Hanna Instruments HI 120 - Manual (Page 12)

12
pH MEASUREMENTS
Make sure the instrument has been calibrated before
taking pH measurements.
• Press MODE to enter pH mode.
Note: To change pH resolution, press MODE again or
simply Resolution from the left keyboard.
• Submerge the electrode tip and the temperature
probe approximately 4 cm (1½”) into the sample to
be tested. Allow time for the electrode to stabilize.
• The pH is displayed on the primary LCD and the
temperature on the secondary LCD.
OUT CAL RANGE feature warns the user if the current reading is out of the
calibrated area. The calibrated area is that part of the pH range in which
the calibration point assures an accurate reading. If the reading is taken out
of the calibration area, the “OUT CAL RANGE” message will blink. The
calibrated area is calculated in according with the pH resolution used during
the reading. To avoid having this message, the calibration points have to be
well distributed in the desired measurement range.
If measurements are taken successively in different samples, it is recommended
to rinse the electrode thoroughly with deionized water or tap water and then
with some of the next sample to prevent cross-contamination and to condition
the electrode before immersing it into the sample solution.
The pH reading is affected by temperature. In order to measure the pH
accurately, the temperature effect must be compensated for. To use the
Automatic Temperature Compensation feature, connect and submerge
the HI 7662-T temperature probe into the sample as close as possible to the
electrode and wait for a few seconds.
If the temperature of the sample is known, manual temperature
compensation can be performed by disconnecting the temperature probe.
The display will then show the default temperature of 25 ºC (77 ºF) or the
last temperature reading with the “ºC” (or “ºF”) tag blinking. The
temperature can be adjusted with the ARROW keys or the numerical
keypad (from –20.0 ºC to 120.0 ºC or from –4.0 ºF to 248.0 ºF).