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A modularly structured unit is comprised of a flow resistance element and an orifice plate adjacent thereto, preferably for use in the main flow duct of a thermal mass flow rate measuring or control device. The flow resistance element can be combined with various orifice plates having different open

A modularly structured unit is comprised of a flow resistance element and an orifice plate adjacent thereto, preferably for use in the main flow duct of a thermal mass flow rate measuring or control device. The flow resistance element can be combined with various orifice plates having different opening diameters.

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1. A modularly structured flow conditioning unit comprising: a flow resistance element built up of a multitude of parallel and adjacent ducts;an orifice plate in immediate contact with the flow resistance element and adapted to be used in a main flow duct of a thermal mass flow rate measuring or con

1. A modularly structured flow conditioning unit comprising: a flow resistance element built up of a multitude of parallel and adjacent ducts;an orifice plate in immediate contact with the flow resistance element and adapted to be used in a main flow duct of a thermal mass flow rate measuring or control device, wherein the orifice plate only includes one opening wherein the one opening comprises a center opening, and wherein the flow resistance element is adapted to be combined with various orifice plates having different diameters for the center opening;wherein the flow resistance element includes first and second end faces with the multitude of parallel and adjacent ducts extending through the flow resistance element from the first end face to the second end face, and wherein each of the orifice plates is configured to contact at least one of the first and second end faces to cover a first plurality ducts of the multitude of parallel and adjacent ducts, leaving a second plurality of the multitude of parallel and adjacent ducts uncovered: andwherein one entire side of the orifice plate forms a contact surface that is in direct abutting contact with the flow resistance element over an entirety of the contact surface. 2. The modularly structured flow conditioning unit according to claim 1, wherein the multitude of parallel and adjacent ducts are defined by walls having wall thicknesses of from 0.5 mm to 0.05 mm. 3. The modularly structured flow conditioning unit according to claim 2, wherein the flow resistance element comprises a photopolymerized element of a plastic material comprised of layers grown over an appropriate mask. 4. The modularly structured flow conditioning unit according to claim 3, wherein the flow resistance element includes ducts having an approximately trapezoidal cross-section. 5. The modularly structured flow conditioning unit according to claim 1, wherein one single flow resistance element having a large opening cross-section cooperates with a respective one of a plurality of orifice plates, with each plate comprising a disk having only the one opening, and wherein the one opening is defined by a diameter determining a maximum rate of flow. 6. The modularly structured flow conditioning unit according to claim 1, wherein the orifice plate is arranged in a flow direction immediately upstream or downstream of the flow resistance element and is in direct abutting contact therewith. 7. A modularly structured flow conditioning unit comprising: a flow resistance element including a plurality of parallel and adjacent ducts;an orifice plate in immediate contact with the flow resistance element, the orifice plate only including one opening, wherein the one opening comprises a center opening defined by a diameter, and wherein the flow resistance element is adapted to be combined with a selected one of a plurality of orifice plates, with each orifice plate only including the one opening and each orifice plate having this one opening comprising the center opening, and wherein each center opening of the plurality of the orifice plates is defined by a different diameter to provide a desired flow rate;wherein the selected one of the plurality of orifice plates is configured to contact an end face of the flow resistance element to cover a first plurality of the ducts and leave a second plurality of the ducts uncovered; andwherein one entire side of the orifice plate forms a contact surface that is in direct abutting contact with the flow resistance element over an entirety of the contact surface. 8. The modularly structured flow conditioning unit according to claim 7, wherein the flow resistance element and orifice plate are adapted to be used in a main flow duct of a thermal mass flow rate measuring or control device. 9. The modularly structured flow conditioning unit according to claim 7, wherein the flow resistance element comprises a single body that includes the plurality of parallel and adjacent ducts which cooperate with each other to define an opening cross-section, the single body having one of a large opening cross-section for a high flow rate or a small opening cross-section for a low flow rate. 10. The modularly structured flow conditioning unit according to claim 9, wherein the selected one of the plurality of orifice plates comprises one of a first orifice plate having a smaller diameter center opening to cover a first number of duct openings in the single body or a second orifice plate having a larger diameter center opening to cover a second number of duct openings in the single body that is less than the first number. 11. A method of assembling a modularly structured flow conditioning unit comprising the steps of: (a) providing a flow resistance element;(b) selecting one of a plurality of orifice plates each having a center opening defined by a different diameter to provide a desired flow rate when combined with the flow resistance element; forming each orifice plate as a disk having only one opening wherein the one opening is the center opening; and(c) disposing the selected orifice plate in immediate contact with the flow resistance element. 12. The method according to claim 11, including positioning the orifice plate selected in step (b) adjacent to the flow resistance element in a main flow duct of a thermal mass flow rate measuring or control device. 13. The method according to claim 11, wherein the flow resistance element includes first and second end faces, and including forming the flow resistance element to include a plurality of parallel ducts which extend through the flow resistance element from the first end face to the second end face. 14. The method according to claim 13, including abutting a selected one of the plurality of orifice plates against one of the first and second end faces to cover up a certain number of the parallel ducts and leaving the remaining plurality of parallel ducts uncovered. 15. A modularly structured flow conditioning unit assembly comprising: a flow resistance element, wherein the flow resistance element includes a plurality of parallel ducts; anda plurality of orifice plates having different opening diameters, wherein each orifice plate is adapted to be used in a main flow duct of a thermal mass flow rate measuring or control device, wherein each orifice plate comprises a disk having only one opening, and wherein a selected one of the plurality of orifice plates is configured to contact an end face of the flow resistance element to cover a first plurality of the parallel ducts, leaving a second plurality of the parallel ducts uncovered at the one opening, and wherein the flow resistance element is adapted to be combined with each orifice plate such that each one of the orifice plates can be arranged in immediate contact with the flow resistance element to amend the flow resistance. 16. The modularly structured flow conditioning unit assembly according to claim 15, wherein the flow resistance element includes first and second end faces, and wherein the plurality of parallel ducts extend through the flow resistance element from the first end face to the second end face. 17. The modularly structured flow conditioning unit according to claim 7, wherein each orifice plate comprises a disk having only the one opening. 18. The method according to claim 11, wherein step (c) further includes forming one entire side of the orifice plate as a contact surface that is in direct abutting contact with the flow resistance element over an entirety of the contact surface. 19. The modularly structured flow conditioning unit assembly according to claim 15, wherein one entire side of the orifice plate forms a contact surface that is in direct abutting contact with the flow resistance element over an entirety of the contact surface.