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Teledyne API – Model T700 Dynamic Dilution Calibrator Overview of Operating Modes and Basic Operation
113
4.2.4. GENERATE GPTPS: PERFORMING A GAS PHASE TITRATION
PRE-SET
The GPT Pre-Set feature simulates a GPT mixing operation in order to determine the
exact output of the calibrators O
3
generator. As described in Section 4.2.3.1, all other
things being equal, the concentration of the NO
2
being generated using the GPT feature
will be equal to the amount of O
3
used. Therefore, the more accurately the O
3
generator
performs the more accurate the NO
2
output will be.
When operating in GPTPS mode diluent gas (zero air) is substituted for the NO gas that
would be mixed with the O
3
in normal GPT mode. The resulting unaffected O
3
output
of the O
3
generator is shunted through the T700’s internal photometer, which measures
the ACTUAL O
3
concentration in the gas.
Once the exact
O
3
concentration being output by the generator is determined, the
calibrator’s software adjusts the O
3
drive voltage up or down so that the output of the
generator matches as closely as possible, the target concentration requested. This
adjusted generator setting will be used during any subsequent real GPT operation.
Note
The T700 has a learning algorithm during the O
3
generation (see Section 4.2) or
Gas Phase Titration Pre-Set Mode (GPTPS) (Sections 4.2.3.5 and 4.2.4). It may
take up to one hour for each new concentration/flow (point) that is entered into
the instrument. Once the instrument has several points memorized in its cache,
any new point that is entered will automatically be estimated within 1% error
(with photometer) and 10% error (with O
3
generator and GPTPS).
Note
This adjustment is only valid for the O
3
concentration used during the Pre-Set
operation. GPT Presets must be re-run for each different target NO
2
value.
In order to keep the resulting concentration of O
3
consistent with the GPT mixture being
simulated, the instrument’s software adjust the flow rate of the diluent gas to substitutes
an amount of diluent gas equal to the amount of NO gas that would normally be used.
4.2.4.1. T700 Calibrator GPTPS Operation
The following table and figures show the status of the T700’s internal pneumatic
components and internal gas flow when the instrument is in GPTPS generating modes.
Table 4-6: Status of Internal Pneumatics During GENERATE GPTPS Mode
VALVES
(X = Closed; O = Open)
MFCs
MODE
CYL
1
CYL
2
CYL
3
CYL
4
PURGE DILUENT GPT
O
3
GEN
PHOT M/R
CAL1 CAL2
1
DILUENT
PHOT
PUMP
GPTPS X
X X X X O O O
Switching
OFF
OFF
ON ON
1
Only present if multiple cal gas MFC option is installed.
2
The valve associated with the cylinder containing NO source gas is open.
3
In instrument with multiple MFCs the CPU chooses which MFC to use depending on the target gas flow requested.
06873B DCN6388