Oscillometric measurement

High-frequency conductivity (oscillometric) measurement. Oscillometry (Blaedel and Petitjean 1956), i.e., the high-frequency method of chemical analysis to measure or follow changes in the composition of chemical systems was introduced to measure absorbed dose... 

In practice combined volumetric-gravimetric measurements have been fairly successful [0.31]. Also densimetric-volumetric and densimetric gravimetric measurements using magnetic suspension balances (2 positions and 3 positions types respectively) can be recommended. If swelling sorbent materials are considered (slow) oscillometric measurements are recommended. Chap. 5. In case of multicomponent sorption systems (N > 2) a gas analyzing system has to be used in any case. 

Spring balances for gravimetric and/or oscillometric measurements are not considered. Uncertainties of measurements often are to large and, in case of oscillations, the flow field of the surrounding gas becomes turbulent, i. e. the friction forces exerted by the gas on the sorbent sample cannot reliably be calculated from the Navier-Stockes-equations, cp. Chap. 5. 

Figure 5.2. Experimental setup for oscillometric measurements of gas adsorption equilibria using a rotational pendulum [5.1, 5.2].

These numerical values of dispersions (Ox) provided one can expect relative uncertainties of Gibbs excess masses measured with the rational pendulum to be limited by (a GE/mQg)<2%. This is about the accuracy of standardized volumetric / manometric measurements, cp. Chap. 2. To realize accurate oscillometric measurements it is most important to determine the (A) and ( ) parameters related to the various oscillations of the pendulum as accurate as possible, cp. Eq. (5.39). For this it is necessary to choose an initial amplitude (uo) of about 2-3 times the size of (ai, but less than 60 ° as for higher values of (Uo) measurable deviations of the oscillation from ideal harmonic behavior occur. Also it is necessary to observe at least 10 periods within an oscillation if not more, to get reliable (A, co)-data. To ensure this, the use of diodes with characteristic detection times less than 0.1 ms is recommended [5.7]. 

Figure 5.6 shows a top view of the ring slit on the disk of the pendulum filled with activated carbon Norit R1 Extra powder. Uniform distribution of the powder within the slit is mandatory to get reproducible results of oscillometric measurements. 

As can be seen the rngg j -data deviate only slightly, i. e. within experimental uncertainties which are about three times the size of the graphical symbols used, from the abscissa axis. Hence both measurement methods lead to the same experimental results thus proving consistency of oscillometric measurements, i. e. the key equation (5.39). 

In this section we will provide the reader with the basic equations allowing one to calculate from combined oscillometric and gravimetric measurements both the mass of gas (m ) adsorbed or absorbed in a swelling sorbent material of mass (m ) and its volume (V ) in the sorbate state at given pressure (p) and temperature (T) of the sorptive gas and sorbent material. We start by mentioning the result of oscillometric measurements, cp. Sect. 2.2, namely the relation (5.25)... 

Figure 5.16. Scheme of an instrument for manometric-gravimetric-oscillometric measurements of binary coadsorption equilibria in swelling materials (polymers, resins etc.) without sorptive gas analysis by GC or MS. 

By choosing proper materials for the pendulum, for example titanium for the disk, gold alloy for the torsional wire etc., oscillometric measurements can be performed in a fairly broad range of temperature and pressure and even in corrosive gas atmospheres where other techniques may fail or simply become inapplicable. 

Combining the dielectric measurements with either manometric, gravimetric or oscillometric measurements of gas adsorption equilibria states, one gets calibration curves allowing one the determination of Gibbs excess adsorbed masses by purely electric measurements which normally can be performed fairly quickly and on site in industrial situations. 

It should be emphasized that in principle impedance measurements also can be added to other experimental methods aiming at an analysis of gas sorption systems. Examples for these are volumetric-gravimetric measurements. Chap. 4, oscillometric measurements. Chap. 5, or ZLC-... 

Combined dielectric gravimetric oscillometric measurements of sorption equilibria of methane (CH4, 5.5) in polycarbonate (Goodfellow, UK), cp. Chap. 5, Sect. 3.4, (Figs. 6.30, 6.31). 

Ad 4. Dielectric-gravimetric-oscillometric measurements of sorption equilibria of methane in (swelling) polycarbonate. 

