Emerson NGA 2000 TO2 - Manual (Page 20)

Instruction Manual
760008-A
September 2001
2-2 Installation Rosemount Analytical Inc. A Division of Emerson Process Management
Model NGA 2000 TO2
The same temperature restrictions apply to
the location of the zero and span gas cylin-
ders.
2-4 GASES
a. Requirements
The TO2 Analyzer Module requires only a
standard of accurately known composition
for use as a span gas. The span gas
should be supplied from a cylinder
equipped with a clean, metallic dia-
phragm, two-stage regulator. A shutoff
valve is recommended.
Calibration Gases
The TO2 module does not require routine
zero calibration. The zero is factory set
and does not experience routine drift.
Over long periods of time, the zero may
experience minor drift. For low ppm
range analyzers, you may wish to check
the zero at one year intervals. Oxygen-
free nitrogen is recommended for use as
zero gas. This gas is certified to <0.5
ppm oxygen and can be improved by
passing the zero gas through an oxygen
scrubber such as Millipore™ Waferpure
or Semigas Nanochem® resin purifiers. A
mixture of trace oxygen in a background
of nitrogen is recommended as span gas.
For maximum accuracy, the concentration
of trace oxygen in the span gas should be
as high as possible for the range of
measurement.
b. Sample
The sample must be clean and dry before
entering the Analyzer Module. Sample
should be filtered for particulates down to
two microns, and should have a dew point
at least 5
°C (13 °F) below the coldest ex-
pected ambient temperature.
c. Pressure
Constant between 13.8 and 69 hPa -
gauge (0.2 and 1.0 psig) sample inlet
pressure is recommended. If a needle
valve is used upstream of the Analyzer
Module to control flow, the inlet pressure
to the needle valve should not exceed
345 hPa (5 psig). A constant sample flow
rate between 1.0 to 3.0 SCFH (0.5 to 1.5
l/min) is recommended for best results.
The Analyzer Module must vent to at-
mosphere to avoid back pressure influ-
ences on the oxygen reading.
2-5 GAS CONNECTIONS
(See Figure 2-3. ) Connect inlet and outlet
lines for sample to appropriately labeled fit-
tings on the rear panel. SAMPLE IN and
SAMPLE OUT are 1/4-inch ferrule-type com-
pression fittings. Zero and span gases should
be introduced at the SAMPLE IN fitting at
normal sample inlet flow rate.
Metallic tubing is recommended for the sam-
ple line. The use of plastic, Teflon, or other
non-metallic tubing can result in ambient oxy-
gen permeation through the tubing causing
higher than expected reading. Exhaust tub-
ing should be 1/4 inch (6.3 mm) or larger, and
can be metallic or non-metallic.
CAUTION .
GAS OVERPRESSURE
At no time should sample, zero or span
gas inlet pressure exceed 69 hPa - gauge
(1.0 psig). Damage to the Sensor may oc-
cur if this pressure level is exceeded.
CAUTION .
SAMPLE FLOW
Do not test the sample pressure by block-
ing the exhaust. When the pressure is re-
leased the sudden surge of flow will spin
the internal flowmeter off its bearings and
destroy it.