Hach 8450, Instrument Manual

Page: 51 / 66

Page 51
16116Maintenance.fm
Maintenance and Troubleshooting
Section 4 Maintenance and Troubleshooting
4.1 Maintenance Overview
This chapter provides information on normal maintenance procedures and
troubleshooting. Maintenance and troubleshooting for the 8450 Residual
Free-Chlorine Meter comprises three major categories: 1) Issues related to
calibration, 2) Issues related to probe maintenance, and 3) Handling of error
messages.
4.2 Probe Maintenance and Poor Probe Output
Periodic maintenance of the chlorine probe is required to ensure it’s proper
operation. The period of time between maintenance depends upon the
environmental conditions in which the probe is operating (i.e., the dirtier the
application, the more frequent the maintenance).
Some of the main indications that the probe may require maintenance are:
• Unstable or erratic readings.
• Inability to maintain system zero or consistently high zero offsets.
• Relative Probe Sensitivity below 60%.
4.2.1 Membrane Troubleshooting and Maintenance
A damaged membrane (pierced or torn) will result in highly unstable readings.
The first step in maintaining the chlorine probe is to ensure that the probe’s
membrane is clean and intact. To check for punctures, remove the probe from
its installation site and wipe the probe (tip area) dry. While holding the probe
vertically, remove the Teflon
®
fill screw and observe the tip area for leakage.
Replace the membrane if leakage is observed.
The porous properties of the membrane material make it subject to fouling or
clogging, thus reducing the probe’s ability to respond to chlorine. Clean the
membrane by gently wiping it with a soft, moist cloth. Care should be
exercised while wiping the membrane because this can possibly stretch it and
cause erratic readings. Replace the membrane after 4 to 5 cleanings.
4.2.2 Quick Membrane Replacement Procedure
If cleaning the membrane is not successful, replace it. Because some
applications require relatively frequent membrane changes, it is not always
necessary to completely disassemble the probe (thus requiring electrolyte
replacement) when changing the membrane. The following procedure
describes a simplified membrane change. This procedure will reduce the time
it takes for the probe to stabilize after a membrane change.
Note: The entire probe should be completely disassembled and filled with fresh
electrolyte at least every 4 months (see section 2.10 on page 24 ).
Note: The membrane cannot be changed simply by removing the membrane holder
and inserting a new membrane. That would result in unstable and erratic
operation.
1. Loosen the three body screws at the back of the probe 1/8- to 1/4-in. Hold
the probe with the membrane cap pointing up.
Note: Free Chlorine membranes must be pre-wetted before installation. To do this,
float either side of the membrane on top of clean water (do not wet both sides).