BS IEC IEEE 62582-5 pdf free download
BS IEC IEEE 62582-5 pdf free download.Nuclear power plants一 Instrumentation and control important to safety一 Electrical equipment condition monitoring methods Part 5: Optical time domain reflectometry.
OTDR measurements allow analysis of the condition of the entire fibre, particularly of longitudinal subsections of the fibre, or even identification of discrete points such as splices. It also permits calculation of the fibre length, although this is outside the scope of this international standard.
Optical cables in safety related applications in nuclear power plants may be shorter than in general applications. Measurement of short optical cables (< 500 m) requires OTDR instruments with high resolution.
The OTDR measurement is affected by the propagation speed and the backscattering behaviour of the fibre. Best accuracy is obtained by measuring the attenuation from both ends of the fibre and averaging the two backscatter traces. Therefore, measurements shall normally be repeated from both ends. This is especially useful in case of unexpected discontinuities. However, the improvement to the accuracy from measurements on both ends is limited and measurements from one end are acceptable in cases where two ends are not accessible.
7 OTDR measurements procedure
7.1 General
For condition monitoring one supervisory channel over all cable segments shall be accessible for OTDR measurements. This could be one spare fibre in each cable segment, one multiplexer channel or the use of an OTDR wavelength not disturbing the data transmission in a fibre (or vice versa) using splitters.
7.2 Instrumentation
An OTDR may contain a number of parts, or modules, which provide the required functions. These include a waveform generator (laser diode), a detector, a signal processing function and a display. The instrument will also provide facilities to allow connection to the fibre cable under test, such as a directional coupler and a fibre connector. The configuration of the OTDR is shown in Figure 1.
The contact between the instrument fibre (adaptor cord) and the FUT shall be of a type assuring repeatability and be clean and free from debris. A mechanical splice is usually used as the contact.
The OTDR shall have a sufficient dynamic range to allow measurement over the FUT.
The instrument may contain facilities for changing the wavelength of the test pulses. In addition, the OTDR may allow operation in either single-mode or multimode configuration.
A typical design of an OTDR consists of two main parts. These include the main frame, with a microprocessor and a waveform display; and a plug-in unit that houses the laser diode, the detector, a directional coupler and the fibre connector. Different plug-in units with separate wavelengths can be used together with the same main frame. The plug-in units can be adapted to either single-mode or multimode applications.
The configuration of the OTDR is shown in Figure 1.
A sequence of pulses of light is sent from a laser diode, and is transmitted via an optical directional coupler and an optical connector into the fibre. The back scattered light, due to Rayleigh scattering, is reflected back to the OTDR via the connector and is led through the directional coupler to the detector. The detector converts the light to an electrical analogue signal, which is amplified and sent to an A/D converter. A microprocessor treats the digital signal and generates a presentation on the waveform display. The adaptor cord is typically 1 km to 2 km long and may act as an attenuator. It is usually connected to the FUT with a mechanical splice. In this way dirt is avoided in the OTDR-connector.BS IEC IEEE 62582-5 pdf download.
