= Bourdon tube pressure gauge
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A \b[Bourdon tube pressure gauge] combines a pressure-sensitive <Bourdon tube> with a motion-transmission mechanism, pointer and calibrated scale. Pressure-driven <elastic deformation> moves the free end of the tube; a linkage and geared movement convert that motion into an indication on the dial. WIKA's technical diagram identifies the tube, end piece, link, movement, pointer and pressure connection as distinct parts.<Elastic element pressure gauges by WIKA>[IN00.01,09/2010, p1, labelled Bourdon-gauge mechanism]{ref}
The complete gauge is a <measuring system>. Its <measurement indication> depends on the sensing tube and the motion transmission, including possible <backlash> and <hysteresis>. For a vented case, the tube responds to pressure relative to the surrounding atmosphere, so the intended quantity is <gauge pressure>. The dial alone does not define an <absolute pressure> reference.
For an original <instrument calibration> comparison, connect the gauge and a suitable pressure reference to a common fluid source. Apply several increasing pressure steps, wait for stable readings, and return through the same pressures. Record each discrepancy $e=p_{\rm gauge}-p_{\rm ref}$ and distinguish the two loading directions. This tests the assembled readout rather than only the elastic element.
The locations of the pressure ports can matter as much as their shared supply. If the test gauge's port is $0.5\,\mathrm m$ below the reference port in a stationary water-filled connection, take $\rho=1000\,\mathrm{kg\,m^{-3}}$ and $g=9.81\,\mathrm{m\,s^{-2}}$. <Hydrostatic pressure> gives
$$
p_{\rm lower}-p_{\rm upper}=\rho g\Delta h=4905\,\mathrm{Pa}=4.905\,\mathrm{kPa}.
$$
Without that correction, a correct lower gauge can appear to overread the upper reference. These are original apparatus values, not manufacturer test data.
Read the error specification for the actual model and size. WIKA's June2025 US sheet, for example, states an accuracy of $\pm1.0\%$ of span for the specified four- and six-inch versions, while listing a different specification for the smaller version.<Bourdon Tube Pressure Gauges, Stainless Steel Series by WIKA>[23X.50,06/2025, p1, Accuracy class]{ref} A percentage of span is not the same percentage of the instantaneous reading. Retain range, conditions, corrections and <measurement uncertainty> with the reported result.
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