Method for measuring a fluid composition parameter by means of a flow sensor

• US 20100089118A1
• Filed: 08/25/2009
• Published: 04/15/2010
• Est. Priority Date: 10/09/2008
• Status: Active Grant

• Current Assignee: Sensirion AG (Sensirion Holding AG)
• Original Assignee: Sensirion AG (Sensirion Holding AG)
• Inventors: Hornung, Mark, Wehrli, Samuel, Mayer, Felix
• Granted Patent: US 8,408,050 B2
• Time in Patent Office: Days
• US Class Current: 73/1.160
• CPC Class Codes: G01F 1/692 Thin-film arrangements
• CPC Class Codes: G01N 27/18 caused by changes in the thermal conductivity of a surrounding material to be tested G01N27/20 takes precedence

Abstract

The flow of a fluid of unknown composition is measured by leading the fluid over a first temperature sensor, a heater and a second temperature sensor. The temperature difference DTP between the temperature sensors is measured, as well as the temperature T of at least one of them. In addition, calibration data is used to store the temperature Tref of a known reference fluid. The offset T−Tref at a given temperature difference DTP is a direct measure of the composition of the fluid and allows to retrieve any parameter depending on the same.

Claims

1. A method for measuring a parameter depending on the composition of an unknown fluid by means of a flow sensor, wherein said flow sensor comprises a heater arranged between a first and a second temperature sensor, said method comprising the steps of

leading said unknown fluid over said first temperature sensor, said heater and said second temperature sensor,

measuring a temperature difference DTP between a temperature TP2 at said second temperature sensor and a temperature TP1 at said first temperature sensor as well as a single temperature T, which single temperature is equal to k1.TP1+k2.TP2 with k1≠

−

k2,

retrieving first calibration data, which first calibration data was obtained from a calibration measurement carried out with a reference fluid of known composition, and which first calibration data is such that it allows to calculate the value of the single temperature that the reference fluid exhibited at a given temperature difference,

using said first calibration data to calculate a reference temperature Tref(DTP) equal to the single temperature of said reference fluid at said temperature difference DTP, and

deriving said parameter from a temperature offset D=T−

Tref(DTP) between said single temperature T measured for said unknown fluid at said temperature difference DTP and the single temperature of said reference fluid at said temperature difference DTP.

2. The method of claim 1 wherein said single temperature T is the temperature measured by said first temperature sensor.

3. The method of claim 1 wherein said single temperature T is the temperature measured by said second temperature sensor.

4. The method of claim 1 comprising the step of providing second calibration data for calculating said parameter from said temperature offset D.

5. The method of claim 4 wherein said second calibration data relates said temperature offset D and a fluid temperature TF to said parameter.

6. The method of claim 1 wherein in said step of deriving said parameter from the offset D said parameter is determined as a function of said temperature offset D and a fluid temperature TF.

7. The method of claim 1 wherein said unknown fluid is a mixture of two known fluids and wherein said parameter is a mixture ratio of said known fluids.

8. The method of claim 1 wherein said flow sensor comprises a substrate having an opening or recess and a membrane arranged over said opening or recess, and wherein said temperature sensors and said heater are arranged at least partially on said membrane.

9. The method of claim 1 wherein said temperature difference DTP and said single temperature T are measured at non-zero flow.

10. The method of claim 1 wherein said temperature difference DTP and said single temperature T are measured for a laminar flow of said unknown fluid.

11. The method of claim 1 wherein said flow sensor comprises an interface to external circuitry and said method comprises the step of providing said offset D at said interface.