Method and device for measuring the flow of a fluid
AssigneeSensirion AG
InventorsFelix Mayer, Andreas Martin Haeberli
Life of this patent
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Abstract
To measure the flow in a liquid, the liquid (1) is led in a duct (2) along a flow sensor (3). The flow sensor (3) is integrated together with a processing and control circuit on a semiconductor substrate. It comprises a heating and, symmetrically thereto, two temperature sensors. The flow is determined from the temperature difference between the temperature sensors and/or from the power dissipation of the heating. For calibrating the sensor, a valve (4) is provided by means of which the duct (2) can be interrupted. This arrangement allows a flow measurement of high accuracy.
Claims20
Flow sensor for liquids with a semiconductor substrate (5), wherein a heating element (R1) in thermal contact with the liquid to be measured and at least one temperature sensor (R1;
- 10, 11) in thermal contact with the liquid to be measured are arranged on the semiconductor substrate, characterized in that a processing and control circuit (7) is integrated on the semiconductor substrate (5) for processing signals of the temperature sensor (R1;
- 10, 11).
Flow sensor for liquids of any of the preceding claims characterized in that the processing and control circuit (7) is designed in CMOS technology.
Flow sensor for liquids of any of the preceding claims characterized in that the heating element (R1) serves as temperature sensor.
Flow sensor for liquids of any of the preceding claims characterized in that, in a flow direction before and after the heating element, temperature sensors (10, 11) are arranged and the processing and control circuit (7) is designed for determining a flow velocity from a temperature difference between the temperature sensors (10, 11).
Flow sensor for liquids characterized in that it is designed for determining a flow velocity from a parameter depending on the power dissipation of the heating element (R1).
Flow sensor for liquids of any of the preceding claims, characterized in that two resistors (R1, R2) with substantially equal temperature dependence are arranged on the semiconductor substrate (5), wherein a first one of the resistors is the heating element (R1) and a second one of the resistors is a reference resistor (R2), and that a feedback loop (A, T1, T2) is provided that regulates the power through the first resistor (R1) such that, between the resistors, a fixed temperature difference is established, and in particular that the feedback loop (A, T1, T2) regulates the current in both resistors (R1, R2) proportionally or equally.
Flow sensor for liquids of any of the preceding claims characterized in that the heating element (R1) and the temperature sensor (R1;
- 10, 11) are arranged on a membrane (12), which extends over an opening or recess (13) in the semiconductor substrate (5).
Flow sensor for liquids of any of the preceding claims characterized in that it comprises a valve (4) that can be closed by the processing and control circuit (7) for a calibration of the flow sensor.
Flow sensor for liquids of any of the preceding claims characterized in that the temperature sensor is a thermopile, and in particular that the thermopile comprises contacts between polysilicon and aluminium and/or between differently doped polysilicon.
Method for measuring the flow amount of a liquid, in particular with a flow sensor for liquids of any of the preceding claims, characterized
- in that the liquid is led in a duct in thermal contact past a heating element (R1),
- in that a measuring parameter (U1) is determined that depends on a power dissipation of the heating element (R1) or on a temperature in the duct at the heating element, and
- in that from a change of the measuring parameter the presence of a gas bubble in the liquid is deducted.
Method of any of the preceding claims characterized
- in that a flow velocity of the liquid is determined from a temperature difference before and after the heating element (R1),
- in that the flow amount is determined from an integration of the flow velocity and in that
- upon presence of a gas bubble, a flow velocity of a gas in the gas bubble is determined from the temperature difference.
Dependencies are inferred from the claim text.