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Thermal Conductivity Analyzer Part II: Analysis Unit
Teledyne Analytical Instruments Part II: 2-7
Figure 3-6: FET Series Resistance
2-11 Signal Wiring Recommendations
The signal leads are the bias and sensor leads ref fig. 3.4, and reference
D-73170 interconnection diagram. The maximum interconnection distances
between the 2010 control unit and the analysis unit is limited by the sensor
signal requirements. The sensor has two limiting factors. The first is series
resistance which is limited to a maximum of 2.5 ohms. Refer to the intercon-
nection diagram for wire gages and distances which will meet this require-
ment.
The second issue is one of signal quality. At greater distances prob-
lems associated with signal degradation increases. Signal degradation prob-
lems have two major issues. The first is associated with the local installation
environment. The number, proximity, and power associated with local
sources of EMI radiation can not be accounted for by TAI. These issues can
only be controlled by the end user. The other factor is the amplitude of the
signals generated by the thermal conductivity cell. This signal level is a
function of the gas composition of the gases involved. This signal level can
vary from micro-volts to mili-volts dependent on application. Consult TAI
for recommendations based on sample stream composition. Signal quality
and operating distances can be increased by the uses of better quality
shielded low loss cable. The cable configuration should be twisted pair with
double shielding for best performance. The signal cable should not be run
with AC power or digital signals.
2-12 Testing the System
After The Control Unit and the Analysis Unit are both installed and
interconnected, and the system gas and electrical connections are complete,
the system is ready to test. Before plugging either of the units into their
respective power sources: