Error calibration offset

To replace the concentration term by the respective signal term one can use Eq. 2-59. From this result both variances for the special points x, = 0 and x, = x follow immediately. The first variance then characterizes the error of the calibration offset. v2 ( ). The second term, in brackets in Eq. 2-61, shows that we can expect minimum errors of the calibration process around the middle of the calibration (concentration) range, x, xc ... 

E° [equation (15.4)] is also referred to as the offset, the zero potential point, or the isopotential point, since theoretically it is defined as the pH that has no temperature dependence. Most pH electrode manufacturers design their isopotential point to be 0 mV at pH 7 to correspond with the temperature software in most pH meters. The offset potential is often displayed after calibration as an indication of electrode performance. Typical readings should be about 0 30 mV in a pH 7 buffer. In reality, E° is composed of several single potentials, each of which has a slight temperature coefficient. These potentials are sources of error in temperature compensation algorithms. 

Elemental balancing permits the determination of (other) metabolic rates provided the stoichiometry is known. Carbon balances are the most useful but the carbon lost via the exhaust gas (as C02) and culture liquid (as HC03) must be measured. Heinzle et al. [161] determined that the state predictions based on experiments with a small quadrupole mass spectrometer were not useful due to unacceptable error propagation for instance, a 1 % relative offset calibration error could result in a prediction error for an intracellular storage material (PHB)... 

I. Reda, J. Hickey, C. Long, D. Myers, T. Stoffel, S. Wilcox, J. J. Michalsky, E. G. Dutton, and D. Nelson, Using a blackbody to calculate net-longwave responsivity of shortwave solar pyranometers to correct for their thermal offset error during outdoor calibration using the component sum method, Journal of Atmospheric and Oceanic Technology 22 1531 (2005). 

As already mentioned, compensation and calibration methods may be used to improve the accuracy of the output signal. From Figure 3.8a and b and Eqs. 3.11— 3.14, it is obvious that a sensitivity or an offset error can be calibrated by identifying the input/output characteristics at a single point of the transfer function at several temperatures the appropriate temperature coefficients can then be deduced. In case of a superposition of sensitivity and offset deviations, calibration can also be done by measuring the input/output characteristic at at least two points. 

However, this method is not applicable to all situations. Figure 3.8 d shows that detecting the input/output characteristics at several points is not sufficient to calibrate sensitivity and offset errors if there are nonlinear effects involved. Here, a complete system identification might be necessary, depending on the order of the effects. Calibration of this kind of error is possible in theory, but not practicable, considering the expense in time and money. 

Facility Performanee. For gas flow calibration facilities, the precision can be evaluated from the appropriate error budget and from the precision of the eomponent measurements that constitute the system. Difficulty is encoimtered when faeihty accmacy is to be quantified because the hue value of the gas flowrate is not easily obtained. To estimate possible systematic offsets from hue value, approximahons— generally very eonservative, are frequently used. Alternatively, and more preferably, a realistic and highly defensible haeeability scheme either is available or ean be generated and is appropriately used to document the systemahe offset of a calibration faeihty. 

Such a signal can be used to monitor a surface. The automatic error compensation of the four-zone null technique must be replaced by a calibration technique for the offsets. 

These analyses were extended to include the trypsin treated samples. Figure 8 shows sample variability between UT and TT sections for the two techniques (A) optical absorbance and (B) EDX. The TT sections show a reduction to almost zero in optical absorbance but with EDX, although reduced, there is still a variable sulphur content due the residual sulfur in other protein constituents. PLS model predictions for the TT samples showed similar trends but with significant zero offset errors (data not presented). Inclusion of TT treated samples in the calibration data set improved the prediction of these low-S samples but at the cost of increased SEC overall. 

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