Gauge calibration constant

Fig. 7.7. The McLeod gauge. The principles of operation follow. Let the unknown pressure in a system be P when the Hg level is below point 1. Let the volume of the bulb and closed capillary above I be V, which is known. When the mercury is allowed to rise past point I, the gas is trapped and finally compressed into the capillary. Suppose that when the mercury in the reference capillary is at 0, the mercury in the dead-ended capillary is B mm below 0 (i.e., the pressure of the compressed gas is B mm). Since the initial pressure-volume product equals the final pressure-volume product, PV = pv, the volume in thecapillary v will be the height B times the area of the capillary bore A. Thus P = pv/V = B (A/V). Since A and V are known and B is measured, the original pressure (P) may be calculated. Most commercial gauges are provided with a calibrated scale which presents pressures directly. Alternatively, it is possible to devise a linear scale for the McLeod gauge, in one such method the mercury height in the closed capillary is always adjusted to the same point (B0), and then the difference in meniscus heights between the two capillaries is measured (AB). For this case the pressure being measured is P = pv0/V = (B0A/V)AB. As in the previous example, the quantity in parentheses represents the gauge calibration constant.

The calibration curve of each rosetta strain gauge was so obtained and ftg.5 shows the sum of the principal stresses at the measuring points versus pressure inside the vessel. Further tests were carried out to obtain the calibration factor and to check that it remained constant on the whole scan area of the test surface. This was achieved through additional measurements using the SPATE system on fixed points on the surface located very close to the applied rosetta strain gauges. This procedure gave the following results ... 

Q is obtained either from the quantity of gas that flows into the calibration chamber from a supply vessel in which constant pressure prevails or from the quantity of gas flowing into the calibration chamber at a measured pressure through a known conductance. The pressure in front of the inlet valve must be high enough so that it can be measured with a reference gauge. The inlet apertures of the valve (small capillaries, sintered bodies) must be so small that the condition d X is met, i.e. a molecular flow and hence a constant conductance of the inlet valve are obtained (see Section 1.5). The quantity of gas is then defined by p L, where p = pressure in front of the inlet valve and = conductance of the valve. The pumping system consists of a precisely measured aperture with the conductance Lj in a wall that is as thin as possible (screen conductance) and a pump with a pumping speed of PSp ... 

N cuum technology calibration of vacuum gauges in a range from lO to 10 mbar. General methods pressure reduction through constant flow 3/76... 

The adsorption of carbon dioxide or oxygen on praseodymium samples was measured by a constant-volume method using a calibrated Pirani vacuum gauge. Praseodymium oxide was heated in oxygen (4 kPa) at 775°C for 1 h, then evacuated at 750°C for 0.5 h just before the measurement. The sample of praseodymium oxychloride was prepared from praseodymium chloride by heating under oxygen flow... 

Figure 1. Schematic of apparatus A, calibrated variable-volume mercury burette B, reference volume C, main chamber D, mixing pump E, adsorption chamber F, reference chamber G, constant temperature baths H, mercury manometer J, cold-cathode gauge P, Pirani vacuum gauge R, mercury reservoir...

On pressurized tanks, the seal has to be frictionless and useful over a wide range of pressures, temperatures, and corrosion conditions. Displacement detectors can be magnetically coupled, or they can use a torque tube, diaphragm and force bar, spring balance, flexible disk, or the flexible shaft design. All of them can be used to detect a liquid-vapor interface, a liquid-liquid interface, and if the level is constant, they can detect density as well. The external displacers are usually installed with level gauges (Figure 3.117) so that the operator can visually inspect their calibration and performance. 

The pressure gauge used in this experiment should be a direct-reading gauge with a relatively small and constant internal volume. Reproducibility is more important than absolute accuracy since relative measurements are made on air (the standard gas used for calibration) and the other gases. The critical feature is that the same initial P and final P inlet pressures are used in all runs. Thus, one can use capacitance, reluctance, or strain-gauge manometers (see p. 596-597). The latter manometers are the least expensive and are adequate if models with the best resolution are chosen. 

The strain due to bending is measured by an electrical-resistance strain gauge mounted near the region examined by x-rays. The product of this strain and the mechanically measured elastic modulus E of the material is the surface longitudinal stress stress constant K, The best approach is to measure E on the same specimen by direct loading of the same kind as that used, in the x-ray calibration, e.g., by four-point bending.)... 

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