GASCO
Statement of Quality Assurance of Calibration Gas
Mixtures
Gasco gas
mixtures for filling disposable pressure vessels are
produced gravimetrically (by weight) using sensitive
modern balances capable of weighing the relatively
heavy cylinders to an accuracy of plus or minus 0.1
gm. This equipment allows direct measurement
of cylinder content during filling, and eliminates
potential errors associated with indirect, manometric
(pressure based) mixing techniques, which are subject
to inaccuracies due to temperature, gas compressabilities
and non-ideal behavior.
The weights
used to calibrate the balances are all traceable to
National Physical Laboratory (NPL) and NIST standards
which ensures standard gas mixtures are of the highest
possible accuracy. High purity precursor gases
are used to ensure gravimetric filling calculations
hold true.
The certification
accuracy of gravimetric mixtures is dependent on the
concentration levels of particular components and
on molecular weights.
Typically,
the accuracy for a given concentration is:
Concentration
Certified Accuracy
5
to 10 PPM depends on components (typically ±10%)
10
PPM to 50 PPM ±5%
50
PPM to 1% ±2%
1%
to 10% ±2%
10%
to 50% ±2%
Gasco’s non-refillable
products are labeled with the nominal concentration
requested by customers. Gasco does not use the
exact values from the production process. Thus
there is a tolerance which must be added to this figure,
which is typically:
Concentration
Certified Accuracy
10
to 50 PPM ±20%
50
PPM to 1% ±10%
1%
to 10% ±10%
10%
to 50% ±5%
Where analytical
work is required to certify minor components, the accuracy
is plus or minus 2%.
Gasco’s non-refillable
pressure vessels are filled and supplied in accordance
with their ISO 9001 procedures. All incoming
materials are checked and inspected for conformance
to agreed specifications. All dispatched products
are inspected for quality and aesthetics.
|
