Hach 8450, Instrument Manual

Page: 53 / 66

Section 4
Page 53
16116Maintenance.fm
Probe Maintenance and Poor Probe Output
Figure 36 Probe Tip and Anode
Warning: The following procedures require the use of Nitric Acid. Only
personnel experienced in the handling and use of acids should perform this
procedure because serious injury could result if the solution is improperly
handled. Full eye, hand, and body protection is required.
In case of skin contact, immediately flush the affected area with water. If
irritation persists, seek prompt medical attention.
In case of eye contact, continuously flush with clean water and seek immediate
medical assistance.
4.2.3.1 Probe Tip Cleaning
Cleaning only the probe tip may be required when it has been exposed to
contamination, i.e., membrane is broken. To clean the tip, disassemble the
probe and place its tip in a beaker containing a solution of 50% Nitric Acid
(about a ½-in. depth will suffice). Allow the tip to soak in the solution for about
five minutes while ensuring that the acid does not come in contact with the
silver electrode. Rinse the tip thoroughly in distilled water and reassemble the
probe. Perform system calibration.
4.2.3.2 Silver Anode Cleaning
Disassemble the probe and immerse the probe’s electrodes for 45–60
seconds in a beaker containing a 50% solution of Nitric Acid. Do not allow the
probe to sit in the solution longer than this. Remove the probe and rinse it
thoroughly in distilled water. Proceed in cleaning the probe tip as outlined in
the above paragraph. Do not use the same acid that was used to clean the
silver electrode.
Reassemble the probe and perform system calibration procedures.
4.2.4 Testing Thermistor Output
With the probe disconnected from the meter, connect an Ohmmeter to the
plug pins C and D.
Table 7 shows the expected resistance values. A defective
thermistor requires probe body replacement.
Silver Anode
Platinum Tip
Probe Body