Buchi DuMaster D-480, Operation Manual, Page: 45 / 354

Operating instructions DuMaster D-480 ©BÜCHI Labortechnik AG
4 - Understanding the instrument and planning its use 45
Detector (IV)
The following table describes the components of the unit and their functions:
Part Name Function
9 Reference cell 
reacts to fluctuations in the composition of the analysis gas
mixture with an electrical signal to which a measuring
component can be assigned.
10 Measuring cell 
see "Reference cell".
For details on the working principle of the detectors, see
Detecting measuring components and
evaluating the measuring signal
(on page 48).
The thermal conductivity detector (TCD)
Design
The thermal conductivity detector (TCD) consists of two chambers through which the analysis gas
mixture (measuring cell) and the pure carriage gas (reference cell) simultaneously flow through during
the analysis. The chambers form a measuring bridge.
Working principle
The thermal conductivity of the carrier gas reacts sensitively on the addition of small amounts of
foreign gases such as the measuring component N. If this measuring component exists in the
analysis gas mixture, this leads to a disturbance of the measuring bridge that is registered in the form
of an electrical signal.
Further processing of the measuring signal
The TCD measuring signal is digitized, integrated and output by the instrument to the PC, where it is

registered in the form of a measuring peak dependent on time,

and the integral is correlated with the absolute quantity of the respective measuring component
by calibration functions.