Stable differential pressure measuring system

• US 6,564,642 B1
• Filed: 11/02/2000
• Issued: 05/20/2003
• Est. Priority Date: 11/02/2000
• Status: Expired due to Term

• Current Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Original Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Inventors: Clifford, Mark J.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): ALLEN, ANDRE J
• Application Number:
  US09/704,376
• Time in Patent Office: 929 Days
• Field of Search: 737/18, 737/15, 737/20, 737/21, 737/24, 737/36, 737/54, 737/16
• US Class Current: 73/718
• CPC Class Codes: G01L 15/00 Devices or apparatus for measuring two or more fluid pressure values simultaneously
• CPC Class Codes: G01L 19/0038 being part of the housing other details about the housing G01L19/14
• CPC Class Codes: G01L 19/143 Two part housings
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/125 with temperature compensating means non electric temperature compensating means G01L19/04

Abstract

The present invention provides a stable differential pressure measurement system. Two micro-machined semiconductive capacitive sensors each has a diaphragm exposed on one side and having a sealed partially evacuated chamber within the sensor on the other side of the diaphragm. A circuit corrects the slope responses and offsets of the capacitive sensor output signals to provide an accurate differential pressure measurement. Sensitive electronics are buried within the sensors and isolated within the sealed housing to protect them from harsh surrounding media. Such harsh surrounding media can be found when the system is used in an automobile exhaust system.

Claims

1. A stable differential pressure measurement system comprising:

a first micro-machined semiconductive capacitive sensor including a first diaphragm exposed on one side and having a sealed partially evacuated chamber within the first sensor on the other side of the first diaphragm, said first sensor signal proportional to the difference between a first pressure applied across the exposed side of the first diaphragm and a second pressure applied across the chamber side of the first diaphragm;

a second micro-machined semiconductive capacitive sensor including a second diaphragm exposed on one side and having a second sealed partially evacuated chamber within the second sensor on the other side of the second diaphragm, said second sensor providing a second sensor signal proportional to the difference between a third pressure applied across the exposed side of the second diaphragm and a fourth pressure applied across the chamber side of the second diaphragm; and

circuitry for receiving the first and second sensor signals and producing a differential-pressure output signal.

2. A system as defined in claim 1 wherein the first and second partially evacuated chambers have different pressures.

3. A system as defined in claim 1, further comprising:

a first substrate section;

a second substrate section;

a first chimney;

a second chimney;

and wherein;

the first sensor is fixed relative to the first substrate section and is within the first chimney having a substantially fluid-tight attachment to the first substrate section; and

the second sensor is fixed relative to the second substrate section and is within the second chimney having a substantially fluid-tight attachment to the second substrate section.

4. A system as defined in claim 3 wherein:

the first sensor is surrounded by the first substrate section and a first mass of gel; and

the second sensor is surrounded by the second substrate section and a second mass of gel.

5. A system as defined in claim 3 further comprising:

a housing;

first and second intakes;

wherein the first intake structurally cooperates with the first chimney to form a substantially fluid-tight path between the first intake and the first chimney such that a first fluid path exists from the first intake to the first chimney, and the second intake structurally cooperates with the second chimney to form a substantially fluid-tight path between the second intake and the second chimney such that a second fluid path exists from the second intake to the second chimney; and

wherein the first and second chimneys form a substantially fluid-take space within the housing.

6. A system as defined in claim 5 wherein:

the circuitry for combining the first and second signals to produce the differential pressure output signal is located within the substantially fluid-tight space within the housing and is electrically connected to the first and second capacitive sensors.

7. A system as defined in claim 3 wherein:

a first reference capacitor having a capacitance substantially independent of pressure is within the first chimney and is electrically connected to the first sensor; and

a second reference capacitor having a capacitance substantially independent of pressure is within the second chimney and is electrically connected to the second sensor.

8. A system as defined in claim 7 further comprising:

a first integrated circuit;

a second integrated circuit;

and wherein;

the first sensor and first reference capacitor are formed on a first integrated circuit within the first chimney; and

the second sensor and second reference capacitor are formed on a second integrated circuit within the first chimney.

9. A system as defined in claim 5 wherein, responsive to a pressure span, the first sensor signal responds with a slope response different than a slope response of the second sensor signal;

the system including;

circuitry for adjusting the slope responses of the first and second sensor signals to corresponds to a standard slope and providing slope adjusted first and second signals dependent on the adjusted slope responses; and

wherein the output signal is dependent on a difference between the slope adjusted first signal and the slope adjusted second signal.

10. A system as defined in claim 9 further comprising:

offset circuitry for providing an offset signal, and wherein the output signal depends on the offset signal.

