Teledyne 2020 - Explosion proof thermal conductivity analyzer - Manual (Page 15)

2-3
Thermal Conductivity Analyzer Operational Theory 2
Teledyne Analytical Instruments
2.2.3 Effects of Flowrate and Gas Density
Because the flowrate of the gases in the chambers affects their cooling
of the heated filaments, the flowrate in the chambers must be kept as equal,
constant, and low as possible.
When setting the sample and reference flowrate, note that gases
lighter than air will have an actual flowrate higher than indicated on the
flowmeter, while gases heavier than air will have an actual flowrate lower
than indicated. Due to the wide range of gases that are measured with the
Thermal Conductivity Analyzer, the densities of the gases being handled
may vary considerably.
Then, there are limited applications where the reference gas is in a
sealed chamber and does not flow at all. These effects must be taken in
consideration by the user when setting up an analysis.
2.2.4 Measurement Results
Thermal conductivity measurements are nonspecific by nature. This
fact imposes certain limitations and requirements. If the user intends to
employ the analyzer to detect a specific component in a sample stream, the
sample must be composed of the component of interest and one other gas
(or specific, and constant, mixture of gases) in order for the measured
heat-transfer differences to be nonambiguous.
If, on the other hand, the user is primarily interested in the purity of a
process stream, and does not require specific identification of the impurity,
the analyzer can be used on more complex mixtures.
2.3 Electronics and Signal Processing
The Model 2020 Thermal Conductivity Analyzer uses an 8031 micro-
controller, Central Processing Unit—(CPU) with 32 kB of RAM and 128
kB of ROM to control all signal processing, input/output, and display
functions for the analyzer. System power is supplied from a universal
power supply module designed to be compatible with any international
power source. (See Major Internal Components in chapter 5 Maintenance
for the location of the power supply and the main electronic PC boards.)
The Temperature Control board is mounted under the electrical
connection board.. The signal processing electronics including the micro-
processor, analog to digital, and digital to analog converters are located on
the Motherboard at the front door of the unit. The Preamplifier board is