A guided wave radar measurement instrument comprises a probe defining a
guided wave radar transmission line. A pulse circuit is connected to the
probe for generating a very fast stream of pulses on the transmission line
and receiving reflected pulses returned on the transmission line. The
reflected pulses represent a characteristic of a material being measured.
An equivalent time sampling circuit is connected to the pulse circuit
operable to sample reflected pulses to build a time multiplied picture of
the reflected pulses and comprises a ramp generator circuit generating a
saw tooth ramp signal used to selectively delay sampling reflected pulses
to build the time multiplied picture. In one aspect of the instrument, the
saw tooth ramp signal has a controlled ramp start for each cycle and
retrace at an end of the cycle. A processing circuit is connected to the
equivalent time sampling circuit for selectively controlling ramp start
for each cycle and measuring round trip travel time for a pulse from the
pulse circuit.
