Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 60)

<4. COMMISSIONING OF pH/ORP>
4-6
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
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Limits and timing
Zero High/Low
Set the high and low limits of Zero (aspot). During calibration, it is checked whether the new zero
exceeds these high and low limits. Narrowing the band will prevent bad calibration procedures
and calibration of bad sensors, which results in higher accuracy. The default values should be
adjusted to suit the application and the “users” criterion.
Slope High/Low
Set the high and low limits of Slope (sensitivity). During calibration, it is checked whether the
new slope exceeds these high and low limits. Narrowing the band will prevent bad calibration
procedures and calibration of bad sensors, which results in higher accuracy. The default values
should be adjusted to suit the application and the “users” criterion.
Step Range
Set the range over which the stability of a measured value is checked. If variations of a measured
value over the stabilization time are within this set value, the measured value is judged to have
stabilized.
Stabilization time
During calibration, the stability of the pH value is constantly monitored. When variations of the
pH value are within a value set in Step Range over this stabilization time set here, the value
is regarded as being stable. If the pH value does not stabilize within 10 minutes, calibration is
aborted.
Calibr. interval
Set the interval in which a new calibration must take place. If the interval set here is exceeded,
the instrument will be notified according to the setting in “Calib. time exceeded” in the error
configuration.
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Buffers (select set)
Calibration is made using standard calibration buffers. We recommend the NIST (JIS equivalent)
standard buffers for highest accuracy, but the user is free to select DIN 19267, US, or a user-
defined buffer. The standard buffers can be found in Appendix 1.
Three types of user-defined buffer tables can be defined. On the Free programmable screen,
select a buffer table that you wish to set up. When a buffer table is selected on this screen, the
Buffer table 1 to Buffer table 3 screens of the selected buffer table are displayed.
Clear table?
If you select “Yes” and press “Yes” when prompted to clear the table, the contents of the buffer
table will be cleared, the display will return to the Buffer table screen automatically, and the “Table
was cleared” message will be displayed. If you want to perform temperature compensation using
the matrix after clearing the table, matrix values must be redefined.
Check values?
If you select “Yes,” a value check starts. When the check ends, the results will be displayed on
the screen. When the results are normal, the “No error” message appears. In case of an error,
error information is displayed.
l Zero/Slope/ITP
You can enter Zero (aspot), Slope (sensitivity), and ITP values directly in the screen displayed.
These data can be obtained from the manufacturer of the probe, by the users laboratory, etc.
NOTE
It is not necessary to enter this data. In most cases, as the FLXA21 automatically does this while
performing calibration, the feature is used in the case of special electrode systems or where
calibration in the process environment is not possible. See Chapter 5.