Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 - Manual (Page 215)

App.1-3
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
n Checking ORP sensor electrodes
The normal functionality of the ORP sensor electrode is determined by measuring the ORP value
of the solution with a known ORP value, and by checking if the value is within the tolerable range.
To check the ORP sensor before regular operation, follow the procedure below.
The electrode is checked in measurement mode.
l Solution for checking
Use solutions with a known ORP value, such as quinhydrone, ferrous, and other solutions.
l Checking procedure
(1) Pour 50 to 100 ml of the solution into a clean 200-ml beaker.
(2) Remove the ORP sensor from the holder. Flush the measurement solution remaining on the
sensor with water and wipe off the water. If the detecting part and liquid outlet of the sensor
are stained, clean them with water.
(3) Immerse the tip of the ORP sensor into the solution. Read the ORP value after the reading
becomes stable (usually 5 to 10 minutes).
Measure the solution temperature and check if the ORP value at the temperature is in the
tolerable range.
l Yokogawa’s checking solution and tolerable range
Yokogawa offers the following reagents for checking. Use them as described below.
Quinhydrone (part number: K9024EC)
Ferrous (part number: K9024ED)
Quinhydrone solution
Put one bag of the reagent into a wide-mouthed jar (at least 250 ml) and pour deionized
water into the jar to make a total solution volume of 250 ml. Cold deionized water may not
dissolve the reagent completely and the reagent may partly float on the surface, but this
does not cause any problem for measurement.
Ferrous solution
Put one bag of the reagent into a wide-mouthed jar (at least 250 mL) and pour 2 mol/l
solution of sulfuric acid to make a total solution volume of 250 ml.
When using concentrated sulfuric acid, first pour approximately 150 ml of pure water into a
wide-mouthed jar that contains the reagent. Add 14 ml of concentrated sulfuric acid while
stirring the solution. Add more pure water to further dissolve the reagent and make a total
solution volume of 250 ml.
CAUTION
Be careful to touch the concentrated sulfuric acid.
Figure 1 shows the ORP values of the checking solutions prepared with Yokogawa’s reagents.
If the measured ORP value is in the tolerable range, the electrode of the ORP sensor is working
normally.
If the ORP value is out of the range, calibrate the sensor. If the ORP value is slightly out of range,
verify whether the checking solution has been properly prepared.
App.
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