Vibrating fork liquid level switch with verification

Patent metadata

Field	Value
Publication number	US-11828641-B2
Application number	US-202217699526-A
Country	US
Kind code	B2
Filing date	Mar 21, 2022
Priority date	Mar 21, 2022
Publication date	Nov 28, 2023
Grant date	Nov 28, 2023

Abstract

A vibrating fork liquid level switch includes a vibrating fork assembly arranged to vibrate at a first frequency when in contact with a process fluid and at a second frequency when in contact with air. A drive circuit connected to the vibrating fork assembly is configured to drive the vibrating fork assembly into oscillation. Sense circuitry senses an oscillation frequency of the vibrating fork assembly. Output circuitry provides a first output when the sensed oscillation is at the first frequency and a second output when the sensed oscillation is at the second frequency. Control circuitry controls power applied to the vibrating fork assembly by the drive circuit between a first and a second power level. Verification circuitry verifies the oscillation frequency of the vibrating fork assembly when power applied to the vibrating fork assembly by the drive circuitry is changed.

First claim

What is claimed is:

1. A vibrating fork liquid level switch, comprising:
a vibrating fork assembly arranged to vibrate at a first frequency when in contact with a process fluid and at a second frequency when in contact with air;
a drive circuit comprising an oscillator connected to the vibrating fork assembly configured to drive the vibrating fork assembly into oscillation;
sense circuitry configured to sense an oscillation frequency of the vibrating fork assembly;
output circuitry configured to provide a first output when the sensed oscillation is at the first frequency and a second output when the sensed oscillation is at the second frequency;
control circuitry configured to control power applied to the vibrating fork assembly by the oscillator of the drive circuit between a first and a second power level; and
verification circuitry configured to verify the oscillation frequency of the vibrating fork assembly when power applied to the vibrating fork assembly by the oscillator of the drive circuitry is changed.

2. The vibrating fork liquid level switch of claim 1 including a switch configured to be operated by the control circuitry to selectively disconnect the drive circuit from the vibrating fork assembly, and thereby control the power applied to the vibrating fork assembly.

3. The vibrating fork liquid level switch of claim 2 wherein the verification circuitry is configured to measures a first oscillation frequency of the vibrating fork assembly when the switch is closed.

4. The vibrating fork liquid level switch of claim 3 where in the control circuit is configured to opens the switch for a period of time and subsequently closes the switch, and the verification circuity is configured to measures a second oscillation frequency of the vibrating fork assembly when the switch is subsequently closed.

5. The vibrating fork liquid level switch of claim 4 including a frequency comparator configured to verify the oscillation frequency of the vibrating fork assembly by comparing the first and second oscillation frequencies.

6. The vibrating fork liquid level switch of claim 1 wherein the control circuitry is configured to adjusts a power level applied by the drive circuit to the vibrating fork assembly.

7. The vibrating fork liquid level switch of claim 1 wherein the control circuitry is configured to controls power applied to the vibrating fork assembly by the drive circuit to the first power level, subsequently to the second power level and subsequently to the first power level.

8. The vibrating fork liquid level switch of claim 7 wherein the verification circuitry is configured to measures the oscillation frequency when the drive circuit is at the first power level prior to the second power level.

9. The vibrating fork liquid level switch of claim 8 wherein the verification circuit is configured to measures a second oscillation frequency of the vibrating fork assembly when the drive circuit is operated at the first power level subsequent to being operated at the second power level.

10. The vibrating fork liquid level switch of claim 9 wherein the verification circuitry is configured to compares the first oscillation frequency with the second oscillation frequency and responsively provides a verification output.

11. The vibrating fork liquid level switch of claim 1 wherein the verification circuitry is implemented in a microcontroller.

12. The vibrating fork liquid level switch of claim 1 wherein a the verification circuitry is configured to perform a verification test in response to a receipt of a command received locally.

13. The vibrating fork liquid level switch of claim 1 wherein a the verification circuitry is configured to perform a verification test in response to a receipt of a command received from a remote location.

14. The vibrating fork liquid level switch of claim 1 wherein the first and second outputs are provided on a two-wire process control loop.

15. A method for operating a vibrating fork liquid level switch, comprising:
causing a vibrating fork assembly to vibrate at a first frequency when in contact with a process fluid and at a second frequency when in contact with air;
driving the vibrating fork assembly into oscillation using an oscillator of a drive circuit;
sensing an oscillation frequency of the vibrating fork assembly; and
providing a first output when the sensed oscillation is at a first frequency and a second output when the sensed oscillation is at a second frequency;
controlling power applied to the vibrating fork assembly from the oscillator between a first and a second power level; and
verifying operation of the vibrating fork liquid level switch based upon frequency of the vibrating fork assembly when power applied to the vibrating fork assembly from the oscillator is changed.

16. The method of claim 15 including controlling a switch to selectively disconnect drive circuit from the vibrating fork assembly.

17. The method of claim 15 includes adjusting a power level applied by the drive circuit to the vibrating fork assembly.

18. The method of claim 15 including controlling power applied to the vibrating fork assembly to the first power level, subsequently to the second power level and subsequently to the first power level.

19. The method of claim 15 wherein verifying includes measuring the oscillation frequency when vibrating fork assembly is at the first power level prior to the second power level.

20. The method of claim 19 wherein verifying includes measuring a second oscillation frequency of the vibrating fork assembly when the drive circuit is operated at the first power level subsequent to being operated at the second power level.

21. The method of claim 20 wherein verifying includes comparing the first oscillation frequency with the second oscillation frequency and responsively provides a verification output.

22. The method of claim 15 wherein the verifying is performed in response to a receipt of a command.

Assignees

• Rosemount Inc

Inventors

• Collins-Dippel Sean Daniel

Classifications

• G01F23/22 Primary

  by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water (involving the use of floats G01F23/30) · CPC title

• G01F25/20

  of apparatus for measuring liquid level · CPC title

• G01F23/2967 Primary

  for discrete levels · CPC title

• H01H35/18 Primary

  Switches operated by change of liquid level or of liquid density, e.g. float switch (by magnet carried on a float H01H36/02) · CPC title

• H01H9/54

  Circuit arrangements not adapted to a particular application of the switching device and for which no provision exists elsewhere · CPC title