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Thermal Conductivity Analyzer
The Temperature Control Board keeps the temperature of the measuring
cell regulated to within 1 ° C at 60 ° C. A thermistor is used to measure
the temperature located under the TC detector, the main board regulates
the power in a cartridge-type heater. The result is a sensor output signal
that is temperature independent.
In the presence of dissimilar gases, the sensor generates a
differential voltage across its output terminals. A differential amplifier
converts this signal to a unipolar signal, which is amplified in a variable
gain amplifier, providing automatic range switching under control of the
CPU. The output from the variable gain amplifier is sent to an 18-bit
analog-to-digital converter.
The digital concentration signal, along with input from the control
panel, is processed by the CPU and passed on to the 12-bit DAC, which
outputs 0-1 V dc Concentration and Range ID signals. By user selection,
the converter can also provide 4-20 mA dc concentration signal and
range ID outputs.
The CPU also provides appropriate control signals to a Beagle
Bone PCB to update a touchscreen LCD Display, Alarms, and External
Valve Controls, and it accepts digital inputs for external Remote Zero
and Remote Span commands.
The RS-232 port provides two-way serial digital communications
to and from the CPU. A Profibus port is also available in version DP-
V0. A GSD file is needed by the Profibus master to connect to the
2000RS. Request the GSD file from the factory. These and all of the
above electrical interface signals are described in detail in chapter 3
Installation.
Teledyne Analytical Instruments
Operational Theory
11
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