Pressure measuring devices

If fluid A is a gas, the density p will normally be small compared with the density of the manometer fluid so that  

The quantity of liquid expelled from the well is equal to the quantity pushed into the column so that  

If 0 is the angle of inclination of the manometer (typically about 10-20°) and L is the movement of the column of liquid along the limb, then  

It may be noted that the pressure measuring devices (a) to (e) all measure a pressure difference AP(= Pj — Pi). In the case of the Bourdon gauge (f), the pressure indicated is the difference between that communicated by the system to the tube and the external (ambient) pressure, and this is usually referred to as the gauge pressure. It is then necessary to add on the ambient pressure in order to obtain the (absolute) pressure. Even the mercury barometer measures, not atmospheric pressure, but the difference between atmospheric pressure and the vapour pressure of mercury which, of course, is negligible. Gauge pressures are not, however, used in the SI System of units. 

Pressure signal transmission—the dWerential pressure cell 

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If a pressure measuring device were run inside the capillary, an oil gradient would be measured in the oil column. A pressure discontinuity would be apparent across the interface (the difference being the capillary pressure), and a water gradient would be measured below the interface. If the device also measured resistivity, a contact would be determined at this interface, and would be described as the oil-water contact (OWC). Note that if oil and water pressure measurements alone were used to construct a pressure-depth plot, and the gradient intercept technigue was used to determine an interface, it is the free water level which would be determined, not the OWC. 

To avoid maintenance problems, the location of pressure measurement devices must be carefully considered to protect against vibration, freezing, corrosion, temperature, overpressure, etc. For example, in the case of a hard-to-handle fluid, an inert gas is sometimes used to isolate the sensing device from direct contact with the fluid. 

Elastic-Element Methods Elastic-element pressure-measuring devices are those in which the measured pressure deforms some elastic material (usually metallic) within its elastic limit, the magnitude of the deformation being approximately proportional to the applied pressure. These devices may be loosely classified into three types Bourdon tube, bellows, and diaphragm. 

Head Devices A variety of devices utilize hydrostatic head as a measure of level. As in the case of displacer devices, accurate level measurement by hydrostatic head requires an accurate knowledge of the densities of both heavier-phase and lighter-phase fluids. The majority of this class of systems utilize standard-pressure and differential-pressure measuring devices. 

Further details on pressure-measuring devices are found in Sec. 22. 

Pressure-measuring device This is provided for the operation of alarm or trip devices in the event the pressure within the casing falls below the permitted minimum. 

Tensiometer Measures the matric potential of a given soil, which is converted to soil moisture content Commonly consists of a porous ceramic cup connected to a pressure-measuring device through a rigid plastic tube... 

The pitot tube is a device for measuring v(r), the local velocity at a given position in the conduit, as illustrated in Fig. 10-1. The measured velocity is then used in Eq. (10-2) to determine the flow rate. It consists of a differential pressure measuring device (e.g., a manometer, transducer, or DP cell) that measures the pressure difference between two tubes. One tube is attached to a hollow probe that can be positioned at any radial location in the conduit, and the other is attached to the wall of the conduit in the same axial plane as the end of the probe. The local velocity of the streamline that impinges on the end of the probe is v(r). The fluid element that impacts the open end of the probe must come to rest at that point, because there is no flow through the probe or the DP cell this is known as the stagnation point. The Bernoulli equation can be applied to the fluid streamline that impacts the probe tip ... 

Fig. 3.5 Examples of electromechanical and electronic pressure measuring devices.

Elastic deformation, 21 719 ceramics, 5 613-615 coal, 6 724-725 Elastic diffusion, 23 102 Elastic element pressure measuring devices, 20 681-682 Elastic interactions, 13 498 Elasticity, 19 743... 

Pressure loss coefficient, 13 261 Pressure measurement, 11 783 20 644-665. See also Vacuum measurement electronic sensors, 20 651-657 mechanical gauges, 20 646-651 smart pressure transmitters, 20 663-665 terms related to, 20 644-646 Pressure measurement devices. See also Pressure meters Pressure sensors location of, 20 682 types of, 20 681-682 Pressure meters, 20 651 Pressure microfiltration/ultrafiltration,... 

A small reaction bomb fitted with a sensitive pressure-measuring device is flushed out and then filled with pure reactant A at 1-atm pressure. The operation is carried out at 25°C, a temperature low enough that the reaction does not proceed to any appreciable extent. The temperature is then raised as rapidly as possible to 100°C by plunging the bomb into boiling water, and the readings in Table P3.21 are obtained. The stoichiometry of the reaction is 2A B, and after leaving the bomb in the bath over the weekend the contents are analyzed for A none can be found. Find a rate equation in units of moles, liters, and minutes which will satisfactorily fit the data. 

