Model PH220 Version 3.1 11/2005
4
Calibration (pH only)
The sensitivity of a pH electrode degrades over time, it is very important to frequently
calibrate the meter to the electrode. pH electrodes can be thought of as batteries in that
they run down with time and use.
Calibration is performed using standard buffer solutions at room temperature (78°F, 25°C).
Buffer solutions are solutions of a known pH that have the useful property of resisting
changes in pH. These can be purchased already mixed or in capsule form and are usually
available in three pH values, pH 4.00, pH 7.00 and pH 10.00.
Calibration is always performed using the pH 7.00 buffer first, followed by a second
calibration. Select pH 4 buffer for the second calibration if typical measurements will be
less than pH7 or use a pH 10 buffer if typical measurements will be greater than ph 7.
In order to obtain the most accurate results possible, a pH meter should be
calibrated at least once each day. Note that the mV (ORP) function does not require
calibration.
pH Calibration Procedure
1.
Place the electrode into a 7.00 pH buffer solution. Press and hold the
CAL
button until
“CAL” appears in the display.
2.
The instrument automatically recognizes the solution and calibrates to that value.
Note that if the solution is off by more than 1 pH unit from the 4, 7, or 10 pH buffer, or
if the electrode slope is low, the instrument will assume an error and abort the
calibration (End will be displayed, and the unit will return to the normal measurement
mode.)
3.
During calibration, the pH reading flashes on the main display.
4.
When calibration is complete, the instrument automatically displays ‘SA’ followed by
‘End’ and then returns to the normal operation mode.
5.
For a two or three point calibration, repeat steps 1-4. When doing a 2 or 3 point
calibration, calibrate with pH 7 buffer first, then follow with pH 4 and/or pH 10.
CAL Reminder Display
When in pH measurement mode, the CAL icon will appear if a calibration has not been
performed after 15 on/off cycles of the instrument. The CAL display is simply a reminder
and will turn off when the pH electrode is recalibrated. The reminder does not affect
function in any way.
