Xylem CL500 ONLINE CHLORINE ANALYZERS - Manual (Page 9)

CL500 (2/08) Page 5
REV 2.0
3.0 Theory of Operation
The CL500 has two solenoid valves, one for sample water (FLOW) and one for draining
of the cuvette (PURGE). A third solenoid, along with four check valves forms a reagent
pump. Sample water flow is controlled by the FLOW solenoid valve. The PURGE
solenoid valve is used to empty the measurement cuvette.
The measurement chamber consists of a sample inlet, a purge drain, and an overflow. The
reagent is added below the cuvette. A green LED provides the 515 nm source lamp, a red
LED is used for sample level and flow measurement. A single detector is located 180 º
from the green LED. A replaceable glass cuvette separates the sample water from the
optical devices and maintains the measurement path length. Sample water flows in the
inlet at the bottom, through the measurement cuvette and out through overflow drain. This
flow is used to both fill the cuvette and flush the system.
The reagents consist of two replaceable bottles. One bottle has a buffer to control the pH;
the second has an indicator that contains the DPD, which produces color when chlorine is
present in the sample. The degree of color is dependant on the amount of chlorine in the
sample water.
The measurement chamber is open to view operations in the cuvette. A white LED
illuminates the chamber for a clearer view. The white LED will flash to attract attention in
the case of a warning or failure. Most warnings and failures are displayed on the screen.
During normal operation the CL500 will run through a timed cycle. A simplified cycle
will consist of the following sequences:
• Flushing – continuous sample flow
• Zeroing – no flow with cuvette full
• Purging – PURGE valve opens
• Adding Reagents – one pulse of the reagent pump
• Mixing with sample – sample flow pulses in
• Reading resulting sample – no flow with cuvette full
• Purging – PURGE valve opens to remove reacted sample
The cycle above does not describe all the actions and testing that occurs. The CPU
continuously diagnoses the entire system for correct operation and sample water flow. If
an error occurs, a message is posted to the message queue.
The reagent is added from the front, below the cuvette, by a single pulse of the reagent
solenoid. When the reagents require replacement, the PRIME button is pushed to bring
new reagents into the system. The reagent solenoid is pulsed several times to draw fluid
from the two reagent bottles and fill the tubes with new reagent. A complete prime takes
less than a minute.
The SERVICE button empties the cuvette, stops the flow of sample water, and clears any
errors. This provides a convenient way to replace reagents and the measurement cuvette. If
more extensive servicing is performed, all power to the CL500 should be removed. If the
CL500 is to be turned off, it is recommended that the instrument be placed in SERVICE
mode before removing power. This ensures that the cuvette is emptied and the flow is off.