Gases, GAS Connections, GAS Overpressure

Instruction Manual

760008-A September 2001

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.

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.

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

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.

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

2-2 Installation

Rosemount Analytical Inc. A Division of Emerson Process Management