RU2608394C1 - Device for measuring parameters of physical fields - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: device relates to optical measurements, in particular to devices for measuring parameters of physical fields (temperature, pressure, tension, etc.) using optical sensors. Disclosed device for measuring parameters of physical fields includes series-connected four-frequency signal source, first fibre-optic cable, optical sensor, second fibre-optic cable; as well as first photodetector, first amplitude detector, second amplitude detector, controller for determining parameter of physical field. First amplitude detector is connected to first input of controller for determining parameter of physical field, and second amplitude detector is connected to its second input. Device includes an optical signal splitter, two optical selective filters, second photodetector, two band-pass filters, wherein output of second fibre-optic cable is connected to optical signal splitter, and first output of optical signal splitter is connected through series-connected first selective filter, first photodetector, first band-pass filter to first amplitude detector, and second output of optical signal through splitter is connected through series-connected second optical selective filter, second photodetector, second band-pass filter to second amplitude detector.

EFFECT: technical result is higher accuracy of measurements and simplified design.

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Description

The technical solution relates to the technique of optical measurements, in particular to devices for measuring the parameters of physical fields (temperature or mechanical tension) using optical sensors, including sensors in integrated and fiber-optic design (Fabry-Perot interferometers, Bragg gratings, sensors on thin-film filters etc.), in which there is a dependence of the frequency shift of their spectral, as a rule, band resonance characteristic, depending on the parameters of the applied physical fields.

A device for measuring the parameters of physical fields is known (see electronic resource www.forc-photonics.ru , “Fiber Optic Probe Thermometer”, file termometr_final.pdf, LLC IP NTsVO-Photonika, October 14, 2008), which contains series-connected a broadband laser emitter, an optical splitter-circulator, an optical fiber cable, an optical sensor, a unit for spectral analysis of the received radiation, and a photodetector unit connected to the input of the controller for determining the parameter of the physical field in which the mathematical processing of spectral bias, according to which, taking into account the calibration, the parameter of the physical field is determined, in a particular case the temperature. Known similar devices for measuring parameters and other physical fields.

The device operates as follows. Generate broadband radiation in a laser emitter, transmit it to the optical sensor via a fiber optic cable, receive radiation converted in the optical sensor in the spectral analysis unit of the received radiation and the photodetector unit, and determine the parameters of the physical field by accurately recording the spectral shift of the resonant wavelength of the optical sensor .

The disadvantage of this device is the need to use complex expensive unit spectral analysis of received radiation and a photodetector unit for recording spectral bias (as a rule, these are optical spectrum analyzers). Optoelectronic spectral signal processing also seems to be complex and requires either tunable laser emitters, or complex spectral filtering systems, or several photodetectors, or, as an option, a system of CCD array receivers. All this leads to the appearance of additional sources of errors in the measurement of the parameters of physical fields and a decrease in their accuracy in general.

The prototype of the technical solution is a device for measuring the parameters of physical fields (see RF Patent No. 122174 U1 "Device for measuring the parameters of physical fields", IPC G01K 11/32 (2006.01), application 2012124693/28, published on November 20, 2012, Bull. No. 32), which contains a four-frequency laser emitter connected in series, a first fiber-optic cable, an optical sensor, a second fiber-optic sensor, a photodetector, the output of the photodetector through the first selective filter and the first amplitude detector connected to the first input of the controller determining the parameter of the physical field and in parallel through the second selective filter and the second amplitude detector to its second input.

The prototype works as follows. In a four-frequency laser emitter, a pair of signals of close amplitude with an average frequency corresponding to a certain frequency of the passband of the optical sensor for a given parameter of the physical field and a difference frequency sufficiently narrow so that both signals fall into the specified passband are transmitted, transmit the generated pair of signals to the optical the sensor in the first optical medium, receive a pair of signals transmitted through the optical sensor transmitted in the second optical medium, additionally a generator a second pair of signals with an average frequency corresponding to the second determined frequency bandwidth of the optical sensor for the same specified parameter of the physical field, and a second difference frequency not equal to the first, narrow enough so that both signals fall into the specified bandwidth, so that the average the frequency of both pairs corresponds to the center frequency of the passband of the optical sensor, and the difference between the average frequencies of the pairs is equal to its half width, transmit the second generated pair of signals to the optical for the sensor using the first optical medium, a second pair of signals transmitted through the optical sensor transmitted through the second optical medium is received, the beats of the pairs of signals at the first and second difference frequencies and the amplitudes of their envelopes are extracted, and to determine the parameter of the physical field, the difference between the amplitudes of the envelopes is found by Depending on the difference in envelope amplitudes, the generalized detuning of the optical sensor passband from the average frequency of the first and second generated signal pairs is determined, which is uniquely related on with the parameter of the measured physical field.

