Direct Pressure Measurement

Manometers consisting of liquid columns of, commonly, mercury or a fluid such as silicone oil, have been used extensively in the past to measure gas mixtures in, for example, experimental, static investigations of the overall kinetics of gas-phase reactions. They continue to be used in many applications, including the establishment of primary pressure standards in several countries. 

Where h is the difference in height between the two levels and g is the local acceleration due to gravity. 

A much more convenient method of direct pressure measurement involves the deflexion of a sensing element (e.g. a tensioned diaphragm made of a suitable metal or ceramic or a Bourdon tube) which separates 

Capacitance diaphragm gauge FS= 1330 mbar Uncertainty = 0.2% reading 

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Measurement of pressures in the rough vacuum range can be carried out relatively precisely by means of vacuum gauges with direct pressure measurement. Measurement of lower pressures, on the other hand, is almost always subject to a number of fundamental errors that limit the measuring accuracy right from the start so that it is not comparable at all to... 

R.T. Keyes, JChemPhys 24, 191-201(1956) (Rate of reaction of TNT in deton by direct pressure measurement) Q) R.D. Cowan ... 

M,A.Cook et al, JChemPhys 24, 191-201 (1956) (Rate of reaction of TNT in detonation by direct pressure measurements) 22)Dunkle s Syllabus (1957-1958) (See Vol 4 of Encycl, p XLIX) p 126 (Reaction front in detonation) 135-42 (Thermal decomposition of solids) 23)M.A.Cook, "The Science of High Explosives , Reinhold NY(1958), pp 123-42 (Reaction rate in detonation) 174-87 (Thermal decomposition of soli ds) 386-89 (Thermochemistry of detonation and expltr) 24)F.A.Baum, K.P.Sranyukovich B.I.Shekhter "Fizika Vzryva , Moscow (1959), pp 81-108 (Thermochemistry of explosives) 25)K.K.An-dreev A. F. Belyaev, " Teoria Vzryvcha-rykh Veshchestv Moscow(1960), p 49-56 (Thermal expln in gases) p 56—61 (Thermal explosion in solids) 26) Encycl of Expls PATR 2700, Vol 1 (I960), p A501 (Atomic expins, chain reactions in) 27)F.M.Turner,... 

If measurements of the shock velocity in water are available at various distances from the charge, one can compute shock pressures at these distances. This approach can be used close to the charge where direct transducer measurements present formidable problems. An exptl arrangement for measuring shock velocity is shown in Fig 16 (Ref 1). Measurements thus obtained are compared with theoretical predictions in Fig 17 (closed circles). Also shown are direct pressure measurements (open circles). 

Figure 5.1 Instruments used for direct pressure measurement...

Direct pressure measurements may be made with conventional manometers using mercury, silicone oils, hydrocarbon oils, butyl phthalate and other fluids. Apart from the danger of their affecting the reaction studied directly, by chemical reaction, vapour adsorption or modifying the surface of the RV, they produce a varying dead space . It is important to keep the dead space between 1 and 4 %... 

Direct pressure measuring devices Pressure bombs Drill-stem test Wire-line formation test When well is tested or completed... 

The direct pressure measurement has the advantage that absolute pressures can be obtained and pressure fluctuations can be observed. More modem equipment applies electronic pressure sensors instead of Hg-manometers to avoid the problems caused by the... 

Delis K, Azizi ZA, Nicolaides AN, et al. Determining the optimum intermittent pneumatic compression (IPLC) stimulus for lower limb venous emptying using direct pressure measurements. BrJ Surg 1996 (abstract) 83(suppl 2) 148. 

For a direct pressure measurement, the difference between the pressure to be measured and a known reference pressure is measured. Because of this measurement method engineers specify three different kinds of pressure (see DIN 1314) ... 

At equilibrium and in the flat portion of a thin-liquid film, the disjoining pressure, O, equals the capillary pressure. Pc- Therefore, measurements of the capillary pressure are used to evaluate fl. Two methods can be utilized to determine Pc, i.e. direct pressure measurements and lamella-profile measurements. In the latter case, the mean curvature of the meniscus is obtained and Pc is determined by using Laplace s equation. 

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