Patent ID: 6879282

Claim:
A guided wave radar transmitter comprising: a probe defining a transmission line and including a reference marker proximate a top end of the probe, the probe comprising one of a single rod probe, a coaxial probe or a twin rod probe; a pulse circuit connected to the probe for generating pulses on the transmission line and receiving a reflected signal from the transmission line, the reflected signal selectively including a fiducial pulse representing the reference marker, the fiducial pulse being a negative pulse for a coaxial probe or a twin rod probe and being a positive pulse for a single rod probe; and a controller operatively connected to the pulse circuit, the controller comprising a negative comparator for detecting a negative pulse and a positive comparator for detecting a positive pulse, each said comparator comparing the reflected signal to a select reference signal, and selector means for selectively operating one of the negative comparator and the positive comparator according to the type of probe being used for detecting the fiducial pulse.