HF scientific CLX Online Residual Chlorine Monitor (Old) - Manual (Page 11)

CLX (9/07) Page 5
REV 3.1
3.0 Theory of Operation
The CLX 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 from the top. 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 LEDs from the detector 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. A white LED backlights 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 CLX 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 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 purge 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 CLX should be removed. If the
CLX 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.