SU1555624A1 - Method and apparatus for measuring optical density - Google Patents

Abstract

The invention relates to technical physics and can be used in spectral, mainly atomic absorption, instrument making. The purpose of the invention is to improve the accuracy of measurements of optical density. In order to achieve the goal, the light signals in the channels of unabsorbed radiation are delayed and at this moment measurements are made in the channel of the absorbed radiation. Then, the channel of absorbed radiation is blocked and measurements are taken in the channel of the unabsorbed measurement. For the signal delay, there is a delay line 6, which can be made on the basis of fiber optics in the form of a light guide, connected between the input and output of the optical system 3. Electron-optical shutter 5 serves to block the channel of the absorbed radiation. The shutter 5 is controlled by one-shot 15 and 14. Spectral lamps 1, 2 are controlled by a generator 13. The light signal is extracted by a monochromator 7 and a photodetector 8. The recording system 9 processes light signals of 2 s.s. f-ly, 2 ill.

Description

1

The invention relates to technical physics and can be applied in spectral instrumentation, atomic absorption spectrometry.

The purpose of the invention is to improve the accuracy of optical density measurements in the time division mode.

FIG. 1 shows a block diagram of the device that implements the proposed method; in fig. 2 - time diagrams.

The device contains sources (lamps) 1 and 2 of the continuous and line spectra, respectively, the beam splitter 3. Between the input and output of the beam splitter 3, an atomizer 4 and an electron-optical shutter 5 are connected in series. Line 6 delay

(Fig. 2b) within Ј, recorded by system 9. At the end of the interval €, the one-shot 15 is started, which

It produces a pulse duration of Ј2 (Fig. 2d). This pulse is controlled by block 6, so that the latter blocks the passage of light (absorbed radiation) to the input of block 7. But during

Yu of the same duration at the input of block 7 a light signal acts, which comes from the shutter 5 (Fig. 2c). System 9 registers, for a duration of 2, a delayed signal (Fig.

15 In the general case, the durations are и, and can be different, but can be equal. It is only necessary that these durations be not less than the time of formation of light signals until

35

(shutter) is connected in parallel (between 20 steady-state values, since the input and output) to the atomizer 4 and the shutter 5. The required interval is allocated by the monochromator 7, the Photodetector 8 converts the light signal into an electrical signal, which goes to the registration system 9-25. It consists of a logarithmizer 10, an analog-digital converter 11 and a control and calculation device 12 made on the basis of a microcomputer (for example, an IVC-2 complex). Pulse generator 13, part of IVC-2, produces control signals for power supply units (not shown) of sources 1 and 2, It can also be performed on the basis of two series-connected generators G5-54, whose outputs except source control 1 and 2 through the elementary circuit OR are combined and connected to the input of the one-shot 14, which through the one-shot 15 controls the gate 5 In addition, the generator 13 synchronizes the operation of the device.

The device works as follows.

The pulse generator 13 generates control pulses of sources 1 and 2, which are sequentially represented in FIG. 2, In the initial state, the shutter 6 is open, the source 1 receives a signal (FIG. 2a). 0 The light pulse of the source 1 at this moment is shown in FIG. 26. Simultaneously, the one-shot 14 (FIG. 2d) starts up, which produces a pulse of duration (FIG. , 2d. The duration of this pulse is numerically equal to the delay of the light pulse (FIG. 2c) 9 by the insertion line. Part of the light signal

Before this stage, the amplitudes of the signals are small, and the phenomenon of non-stationary ™ can lead to greater error and measurements. FIG. 2 g, d, these durations are not equal (Ј,: cr) (which indicates that the registration of the delayed signal can be carried out for a longer time than was mentioned above; the maximum duration of the registration of the delayed signal cannot exceed its duration, otherwise, there will be a large error in the measurements due to the uncertainty of the measured signal amplitudes.

After the end of the interval L, the shutter 6 is turned on and transmits the radiation in the absorbed channel, the circuit returns to its original state and is ready to process the signal coming from the lamp 2. Here the work cycle is completely analogous to that described.

