Buchi DuMaster D-480, Руководство по эксплуатации

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Operating instructions DuMaster D-480 ©BÜCHI Labortechnik AG
4 - Understanding the instrument and planning its use 48

The post combustion tube is used to complete oxidation of the sample.

The gas stream is predried in the water condenser (8) as well as the gas drying. In the
downstream gas drying and drying tube (8), the residual moisture is removed.
Detection of measuring components and evaluation of the measuring signal
Introduction
The following section explains how the measuring components are detected in the reaction gas
mixture and how the measuring signal is evaluated.
Process
Detection of the measuring components and evaluation of the measuring signal take place in the
following phases:

Depending on the type and concentration of the measuring component, the thermal conductivity
detector sends an electrical measuring signal to a microcontroller. This controller integrates the
measuring signal. Cf.
The thermal conductivity detector (TCD)
(on page 45).

In the PC the measuring signal

is recorded dependent on time

and displayed as an integral.

The integral value is assigned to an absolute nitrogen content of the sample via a non-linear
calibration. See
Background knowledge required for calibration
(on page 51).

The nitrogen percentage of the sample is calculated from the found absolute nitrogen content
and the sample weight. An empirical factor (protein factor) translates the nitrogen content to the
protein content.
Formulas for determining element concentration of analysis samples (Solids)
Process
During an analysis, the system first measures the absolute element content of the sample.

The peak area value of the N component of the sample is determined.

The blank value is factored in.

The absolute N content of the sample is computed on the basis of the calibration coefficients.

The daily factor is factored in.
The N concentration of the sample is calculated from the computed absolute N content and the
sample weight by the following formula:
where:
c = element concentration in [%]
a = absolute element content in [mg]
f = daily factor
w = sample weight in [mg]