Guided wave radar level transmitter with automatic velocity compensation

DETAILED DESCRIPTION In accordance with the invention there is provided a guided wave radar transmitter with automatic velocity compensation.
Broadly, in accordance with one aspect of the invention there is disclosed a guided wave radar transmitter comprising a probe defining a transmission line including a relatively low impedance change target marker above an expected sensing region of the probe.
A pulse circuit is connected to the probe for generating pulses on the transmission line and receiving a reflected signal from the transmission line.
The reflected signal selectively includes a target pulse representing the target marker and a level pulse representing material along the length of the probe.
A controller is operatively connected to the pulse circuit.
The controller normally operates at a relatively low gain to determine a level time to the level pulse to determine material level, and periodically operates at a relatively high gain to determine a target time to the target pulse.
The target time is used to compensate the level time for properties of vapor above the material level.
There is disclosed in accordance with another aspect of the invention a time domain reflectometry measurement instrument including a probe defining a transmission line and including a reference marker proximate a top end of the probe and a relatively low impedance change target marker above an expected sensing region of the probe.
A pulse circuit is connected to the probe for generating pulses on the transmission line and receiving a reflected signal from the transmission line.
The reflected signal selectively includes a fiducial pulse representing the reference marker, a target pulse representing the target marker and a level pulse representing material along the length of the probe.
A time sampling circuit is connected to the pulse circuit for developing a time representation of the reflected signal.
A controller is operatively connected to the pulse circuit and the time sampling circuit.
The controller comprises measurement means operating at a relatively low gain for determining a level time between the fiducial pulse and the level pulse to determine material level