Yokogawa AC8 Calibration Units - Manual (Page 4)

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IM 11M6D2-02E-A
Figure 3.1: AC4/AC8 Dimensional Drawing
3.3 GAS SOURCES
Zero Gas
Typically, 1% oxygen balanced in nitrogen is used, however,
an oxygen mixture between 0.5% and 8% is acceptable.
NEVER USE PURE NITROGEN FOR ZERO CALIBRA-
TION GAS. A compressed gas cylinder containing the zero
gas is fitted with a dual stage regulator. Zero calibration gas
cylinders with regulators may be purchased from a local
compressed gas supplier. Follow the operation and safety in-
structions as supplied from your gas supplier. The maximum
pressure of the calibration unit is 35 psi.
NOTE
The compressed gas cylinder must have the same CGA connec-
tion fitting as the dual stage regulator (see accessories).
Span Gas
Typically, a clean dry air source is recommended, such as
instrument air (20.6% oxygen). An in-line filter is recom-
mended to remove any moisture or dirt prior to the calibra-
tion unit. A regulator must be attached to the instrument air
source in order to reduce the flow to an appropriate pressure
(35 psig max) prior to reaching the calibration unit.
Reference Air
The reference air is the same air as the span gas. Thus, the
reference air is also clean dry instrument air. Unlike span gas,
which is use only during calibration, reference air flows to
the back side of the zirconium cell and should be used at all
times.
IMPORTANT
When the instrument air has a nitrogen backup (used for air
failure), instrument air for the reference gas should not be used.
In this instance the probe must use either bottled air (20.6%
oxygen balanced in nitrogen) or natural convection for reference
air flow.