Manometer hydrostatic

0-10 V, 4-20 mA for recorder or controller units). Additionally, there are digital PC-interfaces or pressure-dependent trigger contacts, which are used for further evaluation or control. 

In recent time so-called field-bus interfaces (e.g. PROFIBUS, DeviceNet, LON) gain more importance. They may be used to integrate vacuum pressure transducers into complex process control systems without additional expense for cabling. 

As the basic advantage of a hydrostatic manometer, the measurement result can be calculated from fundamental parameters making a calibration unnecessary. This has established their status of being the standards for calibration. Today these instruments are loosing their importance for every-day work since they are sometimes not very practical in use and if mercury is involved they pose an environmental hazard. 

For a U-tube manometer, which consists of a glass tube with constant diameter bent in the form of a U filled with liquid, the pressure difference between the pressure to be measured and a reference pressure is determined using the following 

Here p is the density of the manometer liquid g, the earth s gravitational acceleration and Ah, the difference of height of the two columns of liquid. If mercury at a temperature of 0 °C is used and Ah is measured in millimetre, pressure values can be stated in Torr (mm Hg). Inserting p, g and Ah in the Sl-units kilogram, metre and second the result is given in the Sl-pressure unit Pa. 

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From the calibration point of view, manometers can be divided into two groups. The first, fluid manometers, are fundamental instruments, where the indication of the measured quantity is based on a simple physical factor the hydrostatic pressure of a fluid column. In principle, such instruments do not require calibration. In practice they do, due to contamination of the manometer itself or the manometer fluid and different modifications from the basic principle, like the tilting of the manometer tube, which cause errors in the measurement result. The stability of high-quality fluid manometers is very good, and they tend to maintain their metrological properties for a long period. 

Since the density of air is effectively zero, the contribution of the air to the 3-ft manometer reading can be neglected. The contribution to the pressure due to the carbon tetrachloride in the manometer is found by using the hydrostatic equation. 

Several terms for pressure measuring devices are used interchangeably including transmitters, transducers, gauges, sensors, and manometers. More precisely, a gauge is a self-contained device that converts a force from the process to a mechanical motion of needle or other type of pointer. A manometer is a term reserved for an instrument that measures the hydrostatic head of a liquid and generally operates near atmospheric pressure. A transducer or transmitter combines the sensor with a power supply and a converter— generally mechanical-to-electrical or mechanical-to-pneumatic. The sensor... 

The hydrostatic pressure results from the weights of the continuous and dispersed phase and can, thus, serve as a measure for the particle mass or volume concentration. In the context of analytical sedimentation, it was already utilised by Ostwald and Hahn (1922), who quantified the rate of sedimentation of flocculated suspensions by means of a hydrostatic pressure gauge. More recent papers report on the manometric determination of the hydrostatic pressure in analytical cuvettes centrifuges with electronic pressure transmitters (Bickert 1997 Beiser 2005). In contrast to the detection systems portrayed above, these manometer centrifuges do not measure a local particle concentration, but the total mass of all particles that are suspended above the point of measurement. The cumulative function of the volume weighted size distribution (gsfxstokes)) can be, thus, computed liom the time derivative of the hydrostatic pressure. In that regard, the manometric detection shows similarity to the sedimentation balance. 

With systems containing liquid columns, for example, a U-tube containing mercury used as a null manometer which may be only approximately balanced, or a piston gauge in which oil is used, the hydrostatic heads -evaluated according to equation (1) - of all the fluids must be added or subtracted appropriately. It may be most straightforward if all fluid heads are first converted into the corresponding heights of one fluid (most usually mercury) by multiplication by the inverse ratio of their densities at... 

Consider a case in which there is no flow, so Vx = Vy = V = 0. Also, all r j = Txy =...= 0 since there is no deformation that can generate stresses. The three components of the momentum equation then reduce to d

constant with (P independent of x and y at each value of z- This is simply the basic equation of hydrostatics, which describes, for example, the operation of a manometer in which differences in liquid height are used to measure pressure differences. 

In order to obtain data on the accuracy that could be expected in measuring total hydrostatic head under simulated loading conditions, we tested a standard strain gage differential pressure cell, and a modified single leg mercury manometer in which the resistance change of a loop of fine wire in the manometer bore is directly proportional to the mercury rise due to applied pressure. The strain gage cell as supplied to us had a calibration accuracy of i 1/4 per cent. Laboratory... 

Estimation of Osmotic Pressure.—(i) Direct.— The solution of known concentration is enclosed in a semipermeable container attached to a manometer tube. The container is immersed in a vessel containing an excess of the solvent, some of which diffuses into the container causing a rise of the solution in the manometer tube. When equilibrium is reached, the osmotic pressure of the diluted solution inside the container is balanced by the hydrostatic pressure of the liquid in the manometer, and can be measured in atmospheric units. Modifications of the apparatus include the use of a mercury manometer to avoid excessive dilution of the mixture, and the employment of metallic containers with frames to support the membranes. 

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