BUCHI DuMaster D-480 - Manual (Page 52)

Operation Manual D-480 ©BÜCH Labortechnik AG
4 - Understanding the instrument and planning its use 52
Filling the post combustion tube
The following picture shows the fillings and filling heights of the post combustion tube:
Legend:
1 Silver wool
2 Corundum balls (76 mm)
3 200 g CuO + 15 g Pt catalyst (180 mm)
4 Corundum balls (50 mm)
5 Wire mesh ronde (22 mm)
6 Spacer
Working temperature 800 °C
Background knowledge required for calibration
Important calibration principles
Perfect calibration of the instrument is a key condition for achieving correct analysis results. The
calibration has to be carried out over the whole measuring range.
For successful calibration the user must be familiar with the analyzer and the operating instructions.
The personnel performing calibration must therefore be authorized and must have undergone
appropriate training.
Purpose of instrument calibration
The analyzer does not measure the absolute content of an element in the sample but rather only
changes of the element portion in the combustion gases. These changes cause an electrical signal in
the detector that is recorded and integrated by the software depedent on time.
In order to create a correlation between the integrated detector signal and the absolute element
content of the analysis samples, a series of calibration samples with known element content and
different sample weights are measured. The software computes the calibration factors on the basis of
the known element contents and the sample weights of the calibration samples.
Conditions for perfect calibration
In order to be able to calibrate the instrument perfectly, the following conditions must be met:
 The instrument must have passed the leak test.
 The instrument blank values must be low and roughly constant.
 Only use suitable substances of at least p.a. quality or certified standards as calibration samples.
 The concentration values of the calibration samples must cover the whole measuring range.
When to calibrate the instrument
It is always necessary to calibrate the instrument when one of the following is true:
 You have removed components that influence analysis results, e.g. the detector.