Guided wave radar level transmitter

A process instrument comprising:

• a housing;
• a probe for sensing a characteristic of a process;
• a control circuit disposed in the housing and electrically connected to the probe for measuring the sensed characteristic;
• and
• a safety barrier comprising a plurality of series connected capacitors electrically connected between the control circuit and the probe.

A guided wave radar measurement instrument comprising:

• a probe defining a guided wave radar transmission line;
• a pulse circuit 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 representing a characteristic of a material being measured;
• an equivalent time sampling circuit connected to the pulse circuit operable to sample reflected pulses to build a time multiplied picture of the reflected pulses, comprising a ramp generator circuit generating a sawtooth ramp signal used to selectively delay sampling reflected pulses to build the time multiplied picture, the sawtooth ramp signal having a controlled ramp start for each cycle and retrace at an end of the cycle;
• and
• a processing circuit 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.

A time domain reflectometry measurement instrument comprising:

• a probe;
• a pulse circuit connected to the probe for generating a very fast stream of pulses on the probe and receiving reflected pulses returned on the probe, the reflected pulses representing a characteristic of a material being measured;
• an equivalent time sampling circuit connected to the pulse circuit operable to sample reflected pulses to build a time multiplied picture of the reflected pulses, comprising a ramp generator circuit generating a sawtooth ramp signal used to selectively delay sampling reflected pulses to build the time multiplied picture, the ramp generator circuit comprising a ramp comparator that latches at a start voltage during each cycle until receiving a start ramp signal and retraces to the start voltage at an end of the cycle;
• and
• a processing circuit connected to the equivalent time sampling circuit for selectively generating the start ramp signal for each cycle and measuring round trip travel time for a pulse from the pulse circuit.

A guided wave radar transmitter comprising:

• a probe defining a transmission line and including a reference marker proximate a top end of the 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 and a level pulse representing material along length of the probe;
• and
• a controller operatively connected to the pulse circuit, the controller determining a level time between the fiducial pulse and the level pulse to determine material level, the controller comprising a latching comparator circuit for detecting the fiducial pulse and enabling level detection.

A guided wave radar transmitter comprising:

• a probe defining a transmission line and including a reference marker proximate a top end of the 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 level pulse representing material along length of the probe;
• and
• a controller operatively connected to the pulse circuit, the controller including a comparator for comparing the reflected signal to a threshold signal, the threshold signal being selected from a fixed threshold circuit or a proportional threshold circuit.

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.

A guided wave radar transmitter comprising:

• a probe defining a transmission line;
• 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 pulses representing impedance changes along length of the probe;
• and
• a controller operatively connected to the pulse circuit, and including a comparator receiving the reflected signal for comparing the reflected signal to a reference signal to detect the pulses, and a gain selection circuit for generating plural levels of gain and selector means for selectively connecting the gain selection circuit to the comparator to generate the reference signal to selectively control a reference value.