Hach-Lange pHD sc - Manual (Page 27)

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Section 5 Maintenance
DANGER
Only qualified personnel should conduct the tasks described in this section of the
manual.
DANGER
Explosion hazard. Do not connect or disconnect equipment unless power has been
switched off or the area is known to be non-hazardous.
5.2 Cleaning the Sensor
CAUTION
Before cleaning with acid, determine if the chemical reaction between the acid and
the sample will create a hazardous chemical reaction. (For example, do not put a
sensor that is used in a cyanide bath directly into a strong acid for cleaning
because this chemical combination may produce poisonous cyanide gas.)
1. Clean the exterior of the sensor with a stream of water. If debris remains remove loose
contaminate buildup by carefully wiping the entire measuring end of the sensor
(process electrode, concentric metal ground electrode, and salt bridge) with a soft
clean cloth. Rinse the sensor with clean, warm water.
2. Prepare a mild soap solution of warm water and dish detergent or other non-abrasive
soap that does not contain lanolin such as laboratory glass cleaner.
Note: Lanolin will coat the glass process electrode and can adversely affect sensor performance.
3. Soak the sensor for 2 to 3 minutes in the soap solution.
4. Use a small soft bristle brush (such as a toothbrush) and scrub the entire measuring
end of the sensor, thoroughly cleaning the electrode and salt bridge surfaces. If
surface deposits cannot be removed by detergent solution cleaning, use muriatic acid
(or other dilute acid) to dissolve them. The acid should be as dilute as possible.
Experience will determine which acid to use and the appropriate dilution ratio. Some
stubborn coatings may require a different cleaning agent.
DANGER
Acids are hazardous. Always wear appropriate eye protection and clothing in
accordance with material safety data sheet recommendations.
5. Soak the entire measuring end of the sensor in dilute acid for no more than 5 minutes.
Rinse the sensor with clean, warm water then place the sensor back into the mild
soap solution for 2 to 3 minutes to neutralize any remaining acid.
5.1 Maintenance Schedule
Maintenance Task 90 days Annually
Clean the sensor 1 x
Inspect sensor for damage x
Replace Salt Bridge and fill solution 2 x
Calibrate Sensor (as required by regulatory agency) Per the schedule mandated by your regulatory agency.
1 Cleaning frequency is application dependent. More or less frequent cleaning will be appropriate in some applications.
2 Salt bridge replacement frequency is application dependent. More or less frequent replacement will be appropriate in some
applications