CHAPTER 2, INSTALLATION AND OPERATION
98307600 Rev. C-1 2-39
2.6.2 Over Range Adjustment
Over-ranging is also enabled from the ANALOG OUTPUT MENU. The OVER RANGE
setting is the auxiliary range the operator chooses to track the data should the data
exceed full scale of the original range. The over-range setting has no impact on
the measurement range of the analyzer; it only affects the analog output scaling.
With over-ranging enabled, as the concentration reaches 90% of the full scale
value for the selected output range, the software generates a positive spike that
takes the indicator from the 90% position to the 100% position. The output data is
then scaled for the full scale chosen for over-range. As the output drops back to
80% of the original full scale, the software generates a negative spike from the
displayed value to zero. The output then reverts to the original range. See
Figure 2-30 for an example of over-range on a typical strip chart recorder.
Figure 2-30. Over Range as Seen on a Strip Chart Recorder
The range value should generally be set first. However, because the range value
must be less than the currently selected over-range value, it may be necessary to
increase the over-range value to the desired setting first. The over-range value is
limited to be equal to or greater than the currently selected range value. For
practicality, it is recommended that the over-range be set to a value between 2 and
5 times the range value. For example, if the desired monitoring range is 0.2 ppm,
the over-range should be set between 0.4 and 1.0 ppm.
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