The disadvantage of the prototype device is the need for detection, filtering and processing of two unequal difference frequencies and the simultaneous processing of two measurement channels. Determination of the difference in amplitudes from the middle frequencies of the first and second generated pairs of signals, each of which is exposed to noise and interference of various nature. All this leads to the appearance of additional sources of errors in the measurement of the parameters of physical fields and a decrease in their accuracy in general.

The technical result consists in increasing the accuracy of measurements, simplifying and cheapening the device for measuring the parameters of physical fields.

The technical result in a device for measuring the parameters of physical fields, containing a series-connected source of a four-frequency signal, a first fiber optic cable, an optical sensor, a second fiber optic cable; as well as a first photodetector, a first amplitude detector, a second amplitude detector, a physical field parameter determination controller, wherein a first amplitude detector is connected to a first input of a physical field parameter determination controller, and a second amplitude detector is connected to its second input, an optical splitter is introduced signal, two optical selective filters, a second photodetector, two band-pass filters, while the output of the second fiber-optic cable is connected to the optical signal splitter, and the first output of the optical signal splitter through a series-connected first optical selective filter, the first photodetector, the first bandpass filter connected to the first amplitude detector, and the second output of the optical signal splitter through a series-connected second optical selective filter, the second photodetector, the second bandpass filter to the second amplitude detector.

The device can be performed using an optical sensor based on a Bragg fiber grating.

The device can be performed using an optical sensor based on a Fabry-Perot interferometer.

The device can be performed using an optical sensor based on a thin-film filter.

In FIG. 1 shows a block diagram of a device for measuring parameters of physical fields.

In FIG. Figure 2 shows the dependences of the amplitudes of the beat envelope of the signals of the first and second pairs transmitted through the optical sensor and their difference on the generalized detuning of the passband of the optical sensor 3 for the case when four signals of the same amplitude with an average frequency corresponding to the center frequency of its strip are fed to it from a laser source transmission at a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are the same, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor. Dependencies are given under the assumption that the optical sensor has a triangular spectral characteristic, for example a triangular Bragg grating.

A device for measuring the parameters of physical fields (Fig. 1) contains a series-connected source of a four-frequency signal 1, a first fiber-optic cable 2, an optical sensor 3, a second fiber-optic cable 4; as well as a first photodetector 5, a first amplitude detector 6, a second amplitude detector 7, a physical field parameter determination controller 8, wherein the first amplitude detector 6 is connected to a first input of a physical field parameter determination controller 8, and a second amplitude detector 7 is connected to its second input, an optical signal splitter 9, two optical selective filters 10 and 11, a second photodetector 12, two band-pass filters 13 and 14, while the output of the second fiber-optic cable 4 is connected to the optical splitter signal 9, and the first output of the optical splitter of signal 9 through a series-connected first optical selective filter 10, the first photodetector 5, the first band-pass filter 13 is connected to the first amplitude detector 6, and the second output of the optical splitter of signal 9 through a series-connected second optical selective filter 11, the second photodetector 12, the second band-pass filter 14 is connected to the second amplitude detector 7.

The device can be performed using an optical sensor 3 based on a Bragg fiber grating.

The device can be performed using an optical sensor 3 based on a Fabry-Perot interferometer.

The device can be performed using an optical sensor 3 based on a thin-film filter.

The four-frequency signal source blocks 1, the first photodetector 5, the first amplitude detector 6, the second amplitude detector 7, the physical field parameter determination controller 8, the second photodetector 12, the first bandpass filter 13, and the second bandpass filter 14 have a power supply system that is not shown in FIG. one.

Consider the operation of the device for measuring the parameters of physical fields.

For example, when measuring the parameters of physical fields (temperature or mechanical tension), the optical sensor 3 is placed on the object of study. Next, turn on the power system of the above blocks and measure.

When measuring the parameters of physical fields using a four-frequency source of laser radiation 1 simultaneously generate four signals of the same amplitude with an average frequency corresponding to the center frequency of the passband of the optical sensor 3 at a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are the same, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor 3.

Then, the generated signal pairs are transmitted to the optical sensor 3 via the first optical medium, for which the first fiber-optic cable 2 is selected.

