Nonlinearity, weighing

Different Approaches for Linearity Determination. The first approach is to weigh different amounts of authentic sample directly to prepare linearity solutions of different concentrations. Since solutions of different concentration are prepared separately from different weights, if the related substances reach their solubility limit, they will not be completely dissolved and will be shown as a nonlinear response in the plot. However, this is not suitable to prepare solutions of very low concentration, as the weighing error will be relatively high at such a low concentration. In general, this approach will be affected significantly by weighing error in the preparation. 

The architecture of a common NN is shown in Fig. 10.8. The design depends on the types of sensor responses, on their dynamic range, drift, and so on. In short, it depends on all the complexities of the transfer functions of different types of sensors. Once again there is an input layer containing m input elements. It is massively interconnected to the n nodes of the next hidden layer %n at which the weighing factors Wn operate on the signal. There can be more than one hidden layer, if necessary. The connection to the output layer 0O has the form of nonlinear transfer function /hid for example,... 

This is useful for pattern recognition. The parameter / influences the nonlinearity of the hidden layer transfer function. The training of the NN is then based on the feedforward and backpropagation algorithm, in which the weighing factors Wn are adjusted during the NN learning in order to minimize the difference between the desired output D and the actual output Y. 

Another property that could also be used is the density, which varies in a nonlinear way between 0.9478 g/mL for cyclohexanone and 1.600 g/mL for tetrachloroethane at 20°C. In this case, a calibration curve should be constructed from known solutions or provided by the instructor. The density of each distillation sample can be measured by pipetting 1 mL into a small, previonsly weighed vial and then weighing again (to the nearest 0.1 mg). 

Fig. 29.4 Propoties of weighing insbumcaits The dashed line with the assoeialed grey area represents the sensitivity offset of the instrnment, snpeiimposed is the nonlinearity (blue area, indicating the deviation of the characteristic curve from the straight line). The red circles represent the measurement values caused by eccentric loading, and the yellow circles represent the distribution of the measurement values due to repeatability, from Mettler-Toledo [13] with permission...

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