Sample Gas Flow Valves And Routing; Flow Rate Control - Critical Flow Orifices; Table 6-2. Valve Cycle Phases - Teledyne T200 User Manual

SAMPLE GAS FLOW VALVES AND ROUTING

As discussed in Section 6.1, the measurement of NO
gas flow cycles through different routes that include and exclude various scrubbers and
converters. There are several valves that perform this function:
• The NO/NO
the unit's NO
• The Auto Zero valve directs the sample gas stream to completely bypass the reaction
cell for dark noise measurement once every minute, which is then subtracted as a
measurement offset from the raw concentration signal.
NO/ NOX
PHASE VALVE
STATUS
Open to
NO
Auto Zero
Measure
valve
Open to
NO
X
NO
2
Measure
converter
Open to
Auto
Auto Zero
Zero
valve
F R
LOW
Sample gas flow in the analyzer is created via the use of several flow control assemblies
(see Figure 6-6 for an example) located in various places in the gas streams of the
instrument. These assemblies consist 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 sintered filter
•
• a spring (applies mechanical force needed to form the seal between the o-rings, the
critical flow orifice and the assembly housing)
186 Teledyne API T200 NO/NO
valve directs the sample gas either directly to the reaction cell or through
X
converter, alternating every ~8 sec.
2

Table 6-2. Valve Cycle Phases

AUTO
ZERO TIME
VALVE INDEX
STATUS
Wait period (NO dwell time). Ensures reaction cell has
0 - 2 s
been flushed of previous gas.
Open to
reaction cell
Analyzer measures chemiluminescence in reaction
2 - 4 s
cell.
Wait period (NO
4 – 6 s
has been flushed of previous gas.
Open to
reaction cell
Analyzer measures NO + O
6 – 8 s
reaction cell.
Cycle repeats every ~8 seconds
Wait period (AZERO dwell time). Ensures reaction cell
0 – 4 s has been flushed of sample gas and chemi-
Open to
luminescence reaction is stopped.
vacuum
manifold
Analyzer measures background noise without sample
4 - 6 s
gas
Cycle repeats every minute
C - C
ATE ONTROL RITICAL
/NO Analyzer with NumaView™ Software
2 x
, NO and NO requires that the sample
x 2
ACTIVITY
dwell time). Ensures reaction cell
X
chemiluminescence in
3
F O
LOW RIFICES
FIGURE
Figure
6-3
Figure
6-3
Figure
6-4
083730200A DCN7962