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ATI A15/66 Residual Sulfite Monitor

O&M Manual

Rev-W (8/10)

SAMPLE SYSTEM CLEANING

Dechlorination systems often suffer from sampling system contamination that changes the sulfite

concentration in the sample during transport to the monitor. This occurs because sulfur reducing bacteria

grow in the sample lines. When the amount of bacterial fouling is high, the sulfite in the sample is

consumed by the bacteria during the time it is flowing through the system.

To eliminate this problem, sample lines should periodically be cleaned with high levels of chlorine.

Injecting sodium hypochlorite solution to provide 50-100 PPM of chlorine in the sample line for a few

minutes every few days will usually control growth in the system. The A15/66 monitor provides software

to either completely or partially automate this cleaning procedure.

The A15/66 chemistry module contains two relays, which are controlled by the “C” and “D” relays

located in the monitor. These relays are used for separate purposes, one to start a chlorine injection

pump or to energize a solenoid valve and one to stop the chemistry module air pump while the cleaning

process proceeds. The highly chlorinated cleaning solution can be allowed to run through the entire

chemistry module as long as the air pump is not running. The timing of the cleaning control relays must

be set so that all highly chlorinated water is flushed from the unit prior to the air pump restarting.

If the automatic cleaning function is to be used, relays “C” and “D” must be connected to the

chemistry module as shown in Figure 6. A 3 conductor cable must be used to connect the chemistry

module to the monitor enclosure. A relay inside the chemistry module (Figure 6) is supplied for use in

controlling an external pump or solenoid valve. The user must provide the pump or solenoid to be used

for feeding cleaning chemicals. Normally, a metering pump feeding sodium hypochlorite or a solenoid

valve controlling the release of sodium hypochlorite by gravity is used for this purpose.

When the cleaning cycle is activated, the relay controlling the external pump will energize,

starting the feed of chlorine solution. At the same time, the relay controlling the air pump will stop air flow

and the display will flash the “Cleaning Cycle” message. At this point, outputs and alarm relays are

locked in a hold state. At the end of the cleaning cycle, the relay controlling chlorine feed will deactivate,

stopping chemical feed. The display will flash an “Hold Cycle” message, indicating that cleaning is

complete but that the air pump has not yet restarted. At the end of the inhibit time, the air pump will start

and the unit will begin to restabilize on the sulfonated sample. After about 3 more minutes, the output

hold will release and the unit will resume normal operation.

CLEANING SYSTEM OPERATION

The A15/66 contains two cleaning modes, Auto and Manual. The selection is made in step 18 of

the configuration menu. If cleaning is required on a daily basis, you can completely automate the

cleaning process by selecting Auto. In this mode, cleaning can be done without operator attention as

often as is needed. Normally, twice a day would be the maximum frequency. If cleaning is required only

every few days or once a week, select Manual mode for cleaning. In manual mode, the cleaning process

must be activated by the operator.

If Auto mode is selected, the default frequency will be once every 24 hours. The frequency can

be changed by starting from display D6 (see page 20). The display will indicate “AUTO CLEAN”. Press

the CAL key and the display will change to “NEXT CYCLE XX.X HRS”. Press ENTER and the display

will read “CLEAN C: WAITING”. Press ENTER and the display will change to “REPETITION: 24.0h. Use

the UP or DOWN keys to adjust the frequency as desired. A frequency of more than once every hour is

not recommended because the unit is off line for about 10 minutes during the each cleaning cycle. After

selecting the cleaning frequency, press ENTER and the new frequency will be stored.

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