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20 Maintenance
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ection 4: Maintenance 389VP Instruction Manual
January 2013 PN 51-389VP
389VP ORP
Platinum Electrode Check
The platinum electrode may be checked as follows. There are two types of standard solutions
which may be used to check the ORP electrode/transmitter system:
Type 1: One type of commonly used ORP standard solution is the saturated quinhydrone solution
(PN R508-160Z). Refer to Section 3.3.
Type 2: A second ORP standard solution can be prepared from the following recipe: Dissolve 39.2
grams of reagent grade ferrous ammonium sulfate, Fe(NH
4
)
2
(SO
4
)
2
• 6H
2
O and 48.2 grams of
reagent grade ferric ammonium sulfate, FeNH
4
(SO
4
)
2
• 12H
2
O, in approximately 700 milliliters of
water (distilled water is preferred, but tap water is acceptable). Slowly and carefully add 56.2 mil-
liliters of concentrated sulfuric acid. Add sufficient water to bring the total solution volume up to
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) will produce a nominal ORP of
4.3
4.3.1
TABLE 4-1. R
O
and R
1
values for temperature compensation elements
Temperature R
O
R
1
Compensation Element
3K 2934 .0045
PT-100 107.7 .00385
TABLE 4-2. Temperature vs. Resistance of auto T.C. elements
Resistance
Temperature °C (Ohms) ±1%
3K PT-100
0 2670 100.0
10 2802 103.8
20 2934 107.7
25 3000 109.6
30 3066 111.5
40 3198 115.4
50 3330 119.2
60 3462 123.1
70 3594 126.9
80 3726 130.8
90 3858 134.6
100 3990 138.5
CAUTION
The solution used during the following check is an acid and should be handled with care. Follow the
directions of the acid manufacturer. Wear the proper protective equipment. If contact with skin of
clothing is made, immediately rinse with plenty of clean water.