Emerson Rosemount 396P Quick Start Manual page 42

Quick Start Guide
Note
You may get erroneous pH results immediately after acid soak due to
reference junction potential buildup. Replace the sensor if cleaning
does not restore sensor operation.
4.4 Check platinum electrode
Check the platinum electrode as follows. There are two types of standard
solutions which may be used to check the oxidation reduction potential
(ORP) electrode/transmitter system.
Type 1: One type of commonly used ORP standard solution is the saturated
quinhydrone solution (PN R508-8OZ). Refer to
and 396PVP oxidation reduction potential (ORP)
WARNING
The solution used during the following check is an acid.
Handle the solution with care.
Follow the manufacturer's directions.
Wear the proper protective equipment.
If contact with skin or clothing is made, immediately rinse with plenty of
clean water.
Type 2: A second ORP standard solution can be prepared from the following
recipe:
Procedure
1. Dissolve 39.2 grams of reagent grade ferrous ammonium sulfate,
Fe(NH
ammonium sulfate, FeNH
(700 ml) of water.
Distilled water is preferred, but tap water is acceptable.
2. Slowly and carefully add 1.9 oz. (56.2 ml) of concentrated sulfuric
acid.
3. Add sufficient water to bring the total solution volume up to 33.8 oz.
(1000 ml).
This standard ORP solution, although not as simple to prepare as the
quinhydrone recipe, is much more stable and will maintain its millivolt value
for approximately one year when stored in glass containers. This solution
(ferric/ferrous ammonium sulfate) produces a nominal ORP of 476 +20 mV
at 77 °F (25 ºC) when used with a saturated KCL/AgCl reference electrode
and platinum measuring electrode. Expect some tolerance in mV values due
to the rather large liquid reference junction potentials that can arise when
42
) (SO ) ● 6H O and 48.2 grams of reagent grade ferric
4 2 4 2 2
Calibrate Rosemount 396P
sensors.
(SO ) ● 12 H O in approximately 23.7 oz.
4 4 2 2
November 2020
Emerson.com/Rosemount