SU1518730A1 - Method of measuring optical characteristics of dispersing media - Google Patents

Abstract

A method for measuring the optical characteristics of scattering media relative to the field of optical-physical measurements. The purpose of the invention is to improve the measurement accuracy in the presence of background illumination and instrumental limitations on the accuracy of the alignment of the optical axes of the emitter and receiver. The method consists in preliminarily measuring the level of background illumination and the mixture of signal and background at a fixed value of the field of view of the receiver, calculating an intermediate parameter characterizing the background measurement error, calculating the optimal value of the field of view angle. Based on the solution given in the equation, the angle of view is set to the optimum and the optical signal is then emitted, the scattered optical signal is received and converted into an electrical one, and the desired optical characteristics are calculated. By carrying out a sequence of preliminary operations to determine the optimal value of the field of view of the optical system, it is possible to minimize the relative measurement error. 1 il.

Description

The invention relates to optical physical measurements and can be used to monitor the level of aerosol contamination, in optical location, etc.

The purpose of the invention is to improve the measurement accuracy in the presence of background illumination and instrumental limitations on the accuracy of the alignment of the optical axes of the emitter and receiver.

The drawing shows a block diagram of the device, the implementation of the proposed method.

The device contains a control unit 1, a variable delay formation unit 2, a pulse distributor unit 3, a receiver 4 optical system, a photo-receiver 5, a gated amplifier 6, a memory 7, an analog-to-digital converter (ADC) 8, a transmitter 9, an emitter 10, a photo-receiver 11 reference channel, an electronic counter 12, a generator of 13 clock pulses, an electromechanical drive 14 and a recorder 15.

00

with

(Lyusob osues riiJUiior as follows.

LS ishch, in a state with shriksihaaplh values w x dstios gay or chatel and receiver to the center of the sighted volume of the investigated medium R, and R, the angular divergence of the radiation E and the magnitude of the angular view of the receiver 0, measure the level of the background illumination. For this, a signal from control unit 1 starts a block of 2 fopes of adjustable delay, which realizes the time distribution of the control signals, From its output, a signal arrives at the input of unit 3 of the distributor pulsol, also controlled by command 1 from block 1, Distributor and helix pulses (demultiplexer , the selector) directs the input signals to the addresses of the input to its control g; The background illumination through the optical system of the receiver 4 enters the .pi state receiver 5, is converted into an electric signal and arrives at the strobing amplifier b. When a gate arrives at its control input, it sends a pulse from block 3 to output pulse 6, a pulse whose amplitude is proportional to the background intensity. In a signaling device 7, including a peak detector, an operational amplifier with a high input impedance and a reset key, this pulse is expanded to the value necessary for the operation of subsequent devices, digitized into the ADC 8 and fed to an indicator 9. Reset the memory device 7 and the start of the ADC 8 is performed by pulses from the pulse distribution unit 3.

Then, the emitter 10 starts up with a pulse from the distributor unit 3, which generates an optical pulse. Part of the radiation scattered by the test medium enters through the optical system of the receiver 4 to the photo receiver 5 and amplifier b, from the output of which the electrical signal carrying information about the scattering properties of the medium The device 7 and the A / D converter 8 are fed to the calculator 9. The temporal position and the ip of the strobe from block 3 to the amplifier b are chosen so that the accelerated medium will have the signal okavgm-:; inside the gate.

At the time of emission of the optical signal by the output pulse of the photo-receiver 11 of the reference channel, to which part of the probing radiation is diverted, an electronic counter 12 is triggered. A clock pulse from the oscillator 13 clock pulses is supplied to its counting input, which synchronizes blocks 1–3 and ADC 8 devices. The output signal of the photodetector 5, delayed relative to the pulse of the photon receiver 11 of the reference channel for the time the light signal travels the distance from the emitter through the volume under study to the receiver, the counter stops counting the pulses, and its output code corresponding to the measured range is fed to the calculator 9.

With a known distance w (base) L between the emitter and receiver and the selected scattering angle, the distances R and R can be easily determined from the measured value of R R + R. After this, the parameter

V PIJ®I b-CRoeJR, e,)

P (0,) - p (0,)

ET

where Rf (0,) and PjC®,) are the measured values of the received background and sum signals for a fixed value b, is the field angle of view of the receiving system RJJ, R, are the distances from the emitter and receiver to the center of the sight volume;

 beam divergence. It is then resolved.

- 36cfl - 18 cQa -b-Q3 on.

0

where 51 02;

Q (R, e, / R,)

with

 permissible angular error of adjustment (this parameter characterizes the instrumental accuracy of the optical-mechanical system of a particular device). Solving this equation makes it possible to determine the optical value of the field angle of view b b opt, minimizing the relative measurement error.

