초록 ▼

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

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.

대표청구항 ▼

1. 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 t

1. 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. 2. The guided wave radar transmitter of claim 1 whereinthe reflected signal selectively including a level pulse representing material along length of the probe; and 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. 3. The guided wave radar transmitter of claim 2 further comprising a processing circuit connected to the controller for selectively resetting the latching comparator for each cycle and measuring round trip travel time for a pulse from the pulse circuit.4. The guided wave radar transmitter of claim 2 wherein the latching comparator compares the reflected signal to a reference signal to detect the fiducial pulse.5. The guided wave radar transmitter of claim 2 wherein the latching comparator comprises an operational amplifier having a diode connected between its output and an input to latch the comparator.6. The guided wave radar transmitter of claim 1 whereinthe reflected signal selectively including a level pulse representing material along length of the probe; and the controller including a signal 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. 7. The guided wave radar transmitter of claim 6 wherein the proportional threshold circuit generates a threshold value as a fraction of a peak of the reflected signal.8. The guided wave radar transmitter of claim 6 further comprising a processing circuit connected to the controller for selectively coupling the fixed threshold circuit or a proportional threshold circuit to the signal comparator.9. The guided wave radar transmitter of claim 1 wherein the selector means comprises a processing circuit connected to the controller.10. The guided wave radar transmitter of claim 9 wherein the processing circuit receives an output from the negative comparator and the positive comparator and detects the fiducial pulse from a falling edge of a first pulse from the negative comparator or from a leading edge of a first pulse from the positive comparator.11. The guided wave radar transmitter of claim 1 whereinthe reflected signal selectively including pulses representing impedance changes along length of the probe; and the controller including a signal comparator receiving the reflected signal for comparing the reflected signal to a signal 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 signal comparator to generate the signal reference signal to selectively control a reference value. 12. The guided wave radar transmitter of claim 11 wherein the gain selection circuit comprises a plurality of resistors each connected by a switch between a voltage reference and the signal comparator and the switches are operated by the selector means.13. The guided wave radar transmitter of claim 12 wherein the gain selection circuit comprises two switches providing four stages of gain.14. The guided wave radar transmitter of claim 12 wherein the switches comprise analog switches and further comprising a processing circuit controlling the analog switches.15. The guided wave radar transmitter of claim 11 wherein the selector means comprises a processing circuit connected to the controller.