Hanna Instruments HI 221 - Manual (Page 8)

8
• The pH is displayed on the primary LCD and the temperature on the
secondary LCD.
• The pH reading is out of range, the closest full-scale value will be displayed
blinking on the primary LCD.
• It is also possible to view the mV reading by pressing the RANGE key.
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.
The pH reading is affected by temperature. In order to measure the pH
accurately, this temperature effect must be compensated for. To use the
Automatic Temperature Compensation feature, connect
and submerge the HI 7669/2W temperature probe into
the sample as close to the electrode as possible and wait
for a few minutes.
If the temperature of the sample is known, manual compensation can be
performed by disconnecting the temperature probe.
The display will then show the default temperature of 25 °C
or the last recorded temperature reading with the “°C”
symbol blinking.
The temperature can now be adjusted with the ARROW keys (from -20.0 ºC
to 120.0 ºC).
ORP MEASUREMENTS
An optional ORP electrode must be used to perform ORP measurements (see
Accessories).
Oxidation-Reduction Potential (REDOX) measurements provide the quantifica-
tion of the oxidizing or reducing power of the tested sample.
To correctly perform a REDOX measurement, the surface of the ORP electrode
must be clean and smooth.
Pretreatment solutions are avaible to condition the electrode and speed up the
response time.
C
MTC
C
pH
SLOW FAST POOR GOOD
ATC
C
SLOW FAST POOR GOOD
mV
C
ATC