Flow sensor for determining an air bubble, particularly in a catheter, and corresponding method

1. A flow sensor for detecting a gas bubble in a liquid flowing through the flow sensor, wherein the flow sensor comprises:

a first and a second temperature sensor configured to measure temperature,

a heat source,

a flow channel for guiding a liquid in a flow direction,

wherein said heat source and said temperature sensors are configured such that they are in thermal contact with said liquid, when said liquid passes through said flow channel, and

wherein with respect to the flow direction the first temperature sensor is arranged upstream the heat source whereas the second temperature sensor is arranged downstream the heat source,

wherein the flow sensor is configured to determine a temperature of the heat source and further comprises an analyzing circuit which is configured to detect a gas bubble in the flow channel using at least said temperature of the heat source; and,

wherein the flow sensor or the analysing circuit is configured to determine said temperature of the heat source using the sum of the temperatures measured by the first and the second temperature sensor.

2. The flow sensor according to claim 1 , wherein the flow sensor comprises a further temperature sensor that is configured to measure said temperature of the heat source.

3. The flow sensor according to claim 1 , wherein the analyzing circuit is configured to conclude that a gas bubble has been detected in the flow channel in case said temperature of the heat source exceeds a pre-determined upper threshold.

4. The flow sensor according to claim 1 , wherein the flow sensor or the analyzing circuit is configured to determine a temperature difference between said temperature at the second temperature sensor and said temperature at the first temperature sensor, wherein the analyzing circuit is configured to conclude that a gas bubble has been detected in the flow channel when said temperature difference is below a pre-defined lower threshold and said temperature of the heat source exceeds a pre-determined upper threshold, and wherein the analyzing circuit is configured to conclude that the liquid in the flow channel stands still, when said temperature difference is below said pre-defined lower threshold and said temperature of the heat source is below said pre-determined upper threshold.

5. The flow sensor according to claim 1 , wherein the analyzing circuit is configured to determine one of: the flow velocity, the mass flow rate, and/or the volumetric flow rate of said liquid using the temperatures measured by the first and second temperature sensor.

6. The flow sensor according to claim 1 , wherein the flow sensor comprises a semiconductor module that comprise a first side facing away from the flow channel and a second side facing the flow channel, wherein the semiconductor module comprises a recess in its first side, which recess comprises a bottom that forms a part of said second side of the semiconductor module.

7. The flow sensor of claim 6 , wherein said heat source and said first and second temperature sensor are at least partially arranged on said bottom on the second side of the semiconductor module.

8. The flow sensor according to claim 1 , wherein said liquid is an infusion liquid.

9. A flow sensor for detecting a gas bubble in a liquid flowing through the flow sensor, wherein the flow sensor comprises:

a first and a second temperature sensor configured to measure temperature,

a heat source,

a flow channel for guiding a liquid in a flow direction,

wherein said heat source and said temperature sensors are configured such that they are in thermal contact with said liquid, when said liquid passes through said flow channel, and

wherein with respect to the flow direction the first temperature sensor is arranged upstream the heat source whereas the second temperature sensor is arranged downstream the heat source,

wherein the flow sensor is configured to determine a temperature of the heat source and further comprises an analyzing circuit which is configured to detect a gas bubble in the flow channel using at least said temperature of the heat source, wherein the flow sensor or the analysing circuit is configured to determine said temperature of the heat source using the sum of the temperatures measured by the first and the second temperature sensor.

10. A flow sensor for detecting a gas bubble in a liquid flowing through the flow sensor, wherein the flow sensor comprises:

a first and a second temperature sensor configured to measure temperature,

a heat source,

a flow channel for guiding a liquid in a flow direction,

wherein said heat source and said temperature sensors are configured such that they are in thermal contact with said liquid, when said liquid passes through said flow channel, and

wherein with respect to the flow direction the first temperature sensor is arranged upstream the heat source whereas the second temperature sensor is arranged downstream the heat source,

wherein the flow sensor is configured to determine a temperature of the heat source and further comprises an analyzing circuit which is configured to detect a gas bubble in the flow channel using at least said temperature of the heat source, and wherein the flow sensor or the analyzing circuit is configured to determine a temperature difference between said temperature at the second temperature sensor and said temperature at the first temperature sensor, wherein the analyzing circuit is configured to conclude that a gas bubble has been detected in the flow channel when said temperature difference is below a pre-defined lower threshold and said temperature of the heat source exceeds a pre-determined upper threshold, and wherein the analyzing circuit is configured to conclude that the liquid in the flow channel stands still, when said temperature difference is below said pre-defined lower threshold and said temperature of the heat source is below said pre-determined upper threshold.

11. A method for detecting a gas bubble in a liquid flowing through a flow sensor, wherein the method comprises the steps of:

letting a liquid pass through a flow channel so that the liquid successively passes along a first temperature sensor, a heat source and a second temperature sensor,

determining a temperature of the heat source upon passing of said liquid through the flow channel, wherein preferably also the temperature of the liquid at the first temperature sensor and at the second temperature sensor are measured upon passing of said liquid through the flow channel, and

detecting a gas bubble comprised by the liquid in the flow channel using at least said temperature being proportional to the temperature of the heat source;

wherein said temperature of the heat source is determined using the sum of the temperatures measured by the first and the second temperature sensor.

12. The method according to claim 11 , characterized in that said temperature of the heat source is measured using a separate temperature sensor associated to the heat source.

13. The method according to claim 11 , characterized in that it is automatically concluded that a gas bubble has been detected in the flow channel in case said temperature of the heat source exceeds a pre-determined upper threshold.

14. The method according to claim 11 , characterized in that the temperature difference between said temperature at the second temperature sensor and said temperature at the first temperature sensor is determined, wherein when said temperature difference is below a pre-defined lower threshold and said temperature of the heat source exceeds a pre-determined upper threshold it is automatically concluded that a gas bubble has been detected in the flow channel, while in case said temperature difference is below said pre-defined lower threshold and said temperature of the heat source is below said pre-determined upper threshold it is automatically concluded that the liquid in the flow channel stands still.

15. The method according to claim 11 , wherein said liquid is an infusion liquid.