Valco Instruments Co. Inc. 500, Instruction Manual

Page: 17 / 37

Calculations
Concentration of the permeant compound in the span outlet stream is inversely
proportional to the carrier flow rate through the chamber. It is determined using
the following equation:
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Where: K = 24.45 / molecular weight of gas
P = permeation rate in ng/min (information included with
the permeation device documentation)
F = Chamber carrier flow (ml/min)
If the permeation rate is known for some reference temperature, the rate at a
second temperature can be estimated as follows:
log P = log P
O
+ 0.034 (T - T
O
)
Where: P
O
= Permeation rate at reference temperature T
O
P = New permeation rate at temperature T
Certified devices should be used only at the temperature
specified on the certificate.
Using any permeation device beyond its recommended
temperature range could result in the destruction of the
device by explosion and/or changes in the membrane
characteristics. If in doubt, contact VICI Metronics with
the part number of the device to determine its maximum
temperature limit.
Sample Calculation
Given:
Permeation rate: 21,000 ng/min Cl
2
@ 30°C
Carrier flow: 500 ml/min
Then:
Concentration (ppm) = K * P
F
(0.346)(21,000)
500
=
14.5 ppm
=
For zero reference measurement, remove the permeation device from the
chamber.