CHAPTER 3, CALIBRATION
98307600 Rev. C-1 3-17
A built-in check verifies that the measured value is not different from the
calibration value by more than 25%. If the difference is greater than 25%, no
updated correction will be made and a message is sent to the EVENT LOG, setting
the CALIBRATION ERROR flag.
Note
The zero value is a reference value only. Regardless
of the state of the SPAN COMP option, the AZS cycle
does not correct for shifts in the zero reading.
The number displayed after CO SPAN RATIO is the factor by which the instrument
gain is multiplied to cause the display and output to agree with the span gas, and
will always be between 0.75 and 1.25. You cannot set this number. This value is
reset to 1.000 any time that the span is set manually via the front panel. (The
assumption is that front panel adjustment is an instrument calibration, thus
preventing compound adjustments.)
3.4.4 Description of AZS Process
The instrument will initiate a full zero/span cycle starting at the prescribed hour.
The valve to admit zero air will be opened and the sample valve closed. The
instrument will allow the cell to fill with the gas for 12 minutes. During the first
10 minutes, no data is taken but the display and outputs are updated with the
actual instrument reading. During the last 2 minutes, the instrument takes readings
every second and averages them to yield a value to be stored as the zero
calibration value.
At the end of 12 minutes, the zero air valve is closed and the span gas valve is
opened, admitting the span gas for 12 minutes. During the first 10 minutes, no
data is taken but the display and outputs are updated with the actual instrument
readings. During the last 2 minutes, the instrument takes readings every second
and averages them to yield a value to be stored as the span calibration value. If
SPAN COMP is set to ENABLED, this is the value which is used to correct all
subsequent readings to the calibration.
To purge the cell of span gas, the zero air valve is switched on for 5 minutes. The
Sample valve is then activated for 1 minute to allow the cell to come back to
monitoring concentration.
At the end of 30 minutes exactly, monitoring resumes including putting data in the
average, etc. (The data averages are not updated during zero/span check.)
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