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Teledyne API – Model T400 O
3
Analyzer
083730400A DCN8130
6.2.1 S
AMPLE
G
AS
A
IR
F
LOW
The flow of sample gas through the T400 analyzer is produced by an internal pump that
draws a small vacuum on the downstream side of a critical flow orifice thereby creating a
controlled airflow through the analyzer’s absorption tube and other components. This
requires the analyzer gas inlets be at or near ambient pressure usually managed by
placing a vent line on the incoming gas line (see connections in Section 2.3.2).
By placing the pump down stream from the sample chamber, several problems are
avoided.
•
First, the pumping process heats and compresses the sample air complicating the
measurement process.
•
Additionally, certain physical parts of the pump itself are made of materials that might
chemically react with the sample gas.
•
Finally, in certain applications where the concentration of the target gas might be high
enough to be hazardous, maintaining a negative gas pressure relative to ambient means
that should a minor leak occur, no sample gas would be pumped into the atmosphere
surrounding analyzer.
INSTRUMENT CHASSIS
Flow / Pressure
Sensor PCA
SAMPLE
PRESSURE
SENSOR
O3 FLOW
SENSOR
Sample Gas
Flow Control
EXHAUST
GAS
OUTLET
Particulate
Filter
PUMP
DRY AIR
INLET
O
3
Scrubber
ABSORPTION TUBE
SAMPLE
GAS INLET
SPAN GAS
INLET
ZERO AIR
INLET
Measure/
Reference
Valve
Figure 6-3. Internal Pneumatic Flow – Basic Configuration
6.2.2 F
LOW
R
ATE
C
ONTROL
To maintain a constant flow rate of the sample gas through the instrument, the T400 uses
a special flow control assembly located downstream from the absorption tube and in the
exhaust gas line just before the pump (see Figure 10-7). This assembly consists of:
•
A critical flow orifice.
•
Two o-rings: Located just before and after the critical flow orifice, the o-rings seal the
gap between the walls of assembly housing and the critical flow orifice.
•
A spring: Applies mechanical force needed to form the seal between the o-rings, the
critical flow orifice and the assembly housing.
Содержание T400
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