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5.1 One-Point Offset Calibration
The 1-Point offset calibration is used to bring the ISE sensor into agreement with a grab sample
analysis obtained by an alternate method to determine fluoride ion concentration. It is also used to
adjust for occasional sensor drift.
It is not necessary to remove the sensor from service to perform a 1-point grab sample offset
“Standardize” calibration.
Offset calibration simply requires the use of the Offset and UP / Down buttons only (after the software
is unlocked), to enter the calibration result. It can be performed as often as desired. This is in most
cases the only calibration required.
Please note that a 1-point offset calibration will only be as accurate as the instrument used to
analyze the grab sample and if performed promptly after making a grab sample determination.
The grab sample should be analyzed in as timely a manner as possible for best results.
There are a variety of methods to perform the grab sample analysis. This includes portable
photometers and laboratory fluoride ion selective electrode methods with the addition of TISAB-II to
the unknown sample to adjust for all background ion effects.
When this method is used, it is typical to add the TISAB-II on a one to one volume basis to the
unknown, and then to determine the fluoride concentration of this diluted sample. The actual fluoride
concentration will then just simply be double the TISAB-II diluted unknown sample.
This grab sample determined concentration of the process sample (by whatever method employed)
will then be entered into the analyzer as described below.
1-point offset calibration procedure
1.
With the sensor installed in service, allow at minimum 3-5 minutes for the sensor to display a
stable reading with the process.
2.
On the ISE module enter Setup and press the UP button to Parameter No. 01, which is a “software
lock”. Toggle to ‘Off’ using the up or down key.
3.
Exit Setup by pressing the down button to parameter P00, then press Mode.
4.
Use the ‘Mode’ key to select ‘OFFSET’.
5.
Use the Up/Down keys to adjust the displayed reading until the display shows the correct value
in accordance with the concentration determined by the grab sample analysis.
NOTE:
If your system includes the FX-300-TOT module that provides a pH compensated total
unbound ion measurement, enter the calibration value by pressing the keys on the ISE module
until the display on the FX-300-TOT module displays the correct reading.
6. Press the “Mode” button to return to PPM (run) mode.
5 Calibration
