Honeywell UDA2182 manual ORP Calibration Using Reference Solution

Input Calibration

8.6 ORP Calibration

8.6.1Introduction

ORP calibration consists of adjusting the reading of the analyzer to match a known value. There are two types of ORP calibration supported:

•To calibrate the system to compensate for changes in electrode potentials over time, the ORP electrode is placed in a reference solution of known ORP value, and the analyzer reading is adjusted to match this value, as described in Section 8.6. Instructions for preparing standard solutions are also provided below. These solutions are stable for only short periods of time (less than 8 hours) and are only approximations of ORP potentials.

•To calibrate the UDA2182 only, not the whole system including electrodes, apply a known millivolt signal to the Analyzer instead of input from the electrode, then adjust the UDA2182 reading to match the actual millivolt input, as described in Table 8-7.

8.6.2ORP Calibration Using Reference Solution

Recommended to adjust for changes in electrode potential over time

An ORP measuring system can be checked by measuring a solution having a known oxidation-reduction potential, then adjusting the UDA2182 to match. Although a reference solution provides only an approximation of ORP potential, the system can be adjusted periodically to compensate for changes in electrode potential over time.

Materials

The materials required to use the ORP standardization method are:

•A solution with a known oxidation-reduction potential. (See “Instructions for preparing solution” below.

•A container for the solution, large enough to immerse the electrode to measuring depth.

•Distilled or de-ionized water to rinse the electrode.

Instructions for preparing solution

To prepare an ORP standardization solution, dissolve 0.1 g of quinhydrone powder in 5 cc of acetone or methyl alcohol (methanol). Add this to not more than 500 cc of a standard pH reference solution (buffer), about 1 part saturated quinhydrone to 100 parts buffer solution. The oxidation potential of this solution is listed below for several temperatures. The polarity sign shown is that of the measuring element with respect to the reference element.

These solutions are unstable and should be used within eight hours of preparation. All mV values in Table 8-5 have a ± 30 mV tolerance.

January 2009 UDA2182 Universal Dual Analyzer Product Manual 151