| 摘要 |
<p>A time-domain reflectometer (TDR), depicted in the figure, forms a pulse width modulated (PWM) signal directly on a transmission line, where the PWM width is proportional to range to a discontinuity on the transmission line. Two PWM detection methods can be used: (1) real-time, wherein the PWM signal is detected in real-time; and (2) expanded-time, wherein the PWM signal is time-expanded before detection for higher accuracy. Both methods convert the analog transmission-line PWM signal to a digital output PWM signal of identical duty-cycle for averaging, counting, or other processing to indicate range. In a preferred mode, a transmission line is sampled at a floating offset frequency relative to the transmission-line PWM frequency to form a PWM output having a floating time-expansion factor but a precise duty-cycle related to the location of the discontinuity. The essence of this TDR is low cost, precision and absolute simplicity. Applications include precision tank level sensing.</p> |
