Teledyne 2000XTC - Thermal conductivity analyzer - Manual (Page 15)

Thermal Conductivity Transmitter Operational Theory
Operational Theory
2.1 Introduction
The 2000 XTC is comprised of two subsystems:
1. The thermal conductivity sensor and transmitter
2. Galvanic isolator and power supply
The system directs a sample gas into the transmitter. Internally, the
sample is passed to the sensor and heated without contaminating or
altering the sample in any way. The thermal conductivity sensor is a
solid-state device that translates the amount of gas present in the sample
into a change in resistance (expressed in ohms). The electronic signal
processing and control circuits provide a linear output signal
compensated for ambient temperature fluctuations over a wide range.
Increased stability is achieved using integral heaters that control the
temperature of the sensor cell.
2.2 The Thermal Conductivity Sensor
The Thermal Conductivity Transmitter is designed to measure the
concentration of a component in a binary stream of gas. It can be used to
determine the concentration of a sample stream containing a composite
mixture of impurities by comparing the difference in thermal conductivity of
the sample stream with calibrated reference points.
Thermal conductivity measurements are non-specific by nature.
The thermal conductivity of a gas mixture depends on the conductivities
of the individual components of the mixture and their relative
concentration. The transmitter is calibrated at the factory to be linear
over the range and mixture of interest specified by the customer at the
time of purchase. In order to accurately detect and quantify a component
in a sample stream, the sample must be composed of the particular
component and background gas specified at the time of purchase. The
transmitter can be used with other binary gas mixtures, but the output
signal may or may not be linear across the sensor output range. Consult
the factory for additional information regarding the use of this
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