Hach-lange ORBISPHERE 31xxx Installation and Maintenance Manuel d'utilisateur télécharger pdf (Page 32)

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Maintenance

5.3 Chemical cleaning: oxygen and ozone sensor cell

Note: Not applicable for H

2

sensors.

The following supposes that the sensor has been taken apart. For disassembly and assembly

procedures, see Disassembly and assembly on page 25.

Conditions

Wear on the membrane, and chemical reactions within the sensor, requires that the sensor be

serviced regularly to restore its original sensitivity. Service includes electrode cleaning and

membrane replacement. A clear sign that a sensor maintenance is required is when

measurements are noticeably less stable than usual, and when a calibration does not improve

the situation.

Method description (see following step-by-step procedure)

• Electrochemical cleaning with 32301 (if available)

… when not available or results are insufficient:

• Anode and cathode chemical cleaning

• Central electrode polishing

• Final rinsing

Note: To eliminate any silver residue that ammonia cleaning cannot remove, it is sometimes required to

repeat the chemical cleaning using nitric acid (HNO

3

, not over 70% by weight).

5.3.1 Membrane support cleaning

5.3.2 Electrodes ammonia cleaning

Empty and rinse the electrolyte reservoir under tap water.

Rinse membrane support under water and wipe it dry.

Check for the presence of any residue on the surfaces.

Residue can be removed by placing the support in a container

of nitric acid (HNO

3,

not over 70% by weight) until it recovers

its original appearance (normally within 30 seconds)

Rinse one minute under tap water and check again for

surface cleanliness.

CAUTION

Nitric acid is dangerous! Please refer to the safety

information from your chemical supplier.

Fill the sensor electrolyte reservoir with a solution of 25% by

weight ammonium hydroxide (NH

4

OH) in water and leave for

10 minutes.

Rinse with tap water for at least one minute.

Inspect the sensor head. The counter electrode should be a

silver-white color.

If the counter electrode still shows deposits, repeat the

procedure.

CAUTION

Ammonia is dangerous! Please refer to the safety

information from your chemical supplier.

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