Operational Theory; Sensor Theory; Principles Of Operation - Teledyne 2000RS Operating Instructions Manual

Thermal conductivity analyzer

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Thermal Conductivity Analyzer

Operational Theory

2.1 Introduction

The analyzer is composed of two subsystems:

1. Thermal Conductivity Sensor

2. Electronic Signal Processing, Display and Control.

The sensor is a thermal conductivity comparator that continuously

compares the thermal conductivity of the sample gas with that of a

reference gas having a known conductivity.

The electronic signal processing, display and control subsystem

simplifies operation of the analyzer and accurately processes the

sampled data. A microprocessor controls all signal processing,

input/output, and display functions for the analyzer.

For greater clarity, Figure 2-1 presents two different illustrations,

(a) and (b), of the operating principle of the thermal conductivity cell.

The thermal conductivity sensor contains two chambers, one for the

reference gas of known conductivity and one for the sample gas. Each

chamber contains a pair of heated filaments. Depending on its thermal

conductivity, each of the gases conducts a quantity of heat away from

the filaments in its chamber. See Figure 2-1(a).

The resistance of the filaments depends on their temperature. These

filaments are parts of the two legs of a Wheatstone bridge circuit that

unbalances if the resistances of its two legs do not match. See Figure

2-1(b).

Teledyne Analytical Instruments

Operational Theory

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