The adjustment signal from the output of the calculator 9 is fed to an electromechanical actuator 14, by means of which the angular field of view of the optical system of the receiver 4 is set equal to the optimal G. This can be done, for example, by changing the diameter of the aperture of the aperture of the field of view of the receiving optics (using, for example, an iris diaphragm), which is usually installed in the focal plane of the lens. Note that after calculating b, it is possible to manually set the optimal

Formula

and

6

3 o b

e te and u

The method of measuring the optical characteristics of the scattering media, which consists in directing electromagnetic radiation into the medium, receiving the scattered radiation, converting the scattered radiation into an electrical signal and calculating the desired optical characteristics, characterized in that, in order to measure the accuracy background illumination and instrumental limitations

the total angle of the field of view of the receiving system-15 and the accuracy of the adjustment, previously.

we determine the optimal value of the angle

From the field of view, for which, prior to the direction of the electromagnetic radiation, the value of the angle B is recorded, the view of the receiving system is measured, the signals P (b,) of the background illumination are measured, electromagnetic radiation, identical to that used for measurements, is sent to the medium

Further, the signal transmitted through blocks 1-3, the emitter 10 generates an optical pulse, scattered by the medium, the radiation is received, measured by - 20 s and fed to the calculator 9 to calculate the desired optical characteristic (for example, the scattering coefficient) by known methods. The result of the calculation is provided to the recorder 15.

The use of the proposed method for measuring the optical characteristics of scattering media provides, in comparison with existing methods, an increase in measurement accuracy when operating in real conditions, i.e. in the presence of intensive background illumination and with the inevitability of instrumental limitations on the accuracy of the alignment of the optical axes of the emitter and receiver.

Let us estimate the gain in the accuracy of dispersion coefficient measurements for specific conditions. Let the instrumental alignment error J 32 10 rad, the spectral brightness of the daytime sky background B 10 "A-sterr (average value for middle latitudes), be admissible. Then, according to the method, we get the optimal value, 5 mrad, the error is about 7%. When setting non-optimal values of 0, for example, 1 and 6 mrad, the relative error is significantly higher from 25%, i.e. there are 50 gains in measurement accuracy of about 3.5 times.

measure the signal P (b,) cw1.1m scattering the nn and background signal, determine the distance R, respectively, from the radiator and from the radiation receiver to the center of the measured volume of the medium, and diverge the number

6d radiation beam, 35

., P (fj) 6- (Ro./Rie)

 pj (0,) - p; (ej eG

determine the optimal value of the field angle of view 6 from the equation

0

-

- i- "

- SALIC - 18cQfi2 + 3cQ2 “Oh,

eat

 (R ..

- permissible absolute angular

adjustment error, set the angle of view

system, equal to the optimal.

measure the signal P (b,) cw1.1m of the scattered n and background signal, determine the distance R, respectively, from the emitter and from the radiation receiver to the center of the measured volume of the medium and the divergence number

6d beam, you

., P (fj) 6- (Ro./Rie)

 pj (0,) - p; (ej eG

determine the optimal value of the field angle of view 6 from the equation

- SALC - 18cQfi2 + 3cQ2 "

- i- "

ABOUT,

eat

 (R ..

- permissible absolute angular

adjustment error, set the angle of view

system, equal to the optimal.

Claims (1)

Claim The method of measuring optical is characteristic of scattering media, namely that they direct electromagnetic radiation into the medium, receive the scattered radiation, convert the scattered radiation into an electrical signal and calculate the desired optical characteristics, characterized in that, in order to increase the accuracy of measurements in the presence of background illumination and instrumental limitations on the accuracy of alignment, preliminary. determine the optimal value of the angle of the field of view, for which the direction of angle b is fixed, the field of view of the receiving system is measured, the signals P “(Θ,) of the background illumination are measured, electromagnetic radiation identical to that used in the measurements is sent to the medium, the signal Pj (Θ is measured ,) the sum of the scattered and background signal, determine the distance R and R, respectively from the emitter and from the radiation receiver to the center of the measured volume of the medium and the divergence θ _{0 of the} radiation beam, calculate the parameter _{γ =} ______ b = (M '/ ^R i ^e J ² - θΤ ’determine the optimal value of the angle of view 6 from the equation I. ¹ - - ЗБСЯ ³ _ i8cQfi ² + 3cQ ² I - where I - &²; 0 = (R ^ / R,) ² ; c = 9γ ⁴ / Υ ² ; y is the permissible absolute angular error of adjustment, and the angle of the field of view of the receiving system is set equal to optimal. 3.5 times.