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Maintenance
● Checking the state of the ORP electrode
ORP standard solution can be used to check the state of the ORP electrode.
This solution is only used to check the state of the ORP electrode; it is not used to
calibrate the instrument. The procedure for checking the electrode using HORIBA ORP
standard solution powder 160-22 or 160-51 is explained below.
1. Add one bag of 160-22 or 160-51 standard solution powder to 250 mL of
deionized water and mix thoroughly.
When mixing, the excess quinhydrone (a black powder) will float to the surface of the
solution.
2. Immerse a washed and dried ORP electrode in the prepared standard solution
and measure the mV value.
If the electrode and the instrument are working properly, numerical values within ±15
mV of those indicated below should be obtained.
The ORP value varies by temperature. Check the appropriate ORP value for the
temperature of the standard solution.
3. If the ORP value is not within ±15 mV, replace the reference electrode internal
solution.
If the surface of the metal electrode is dirty, wipe it gently with a soft material such as
absorbent cotton moistened with alcohol or a neutral cleaning solution, or immerse in
dilute nitric acid (1:1 nitric acid) to remove the dirt.
4. Repeat the measurement.
If the ORP value is within ±15 mV, the electrode is normal.
If not within ±15 mV, the electrode may have failed. Replace the electrode.
Note
・ If the prepared standard solution is left out in air for one hour or more, that the ORP value
might change. Do not use the ORP standard solution that was prepared more than an hour
before.
・ When measuring a solution that has low concentrations of oxidants and reductants after
conducting an operational check using a standard substance, the measured values may not
stabilize or the repeatability might be poor. If this is the case, use the ORP electrode after
immersing it in the solution again and mixing it thoroughly.
• ORP value based on the temperature of ORP standard solution
Temp.
Phthalic-acid chloride + quinhydrone
(°C)
5
10
15
20
25
30
35
40
98
160-22
(mV)
274.2
270.9
266.8
262.5
257.6
253.5
248.6
243.6
160-51
Neutral phosphate + quinhydrone
(mV)
111.9
106.9
101.0
95.0
89.0
82.7
76.2
69.0
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