Density compensation

Head meters with density compensation. Head meters such as orifices, venturis, or nozzles can be used with one of a variety of densitometers [e.g., based on (a) buoyant force on a float, (b) hydrauhc couphug, (c) voltage output from a piezoelectric ciystal, or (d) radiation absolution]. The signal from the head meter, which is proportional to pV" (where p = fluid density aud V = fluid velocity), is multiphed by p given by the densitometer. The square root of the produc t is proportional to the mass flow rate. 

Velocity meters with density compensation. The signal from the velocity meter (e.g., turbine meter, electromagnetic meter, or sonic velocity meter) is multiplied by the signal from a densitometer to give a signal proportional to the mass flow rate. 

EXPLAIN the process of density compensation in level detection systems to include ... 

Density compensation may also be accomplished through electronic circuitry. Some systems compensate for density changes automatically through the design of the level detection circuitry. Other applications compensate for density by manually adjusting inputs to the circuit as the pressurizer cools down and depressurizes, or during heatup and pressurization. Calibration charts are also available to correct indications for changes in reference leg temperature. 

DESCRIBE density compensation of a steam flow instrument to include the reason density compensation is required and the parameters used. 

Three-element feedwater system, plus density compensation with drum pressure. 

To improve the accuracy of HTG systems, a third transmitter located at a fixed distance above the bottom transmitter can be used for density compensation (Figure 3.109). These tank expert packages, in addition to level, can also calculate mass, density, and volume on the basis of measurements from three or more d/p cells and one temperature transmitter. Most manufacturers offer optional digital communication and the ability for remote adjustments of suppression and linearization. "Smart" level transmitters can convert the level readings of spherical or cylindrical tanks into actual volume percentage readings (Figure 3.113). 

Figure 15. Fractograms of chromatographic silicas identified (by letter) in Table 11 obtained by using (a) sedimentation FFF system Sed 1 and (b) flow FFF system Flow II. The diameter scale at the top is obtained by using a calibration process based on equation 10 and the measured retention times of polystyrene latex standards. For sedimentation FFF, density compensation is carried out by adjusting the spin rate for each support material in accordance with its density (20). The corresponding spin rates utilized are A, 465 B, 479 C, 425 D, 500 ...

To see that the last point is not necessarily true it is only necessary to state its implications a little more carefully. While it is, perhaps, not unreasonable to expect that the total electron density at symmetry-equivalent points in a molecule to be the same, point 3 above goes very much further than this. What it says is that in an n-electron system the total electron density at symmetry-equivalent points is the same because it is composed of n separate electron densities, each of which is separately identical at symmetry-equivalent points in the molecule. This is surely a priori unreasonable to ask that the separate electron densities compensate for each others distributions to give a symmetrical electron distribution is fair but to ask each electron individually to have a symmetrical distribution is a little restrictive. In practice, it is found that even this weak and reasonable constraint is not obeyed in every case. 

A density compensation procedure has recently been developed whereby a calibration plot obtained using, for example, polystyrene bead standards can be used to obtain a particle size distribution for a material of different density. Equation (5) shows that 6 is inversely dependent on the product ApG. If a change in Ap is compensated by a change in G so that the product remains constant, then 5 will be independent of Ap and particles of a given diameter, even if different in density, will elute in the same time. The procedure for obtaining the PSD of particles of arbitrary density from the recorded fractogram has also been described. ... 

The apparent lift experienced by micron size particles migrating close to a wall has not been satisfactorily explained. Our empirically derived lift force expression is consistent with the observation that calibration plots of log(retention time) versus log(diameter) are invariably quite linear over a wide range of particle sizes. Work is in progress to more fully elucidate the nature and mechanism of the lift forces. In the meantime, rapid and accurate particle size analysis, with the advantage of collectable size fractions, can presently be achieved based on empirical calibration and density compensation. 

The exchange current densities io,io (cf. Section 6.7) contain the concentrations as well as the equilibrium potential terms. In addition, their absolute values must be equal since the partial current densities compensate each other for = 0 (i=0). 

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