Heath Consultants Gas Delivery Unit (GDUnet) - Manual (Page 19)

INTRODUCTION
1-3
1.2 CALIBRATION GASES
net is connected to cylinders of calibration gas to ensure
that a consistent standard can be maintained against which the
instrument can be checked.
net can connect up to 8 gas cylinders (a 4 gas cylinder
version is also available).
1.2.1 Recommended Types
The instrument should be calibrated in the gas it will be used in,
rather than using calibration factors, i.e. Propane instruments
should be calibrated with Propane gas etc.
Gases should be full scale or mid range of scale rather then
lower end; i.e. calibrate 100% LEL range at 50% LEL rather
than 10% LEL.
Heavier hydrocarbon gases may take longer to clear the system
than lighter ones like Methane, and should be carefully organised
in terms of location on the manifold position and test sequence.
1.2.2 Traceability
Gases should be analysed and traceable to National Standard.
air components.
1.2.3 Limits of Preparation
The limits of preparation of the gas should be clear, e.g. ±2%.
These limits should be better than the accuracy required from
the instrument.
The accuracy of preparation of the gas mixtures together with
the analysis accuracy should be clearly marked on the cylinder.