Yokogawa PH72 Personal pH/ORP Meter - Manual (Page 66)

IM 12B03D02-01E
8-3
8. ORP Meter
8.3 Checking the ORP Sensor
Use a check solution to verify that the ORP sensor operates properly. The oxidation-
reduction potential of the check solution to be used should have been correctly
determined by a normal ORP sensor. The following explains how to check an ORP
sensor using a quinhydrone reagent (spare part).
Preparing a Quinhydrone Solution
Prepare a 250 ml solution in a wide mouthed bottle by dissolving one pack of
quinhydrone reagent in deionized water. If the temperature of deionized water is low, the
reagent may not be dissolved completely and some powder may float on the surface of
the solution. This will not affect the ability of the solution. A quinhydrone solution may
change with time, so it should be prepared and used within the same day.
Procedure
(1) Pour 50 to 100 ml of the prepared check solution into a clean container (200 ml).
(2) Rinse off the remaining sample solution, if any, from the electrode with water and
then wipe off water drops.
(3) Immerse the electrode tip in the check solution and wait until the reading has
stabilized. This should take 5 to 10 minutes.
(4) Read the mV value and solution temperature. The mV reading at the solution
temperature must be within the tolerance (
؎40 mV) shown in Figure 8.2. If it
falls within the tolerance, the sensor is normal. If not, clean the sensor following
the procedure in Section 8.2.