Metek 920, Руководство оператора с основными требованиями по охране здоровья и безопасности

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Controller / User Interface | 4-51
Spanning Dual Range
The Model 920 Analyzer is equipped with dual ranging algorithms used
for SO
2
measurement. With this algorithm, an analyzer can be used in ap-
plications where the SO
2
concentrations may greatly vary.
The analyzer has, for example, a ± 1% accuracy of reading for SO
2
con-
centrations ranging from 50–5000 ppm. Two separate Span functions are
used to obtain the accuracy over the wide dynamic range. The
low range
Span requires a Calibration gas ranging from 20–500 ppm. The high range
Span needs a Calibration gas ranging from 2500–7500 ppm.
Although these two separate ranges are discussed here, a single output
from the analyzer is available (typically output #4 and on the display
labelled “
SO
2
”). The output is accurate over the entire SO
2
concentration
ranges.
If your analyzer is equipped with a Measuring Cell other than a
40 cm cell, contact the factory to obtain new high range and low range
span points.
To perform a dual range span:
1. From CAL mode, enter the component concentration of Species 1
( Conc1 ) from the tag concentration of the calibration cylinder.
Example :
If the tag concentration is 250 ppm, press:
F4 1 Del 250 Ent Ent
2. Zero the analyzer to remove sample gas contaminants.
3. Ensure that the Span gas mixture is connected to the analyzer’s
Calibration Gas Port and turned on.
4. Span the low range SO
2
by turning on the Calibration gas mixture
(press F2 1 ). Run the low range Span gas through the analyzer for at
least 5 minutes (typical flow rates are 1–2 SCFH).
When the readings have stabilized at or near ‘ 0 ’, press Ent . Turn off
the Calibration gas.

NOTE

See “Manually Zeroing
the Analyzer” in Chapter 3.

See “Manual Span” in
this chapter.