Operational Guide 25
pH
Calibration
If the instrument is not calibrated the calibration history has been deleted, or it
has been calibrated only at one point, the electrode condition and the electrode
response gauges will be empty.
For a continuous display of the electrode’s condition and response, daily
calibration is necessary. This information can also be viewed in the GLP data.
Junction Condition (HI11311 and HI12301 Only)
edge’s pH Sensor Check™ feature assess the health of the pH electrode’s
reference junction during each calibration. The junction gauge may be viewed
directly in GLP but will also blink a warning on the display if the junction is
compromised (not 100%). Should this happen, the junction condition will
appear on the display with the junction blinking. The Junction Condition is a
function of the electrode’s reference impedance which should be kept low. If the
reference junction becomes fouled from a precipitate or coating, the impedance
will rise and cause the pH measurement to drift. This diagnostic feature serves
as a warning to clean the sensor.
Calibration in Basic Mode
Procedure
Basic mode operation permits up to three-point bu er calibration.
For accurate measurements, at least a two-point calibration is recommended.
However, a single point calibration can also be used.
The calibration bu ers can be selected from the calibration bu er list that
includes the standard bu ers, pH 4.01, 6.86, 7.01, 9.18 and 10.01.
Three-Point Calibration
Submerse the pH electrode approximately 3 cm (1¼”) into a bu er solution and
stir gently. Press CAL. The “CAL” tag will appear and the “7.01” bu er will be
displayed on the third LCD line. If necessary, press the
ARROW keys to select a di erent bu er value.
The “
” along with “STIR” tag will be displayed and
“WAIT” will blink on the LCD until the reading is stable.
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