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Principles of Operation Teledyne API – Model T700 Dynamic Dilution Calibrator
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In this case, Totalflow is calculated as:
Equation 10-4
flow
flowflow
OGASNOTotalflowDIL
3
= - -
WHERE:
NOGAS
flow
= NO source gas flow rate (For calibrator’s with multiple source gas
MFC, NOGAS
flow
is the sum of the flow rate for all of the active cal
gas MFCs)
Totalflow
= total gas flow requirements of the system.
O
3 flow
= the flow rate set for the O
3
generator.
DIL
flow
= required diluent gas flow
Again, this is a dynamic process. An optional photometer can be added the T700
calibrator that allows the CPU to tracks the chemiluminescent reaction created when the
NO and O
3
interact to measure the decrease in NO concentration as NO
2
is produced.
This information, along with the other data (gas temperature and pressure, actual flow
rates, etc.) is used by the CPU to establish a very accurate NO
2
calibration mixture.
10.2. PNEUMATIC OPERATION
The T700 calibrator pneumatic system consists of the precision dilution system and
valve manifold consisting of four gas port valves and one diluent air valve. When
bottles of source gas containing different, gases are connected to the four source-gas
inlet-ports, these valves are used to select the gas type to be used by opening and closing
off gas flow from the various bottles upstream of the MFCs.
IMPORTANT
IMPACT ON READINGS OR DATA
Exceeding 35 PSI may cause leakage that could cause unwanted gases to
be included in the calibration mixture. Each valve is rated for up to 40 PSI
zero air pressure and the source gas pressure should be between 25 to 30
PSI and never more than 35 PSI.
By closing all of the four source gas input valves so that only zero air is allowed into the
calibrator, the entire pneumatic system can be purges with zero air without having to
manipulate the MFCs.
For an instrument in which the O
3
generator and GPT pneumatics are installed, a glass
volume, carefully selected per the U.S. E.P.A. guidelines is used to optimize NO
2
creation.
See Figure 3-21 and Section 3.3.2 for descriptions of the internal pneumatics for the
T700 calibrat
o
r.
06873B DCN6388