Permeation tube (used with izs option), Ermeation, Used with – Teledyne 6200A - Sulfides analyzer User Manual
Page 87: Option, 5 permeation tube (used with izs option)
TAI Model 6200A SO
2
Analyzer Operator Manual, 02164, Rev. G
6.5 Permeation Tube (used with IZS option)
SO
2
is normally a gas at room temperature and pressure, but can be liquefied at moderate
pressures. The permeation tube consists of a small container of SO
2
liquid, with a small window
of PTFE which is permeable to SO
2
. The gas slowly permeates through the window at a rate in
the nanogram/min range. If the tube is kept at constant temperature, usually about 50
o
C, the
device will provide a stable source of SO
2
gas for a year or more. The IZS permeation tube is
intended to be used as a periodic span check and is not to be used as a calibration device.
See below for permeation tube ordering information.
The permeation tube SO
2
concentration is determined by the permeation tube specific output (ppb @
1 slpm @ 50
o
C), the permeation tube temperature (
o
C) and the air flow across it (slpm). The specific
output is a fixed function of the permeation tube and is noted on shipping container.
The temperature is set at 50.0
o
C. Check SETUP-MORE-VARS and scroll to the IZS_SET variable
to verify that the temperature is properly set. It should be set to 50
o
C with over-and-under
temperature warnings set at 49
o
C and 51
o
C. There is a 50 cc/min purge flow across the permeation
tube at all times to prevent build-up of SO
2
gas in the tubing.
If desired, the output of the permeation tube can be adjusted by adjusting the oven temperature up or
down slightly. The adjust increment is 0.1
o
C to facilitate small adjustments of the setpoint
temperature.
When the IZS system is in SPAN mode, the flow across the permeation tube is the sum of the
reaction cell flow and the purge flow, which is about 700 cc/min. The gas concentration can be
calculated using following equation;
F
PxKm
C
=
where
P=permeation rate, ng/min.@ 50
o
C.
Km=(24.46)/molecular weight, where 24.46 is the molar volume in liters @ 25
o
C,
760mmHg
Km for SO
2
=0.382, H2S=0.719.
F=total flow rate (sum of sample flow and purge flow), cc/min.
C=concentration, ppm.
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