YOKOGAWA FU20, User Manual

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IM 12B07K02-01E
< 3. Maintenance >
3-1
3. Maintenance
The sensor has limited life. If buffer solution calibration becomes impossible due to deterioration
of the sensor, replace it with a new one. After the sensor is replaced, always carry out a buffer
solution calibration.
NOTE
A glass electrode whose glass membrane has dried out does not provide stable readings until
it gets used to the solution. Place in advance the glass electrode in the 3 mol/L KCl solution for
several hours. When storing the sensor, use a sensor cap (supplied with it on shipment) to its tip.
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Cleaning Electrode and Liquid Junction
Staining of an electrode or liquid junction can cause measurement errors. Therefore, if he
measured solutions tend to stain the electrode, the electrode and liquid junction must be cleaned
periodically - depending on the degree of staining.
To clean the sensor, proceed as follows:
(1) Take out the sensor.
(2) Clean the electrode or liquid junction as follows. Different cleaning solutions may be
required depending on the staining.
● Stains due to suspended Solids, Sticky Materials, Microbes or the like
Using soft tissue paper, wipe the stains off the electrode or liquid junction. In addition, clean
off remaining stains by rinsing with water.
● Stains due to Oily Materials
Wash off stains by submerging in a neutral detergent solution in a beaker, etc, (for from
several tens of minutes to several hours depending on the degree of staining).
● Chemical Stains such as due to Metallic Adsorption
Place the electrode or liquid junction in a diluted hydrochloric acid solution (1 to 2%) for
several minutes (acid washing). Afterwards rinse the sensor with water.
● Protein Deposits
It should be removed with a protein enzymatic solution. For instance a solution containing
8.5 mL concentrated hydrochloric acid and 10 gram pepsin in 1 liter water will do.
(3) Check deterioration of the sensor.
(4) Calibrate the sensor with buffer solution.
(5) Mount the sensor again.
CAUTION
Avoid using non-polar solvent like tri-chloro ethylene, toluene or hexane. Cleaning with iso-
propanol or methanol is acceptable.
The non-polar solvents will break up the gel-layer on the glass bulb and requires that the
electrode to be soaked in water for at least 12 hours before functioning normally again.
The Teflon (PTFE) diaphragm of the sensor can sometimes be regenerated by putting it in hot
(approx. 70°C) 3 molar Potassium Chlorine (KCl) solution and letting it cool to room temperature.
For details of calibration procedure, refer to relevant user’s manual of transmitter/converter.
4th Edition : Nov.20,2018-00