Teledyne GFC-7000T - Trace CO2 Analyzer - manual - Manual (Page 73)

FAQ Model GFC7000TA Carbon Dioxide Analyzer
Teledyne Analytical Instruments 55
GFC Wh
ee
l
Hous
ing
SAMPLE CHAMBER
GFC M
o
tor
He
at Sy
nc
Purg
e Gas
F
low
C
o
nt
ro
l
Ext
e
rn
al CO2
Sc
rub
ber
(O
pt
io
n
51
on
ly
)
Figure 5-2: Internal Pneumatic Flow – Ambient Zero/Pressurized Span Valves
5.4.2. Ambient Zero/Ambient Span Valve
This valve option is intended for applications where zero air is supplied by a zero air generator like a
bottle of N
2
and span gas are being supplied by Gas Dilution Calibrator like the Teledyne Instruments
Model 700 or 702. Internal zero/span and sample/cal valves control the flow of gas through the
instrument, but because the calibrator limits the flow of span gas no shutoff valve is required.
In order to ensure that span gas does not migrate backwards through the vent line and alter the
concentration of the span gas, a gas line not less than 2 meters in length should be attached to the vent
span outlet on the rear panel of the analyzer. To prevent the buildup of back pressure, this vent line
should not be greater than 10 meters in length.
The following table describes the state of each valve during the analyzer’s various operational modes.
Table 5-2: Ambient Zero/Ambient Span Valve Operating States
Mode Valve Condition
SAMPLE
(Normal State)
Sample/Cal Open to SAMPLE inlet
Zero/Span Open to IZS inlet
ZERO CAL
Sample/Cal Open to ZERO/SPAN valve
Zero/Span Open to IZS inlet
SPAN CAL
Sample/Cal Open to ZERO/SPAN valve
Zero/Span Open to PRESSURE SPAN inlet