Teledyne 9110EH - Nitrogen Oxides Analyzer - Manual (Page 52)

Optional Hardware and Software Model 9110EH Instruction Manual
Table 5-1: IZS or Z/S Valve States
Mode Valve Condition Valve Port Connection
NO = normally open port
NC = normally closed port
COM = common port
Sample/Cal Open to sample gas inlet NO Æ COM SAMPLE
Zero/Span Open to zero air inlet NO Æ COM
Sample/Cal Open to zero/span inlet (activated) NC Æ COM ZERO CAL
Zero/Span Open to zero air inlet NO Æ COM
Sample/Cal Open to zero/span inlet (activated) NC Æ COM SPAN CAL
Zero/Span Open to span gas inlet / IZS gas (activated) NC Æ COM
The state of the IZS valves can also be controlled:
• Manually from the analyzer’s front panel by using the SIGNAL I/O controls located
under the DIAG Menu (Section 6.8.1),
• By activating the instrument’s AutoCal feature (Section 7.8),
• Remotely by using the external digital control inputs (Section 6.9), or
• Remotely through the RS-232/485 serial I/O ports (Section 6.9.10).
Sources of zero and span gas flow must be capable of supplying at least 600 cm 3 /min as
the analyzer draws about 500±50 cm³/min into the instrument. Both supply lines should be
vented outside of the analyzer’s enclosure. In order to prevent back-diffusion and pressure
drop effects, these vent lines should be between 2 and 10 meters in length.
5.6.2. Internal Zero/Span (IZS)
The M9110EH can be equipped with an internal zero air and span gas generator system (IZS).
This option includes a heated enclosure for a NO
2
permeation tube, an external scrubber for
producing zero air and two valves for switching between the sample gas inlet and the
output of the zero/span subsystem, functionally identical to the zero/span valve option.
The IZS option includes a two stage, external zero air scrubber assembly that removes all
NO & NO
2
from the zero air source. The scrubber is filled with 50% Purafil Chemisorbant ®
(for conversion of NO to NO
2
) and 50% activated charcoal (for removal of NO
2
). This
assembly also includes a small particle filter.
Span gas is created by passing zero air over a NO
2
permeation tube. This tube contains
liquid NO
2
, which slowly permeates through a permeable membrane into the surrounding
air. The concentration of the NO
2
span gas is determined by three factors:
• Size of the membrane: The larger the area of the membrane, the more permeation
occurs.
• Temperature of the NO
2
: Increasing the temperature of the permeation tube
increases the pressure inside the tube and therefore increases the rate of
permeation.
• Flow rate of the zero air: If the previous two variables are constant, the permeation
rate of the NO
2
into the zero air stream will be constant. Therefore, a lower flow rate
of zero air produces higher concentrations of NO
2
.
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