Temperature compensation module for a fluid flow transducer

Patent metadata

Field	Value
Publication number	US-9255826-B2
Application number	US-201313943551-A
Country	US
Kind code	B2
Filing date	Jul 16, 2013
Priority date	Jul 16, 2013
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

Apparatus and associated methods relate to a temperature-compensated drive for a heating element used in a micro-bridge flow sensor. In some embodiments, the heating element may be located substantially between two temperature sensors. The two temperature sensors may be convectively coupled to the heater by a fluid ambient. When the fluid ambient is flowing, one of the temperature sensors may be upstream of the heating element, and one of the temperature sensors may be downstream. The fluid may be heated by the heating unit, and this heated fluid may then flow past the downstream temperature sensor. The two temperature sensors may be used in a Wheatstone bridge configuration. In some embodiments, an output signal of the Wheatstone bridge may be indicative of a measure of fluid flow. The temperature-compensated drive for the heating element may enhance, for example, the flow meter's disturbance rejection of ambient temperature.

First claim

What is claimed is:

1. A Micro ElectroMechanical Systems (MEMS) die, comprising:
a heating element configured to be substantially in direct thermal coupling with a fluid ambient;
a first temperature sensor configured to be substantially in direct thermal coupling with the fluid ambient;
a second temperature sensor configured to be substantially in direct thermal coupling with the fluid ambient, wherein the heating element is located substantially between the first temperature sensor and the second temperature sensor, and wherein the heating element is convectively coupled to the first temperature sensor and the second temperature sensor via the fluid ambient;
a differential amplifier configured to receive a first signal output by the first temperature sensor and a second signal output by the second temperature sensor, the differential amplifier having an output signal indicative of a flow of the fluid ambient, wherein the signal indicative of the flow of the fluid ambient has a temperature disturbance; and,
a heating-element bias circuit comprising a temperature-varying reference and an amplifier, the temperature-varying reference having an output connected to an input of the amplifier, and wherein the temperature-varying reference output varies in response to a substrate temperature of the MEMS die,
wherein the heating-element bias circuit provides a temperature-varying bias that substantially compensates for the temperature disturbance of the signal indicative of the flow of the fluid ambient.

2. The MEMS die of claim 1 , wherein the heating-element bias circuit comprises a resistor having a magnitude of temperature coefficient of resistance greater than 1000 ppm/° C.

3. The MEMS die of claim 1 , wherein the signal indicative of a flow of the fluid ambient has a temperature coefficient of less than 450 ppm/° C. for a measured flow of a predetermined full-scale.

4. The MEMS die of claim 1 , further comprising a temperature sensor coupled to the MEMS die, the temperature sensor generating an output indicative of the substrate temperature of the MEMS die.

5. The MEMS die of claim 1 , further comprising a gain/offset compensation circuit, wherein the gain/offset compensation circuit receives the signal indicative of the flow of the fluid ambient and generates an output indicative of the flow, the output calibrated to a predetermined reference standard.

6. The MEMS die of claim 1 , wherein the output of the temperature-varying reference is programmable.

7. The MEMS die of claim 1 , further comprising
a third temperature sensor; and,
a fourth temperature sensor,
wherein both the third temperature sensor and the fourth temperature sensor are configured to be substantially in direct thermal coupling with the fluid ambient,
wherein the heating element is located substantially between the third temperature sensor and the fourth temperature sensor, and
wherein the heating element is convectively coupled to the third temperature sensor and the fourth temperature sensor via the fluid ambient.

8. The MEMs die of claim 1 , wherein the temperature-varying reference comprises a band-gap reference which generates a voltage that is Proportional To Absolute Temperature (PTAT).

9. The MEMs die of claim 1 , wherein the temperature-varying reference is configured to be trimmed.

10. The MEMs die of claim 1 , wherein the fluid ambient comprises a gaseous ambient.

11. A fluid flow sensor, comprising:
A Micro ElectroMechanical Systems (MEMS) microbridge flow sensor comprising a heater, a first temperature sensor, and a second temperature sensor, the heater located substantially between the first temperature sensor and the second temperature sensor;
a signal conditioner configured to receive a first signal from the first temperature sensor and a second signal from the second temperature sensor, the signal conditioner having an output signal indicative of a flow of a fluid ambient, the output signal indicative of the flow of the fluid ambient having a natural disturbance due to a temperature variation; and,
a bias generator having a temperature-varying output which is electrically connected to the heater, wherein the temperature-varying output compensates for the natural disturbance due to the temperature variation.

12. The fluid flow sensor of claim 11 , wherein the signal indicative of the flow of the fluid ambient has a temperature coefficient of less than 450 ppm/° C. for a measured flow of a predetermined full-scale.

13. The fluid flow sensor of claim 11 , wherein the MEMS microbridge flow sensor, the signal conditioner, and the bias generator are all manufactured on the same MEMs die.

14. The fluid flow sensor of claim 11 , wherein the temperature-varying output of the bias generator is programmable.

15. The fluid flow sensor of claim 11 , wherein the bias generator comprises a temperature-varying reference and an amplifier.

16. A fluid flow sensor, comprising:
A Micro ElectroMechanical Systems (MEMS) microbridge flow sensor comprising a heater, a first temperature sensor, and a second temperature sensor, the heater located substantially between the first temperature sensor and the second temperature sensor;
a signal conditioner configured to receive a first signal from the first temperature sensor and a second signal from the second temperature sensor, the signal conditioner having an output signal indicative of a flow of a fluid ambient, the output signal indicative of a flow of a fluid ambient having a natural disturbance due to a temperature variation; and,
means for biasing the heater such that the signal indicative of the flow of the fluid ambient is substantially temperature-invariant.

17. The fluid flow sensor of claim 16 , wherein means for biasing the heater comprises:
means for generating a temperature-varying bias; and,
means for electrically communicating the temperature-varying bias to the heater.

18. The fluid flow sensor of claim 16 , wherein means for biasing the heater comprises:
means for generating a temperature-varying reference, and
a buffer.

19. The fluid flow sensor of claim 18 , wherein means for generating a temperature-varying reference comprises:
means for generating a current,
a resistor with a magnitude of temperature coefficient of resistance greater than 1000 ppm/° C.

20. The fluid flow sensor of claim 18 , wherein means for generating a temperature-varying reference comprises:
means for generating a temperature-varying current,
a MEMS based resistor.

Assignees

• Honeywell Int Inc

Inventors

• Milley Andrew Joseph
• Ricks Lamar Floyd
• Becke Craig Scott

Classifications

• G01F1/698 Primary

  Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters · CPC title

• G01F15/022

  using electrical means · CPC title

• G01F1/6845

  Micromachined devices · CPC title

• G01F1/692

  Thin-film arrangements · CPC title

• G01F1/6965

  comprising means to store calibration data for flow signal calculation or correction · CPC title