Effects Of Flowrate And Gas Density; Measurement Results; Electronics And Signal Processing - Teledyne 2000RS Operating Instructions Manual

Thermal Conductivity Analyzer

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 a
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) for the measured heat-
transfer differences to be non-ambiguous.
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 Analyzer uses a microcontroller to control all signal
processing, input/output, and Communication to a display PCB interface
functions for the Analyzer. System power is external with requirements
of 24 vdc and at least 30 watts rating. External fuse recommendation is 2
A 250 V Type T, slow blow.
The temperature control circuit, the signal processing electronics –
including the microprocessor, analog-to-digital, and digital-to-analog
converters – are located on the Main board at the bottom of the case.
The amplifier section is part of the main board. The main board is
accessible after removing the back panel. Figure 2-2 is a block diagram
of the Analyzer electronics.
Teledyne Analytical Instruments
Operational Theory
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