In the generated pairs of signals passing through the optical sensor 3, the amplitudes of the individual components change depending on the direction and magnitude of the frequency shift of its passband, caused by the applied physical field and uniquely determined by the parameter of this field.

Next, using the optical signal splitter 9, the first selective filter 10 and the second selective filter 11, the first and second pair of signals transmitted through the optical sensor 3 are transmitted from the optical sensor 3 to the optical signal splitter through a second optical medium, the second fiber optical cable 4. Next, using the first photodetector 5 and the second photodetector 12, they generate signals corresponding to the beats of the signals of the first and second pairs, which are allocated respectively by the first 13, tuned to frequency Ω1, and second 14 tuned to frequency Ω2, bandpass filters. Further, in the first 6 and second 7 amplitude detectors, respectively, the amplitude of the envelopes of the first U _Ω1 and second U _Ω2 pairs is determined. Next, using the controller determining the parameter of the physical field 8, the amplitudes of the envelopes of the first U _Ω1 and second U _Ω2 pairs are compared. If U _Ω1 > U _Ω2 , then the further determination of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field is performed by the amplitude of the envelope of the first pair U _Ω1 . If U _Ω1 <U _Ω2 , then the further determination of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field is performed by the amplitude of the envelope of the first pair U _Ω2 . The non-zero amplitude of the envelope of the pair, which is currently not determining the magnitude of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field, shows that the amplitude of the envelope of the pair by which the parameters of the physical field are determined corresponds to the value of the frequency bias of the closest to the intersection point the dependences of the amplitudes of the beat envelopes of the signals of the first and second pairs U _Ω1 and U _Ω2 on the generalized detuning of the passband of the optical sensor 3 (Fig. 2), this the ambiguity in determining the magnitude of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field (Fig. 2)

According to the obtained values and the physical field parameter determination controller 8, the dependences of the difference between the amplitudes of the beat envelopes of the signals of the first and second pairs U _Ω1 and U _Ω2 transmitted through the optical sensor 3 on the generalized detuning of the passband of the optical sensor 3 (Fig. 2) and the dependence the direction and magnitude of the frequency shift of the passband of the optical sensor 3 from the parameters of the physical field uniquely determine the measured parameter of the physical field.

In FIG. Figure 2 shows the dependence of the amplitudes of the beat envelopes of the signals of the first and second pairs U _Ω1 and U _Ω2 transmitted through the optical sensor 3 on the generalized detuning of its passband for the case when four signals of the same amplitude with an average frequency corresponding to its center frequency are supplied from the laser radiation source 1 bandwidth at a given value of the parameter of the physical field. The first pair of signals is formed from the first and second signals, the second from the third and fourth. In this case, the difference frequencies of the pairs Ω1 and Ω2 are the same, and the difference between the average frequencies of the first and second pairs is equal to the half-width of the passband of the optical sensor 3. In this case, the device parameters that are optimal in sensitivity and slope of the measurement conversion are provided.

For a given (calibration) parameter of the physical field, the average frequency of the generated four signals will correspond to the detuning “0”, the average frequency of the first pair will be located with the detuning, the average frequency of the second pair with the detuning. Their amplitudes will be equal (Fig. 2). With the frequency shift of the passband of the optical sensor 3, depending on the changes in the physical field parameter, the position of the components of the generated signal pair relative to the passband will change, the amplitudes of the beating envelope of the pairs passing through the optical sensor 3 will change in accordance with the presented dependence U _Ω1 and U _Ω2 (Fig. . 2).

With the known dependence of the magnitude of the detuning of the passband of the optical sensor on the value of the parameter of the applied physical field (for example, for the Bragg fiber optic array, typical values of the detuning depending on the temperature are ~ 0.01 nm / K and on the relative fiber elongation ~ 10 ³ ΔL / L (nm ) (S. A. Vasiliev, O. I. Medvedkov, I. G. Korolev, and E. M. Dianov. Photoinduced fiber gratings of the refractive index and their applications, Photon Express-Nauka, 6, pp. 163-183, 2004 )) determine the value of the parameter of the applied physical field.

Thus, according to the obtained values of the amplitudes of the envelopes of the beats of the first and second pairs U _Ω1 and U _Ω2 passed through the optical sensor 3, in accordance with the presented dependence, the generalized detuning of the passband of the optical sensor 3 is determined and then the dependence of the generalized detuning of the passband of the optical sensor 3 on parameter of the applied physical field in the controller determining the parameter of the physical field 8 uniquely determine the parameter of the measured physical field.

