Hach-lange ORBISPHERE 31xxx Basic User Manual Manuel d'utilisateur télécharger pdf (Page 16)

In addition, the chemical reaction that takes place on the chloridized silver cathode leads to loss of

performance after a certain operation time.

As a result, a sensor service must be carried out to restore its original performance.

Method

The procedure for cleaning the H

2

electrochemical sensor requires the use of the ORBISPHERE

32301 Sensor Cleaning and Regeneration Center. This procedure is explained in detail in the

32301 Operator's Manual.

As an overview, H

2

electrochemical sensor cleaning consists of the following sequence of operations:

• Dechloridization of the cathode: This process removes the chloride film from the silver cathode

surface (carried out by the ORBISPHERE 32301).

• Rechloridization of the cathode: A layer of silver chloride is grown on the cathode's surface

(carried out by the ORBISPHERE 32301).

• Activation of the platinum anode: The center anode surface is polished, and treated with nitric acid.

Troubleshooting

Oxygen sensor

Problem Probable cause Possible solution

Sensor won't calibrate, even after

thorough servicing.

Repeated calibrations go beyond

"expected limits" of instrument.

MOCA 3600 only: Select membrane

from "Options/Membrane" menu.

Then, calibrate the sensor.

Instrument internal barometric

pressure sensor needs calibration.

Calibrate internal barometer against

a certified barometer. Do not correct

for sea level !

Wet membrane interface.

Wipe dry with a tissue and re-

calibrate.

"H

2

S insensitivity" option enabled.

Disable on the measuring

instrument.

"0000" O

2

levels displayed.

Wrong reading scale "XXXX"

selected for display unit.

Change reading scale by selecting

"X.XXX, XX.XX or XXX.X".

Shorter than expected sensor

operation in relatively high dissolved

O

2

concentration.

High O

2

concentrations generate

deposits more quickly.

Install a less permeable membrane.

Turn off the analyzer when sensor is

not in a low O

2

concentration.

Unexpected or inaccurate dissolved

O

2

readings.

Air leak on product sample line.

Set flow rate to 100 mL/min. Wait

until stable, then slowly double this

flow rate.

The stable value of dissolved O

2

reading must be the same as

before. A variation related to flow

rate is a clear sign of an air leak in

the line.

High residual current.

Place sensor in de-aerated sample;

wait for low reading:

Check concentration against low

measurement limit (see tables in

Sensor membrane specifications

on page 3). If concentration is

significantly higher than low limit, try

a sensor service.

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