Radar level measurement Radar level measurement The user's guide

4. Radar level measurementEmission / Echo pulseSample signalSampling with picosecond switchingSampling by cross correlation with asample pulseFig 4.9 Comparison of switch sampling with ‘cross correlation’ sampling. The pulseradar uses cross correlation with a sample pulse. This means that rapid ‘picosecond’switching is not requiredInstead of taking a short voltagesample, cross correlation involves multiplyinga point on the emission or echosignal by the corresponding point onthe sample pulse. The multiplicationleads to a point on the resultant signal.All of these multiplication results, oneafter the other, lead to the formation ofthe complete multiplication signal.Fig 4.10 shows a short sequence ofmultiplications between the receivedsignal (E) and the sampling pulsesignal (M). The resultant E x M curvesare shown on page 58.Then the E x M curve is integratedand represented on the expanded curveas a dot. The sign and amplitude of thesignal on the time expanded curvedepends on the sum of the area of theE x M curve above and below the zeroline. The final integrated value correspondsdirectly to the time position ofthe received pulse E relative to thesample pulse M.The received signal E and samplesignal M in Fig 4.10 are equivalent tothe periodic signal (sine wave) andsample signal in Fig 4.6. The result ofthe integration of E x M in Fig 4.10 isdirectly analogous to the expandedtime signal in Fig 4.6.57