Partial pressure measurement devices which are In common use comprise the measurement system proper (the sensor) and the control device required for Its operation. The sensor contains the Ion source, the separation system and the Ion trap. The separation of Ions differing In masses and charges Is often effected by utilizing phenomena which cause the Ions to resonate In electrical and magnetic fields. 

The linearity range is that pressure range for the reference gas (Nj, Ar) in which sensitivity remains constant within limits which are to be specified ( 10 % for partial pressure measurement devices). 

Process pressure-measuring devices may be divided into three groups ... 

Pressure-Measuring Device. Accurate pressure measurements are made with a manometer if needed. In most instruments the carrier gas, hydrogen, and air (for flame ionization detector) are provided with separate gauges. 

It is suggested that the usual test pressure is between 0.3 and 0.5 MPa and the cavity should be at least 25 ml volume to minimise pressure loss during the course of the test. The low pressure cavity should be of as small a volume as possible and this requirement is helped by the use of rigid porous packing to support the test piece against the pressure of the test gas. The low pressure side is connected to a pressure measuring device. Traditionally (as described in the standard) this is a capillary U-tube manometer which has an adjustable height reservoir and a bypass valve. 

The apparatus and procedure described require great care in setting up and in operation. The effort is eased considerably if an automatic pressure measuring device operating at effectively constant volume is used instead of the manometer9. Probably, all apparatus now has some form of pressure transducer. Improvements as regards accuracy and sensitivity can also be obtained by, for example, having a vacuum instead of atmospheric pressure on the low pressure side. 

Hot-Filament Ionization Vacuum Gage. This gage is the most widely used pressure-measuring device for the region from 10-2 to 10-n torn The operating principle of tins gage is illustrated in Fig. 5. 

In addn to the above mentioned pressure -measuring devices, the following may be... 

Refs l)Marshall 2 (1917), 441-49 (Closed bombs and pressure measuring devices of Rodman, Noble Abel, Bichel and Petavel) 2)D.A.Keys, PhilMag 1921, 473-88 (A piezoelectric method for measuring expln pressures) 3)J C.Karcher, USBurStandards Scient Paper No 445 (Part of Vol 18) (1922)... 

H. Joachim H.Ilgen, SS 27, 76-9 121-25 (1932) (Gas pressure measurements using piezoelectric indicator) 10)Marshall 3 (1932) I33 (Closed bomb and pressure measuring devices) ll)Vennin, Burlot Lecorche (1932), 72-87 (Closed vessel and various pressure measuring devices used between WWI WWII in the laboratories of the Commission des Substances Explosives) 12)C. 

M.Balfour, Engineering 134, 231-32 (1932) (Pressure measurements in ballistic research) 12a)Sukharevskii Pershakov (1933 83 99 (Detn calcn of gas pressures developed on expln in closed vessel) 13)Stett-bacher (1933), 78 (Cylindrical closed bombs for measuring pressure of expln) 91 2, Fig 70 (Pressure bomb of Vieille) 14)Pepin Lehalleur (1935), 82-97 (Closed vessels and pressure measuring devices used in testing of proplnts) 15)H.N.Marsh, ArmyOrdn 17,... 

Studies of characteristics of stick proplnts by closed bomb test) 24)Vivas, Feigenspan Ladreda 4 (1944), 85-6 (Closed bomb and pressure measuring devices used in Spain) 25)R.E.Dufour, Underwriters LabsBull Research, No 30 (1944) CA 38, 3516 (1944)... 

Liquid-Column Methods Liquid-column pressure-measuring devices are those in which the pressure being measured is balanced against the pressure exerted by a column of liquid. If the density of the liquid is known, the height of the liquid column is a measure of the pressure. Most forms of liquid-column pressure-measuring devices are commonly called manometers. When the height of the liquid is... 

Which type of pressure measuring device uses a column of mercury ... 

There are two elements in a head flow meter the primary element is the restriction in the line, and the secondary element is the differential pressure measuring device. Figure 1 shows the basic operating characteristics of a head flow meter. 

Other blood pressure measuring devices are also used routinely. 

Pressure measurement devices such as a manometer are used without disturbing the system being monitored. Another type of reacting system that can be monitored involves one of the products being quantitatively removed by a solid or liquid reagent that does not affect the reaction. An example is the removal of an acid formed by reactions in the gas phase using hydroxide solutions. From the reaction stoichiometry and measurements of the total pressure as a function of time, it is possible to determine the extent of the reaction and the partial pressure or concentrations of the reactant and product species at the time of measurement. 

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