|
The overview of different types of reflectometers is given. The theoretical calculation of factors, such as instability of internal reference clocks and resolution of time interval measurement device, influencing on resolution and uncertainty of signal delay (which can be calculated into length) is given. One of the ways to decrease uncertainty type A of distance measurements is suggested scheme of pulse reflectometer with multistop event timer. Due to ability of measurement averaging it is possible to reduce resolution less then 0.1 mm. In the work principle of operation of the proposed reflectometer and functional scheme are given. The impact of such 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 temperature variation affects mostly on signal delay in photodetector and other electronics. It also changes the delay of optical pulse in fiber coil, which is used for dead zone riddance. The results of theoretical error limits calculations for such reflectometers are presented. The results of experimental studies of reflectometer are presented. It is shown that the proposed scheme of the optical time domain reflectometer and technical solutions make possible the signal propagation delays measurements with an resolution better than 5 ps and combined uncertainty less than 100 ps.
|
