Hanna Instruments HI 9829 User Manual

Page 42

Position the sachet to ensure sensor membrane and ceramic junction are
completely immersed in solution. A value close to 100 ppm and the message
“Not ready...” will be displayed.

• When the reading is stable, the countdown

timer will count down until the display shows
the “Ready” message.

• Press to accept the calibration.
• After the second calibration point is confirmed the display shows the

following messages: “Storing” and “Calibration completed”.

• Press to return to the Calibration menu.
• Press to return to the measurement screen.

Note

The ISE calibration mode can be exited at any time, by pressing the
ESC key.

7.4 ORP CALIBRATION
The “ORP calibration” allows the user to perform a single point custom calibration
(relative mV) or to restore the factory calibration.
The Oxidation-Reduction Potential (ORP), displayed in mV, is the voltage that
results from the difference in potential between the platinum ORP sensor and
the silver/silver chloride reference electrode. ORP values are not temperature
compensated, although ORP values can change with temperature (e.g. reference
electrode potential changes, sample equilibrium changes). It is important to report
ORP values together with the reference electrode used and the temperature.
The inert platinum ORP surface provides an electron exchange site with the
sample (or standard) and its surface. The electron exchange is typically very fast
in well-poised solutions (standards for example), but may be more lengthy in
natural water samples.
Calibration is typically not required for a new ORP sensor, but the process does
establish a baseline that can be used as a comparison for future validations.
Calibration is used to compensate for changes due to contamination of the
platinum surface and drift in the reference electrode.
A relative mV calibration can also be made to remove the voltage attributable to
the Ag/AgCl reference electrode (to display the ORP versus a SHE (standard
hydrogen electrode). This is really an arithmetic correction and is correct only at
the standard temperature. For example, HI 7022L reads 470 mV at 20°C versus
the Ag/AgCl reference. The ORP mV versus a SHE would be 675 mV. (add 205
mV to the observed value).