Thermal mass flow meter and method for its operation

• US 20080289411A1
• Filed: 05/20/2008
• Published: 11/27/2008
• Est. Priority Date: 05/21/2007
• Status: Active Grant

• Current Assignee: ABB AG (ABB Limited)
• Original Assignee: ABB AG (ABB Limited)
• Inventors: Schrag, Daniel, Pape, Detlef
• Granted Patent: US 7,644,612 B2
• Time in Patent Office: Days
• US Class Current: 73/204.11
• CPC Class Codes: G01F 1/696 Circuits therefor, e.g. constant-current flow meters
• CPC Class Codes: G01F 1/704 using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter G01F1/76, G01F25/00 take precedence

Abstract

The disclosure relates to a thermal mass flow meter for determining a material flow through a vessel. The mass flow meter has at least two measuring elements immersed into a vessel with a flowing medium, with one of the measuring elements being heated. It is proposed that the heated measuring element is arranged in front of the unheated measuring element in the flow direction of the medium for at least part of the time, and for part of the time the unheated measuring element is arranged in front of the heated measuring element.

Claims

1. A thermal mass flow meter with at least two measuring elements immersed into a vessel with a flowing medium, with one of the measuring elements being heated,

wherein

the heated measuring element is arranged in front of the unheated measuring element in the flow direction of the medium for at least part of the time, and for part of the time the unheated measuring element is arranged in front of the heated measuring element.

2. The mass flow meter as claimed in claim 1,

wherein

the at least two measuring elements are arranged one behind the other in the flow direction.

3. The mass flow meter as claimed in claim 1,

wherein

the at least two measuring elements can be heated alternately.

4. The mass flow meter as claimed in claim 1,

wherein

a third measuring element is provided and arranged outside of the flow over the first and second measuring elements and can periodically be heated for a short time.

5. The mass flow meter as claimed in claim 1

wherein

a third and a fourth measuring element are provided and arranged outside of the flow over the first and second measuring elements, one behind the other in the flow direction, with the measuring element downstream with respect to the flow direction being heatable.

8. The mass flow meter as claimed in claim 2,

wherein

the at least two measuring elements can be heated alternately.

9. The mass flow meter as claimed in claim 3,

wherein

a third measuring element is provided and arranged outside of the flow over the first and second measuring elements and can periodically be heated for a short time.

10. The mass flow meter as claimed in claim 3,

wherein

a third and a fourth measuring element are provided and arranged outside of the flow over the first and second measuring elements, one behind the other in the flow direction, with the measuring element downstream with respect to the flow direction being heatable.

6. A method of operation of a thermal mass flow meter with at least two measuring elements immersed into a vessel with a flowing medium, with one of the measuring elements being heated,

wherein

the flow is measured by two measuring elements which are alternately heated intermittently,

the measured values of the measuring elements are intermittently compared to one another, and

the flow direction of the flow is detected from the differences between the measured values of the measuring elements in successive phases.

7. The method as claimed in claim 6,

wherein

the flow is measured with two pairs of measuring elements, one behind the other in the flow direction, with precisely one measuring element in each pair being heated and with the order of the heated and unheated measuring elements in the flow direction being different between the pairs,

the measured values of the pairs are compared to one another, and

the flow direction of the flow is detected from the differences between the measured values of the pairs.

11. A method of operation of a thermal mass flow meter, the method comprising:

immersing measuring elements into a vessel carrying a flowing medium;

alternately heating each one of the measuring elements, each one of the measuring elements being intermittently heated;

measuring each one of the measuring elements which are alternately heated intermittently to derive measured values;

intermittently comparing the measured values of the measuring elements to one another; and

detecting a flow direction of the flowing medium based on the intermittent comparing of the measured values of the measuring elements in successive phases.