Thermo Scientific FOCUS GC, Instruction Manual

Page: 184 / 356

Chapter 9
Thermal Conductivity Detector (TCD)
Detector Signal Parameters
184 Instruction Manual
OPERATING SEQUENCE
Setting the TCD Signal Parameters
1. In Main Menu move the cursor until
Signal
is selected. Press ENTER to
display the
SIGNAL
menu.
2. Scroll to
Gain
and set the desired value. When the gain is x10, the system
sensitivity is higher.
3. If required, scroll to
Neg polarity?
and set
YES
to reverse the polarity
output signal as a function of the thermal conductivity of the carrier gas
versus the sample.
4. With all gas flows and temperatures adjusted and stable, and with the
filaments on and stable, scroll to
Offset
and set
OFF
.
5. Zeroing the Signal.
Every time the set condition of filaments temperature and voltage are
changed, an adjustment of the Zero level may be necessary in order to balance
the bridge.Usually this operation is performed by scrolling to
Autozero
function and setting
ON
.
In case of a particularly unbalanced bridge, the Autozero function may not
work and it is necessary to adjust the zero manually as shown in
Figure 9-2. Use the little screwdriver, provided in the standard outfit, to adjust
the zero potentiometer until a signal of
1000
is visualized.