Since the formation times of the coherent signals 1 and 2 can be different, it is advisable to set the time with (and t / i are the longest for one of the lamps. The duration of the lamp control signals (Fig. 2a) should be chosen equal.

When measuring the optical density, the signal obtained at time. can be written as

U, lgl ,, (t), delayed signal

ua igit- Ј, {),

lamp signal 2

.-e fatile, delayed lamp 2 signal

U4 lgI4- (-fc).

40

50

55

(Fig. 2b) for Ј, recorded by system 9. At the end of the interval €, a one-shot 15 starts, which produces a pulse of duration Ј2 (Fig. 2d). This pulse controls unit 6, so that the latter blocks the passage of light (absorbed radiation) to the input of block 7. But for

the same duration at the input of block 7 is a light signal, which comes from the shutter 5 (Fig. 2c). The system 9 registers for a duration of 2, the delayed signal (figv),

In the general case, the durations are Ј, and can be different, but they can be equal. It is only necessary that these durations be not less than the time of formation of light signals to

set value because

five

set value since 0

Before this stage, the amplitudes of the signals are small, and the appearance of non-stationary ™ can lead to greater measurement errors. FIG. 2 g, d, these durations are not equal (Ј,: cr) (which indicates that the registration of the delayed signal can be carried out for a longer time than what was mentioned above, the maximum duration of the registration of the delayed signal cannot exceed its duration, since Otherwise, there will be a large measurement error due to the uncertainty of the measured signal amplitudes.

After the end of the interval L, the shutter 6 is turned on and transmits the radiation in the absorbed channel, the circuit returns to its original state and is ready to process the signal from the lamp 2. Here the work cycle is completely analogous to that described.

Since the formation times of the light signals 1 and 2 can be different, it is advisable to set the durations with (and t / i are the longest for one of the lamps. The duration of the control signals for the lamps (Fig. 2a) should be equal.

When measuring the optical density of the signal obtained at time Ј. can be written as

U, lgl ,, (t), delayed signal

ua igit- Ј, {),

lamp signal 2

.-e fatile, delayed lamp 2 signal

U4 lgI4- (-fc).

0

0

five

Then the optical density of atomic vapors in the atomizer 4 is equal to

D-i 4-U2-U ,, where I is the intensity of the lamps;

to is the atomic absorption coefficient;

C is the concentration of atomic vapors; Ј - fluctuations of the light signal; f is the non-atomic coefficient (its

selective) absorption. Thus, the use of a delay line and an electron-optical shutter leads to an increase in the measurement accuracy by eliminating the influence of fluctuations of light signals in the measurement channel (absorbed radiation), which is equivalent to using two-beam systems that are very complex, especially when the device is operating. with two sources of radiation.

Claims (2)

1. Method of measuring optical time separation mode, in which the intensity of light pulses in the channels of absorbed and unabsorbed radiation from a line or continuous source is measured successively and the result is obtained by calculation, characterized in that, in order to improve the accuracy of measurements, the light pulses in the canopy of an unabsorbed radiation of the corresponding source is additionally delayed by the time, not less than the time of their formation until the steady-state value, and the registration of the signal in the channel ogloschennogo irradiation is carried out for the selected delay, after which the absorbed radiation channel disconnect signal and are registered in the channel unabsorbed radiation, wherein the time registration set not less than the time of forming said light pulses to steady values and their longer duration. 2. A device for measuring optical density, containing sources of line and continuous spectra, a measuring channel including an atomizer and a monochromator, and a comparison channel, with a photodetector installed at the output of the channels, which, in order to improve the measurement accuracy, A beam splitter is installed in the device; it is installed at the input of the reference and measuring channels, an optical delay line of light radiation is additionally installed in the reference channel, and between the atomizer and the output of the optical system is an electron-optical shutter, the control input of which is connected to one of the outputs of the recording system. “O eo