SU1643952A1 - Method for determination of low-frequency noise of pulse light source - Google Patents

Abstract

The invention relates to spectral instrumentation and can be used to certify spectral light sources. The purpose of the invention is to improve the accuracy of measuring the distribution of low-frequency noise components. Set the number of measurements in each series N or the pulse frequency of the light source f. Measurements are made for the limiting values of the frequency range {fn, fk}, with the variable parameter being calculated from the ratio f Nfi, where i n, k. The value of Ј2 low-frequency noise is calculated from the expression Ј2 I n - Јicl, where Јi (i n, k) is the measurement of the noise value for fj. 2 Il.

Description

The invention relates to technical physics and can be used in spectral instrumentation, as well as in the certification of spectral lamps.

The purpose of the invention is to improve the accuracy of measuring the distribution of low-frequency noise components.

Fig, 1 shows a block diagram of a device implementing the method; in fig. 2 is a graph of noise component measurements in the low frequency region.

The device contains a test lamp 1, a monochromator 2, a photodetector 3, an amplifier 4, an integrator 5, an analog-to-digital converter 6 and a recording system 7. All of the listed nodes are synchronized by a pulse generator 8. The lamp 1 is powered. The power supply unit 9 is powered.

Let it be required to measure the noise distribution in the area (1, 10 Hz} with an error of no more than 10%. Choose the number of measurements (samples) N 100. Then, in accordance with the ratio

f Nfi. where f is the frequency of the light source pulses;

fi (i n, k) are the boundary values of the frequency range in which measurements are made, i.e. {fn, fk}, determine f Nfn 100 Hz for fn 1 Hz,

f i for fk 1Q Hz.

These frequencies are sequentially for the first and second series of measurements set on the generator 8. The duration of operation of block 5 is set within 5-10 μs, i.e. A signal from a source operating, for example, with a duration of 100 µs and the indicated frequencies, is sampled in 5-10 µs.

Thus, taking into account the rectangular noise distribution during the operation of the integrator 5, its frequencies are

ABOUT

SA O SJ

Yu

200-100 kHz. This concerns high frequency noise components.

Now it is enough to set the operating current of the lamp 1, the generator frequency of 1000 Hz and carry out the first series of measurements (N 100). Then they will trudge

& Јnch1 + Ј2Hy where Јk is the total noise:

Јnsh - noise at a frequency of 10 Hz; f 8h high frequency noise. Then on the generator 8 set the frequency of 100 Hz and are the second series of measurements

Јп2 Ј2Нч2 + Ј2Вч.

where Јn - total noise;

| nc2 noise at a frequency of 1 Hz;

Ј high frequency noise.

Finally, the noise distribution of the 1-10 Hz band is found by the formula

-1Y-Ј

(one)

Thus, according to the proposed method, it is possible to measure the distribution of noise in the low-frequency region and, at the same time, to compensate for high-frequency noise.

FIG. 2 a-c shows low-frequency harmonic noise; in Fig. 2, g e are the hatched areas characterizing the measurement time q with the number of measurements N different by a factor of two. You can measure the noise distribution in three bands. The durations n-gz characterize the total measurement time in each series.

Used lamp type LT-2 with a wavelength of I - 324.7 nm. Lamp current 100 mA.

The number of measurements in each series is 100. The repetition rates are 1000 and 100 Hz. The rms noise value in the first case is 10, and in the second - 9.2 units (direct reading data from block 6 was used). The calculation by the formula (1) shows that the rms noise value in the 1-10 Hz band is approximately 4.08 units.

The advantages of the method include a higher accuracy of measurements of the low-frequency components of the light source noise, as well as the possibility of taking into account the high-frequency components at any given repetition frequency.

Claims (1)

The method of determining the low-frequency noise of a pulsed light source, which consists in directing the radiation of a measured light source with a frequency f to a photodetector, measuring its signal for N separate and equal to each other by the duration of time samples light, characterized in that, in order to increase accuracy, measurements are made for the boundary values fi, the frequency range, where (n, k, in which the noise is measured, and the number of samples N or the frequency pulse light source f, and unset value is determined depending on the ratio of fi f Nfi, the J value in the low frequency band noise {fn. fk} calculated from the expression  I. where Јi (l n, k) is the measurement results of the noise values for fi (t n, k), and the duration of each of the N samples is much less than the value of f. FIG. 7 y d e B tz JJJ JJ SJJfJ1rj JSJ JffSJjif7 r75 yr 77JJJSJ1 JJ fJSSJJfSSSSJ fJJ SJtJJ SJ FI.2 tz L + i