Precision level measurement based on time-domain reflection (TDR) measurements

[摘要] A system for a high precision multi target levelmeasurement based on guided microwave pulses is presented.A wide-band technique based on time-domain reflectometry(TDR) in combination with a TEM-waveguide as theprobe fulfils the requirements of mm-precision level measurementsin tanks. The coaxial waveguide provides verylow dispersion for wide-band signals. Inside the coaxialwaveguide the different fluids with their specific dielectricconstants influence the waveguide’s characteristicimpedance, so that reflections take place at each discontinuityand separating layer respectively. A second very importantrequirement of the system is a high resolution. Thinlayers (< 10 mm) should be measured reliably. For that reasonthe pulse width must be sufficiently small. In this casea pulse width about 100 ps is suitable. It is obvious, that ahigh bandwidth of the whole system is necessary to providethe precision and the resolution. One further requirement is anearly jitter free generation of two pulse trains with slightlydifferent pulse repetition rates. These pulse trains are usedfor sequential sampling. The following analog to digital conversionof the received signal occurs at a relatively slow rate,in order to allow an A/D conversion with a high resolution.

[学科分类] 电子、光学、磁材料