Low power radar level instrument with enhanced diagnostics

• US 6,295,018 B1
• Filed: 09/27/1999
• Issued: 09/25/2001
• Est. Priority Date: 09/27/1999
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Lovegren, Eric R., Diede, Kurt C.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/407,041
• Time in Patent Office: 729 Days
• Field of Search: 342/124, 342/173, 342/174, 342/175, 73/290 R, 73/866.5
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves

Abstract

A low power radar level instrument with enhanced diagnostics is disclosed. A microwave transceiver generates a microwave signal that travels along a termination, through a reference impedance discontinuity, and into a process product interface. A first portion of the signal is reflected by the reference impedance discontinuity, and a second portion is reflected by a process product interface. A diagnostic signal is provided based upon a characteristic of the first reflected portion. A level output is provided based upon the first and second reflected portions.

Claims

1. A low power radar level instrument with enhanced diagnostics, the instrument comprising:

a probe having a reference impedance discontinuity and extendable into a process product through a process product interface;

a transceiver coupled to the probe, the transceiver adapted to generate a microwave transmit pulse which is transmitted along the probe into the process product, a first portion of the transmit pulse being reflected at the reference impedance discontinuity and forming a first reflected wave pulse, and a second portion of the transmit pulse being reflected at the product interface and forming a second reflected wave pulse, wherein the transceiver is also adapted to receive the reflected first and second portions; and

a processor coupled to the transceiver and adapted to provide a diagnostic signal as a function of amplitude of the reflected first portion, and adapted to provide a level output indicative of process product height based upon time of detection of the reflected second portion.

2. The instrument of claim 1, wherein the reference impedance discontinuity comprises a launch plate.

3. The instrument of claim 1, wherein the transceiver is a micropower impulse radar transceiver.

4. The instrument of claim 1, wherein the instrument is a radar level transmitter couplable to a process control loop, and adapted to transmit the level output on the process control loop.

5. The instrument of claim 4, and further comprising a loop communicator adapted to transmit the level output in accordance with a process industry standard protocol.

6. The instrument of claim 5, wherein the protocol is selected from the group consisting of Highway Addressable Remote Transducer, and FOUNDAION Fieldbus.

7. The instrument of claim 4, wherein the process control loop is a 4-20 mA process control loop.

8. The instrument of claim 4, wherein the transmitter is wholly powered by the process control loop.

9. The instrument of claim 1, wherein the diagnostic output is indicative of a condition in which the probe is fully submersed by process fluid.

10. The instrument of claim 1, wherein the diagnostic output is indicative of a condition in which the probe is disconnected from the instrument.

11. The instrument of claim 1, wherein the pulse width of the microwave transmit pulse ranges from about 200 picoseconds to about 2 nanoseconds.

12. The instrument of claim 1, wherein the diagnostic signal is based upon a comparison of amplitude of the reflected first portion and at least one pre-selected limit.

13. The instrument of claim 12, wherein the at least one pre-selected limit includes an upper limit and a lower limit.

14. A low power radar level instrument with enhanced diagnostics, the instrument comprising:

means for guiding microwave energy through a reference impedance discontinuity and into a process product through a process product interface;

means for generating a microwave transmit pulse that is transmitted along the means for guiding, a first portion of the transmit pulse being reflected at the reference impedance discontinuity and forming a first reflected wave pulse, and a second portion of the transmit pulse being reflected at the product interface and forming a second reflected wave pulse;

means for receiving the reflected wave pulses; and

means for providing a diagnostic signal as a function of amplitude of the reflected first portion, and for providing a level output indicative of process product height based upon time of detection of the reflected second portion.

15. A method of providing enhanced diagnostics with a low power radar level instrument, the method comprising:

generating a microwave transmit pulse and directing the transmit pulse through a reference impedance discontinuity;

receiving a first reflected wave from the reference impedance discontinuity; and

providing a diagnostic output based upon a characteristic of the first reflected wave.

16. The method of claim 15, wherein the characteristic is wave amplitude.

17. The method of claim 15, wherein the diagnostic output is indicative of whether the reference discontinuity is at least partially submerged in process fluid.

18. The method of claim 15, wherein the diagnostic output is indicative of a electrical break in a microwave waveguide.

19. The method of claim 15, and further comprising:

directing the microwave transmit pulse to a process product interface;

receiving a second reflected wave portion from the process product interface;

providing a process product level output based upon reception of the second reflected wave portion.

20. The method of claim 15, wherein providing the diagnostic output includes comparing the amplitude of the first reflected wave with at least one pre-selected limit.

21. A computer readable medium having stored instructions for execution on a processor associated with a low-power radar level instrument, the medium comprising:

instructions for causing a low-power microwave instrument to generate a microwave transmit pulse that is transmitted along a waveguide, a first portion of the transmit pulse being reflected at a reference impedance discontinuity and forming a first reflected wave pulse, and a second portion of the transmit pulse being reflected at a product interface and forming a second reflected wave pulse;

instructions for receiving the reflected wave pulses; and

instructions for providing a diagnostic signal as a function of amplitude of the reflected first portion, and for providing a level output indicative of process product height based upon time of detection of the reflected second portion.