Measurement off-line

If produc t moisture is measured off-line, analytical results can be used to adjust K and Tb manually. If an on-hne analyzer is used, the analyzer controller would be most effective in adjusting the bias Tb, as shown in the figure. 

The main error sources are noise in the wavefront sensor measurement, imperfect wavefront correction due to the finite number of actuators and bandwidth error due to the finite time required to measure and correct the wavefront error. Other errors include errors in the telescope optics which are not corrected by the AO system (e.g. high frequency vibrations, high spatial frequency errors), scintillation and non-common path errors. The latter are wavefront errors introduced in the corrected beam after light has been extracted to the wavefront sensor. Since the wavefront sensor does not sense these errors they will not be corrected. Since the non-common path errors are usually static, they can be measured off-line and taken into account in the wavefront correction. 

The PLS model generated on samples prepared according to the Latin squares experimental design was used to predict the key compact attributes from the real-time spectral data collected for roller compacted samples (Fig. 8). Good agreement was observed between the NIR-predicted values and the values measured off-line using the reference methods (Table 16). 

The spinning solution composition was measured off-line using a Foss NIRSystems Model 6500 VIS-NIR analyzer (wavelength range 400-2500 nm), equipped with a... 

Also shown in Figure 2 are the locations of two cut points defined by the instantaneous purities Pu and Pd, where P is the mass fraction of desired component. It should be noted that on-line species-specific detection for determining cut points is particularly useful in displacement chromatography since the formation of bands in close proximity to each other makes nonspecific detection (e.g., the monitoring of UV absorbance) ineffective. Note also that fixed values for Pu and Pd will in general not correspond to a fixed value for the purity of the product fraction, which is presumed to be measured off-line and will be denoted by the symbol Pp. For example, if the concentration of the desired component in the feed tank to the preparative column is reduced or if the relative sensitivity of the monitoring method to the impurities decreases, the values of Pu and Pd used to define cut points would have to be increased if the desired average purity for the entire product fraction is to be maintained. 

Fig. 3. (a) Schematic of the thin film target for the d/xt formation measurements consisting of the emission, the moderation and the reaction layers, which are prepared by rapidly freezing hydrogen isotopes on the gold foils (not shown) held in vacuum at 3.5 K. [13] The layer thickness (3.43 mg-cm-2, 96 pg-cm-2, and 21 pg-cm-2, respectively) were measured off-line via a particle energy loss (see Fig. 5) (b) Measured Si energy spectra with prompt (I t > 0.02 ps) and delayed (II t > 1.5 ps) time cuts. Fusion in DS reaction layer is separated from that in US D2 due to the pf TOF across the vacuum... 

Because direct dynamic measurements of materials state within the barrel are impossible, the structural and molecular changes relevant to extrusion must be measured off-line and related to real process conditions. In principle, we need to explain not only the effect of applied physical parameters of heat, shear and pressure, but also the effect of formulation. This is not yet possible, and for reasons stated above, the behaviour of carbohydrate (starch) dominated systems will be quite different from proteinaceous systems, since their heat denaturation behaviour and glass to rubber transitions are different in detail during their conversion from a moist powder to a continuous melt. ... 

The analysis of the produced LCV gas is performed directly behind the ceramic candle filter by means of continuous on-line O2 (paramagnetic), CO- and CO2 (NDIR) analysers. In addition, H2, CO, CH4 and N2 concentrations are measured off-line by means of a gas chromatograph. An FTIR is used for measurement of NHj, HCN, CO, COj, CH4, C2H4, C2H2, HCl, COS and HjO. 

The measurement of physical properties is relative easy and can be carried out on-line and/or off-line. Temperature, pH and water activity should be measured and controlled aroimd a set point. Because the sohd substrate is consumed by microorganisms, the particle size, pile and real densities, pore size and surface area must be measured off-line and will change with time. 

Figure 20.3 On-line monitoring of the penicillin V production in a 160 bioreactor over 1-2 weeks using a thermistor-based biosensor equipped with a column containing penicillin V acylase. -I-, on-line biosensor values , penicillin V, penicilloic acid, and / -hydroxypenicillin measured off-line by HPLC o, off-line values of penicillin V measured by HPLC. (From [25] with permission.)...

The values of these two effective volumes constitute useful information for calculating the correct space time and obtaining a better understanding of the system, particularly the relation between the bulk volume of the solid as measured off-line and its effective volume in the reactor. 

Off line thermochemolysis is also possible at much lower temperatures (250°C). " Thermochemolysis reactions with TMAH can be conducted in a sealed glass ampoule thus allowing for more controlled conditions, where internal standards can be added to provide quantitative measurement. Off line thermochemolysis gives similar results as the more time consuming chemical degradation methods used in the analysis of organic matter. ... 

In the manufacture of color master batches, the current industry practice is to perform eritieal color measurements off-line. Typically, a sample of the pelletized color concentrate is diluted with natural resin at a standard ratio and milled, extruded or injection molded into a physieal form suitable for visual and instrumental evaluation. These methods are slow and labor intensive. Furthermore, they do not lend themselves well to statistical process eontrol strategies because of the time lag between production and testing. Since relatively few samples can be examined, laboratory measurements may not give a true indication of the consistency of the concentrate product over the entire manufacturing process. 

As discussed in Section 8.3.2, in addition to the fast and frequent on-hne measurement, some measurements may be available at infrequent and/or irregular times and with significant delays. For example, there may be a combination of MWDs and PSDs measured off-line by chromatographic methods and monomer concentrations measured in real time by spectroscopic methods. In these cases, the so-called multi-rate state estimators maybe applied. In these estimators, the fast measurements are used to estimate the state variables that are observable, while estimation of the non-observable variables is obtained in open-loop mode. When the (infrequent) measurement becomes available, the close-loop estimator is used. Ellis et al. [102] and Mutha etal. [108] used a multi-rate EKF to estimate monomer conversion and average molecular weights in the solution polymerization ofMMA. 

For the quantification of relatively large amounts of vitamin D, e.g. in pharmaceutical preparations, off-line spectrometric procedures can be considered. Spots eluted from the plates can be quantitated by spectrometric or gas-chromatographic procedures (28). Photodensitometry (reflectance spectrometry at 265 nm) and fluorodensitometry (after spraying the plate) are usually sufficiently sensitive to permit the determination of vitamin D in foods (34-36,38). The low concentrations of vitamin D metabolites in human plasma/serum can only be measured off-line by GC (25(OH)D) (40) or radioligand assays (25(OH)D and l,25(OH)2D) (41-43). 

Qn-tine viscometers should be carefully chosen—the amount of care depending on the complexity of the liquid. The viscosity of Newtonian liquids can be measured by any kind of viscometer. If the non-Newtonian liquid of interest is simple, then we wfil be able to correlate any in- or on- line viscosity with its carefully measured off-line equivalent. If however there is no simple correlation, we need to do our best to measure on-fine in the same way as we are measuring off-line. For instance a number of suitable concentric-cylinder type instniments are... 

Fig. 1.43. Comparison between calculated (US process data) and measured (off-line TGA) Mg(OH)2 contents in LDPE during twin screw extrusion. After Smith et al [911]. Reproduced by permission of the Society of Plastics Engineers (SPE).

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