11. A system as defined in claim 9 wherein the circuitry for adjusting other increases or decreases the slope responses of the first and second sensor signals to correspond.

12. A system as defined in claim 1 wherein, responsive to a pressure span, the first sensor signal responds with a slope response difference than a slope response of the second sensor signal;

the system including;

first and second conditioners;

first and second adjustable reference voltage sources electrically connected to the first and second conditioners, respectively, for providing first and second reference voltages to the first and second conditioners, respectively;

wherein the circuitry for combining the first and second signals to produce a differential-pressure output signal includes a differential amplifier;

wherein the conditioners adjust the slope responses of the first and second sensor signals, according to the reference voltages, to correspond to a standard slope and provides adjusted first and second slope responses to the positive and negative inputs of the differential amplifier; and

wherein the differential amplifier subtracts the first and second signals to produce a differential-pressure output signal.

13. A system as defined in claim 12 further comprising:

an offset adjustment operational amplifier having an output electrically connected to a first input of the differential amplifier for adjusting the relative offsets of the adjusted first and second slope responses;

an offset adjustment reference voltage source electrically connected to the offset adjustment operational amplifier for providing an offset adjustment reference voltage to the offset adjustment operational amplifier for adjusting the amount of offset adjustment.

14. A system as defined in claim 13 further comprising:

a time response control circuit portion electrically connected in to a second input of the differential amplifier.

15. An exhaust system for an engine comprising:

exhaust and intake manifolds;

first and second nozzles;

first and second conduits connecting the first nozzle to the exhaust manifold and the second nozzle to the intake manifold;

a first capacitive sensor including a first diaphragm exposed on one side through the first nozzle and first conduit to the exhaust manifold and having a sealed partially evacuated chamber within the first sensor on the other side of the first diaphragm, said first sensor providing a first sensor signal proportional to the difference between a first pressure applied across the exposed side of the first diaphragm and a second pressure applied across the chamber side of the first diaphragm;

a second capacitive sensor including a second diaphragm exposed on one side through the second nozzle and second conduit to the intake manifold and having a second sealed partially evacuated chamber within the second sensor on the other side of the second diaphragm, said second sensor providing a second sensor signal proportional to the difference between a third pressure applied across the exposed side of the second diaphragm and a fourth pressure applied across the chamber side of the second diaphragm; and

circuitry for receiving the first and second sensor signals and producing a differential pressure output signal representing the differential pressure between the exhaust and intake manifolds.

16. A system as described in claim 15 wherein said sensors are micro-machined semiconductive capacitors.

17. A method for performing a differential pressure measurement comprising the steps of:

transporting a first fluid through a first intake to exert a first force on a first mass of gel, the gel transferring the force to a first micro-machined semiconductive capacitive sensor;

transporting a second fluid through a second intake to exert a second force on a second mass of gel, the gel transferring the force to a second micro-machined semiconductive capacitive sensor;

producing, from said first and second sensors, first and second sensor signals proportional to the first and second forces exerted on the first and second capacitive sensors;

inputting the first sensor signal into a first conditioner;

inputting a first reference voltage into the first conditioner

adjusting the first reference voltage to adjust the slope response of the first sensor output signal to correspond to a standard slope;

inputting the second sensor signal into a second conditioner;

inputting a second reference voltage into the second conditioner;

adjusting the second reference voltage to adjust the slope response of the second sensor signal to correspond to the standard slope; and

combining outputs from the first and second conditioners to produce a differential-pressure output signal.

18. A method for performing a differential pressure measurements as defined in claim 17, further comprising the step of:

adjusting the offset of the first and second slope adjusted sensor signals.

19. A method for performing a differential pressure measurement as defined in claim 17, further comprising the step of:

inputting first and second reference capacitor signals into the first and second conditioners to correct for temperature effects.

20. A stable differential pressure measurement system comprising:

a first sensor including a first diaphragm exposed on one side and having a sealed partially evacuated chamber within the first sensor on the outer side of the first diaphragm, said first sensor providing a first sensor signal proportional to the difference between a first pressure applied across the exposed side of the first diaphragm and a second pressure applied across the chamber side of the first diaphragm;

a second sensor including a second diaphragm exposed on one side and having a second sealed partially evacuated chamber within the second sensor on the other side of the second diaphragm, said second sensor providing a second sensor proportional to the difference between a third pressure applied across the exposed side of the second diaphragm and a fourth pressure applied across the chamber side of the second diaphragm; and

circuitry for receiving and combining the first and second sensor signals to produce a differential-pressure output signal.

21. A system as defined in claim 20, wherein said sensors are capacitive sensors.