The overview of different types of reflectometers is given.The theoretical calculation of factors, such as instability of internal reference clocks and resolution of timeinterval measurement device, influencing on resolution and uncertainty of signal delay (which can be calculated intolength) is given.One of the ways to decrease uncertainty type A of distance measurements is suggested scheme of pulsereflectometer with multistop event timer. Due to ability of measurement averaging it is possible to reduce resolution lessthen 0.1 mm.In the work principle of operation of the proposed reflectometer and functional scheme are given. The impact ofsuch factors as chromatic and polarization mode dispersion, timer trigger error, temperature fluctuations are considered.The requirements to laser module due to dispersion characteristics of measured fiber are given. The temperaturevariation affects mostly on signal delay in photodetector and other electronics. It also changes the delay of optical pulsein fiber coil, which is used for dead zone riddance. The results of theoretical error limits calculations for suchreflectometers are presented.The results of experimental studies of reflectometer are presented. It is shown that the proposed scheme of theoptical time domain reflectometer and technical solutions make possible the signal propagation delays measurementswith an resolution better than 5 ps and combined uncertainty less than 100 ps.
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