Metek 920, Operator'S Manual With Essential Health And Safety Requirements

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Overview | 1-3
Sample Flow
The sample gas is drawn from the extraction point through the Sample
Probe and Sample Line (or from a stack via a SCU) to the dual-chambered
Measuring Cell. The gas sample enters the first chamber, flows the length
of the Measuring Cell, crosses to the second chamber, flows the length
of the Measuring Cell in the opposite direction and exits the Measuring
Cell. The gas sample then flows to an aspirator in the Oven, where it
merges with the aspirator drive fluid (Instrument Air or N
2
) and contin-
ues on through the Vent Line (if used), or Vent Pipe which disperses it to
atmosphere.
About the Analyzer Sample System
The sample system consists of the components below (some components
are optional) – see Figures 1-1, 1-2 and 1-3:
Component Function
Sample Path
A small vacuum created by an air-powered aspirator circulates
sample gas through the system.
Steam Jacketed Sample Valve (if used)
The Sample Valve, which extends into the process duct to obtain
a representative sample, consists of:
Isolation Valve – Isolates the sample path from the Sample Probe
that extends into the process duct.
Steam Inlet/Exhaust – Connections for dry, saturated steam,
which is used to heat the sample gas within the Heat Transfer
Block inside the probe.
Heat Transfer Block – Circulates the dry, saturated steam around
the Sample Probe pipe the Sample Probe Assembly to heat the
sample gas.
Steam Jacketed Vent Valve (if used)
Provides a return for the used sample gas to the process duct.
The Vent Valve Assembly consists of:
Isolation Valve – Isolates sample path from process duct.
Steam Inlet/Exhaust – Connections for dry, saturated steam.
Heats the sample gas to avoid plugging in the sample system.
Sample Line This heated line transports the sample gas to the analyzer at a
temperature above its dewpoint.
Aspirator Located within the Analyzer Oven, the Aspirator uses Instrument
Air to create a small vacuum that moves the sample gas from the
extraction point, through the sample system, and returns it to the
process duct.
Measuring (Sample) Cell
This is where the actual measurement takes place.
Manifold (if used) Connection point for the instrument air and Calibration gases.
Preheats calibration gases.