Thermal Conductivity Transmitter
Operational Theory
Control circuitry precisely regulates the temperature of the
measuring cell. These additional controlled heaters are installed to heat
the sample gas and compensate for ambient temperature fluctuations,
enhancing the stability and accuracy of the measuring process. The
heater temperature is adjustable using a set-screw adjustment
potentiometer inside the transmitter unit.
Control of the sample and supporting gases is not provided in the
basic design. TAI offers a variety of supporting gas control panels as
companion accessories to the analyzer to fill this need. In any case,
means must be provided for controlling the flow rates of sample and
calibration gas through the analyzer. A control manifold will be required
for the introduction of zero and span gas, as well as sample gas, into the
sample path. Appropriate pressure reducing regulators will have to be
installed at all gas supply sources; for those customers wishing to
incorporate their own sample controls, a recommended system piping
drawing is shown in Figure 2.2 and a reference drawing is included
among the drawings at the rear of the manual.
2.3 Sample System
A suitable external sample system must be provided by the
customer. The external sample system delivers calibration or sample gas
to the transmitter at suitable pressure and flow rate. Internally, the 2000
XTC uses a brass cell block with stainless steel tubing and connectors.
CAUTION:
IT IS THE RESPONSIBILITY OF THE END-USER TO
ENSURE THAT THE GASES USED IN THIS
INSTRUMENT ARE COMPATIBLE WITH THE
MATERIALS USED IN THE SAMPLE SYSTEM. FAILURE
TO DO SO COULD RESULT IN PERSONAL INJURY AS
WELL AS DAMAGE TO THE INSTRUMENT.
The external sample system should be capable of supplying clean,
particulate-free and moisture-free sample gas to the transmitter. The
sample gas must be regulated between 2-20 psig. A flow control device
such as a flow meter with a needle valve should be incorporated to
maintain gas flow within 0.4-2 SCFH. It is convenient to install valves
in the sample system to allow switching between sample and calibration
gas. Figure 2-2 is a typical sample system for delivering sample and
calibration gases to the transmitter. It uses two (2) 3-way valves to
deliver either sample or calibration (zero or span) gas to the transmitter.
Teledyne
Analytical
Instruments
7
