23
CALIBRA
TION
9. CALIBRATION
9.1. pH CALIBRATION
It is recommended to calibrate the instrument frequently, especially if high accuracy is required.
The pH range should be recalibrated:
• whenever the pH electrode is replaced
• at least once a week
• after testing aggressive chemicals
• when “CAL DUE” is blinking (if enabled), indicating that the calibration has expired
• when “Outside Cal Range” message blinks during pH measurement (if enabled), indicating that the
reading is outside an optimal measurement range enclosed by a minimum of two calibration points.
Procedure
The
HI981914
offers a choice of 7 standard buffers (pH 1.68, 4.01, 6.86, 7.01, 9.18, 10.01 and
12.45) and up to 5 custom buffers for calibration. The set custom buffers are the buffer values
at 25 °C.
When a custom buffer is selected during calibration,
Custom
functional key is displayed.
Press
Custom
to enter custom buffer edit mode. Press / keys to modify the value in a ±1.00 pH
window, according to the temperature reading and then press
Accept
. Press
ESC
to exit without changing.
For accurate pH measurements a five point calibration is recommended, a minimum of a two-point
calibration is suggested.
The instrument will automatically skip the buffers used during calibration and the buffers which are in
a ±0.2 pH window around one of the calibrated buffers.
• For accurate calibration and to minimize cross-contamination, use two beakers for each buffer
solution: one for rinsing the electrode and one for calibration.
• If using a temperature probe separately, ensure that it is positioned close to the pH electrode.
Five-Point Calibration
1. Immerse the pH electrode approximately 4 cm (1½”) into the first buffer solution and stir gently.
2. Press
CAL
. The instrument displays the measured pH, the first expected buffer and the
temperature reading.