The device can be implemented using various types of optical sensors 3, the specific form of which is determined depending on the tasks to be solved and the nature of the applied physical field. It can be a Bragg fiber grating, or a Fabry-Perot interferometer, or a thin-film filter. Dependencies are given under the assumption that the optical sensor has a triangular spectral characteristic, for example a triangular Bragg grating. When using the spectral characteristics of optical sensors with a nonlinear shape, the form of the resulting characteristics U _Ω1 and U _Ω2 will also have non-linear sections, however, this will not affect the unambiguity of determining the physical parameter.

A device for measuring the parameters of physical fields (temperature or mechanical tension) can be implemented on the following elements, designed to operate at a wavelength of 1300 nm (other wavelengths are possible):

- laser radiation source 1 - one laser diode IDL10S-1300 Research Institute "Polyus" or laser diode DMPO131-22 LLC NPF "Dilaz" and two modulators based on a Mach-Zehnder 500-x-13 interferometer from Laser2000;

- fiber-optic cables 2, 4 - reference cords or cables TELECOM-TEST of LLC Production and Trade Company SOKOL LLC;

- optical sensor 3 - Bragg fiber grating, Fabry-Perot interferometer, thin-film filters of IP NTsVO-Photonika LLC;

- optical splitter 9 - FBT 1 × 2, 50/50, G.652 SC / UPC, Svyazstroydetal;

- photodetectors 5, 12 - high-speed fiber-optic InGaAs / InP microwave broadband PIN photodetectors (receiving modules) of NPF DiLaz, for example, DFDMSh-40-16;

- controller 8 - microprocessor controller based on chips from Atmel, Microchip, etc .;

- selective filters 10-11 - Agilent;

- band-pass filters 13-14 - firms K&L Microwave;

- amplitude detectors 6-7 - dual amplitude detector AD8302-a (Analog Devices).

To build a sensor of parameters of physical fields, all of these blocks of generation, reception and processing of signals can be performed on a single chip or in integral design.

Compared with the device of the prototype for measuring the parameters of physical fields using optical sensors, including sensors in integrated and fiber-optic versions, in which there is a dependence of the frequency offset of their spectral characteristics depending on the parameters of the applied physical fields, the proposed device with four-frequency sounding optical the sensor and measuring the parameter of the physical field by the difference between the amplitudes of the envelope of the beats of the pairs of signals transmitted through the optical sensor, e requires:

- firstly, the use of complex expensive optical systems for determining the spectral bias, which significantly reduces the cost of the devices;

- secondly, applications for the analysis of optical signals of selective elements, which have their own dependence on changes in the measured physical fields.

Tests of the experimental device for measuring the parameters of physical fields were carried out on optical sensors made on Bragg fiber gratings made and calibrated on optical spectrum analyzers Yokogawa in the laboratory of KNITU-KAI named after A.N. Tupolev (Kazan), and showed that the use of a four-frequency sensing device of an optical sensor with a parameter measured by the difference in the amplitudes of the envelopes of the beats of the signal pairs made it possible to achieve a temperature measurement error of 0.01 ° C in the range of ± 60 ° C. In this case, the measurement error was determined mainly by the error of the ADC of the temperature determination controller.

All this allows us to talk about achieving a solution to the technical problem - simplification, increasing accuracy and cheaper devices for measuring the parameters of physical fields.

Claims (4)

1. A device for measuring the parameters of physical fields, containing a series-connected source of a four-frequency signal, a first fiber optic cable, an optical sensor, a second fiber optic cable; as well as a first photodetector, a first amplitude detector, a second amplitude detector, a physical field parameter determination controller, wherein the first amplitude detector is connected to a first input of a physical field parameter determination controller, and the second amplitude detector is connected to its second input, characterized in that an optical splitter is introduced signal, two optical selective filters, a second photodetector, two band-pass filters, while the output of the second fiber-optic cable is connected to the optical to the signal coupler, and the first output of the optical signal splitter through the first optical selective filter, the first photodetector, the first bandpass filter connected to the first amplitude detector, and the second output of the optical signal splitter through the second optical selective filter, the second photodetector, the second bandpass filter connected in series to the second amplitude detector. 2. The device according to claim 1, characterized in that the optical sensor is based on a Bragg fiber grating. 3. The device according to claim 1, characterized in that the optical sensor is based on a Fabry-Perot interferometer. 4. The device according to claim 1, characterized in that the optical sensor is based on a thin-film filter.

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