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FOTL - Tutorial 011. The operating principle of OTDR

fiber, волс, OTDR, рефлектометр

Pulse reflectometers OTDR (Optical Time Domain Reflectometer) operate on a similar principle, which is used in reflectometers for testing electrical cables. Reflectometer submits a powerful light pulse into the optical fiber, as well as an electrical reflectometer submits powerful probe pulse in the electrical cable. At the same time it carried out the measurement of power and pulse delay time that is returned back to the OTDR. The difference between the electric OTDR is that the metallic conductor returns only pulses that are reflected by strong inhomogeneities in the cable, that is, from the location of cable deformation, while the optical fiber return pulses are not only places of large irregularities, but also due to the Rayleigh effect scattering. Rayleigh scattering occurs due to changes in the refractive index of the optical fiber when it is stretched during manufacture. Such inhomogeneities arising in the manufacture of the optical fiber is extremely small, but have some effect on the scattering of the light beam that is scattered by these irregularities in all directions, including back to the OTDR.

Passage of the light beam from the optical fiber OTDR

Due to the effect of Rayleigh scattering possible to determine information about the length of the optical cable, the distribution of non-reflecting irregularities of kilometricheskom average attenuation for all the length of the cable, as well as the local welding of optical fiber cable.

Rayleigh scattering coefficient is a very small quantity, hence in the OTDR, using photodetectors with high sensitivity down to -70 dB.

OTDR Construction

OTDR Construction

Modern OTDR often have a modular design, as for the qualitative measurement of single-mode and multimode fiber requires appropriate optical emitters. Typically, the OTDR consists of two main modules:

  • Basic module - is responsible for the post-treatment measurements and display the waveform on the oscilloscope screen, and for setting measurement parameters, etc.
  • Interchangeable optical module - is responsible for measuring and digitizing the primary trace.

The OTDR uses laser emitters with high power level of up to 1000 mW. Laser transmitter sends the pulses into an optical fiber, which are reflected back into the optical connector removable optical module to which the optical fiber was connected. Inside the optical coupler module is installed, which acts as a filter to reverse emission did not fall on the radiator OTDR. Once the module converts the optical signal into an electrical and conduct primary processing, trace data are transferred to the base unit, which made the final processing and display of information on the OTDR screen.

Also, depending on the model, OTDRs may have internal and external drives for storing OTDR, interfaces for connecting to a PC, additional software, etc.

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Jan. 22, 2019, 9:22 p.m.
Allyonz

C++ - Test 001. The first program and data types

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Jan. 22, 2019, 2:15 p.m.
Alex

Qt - Test 001. Signals and slots

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Jan. 20, 2019, 6:39 p.m.
Ivan Otreshko

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Last comments
Jan. 22, 2019, 1:17 p.m.
Евгений Легоцкой

Создайте тогда тему здесь на форуме в разделе Qt с выкладками кода и вашими попытками внедрения делегата, позже гляну или может кто-то ещё глянет из опытных пользователей.
I
Jan. 22, 2019, 1:13 p.m.
IscanderChe

Не проще тогда использовать сразу кастомный делегат с чекбоксом? Я попробовал, но там засада в том, что чекбокс показывается только при щелчке на ячейку, а дефолтно показывается значение. Как ...
Jan. 22, 2019, 12:15 p.m.
Евгений Легоцкой

Если будет не приемлемо потом, то тогда через кастомный Item Delegate нужно будет перерисовать ячейки в той колонке.
I
Jan. 22, 2019, 12:09 p.m.
IscanderChe

Получилось приемлемо. Спасибо!Нюанс только в том, что поле рядом с чекбоксом не пропадает, оно просто пустое, что видно при выделении ячейки. Но этого достаточно.
Jan. 22, 2019, 11:50 a.m.
Евгений Легоцкой

Переопределить метод data для той колонки и роли Qt::DisplayRole, чтобы в том случае возвращался QVariant() я так думаю... Но возможно, что у вас там будут нюансы, если вы туда чекбокс за...
Now discuss on the forum
Jan. 23, 2019, 7:54 a.m.
Михаиллл

Зарание спасибо.А еще на эту тему можно будет сделать статью. Это контент будет уникальным.
Jan. 23, 2019, 7:37 a.m.
Евгений Легоцкой

Hello. Maybe the English will be better for you? I think russian is not native language for you, or did I mistake? Did I undesrtood rightly, that you mean this documentation ( ...
I
Jan. 22, 2019, 1:45 p.m.
IscanderChe

Всем добрый день. Суть задачи: надо, чтобы в одной из колонок QTableView вместо хранимого в QSqlTableModel значения выводился чекбокс и при смене состояния чекбокса значения в базе тоже ...
M
Jan. 22, 2019, 1:15 p.m.
Max-P85

Евгений, огромное спасибо, все работает!
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