Low power radar level transmitter having reduced ground loop errors

• US 6,320,532 B1
• Filed: 05/27/1999
• Issued: 11/20/2001
• Est. Priority Date: 05/27/1999
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Diede, Kurt C.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/321,143
• Time in Patent Office: 908 Days
• Field of Search: 342/124, 342/135, 342/159, 342/198, 342/203
• US Class Current: 342/124
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G01S 13/88 Radar or analogous systems specially adapted for specific applications electromagnetic prospecting or detecting of objects, e.g. near-field detection, G01V3/00
• CPC Class Codes: G01S 7/28 Details of pulse systems

Abstract

A low power radar level transmitter having reduced ground loop errors and a related method are disclosed. A microwave termination is couplable to a reference voltage such as earth ground and is coupled to a microwave transceiver through at least one low frequency isolator. The microwave transceiver generates a microwave signal along the termination which is reflected by a process product interface. A level calculator is coupled to the microwave transceiver to calculate a level of the process product based upon the received, reflected signal. A process loop communicator is coupled to the level calculator and couplable to a process control loop to communicate the calculated level across the process control loop. A power supply is couplable to the process control loop and provides power to all electrical components of the transmitter with energy received from the process control loop.

Claims

1. A low power radar level transmitter having reduced ground loop errors, the transmitter comprising:

a termination electrically couplable to a reference voltage and extendable into a process product;

a low power microwave transceiver electrically coupled to the termination, the transceiver being adapted to generate a microwave signal with the termination and receive a reflected microwave signal from the process product;

a level calculator electrically coupled to the microwave transceiver;

a loop communicator electrically coupled to the level calculator and electrically couplable to a process control loop;

a power supply electrically coupled to the level calculator, the loop communicator, and the microwave transceiver and electrically couplable to the process control loop;

a first low frequency isolator coupling the microwave transceiver to the termination; and

a second low frequency isolator coupling the microwave transceiver to the reference voltage.

2. The transmitter of claim 1, wherein at least one of the low frequency isolators comprises a capacitor.

3. The transmitter of claim 2, wherein the capacitor is a discrete component.

4. The transmitter of claim 2, wherein the capacitor comprises a pair of coplanar circuit traces disposed with respect to each other to provide a capacitance.

5. The transmitter of claim 1, wherein the process control loop is a 4-20 mA process control loop.

6. The transmitter of claim 5, wherein the transmitter is powerable solely with power received front the process control loop.

7. The transmitter of claim 1, wherein the termination is a twin-line termination.

8. The transmitter of claim 1, wherein the process control loop is a two-wire process control loop.

9. The transmitter of claim 1, wherein the process control loop operates in accordance with Foundation Fieldbus.

10. The transmitter of claim 1, wherein the low power microwave transceiver is a micropower impulse radar transceiver.

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

12. A low power radar level transmitter having reduced ground loop errors, the transmitter comprising:

a termination electrically couplable to a reference voltage and extendable into a process product;

a low power microwave transceiver electrically coupled to the termination, the transceiver being adapted to generate a microwave signal with the termination and receive a reflected microwave signal from the process product;

a level calculator electrically coupled to the microwave transceiver;

a loop communicator electrically coupled to the level calculator and electrically couplable to a two-wire process control loop;

a power supply electrically coupled to the level calculator, the loop communicator, and the microwave transceiver and electrically couplable to the two-wire process control loop;

a first bandpass filter coupling the microwave transceiver to the termination; and

a second bandpass filter coupling the microwave transceiver to the reference voltage.

13. A method of calculating a height of a process product with a low power radar level transmitter, the method comprising;

a generating a microwave signal;

passing the microwave signal through a low frequency isolator to inhibit direct current flow;

receiving a microwave signal reflected from the process product; and

calculating the height of the process product based upon the received, reflected microwave signal.

14. The method of claim 13, wherein receiving the microwave signal includes filtering interference.

15. The method of claim 14, wherein the interference has a frequency of less than about 100 Hertz.

16. A low power radar level transmitter having reduced ground loop errors, the transmitter comprising:

means for guiding microwave signals, the guiding means couplable to earth ground;

means for generating a microwave signal along the guiding means and receiving a reflected microwave signal indicative of process product height;

means for calculating process product height based upon the reflected microwave signal;

means for transmitting information related to the process product height over a two-wire process control loop;

means for receiving power from the loop to power the transmitter; and

means for passing microwave signals between the generating means and the guiding means, and blocking substantially all other signals.