Another common failure is neglecting to instruct the patient to measure BP at home in order to use this to guide therapy. Measuring BP at home allows the practitioner to make decisions based on many more samples of BP rather than relying on readings taken every few months in the office. This also leads to overdiagnosis and overtreatment in those who have office hypertension but normal BP at home. However, many office and home devices now utilize the oscillometric technique, which leads to serious inaccuracies in at least 50% of patients. When BP is measured with an automated device, office staff should document the accuracy of each device on each patient, as all automated devices make serious systematic errors in at least 50% of patients, >5 mmHg (2). 

The American Heart Association (AHA) Guidelines 2005 state that Accurate measurement of blood pressure is essential to classify individuals, to ascertain blood pressure related-risk and to guide management. The auscultatory technique with a trained observer and mercury manometer continues to be the method of choice in the office. The oscillometric method can be used for office measurement, but only devices independently validated according to standard protocols should be used, and individual calibration is recommended (3). 

H. Rave, R. Staudt, J.U. Keller Measurement of sorption and swelling behaviour of polymer/C02 systems by a combined oscillometric-gravimetric method. Proeedings. of P3AC2, Brisbane, May 14-18, 2000, World Scientific, Singapore 2000. 

There has not been any prior analytical investigation of the arterial stiffening theory of pseudohypertension. The low arterial comphance theory is tested in this chapter via a mathematical model of oscillometric blood pressure measurement. The computational model will be used to evaluate measurement error introduced by arterial disease or alterations in arterial mechanics in general. Once these errors are established, the model will then be used to investigate the means by which automated blood pressure monitor may detect the occurrence of pseudo-hypertension or provide a correction method by which blood pressure accuracy is unproved even in the presence of arterial disease. 

The control model of the oscillometric blood pressure measurement was represented by the normal parameters of Table 12.1. 

Geddes, L.A., Voelz, M., Gombs, G., Reiner, D. Characterization of the oscillometric method for measuring indirect blood pressure. Ann. Biomed. Eng. 10 271-280,1983. 

Figure 6 (A) Inductance measuring oscillometric cell (From Pungor E (1965) Oscillometry and Conductometry. London Pergamon, with permission). (B) Capacitance measuring oscillometric cell.

There are, however, other measurement methods developed mainly for routine process control in radiation processing, such as high-frequency conductivity (oscillometric) analysis, spectrophotometric evaluation, and conductivity measurement. 

We here present a formula allowing one to calculate numerically the dispersions or mean square deviation (MSD) of Gibbs excess masses of adsorbates which have been measured oscillometrically and... 

Figure 5.7. Reduced masses (Hose, f grav) resulting from oscillometric and gravimetric adsorption measurements of He on activated carbon (Norit R1 Extra) at 293 K. Gibbs excess masses adsorbed (= 0, ) are calculated from (f2o c>...

Eqs. (2.9, 2.10). They show a monotonous increase with increasing sorptive gas density and coincide remarkably well thus proving - in this example -that oscillometric and gravimetric measurements lead (within experimental uncertainties) to identical results. 

Figure 5.9. Experimental setup for oscillometric-gravimetric measurements.

Combined oscillometric and gravimetric measurements provide a basis to determine simultaneously the mass and the volume of a swelling sorbent material like polymers or resins in a sorptive gas atmosphere. However measurements seem in practice to be restricted to determinations of sorption equilibria of these materials as the kinetics of mass uptake often is very slow. To give an example we mention that in case of sorption of CH4 on pellets of Makrolon 2400 at 35 °C, p = 2 MPa, it took more than 4 days till equilibrium was reached. 

Rotational Pendulum for combined oscillometric-gravimetric sorption measurements of gases in swelling (polymeric) materials. IFT University of Siegen, 1999. 

The solubility of carbon dioxide in a special polycarbonate (PC) (Goodfellow, UK) has been investigated experimentally by oscillometric-gravimetric measurements at T = 293 K for pressures up to 6 MPa, [5.7, 5.8]. 

In Figure 5.12 results of measurements are presented. The oscillometric data ( ) show a monotonic increase with the gas pressure (p), while the gravimetric data ( ) are strongly curved, clearly indicating the influence of buoyancy. At pressures above 5 MPa the microbalance reading becomes even negative, i. e. the effect of buoyancy becomes larger than the increase in mass due to absorption of CO2. 

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