes the peak width of absorption of atmospheric components in FIG. 1, and Wo is divisible by NΔW. By doing this, the wave number w1 at the boundary of each integral interval. , w'2... are all divisible by HΔW. The flowchart in FIG. 3 will be explained based on the above points. Wl is the current wavenumber position of the spectrometer. In step (a), make a trial calculation of Wi / NΔW, and in step (b)
Check whether this is divisible by If divisible (Y
Since the wave number Wi of ES) is the boundary of the integral interval, read the integral fraction r, the output r of S, and S at that time (c). Then T w i = engineering s / I
Set r to calculation), set the number M to 0 (e), reset each integrator (to), and calculate (Twi-Twi-1)/'N-α
, calculate Twi-1-1-Mα (
blood). Steps (B) and (H) perform interpolation calculations, so M is initially O. In the next step, the wave number feed motor is driven to advance the wave number of the spectrometer by ΔW.
Set Wl to W1 + ΔW), and set the display value on display 4 to Wi-NΔW (Nori. Now, Wl in step 1 is the wavenumber of Wl in the previous step (a) plus ΔW). Yes, the operation returns to (a). (b)
If the step is not divisible (NO), it means that it is in the middle of the integral interval, and the operation is to add MKI in the step example,
The action jumps to (ch). In this way, the spectrometer is driven at wave numbers ΔW, and interpolation calculations are performed and displayed each time. When the boundary of the integration interval is reached again, W i /NΔW is divisible and the operation is (c)... Proceed with (ru).

Effects According to the present invention, the sampling data in the NΔW interval is averaged by the integral operation and the ratio between the sample optical signal and the reference optical signal is determined, so even if the sampling timing of the individual signals is different. , the total is the ratio of the sample optical signal and the reference optical signal in the same time interval,
Changes that commonly appear in both signals are canceled out, and effects such as absorption of atmospheric components do not appear even during high-speed scanning. According to the present invention, the average of the data between the wave numbers NΔW is used as the sampling data for that section, which means that the wavelength resolution is reduced, but high-speed scanning is performed in the case of infrared spectroscopy, etc. , a regular measurement takes several tens of minutes, so in a case where you want to know the approximate shape of the entire sample spectrum in 2 to 3 minutes, high wavelength resolution is not included. It is desirable to display a correct spectrum shape as a whole with less noise, and the present invention meets such requirements.

[Brief explanation of the drawing]

FIG. 1 is a graph explaining the problems of the conventional example, FIG. 2 is a block diagram of an apparatus according to an embodiment of the present invention, and FIG. 3 is a flowchart of the operation of the apparatus. L...Light source, R...Control light flux, S...Sample light flux,
1.2...Chopper, 3...Beam mixer, M...
・Spectrometer, D...Photodetector, Sr, Ss...Selective amplifier, Ir, I8...Integrator, CPU...Computer, 4...Display R"4゜Agent Patent attorney Agata Hiroshi
Is it too large for intervention? figure

Claims (1)

[Claims] The reference optical signal and the sample optical signal are integrated using the wavelength range that includes multiple chopping operations as an integral interval, and the ratio of the two is determined. A double beam spectrophotometer characterized in that the ratio of the signals of the reference light and the sample light is determined by an interpolation method from the ratio of the integral values of the optical signal and the sample light signal.