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

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Controller / User Interface | 4-47
Manual Zero/Span
The Manual Zero and Manual Span do not activate the solenoid valves.
The gases must be introduced manually into the analyzer and allowed to
flow through the sample system until a stable reading is displayed. The
time required for Calibration gas to reach the analyzer and for a stable
reading to be achieved and displayed is dependent upon the volume of
the sample system and Calibration gas flow rate. The gas flow rate, tem-
perature, and pressure should be as close as possible to the normal operat-
ing conditions.
The Calibration gas mixture component concentrations must be en-
tered before performing the Manual Span.
Manual Zero
See “Manually Zeroing the Analyzer” and “Setting the Zero Gas Flow
Rate” in Chapter 3 for information about how to perform a Manual Zero
on the analyzer.
Manual Span
Although it is unnecessary from an analytical perspective to calibrate the
span of the analyzer on a regular basis, since the response factors to the
various gases do not change, calibration may be necessary to demonstrate
the response of the analyzer to Calibration gas. There may also be occa-
sions where the SO
2
cross-talk needs to be checked after changes to the
optical system have been made. For these purposes, a Calibration gas port
has been provided.
The calibration gas follows the same path that the Zero gas is introduced.
The flow rate of these gases can be adjusted using the flow controlling
rotameter.
To achieve a good result, the following factors are important when run-
ning calibration gases:
• A “good zero” has been performed prior to introducing calibration
gas.
• The calibration gas must reach the Measuring Cell without contamina-
tion or residual sulfur in the system.
• The gas introduced must be at approximately the same temperature as
the sample gas.

NOTE