Teledyne 9110E - Nitrogen Oxides Analyzer - Manual (Page 53)

Model 9110E Instruction Manual Optional Hardware and Software
M9110E Rev B 39
• 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
.
In order to keep the permeation rate constant, the IZS enclosure is heated by a PID
(Proportional/Integral/Derivative) temperature control loop to a constant 50° C (10° above
the maximum operating temperature of the instrument). A thermistor measures the actual
temperature and reports it to the CPU for control feedback. The flow rate across the IZS
oven is controlled with a critical flow orifice to 60±5 cm³/min.
Please note, that the IZS option does not contain the actual permeation tube, which needs
to be ordered separately. See next option for description.
CAUTION
Gas flow must be maintained at all times for units with a permeation tube
installed. Insufficient gas flow allows NO
2
gas to build up to levels that will
severely contaminate the instrument.
Figure 3-12 shows the internal pneumatic connections for a Model 9110E with IZS option
installed. Table 5-1 shows the operational state of the valves associated with the IZS option
during the analyzer’s various operational modes. SPAN gas on the zero/span valve option is
equivalent with the permeation tube NO
2
gas stream on the IZS option.
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 CAL or AutoCal features (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).
5.6.3. IZS Permeation Tubes (Options 53 & 55)
One IZS permeation tube is necessary to operate the IZS option (Option 51). Two different
NO
2
permeation tubes are available, they are identical in size and shape but are designed to
have different permeation rates.
Table 5-2: Available Permeation Source Options
Option Permeation Rate
(± 25%)
Approximate NO
2
Concentration
OPT 53 421 ng/min 300 - 500 ppb
OPT 55 842 ng/min 600 - 1000 ppb
Each tube is shipped with a calibration certificate, traceable to a NIST standard, specifying
its actual NO
2
permeation rate to within ±5%. The calibration is performed at a tube
temperature of 50°C and a flow rate of 0.56 liters per minute.