Yokogawa FS20 Fittings for pH and ORP - Manual (Page 20)

IM 12B6K1-01E-E
18
ATTENTION
Avoid using non-polar solvents like tri-chloro ethylene, toluene or hexane. Even cleaning
with ethanol or acetone is not recommended. These solvents will break up the gel-layer on
the glass bulb and afterwards needs to remain soaked in water for at least 12 hours before
functioning normal. The PTFE diaphragm of the combined electrode can sometimes be
regenerated by putting it in hot (60 to 80 °C) 1 molar Potassium chloride (KCl) solution and
letting it cool to room temperature. After cleaning the probe is re-inserted into the process
by following the reverse procedure (see §3-5).
5-3. Calibration
It is recommended to start calibration with clean electrodes. Always calibrate new
electrodes. With the electrodes connected to the transmitter a calibration can take place.
Check the appropriate chapters in the instruction manual of the pH transmitter for details.
General procedure for calibration
To calibrate a pH transmitter two buffer solutions with known pH value are required. It is
recommended that one buffer solution has a value near pH 7.
Depending on the liquid to be measured the second buffer solution should either be in the
acidic or base area. Normally the buffers pH 4.01 or 9.22 are used.
Generally the procedure for calibration is as follows:
- Clean the electrodes
- Rinse the electrodes
- Immerse the electrodes in the first buffer solution (pH 7)
- Adjust the asymmetry setting of the transmitter for reading a known value
- Rinse the electrodes
- Immerse the electrodes in the second buffer (pH 4 or pH 9)
- Adjust the slope setting of the transmitter for reading a known value
- Rinse the electrodes.
During calibration the temperature compensation should be active. It is advised top
calibrate with buffer solutions at a temperature near the process temperature.
5-4. Replacing the O-rings
The exploded view (see §6) shows the position of the sealing O-rings. The O-rings used
in the wetted part are made of silicone rubber, which has superior resistance to corrosion
suitable for use with most process liquids.
Usually no periodical inspection is necessary. To prevent trouble, replace the O-ring seal
periodically, e.g. every year.