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CALiBrATiON
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 noble metal 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 (e.g. standards),
but may be lengthier in actual samples.
Calibration establishes a baseline that can be used as a comparison for future work. 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 an arithmetic correction and is correct only at the standard temperature. For example, HI7022
ORP Test Solution reads 470 mV at 25 °C versus the Ag/AgCl reference. The ORP mV versus a SHE
would be 675 mV (add 205 mV to the observed value).
Note: The user has to change the actual electrode to an ORP sensor and Parameter must
be changed to Rel. mV for use with ORP electrodes. Suggested ORP models are HI3133B,
HI4430B, or HI3230B.
Please see Setup Table Overview for details on configuration parameters and values.
When switching between Parameters (pH and mV, or Rel. mV), wait a few seconds to accommodate
meter reconfiguration.
Rel. mV Calibration Procedure
1. Tap Calibrate and the meter will open a Rel. mV calibration screen.
2. Place ORP electrode tip into a beaker of standard or a sample with known value HI7021 (ORP
solution for platinum and gold electrodes) reads 240 mV at 25°C, HI7022 (ORP test solution for
platinum and gold electrodes) reads 470 mV at 25 °C.
3. Tap the Relative mV box and a flyout calibration window appears.
4. Tap Clear to remove previous values from the box.
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