Detector - Honeywell ENCAL 3000 Hardware Manual

PROCESS GAS CHROMATOGRAPHY – GENERAL INTRODUCTION
4.1.2

Detector

The thermal conductivity detector (TCD), known as the detector for short, is a relatively
simple, very efficient, robust detector which is very widely used in the natural gas
industry. The most popular detector is the TCD: Thermal Conductivity Detector.
Another reason for the popularity of the TCD in the natural gas industry is the fact that
gas chromatographs are used mainly for the measurement of gas properties like heating
value, Relative density and Wobbe index. The calculation of these parameters is based
on the concentrations of the main gas components.
TCDs newer design in MEMS technology (MEMS = Micro-Electro-Mechanical System),
which are also used in the EnCal 3000 are much smaller in terms of volume. The
components can be integrated at the same time much more accurately, so that the
analytical precision is for example 1 ppm for n-pentane.
Traditionally the two TCD's (reference + measurement detector) are integrated in a so-
called Wheatstone configuration, which increases significantly the signal-to-noise
ration of the measurement.
Figure 4.3: Typical electrical TCD circuit
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