3.17 CALIBRATION
A one point calibration should be performed after manually entering the sensor slope. The slope entered is
checked against the ideal Nernstian slope for the ion, and must be 75-125% of the ideal. The slope displayed
is corrected to the current temperature. For 2 - 5 point calibrations the instrument will automatically set the
slope value.
Procedure:
Refer to electrode manual for specific electrode preparation.
Prepare at least two standards (up to a maximum of 5) within the linear range of the electrode, with
concentration differing by a factor of 10.
Add a constant volume of ISAB to the sample and standard solutions.
Having set the necessary instrument parameters in the SETUP and INSTRUMENT SETUP modes the
following calibration procedure should be carried out:
3.18 ENTERING CAL BUFFER VALUES
The Model 3345 will allow these values to be entered in two ways - either in SETUP or CALIBRATION.
Select the CONC mode using the arrow keys and press . Move the cursor to highlight the SETUP menu
option and press . Select the CAL BUFFERS... menu option using the arrow keys and pressing .
Selecting this menu allows access to five settings. Values can be entered in any order and do not need to be
incremental or decramental.
Adjustments can be made by entering the required value via the numeric keypad.
If a mistake is made the key can be used as a delete key, starting from lowest digit. If you wish to alter
the entered value keep pressing this key until a blank box appears. Pressing the key again will default to the
original value.
Once the corrected value is entered pressing the key will update the display to the new value corrected
to 3 decimal places. If you wish to abort pressing the will return the cursor to CAL 1.
If a value which is higher or lower than the preset instrument default values is entered the unit will automatically
default to the appropriate default values (above or below).
Values can be entered as exponential numbers and these will be shown as standard values.
It is possible to change polarity at any time but the -ve sign can only be applied after entering a number.
Buffer values can be changed at the point of calibration, eliminating the need to exit the calibration routine.
The instrument is now ready to perform a calibration.
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