ATI Q46H/85 PAA System Part 9 – System Maintenance
58
O&M Manual
Rev F (8/17)
9.31 Sensor Acid Cleaning
Over an extended operating period, PAA sensors can slowly accumulate deposits on the surface
of the gold electrode. Typically, this type of buildup occurs over years of operation, but can
sometimes occur more quickly in high levels of manganese, iron, or other metals are dissolved in
the water. The platinum electrode can be “acid cleaned” using nitric acid solutions.
To acid clean the electrode assembly, remove the electrolyte chamber from the sensor so that
the so that both electrodes are exposed. Then follow the procedure below.
1. Place a small amount of 50% nitric acid solution in a beaker. Put in just enough so that the
gold tip of the sensor can be submerged without any contact with the silver coil.
2. Allow the sensor to soak in this acid solution for 2 minutes. Remove the sensor body and
rinse the platinum tip thoroughly with distilled water. Discard the nitric acid safely and
according to all environmental regulations.
3. Fill the beaker with distilled water to the level sufficient to submerge both the tip and the silver
coil. Do not allow the connector at the back of the sensor to be submerged. Allow the
electrodes to soak in distilled water for 30 minutes.
4. Put a new membrane and fresh electrolyte in the electrolyte chamber and reassemble the
sensor. Connect to the PAA monitor electronics and allow the sensor to stabilize for at least
24 hours. The sensor can be placed in the flow cell with ozonated water running through it
during stabilization. However, the readings will not be useful for 24 hours.
9.4 Flow Cell Maintenance
The maintenance on the flow cell is simple cleaning. The flow cell is clear to make examination
of the condition of the sensor easier without interfering with operations. The flow cell may be
cleaned by wiping or by washing with detergents or dilute acids. Do not try to clean with solvents
as the acrylic may craze or crack.
Change the o-ring in the flow cell yearly or if any damage is observed. If insertion of the sensor
into the flow cell becomes difficult, use silicon grease to lubricate the o-rings that hold the sensor
in place. Use only enough grease to provide surface lubrication. Excess grease could foul the
sensor membrane.
THIS ACID CLEANING PROCEDURE INVOLVES THE
USE OF HIGHLY CORROSIVE ACID SOLUTIONS. IT
SHOULD ONLY BE COMPLETED BY TRAINED
PERSONNEL USING PROTECTIVE EYEWEAR AND
GLOVES. IF THERE IS ANY DOUBT ABOUT YOUR
ABILITY TO SAFELY ACCOMPLISH THI
PROCEDURE, RETURN THE SENSOR TO ATI FOR
FACTORY CLEANING!
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