Method of dry-calibrating vortex flow sensors

A method of dry-calibrating vortex flow sensors (henceforth called “vortex sensors” for short) each comprising:

• a measuring tube of predetermined length having a lumen
• through which a fluid whose volumetric flow rate is to be measured flows during operation, and
• which has an axis,
• an internal surface,
• an inlet end, which forms a contour line with the lumen,
• an outlet end,
• a bore size corresponding to a nominal bore, and
• a wall thickness suitable for a permissible pressure of the fluid;
• a bluff body
• which has a cross-sectional area with a geometrical shape selectable by the manufacturer,
• which has a first end connected with the wall of the measuring tube along a first fixing zone and
• a second end connected with the wall of the measuring tube along a second fixing zone,
• which has a surface facing fluid flow and having a first and a second vortex-shedding edge, and
• which is disposed along a diameter of the measuring tube;
• and
• a sensing element
• which is fitted in the bluff body or
• which is mounted downstream of the bluff body on the internal or external surface of the wall of the measuring tube or in said wall,
• said method comprising the steps of:
• producing, by means of a high-resolution electronic camera located on the axis in front of the measuring tube, in the direction of fluid flow, a digitized, two-dimensional overall image of the internal surface of the measuring tube in the area of the bluff body, the bluff body, the two fixing zones, and the contour line of the inlet end;
• dividing the overall image into a first, a second, and a third partial image,
• the first partial image containing virtually only information about the inlet end and the internal surface,
• the second partial image containing virtually only information about the bluff body without the fixing zones, and
• the third partial image containing virtually only information about the fixing zones;
• extracting from the first partial image
• contour information about the contour line and
• first surface defect information relating to the internal surface of the measuring tube;
• extracting from the second partial image
• first edge information about the first vortex-shedding edge of the bluff body,
• second edge information about the second vortex-shedding edge of the bluff body, and
• second surface defect information relating to the surface of the bluff body facing fluid flow;
• extracting from the third partial image
• first shape information about the first fixing zone of the bluff body,
• second shape information about the second fixing zone of the bluff body,
• third surface defect information relating to the surface of the first fixing zone, and
• fourth surface defect information relating to the surface of the second fixing zone;
• forming from the first and second edge information
• distance information and
• angle information relating to the deviation of the vortex-shedding edges of the bluff body from parallelism;
• forming from the distance information
• first roughness information relating to the not exactly straight course of the first vortex-shedding edge,
• second roughness information relating to the not exactly straight course of the second vortex-shedding edge,
• mean-value information for all distances between the vortex-shedding edges along the bluff body, and
• weighting information using a weighting function characteristic of predetermined flow profiles of the fluid;
• forming first cross-correlation information from the first shape information and from first ideal information characteristic of the ideal shape of the first fixing zone, and
• forming second cross-correlation information from the second shape information and from second ideal information characteristic of the ideal shape of the second fixing zone;
• and
• processing in a neural network
• the contour information,
• the first and second roughness information,
• the mean-value information,
• the weighting information,
• the angle information,
• the first, second, third, and fourth surface defect information, and
• the first and second cross-correlation information
• together with respective standard information corresponding to said information and derived from a plurality of wet calibrations into at lease one of
• calibration factor information and
• dimension information about the geometrical dimensions of the calibrated vortex sensor.