Filter
Top Products
Teledyne API – Model T700 Dynamic Dilution Calibrator Getting Started
75
3.3.4. PERMEATION TUBE CALCULATION
The permeation tube concentration is determined by the permeation tube’s specific
output or elution rate (which is normally stated in ng/min), the permeation tube
temperature (C) and the air flow across it (slpm). The elution rate of the tube is
normally stated at an operating temperature of 50°C and is usually printed on the tube's
shipping container. By design, there is nominally 100 cm3/min of air flow across the
tube and the tube is maintained at 50°C. The output of the calibrator is the product of the
elution rate with the total of the 100 cm3/min through the generator and the flow of
dilutant gas.
The temperature is set at 50.0C. Check SETUP-MORE-VARS and scroll to the IZS-
TEMP variable to verify that the temperature is properly set. It should be set to 50C
with over-and-under temperature warnings set at 49C and 51C. There is a 105
cm3/min flow across the permeation tube at all times to prevent build-up of the gas in
the tubing.
This permeation tube source gas is diluted with zero air to generate desired
concentration of the specific gas. The calibrator’s output concentration (gas
concentration) can be calculated using the following equation:
F
KmP
C
Where:
P = permeation rate, ng/min @ 50C.
Km =
M
W
46.24
, where 24.46 is the molar volume in liters @ 25C
and MW is the molecular weight.
760mmHg . Km for SO
2
= 0.382, NO
2
= 0.532, H
2
S = 0.719, and NH
3
=
1.436.
F = total flow rate (sum of 100 cm
3
/min and diluent flow), LPM.
C = concentration, ppm.
Thus,
M
WF
P
C
46.24
Where, Temperature at 50°C = 323
Temperature at 25°C = 298
06873B DCN6388