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9.3 Choosing the Calibration Point
Calibration of the pH probes requires two buffer solutions. One must be
pH 7.0; the other may be pH 4.0, 9.0 or 10.0. The other extra STAT
function is for setting the pH of this second buffer solution.
S T A T p H s l o p e
4 . 0 0
Press and hold
set
to change the value.
9.4 Calibrating the Midpoint (pH7.0)
Before any sensor can be used with the Squirrel, it must be calibrated
using two buffer solutions. An additional CALIBRATION function allows
the setting of both pH 7.0 and pre-selected calibration point (or
‘slope’ -
see above). Select the CALIBRATION function. After a couple of seconds,
the display will change to show the calibration settings (see below).
Place each probe individually in a pH7 buffer solution and allow it time to
settle (the time this takes will depend on the probe, and how it has been
stored or used. See
‘Care and Use of pH Probes’, below). If the
temperature compensation is being measured, then the relevant
temperature probe must be put in the same solution.
B U F F E R 7 c h 9
6 . 6 4 p H 2 0 . 0 C
Once the value has settled, the display should show
‘BUFFER7’ in the top
left-hand corner. If it reads
‘O/RANGE’, then the pH input is too far out of
range to be set as the midpoint. This is typically caused by a pH probe
that has expired. Once the probe has settled, press and hold the
set
button.
‘HOLD TO CHANGE’ will appear on the display and then the
logger will recalibrate itself on the current channel to read 7.00 pH: -
B U F F E R 7 c h 9
7 . 0 0 p H 2 0 . 0 C
