SE506127C2 - Reference scale for calibration of wind tunnel scales - Google Patents

Abstract

This invention is concerning a precalibrated multi-component sensor, here called a master balance, intended for determination of applied forces and moments in the calibration of multi-component sensors, here called object balance, normally used for aerodynamically tests in wind tunnels. During the calibration procedure, the object balance is connected in series with the master balance, which in turn is fastened to a frame, here called a calibration rig. Characteristic for this invention is that the master balance is fastened to the calibration rig frame by an attachment joint in a plane perpendicular to the main axis, common to master and object balances, with the attachment joint being lifted up to the same or nearly the same level as the moment center of the object balance.

Description

506 127 without overloading the measuring beams for sensing the axial force component, which is usually the most sensitive and critical to congestion. Sensing measuring ball vessels, produced by slitting the tubular cylindrical part of the reference wave, means simplified, cheaper production, even if the reference wave is made in one piece.

The measurement guidelines for the different components of wind tunnel waves are often as wide as in relation 1:20. in order to get approximately the same sensitivity to the different components of the scale, one therefore seeks arrange corresponding measuring beams so that at the weaker components, usually axial force, turning and rolling torques, applied forces and torques are taken up as bending load in the measuring beams, whereas in the case of the stronger components, usually normal and lateral force as well as tipping ment, the measuring beams are arranged for tensile and compressive loads.

These principles can be applied to the reference wave in question. At relatively low values of examples Pelvis rolling moment can be obtained by slitting the cylindrical part of the scale vertical measuring beams that are subjected to bending load and thus a higher, acceptable signal level for this component.

Alternatively, this can also be achieved by slitting the bottom of the reference wave so that radial spoke-shaped measuring beams are obtained with load in bending as a result of applied rolling ment.

The reference scale is preferably made of a blank tube with a separate bottom or replaceable central bracket for the object wave, which is bolted, possibly welded to the pipe, so that further reduction obtained for the manufacturing cost compared to the manufacture of the scale in one piece, and that this alternative with interchangeable bracket for the object wave means that one and the same reference wave can is used for a larger number of object scales for different work areas and with different sizes and shape of the fastening joint.

With interchangeability of the bottom of the reference scale when fitted with foamable radial measuring beams you can, by using different combinations of bottom and cylindrical part, get extended adaptability to the needs of different measurement areas.

Preferably, the reference scale has a large cylinder diameter to reduce the risk of hysteresis by thereby maintaining the contact forces in the connection between the cylinder of the scale and the bottom moderate levels and thus acceptable accuracy can be achieved, even if the scale is not made in a single paragraph.

In summary, the present invention proposes a reference wave of improved con- construction. Characteristic of this construction is that the suspension plane's suspension plane is relative the stand of the calibration rig is raised to near the torque center of the object scale. Caliber the torque arms of the ring forces are therefore minimal, which entails (l) Reduced risk of hysteresis by sliding or displacing the boundary surfaces between lan the scales and the rig stand. 2) Less total load on the measuring beams and thus less overhangs and better total measurement accuracy.

BNSDOCID: 506 »127 3) Shorter distances to the torque center provide better accuracy when transforming to this point. 4) Simplified, cheaper production with measuring beams obtained through a number of horizontal and vertical slots in a tubular cylindrical portion of the scale. Alternatively, even the scales can bottom plate is provided with spoke-shaped radial measuring beams as a complement to extended measuring range. 5) The construction allows the recording of the moments, spec roll, without overloading the measuring beams for the axial component. No difficult-to-manufacture membrane is needed. 6) The diameter can be made large at reasonable costs, resulting in lower elongation levels in the the beams are an advantage. 7) The scale may be made of a blank with a separate bottom and fl sas or bolted to the pipe. Lower cost, fits different scales and different measuring ranges.

Figures 1-3 show different variants of a reference wave according to the invention in side view with cross-section. tion.

BNSDOCID: 506 127 Figure description Figures 1-3 show different variants of the reference wave according to the invention installed together with an object scale and with applied power system as follows.

Figure 1 shows a cup-shaped reference wave 1, which is fixed at one end, for example its upper part connected to a stand 2 of the ground-based calibration rig via a tubular part 3.

The circular cylindrical surface 1.1 of the reference wave 1 is provided with horizontal slits 4 which form load sensing measuring elements or measuring beams 5 provided with strain gauges 6, which indicate the magnitude of the given forces applied to the calibration or the moments in an orthogonal coordinate system (xyz).

The reference wave 1 has a bottom 7 in which the object wave 8 is permanently installed centrally with its model end downwards. The object wave 8 is surrounded by a sleeve 9 fixedly connected to the object wave. upper part 10 of the object 8. The torque center of the object wave 8 is denoted by R.

The object wave 8 and the reference wave 1 are subjected to applied given forces and moments through calibration forces with the following designations.

N 1 and N; Horizontal normal forces in the image plane for normal force N and tipping torque m C1 and G2 Horizontal lateral forces perpendicular to the plane of the image for lateral force C and ment n FU and F¿2 Horizontal rolling forces perpendicular to the plane of the image for the rolling moment 2 TI Vertical axial force in the plane of the image.

The load components N, C, T, m, n and f? are reaction forces acting on the object wave 8 which direct calibration loads.

Figure 2 shows a version where the bottom of the reference scale 1 has a detachable central bracket 7.1 for the model end of the object scale. This bracket shall have the least possible hysteresis due to the calibration forces and has the advantage that the reference wave can be used for object scales of different sizes play. Otherwise, this version is designed in the same way as the reference wave according to Figure 1.

Figure 3 shows the version of the reference wave 1 where it has four vertical measuring slips 5.1 milled in the cylindrical part of the reference wave 1. Dimension A between the measurement sections must be minimized. Stretch sensor 6.1 are installed on both the vertical and horizontal measuring beams. The advantage of this is better separation of the wave components if one can tolerate the greater weight of the wave as This causes.

Otherwise, this version is designed similar to the reference wave according to Figure 2.

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Claims (5)

506,127 Claims A pre-calibrated reference sensor (1), here referred to as a reference scale, intended for determining components of applied forces and torques when calibrating an fl component component sensor (8), here called an object scale, for aerodynamic tests, which during the calibration are connected in series with the reference scale ( 1), which in turn is fixed in a stand (2), here called calibration rig, characterized in that the reference wave (1) has a fastening connection to the calibration rig which lies in a plane perpendicular to the object wave (8) and on the same or near the same height as the torque center of the vertically mounted object scale (8). Reference scale according to claim 1, characterized in that it comprises a cylindrical tubular part (1,1), comprising a number of horizontal and vertical slits (4), that said cylindrical pipe part is attached at its one end, for example its upper part to the rig stand via a fl end joint, and at its other end, for example its lower part, has a bottom (7) with central attachment of the object wave (8). Reference scale according to Claim 2, characterized in that its bottom (7) has a central replaceable part (7.1) through a fastening joint with minimal hysteresis loss of applied calibration laser IEI ". Reference scale according to Claim 2, characterized in that the tubular part is made of a blank tube with a separately replaceable bottom, which is bolted or possibly welded to the tube. Reference scale according to Claim 2 or 3, characterized in that the tube-shaped part has a large cylinder diameter in relation to the diameter of the object scale. BNSDOCID: