HF scientific CLX Online Residual Chlorine Monitor - Manual (Page 10)

CLX (1/12) Page 5
REV 5.1
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 cuvette in the measurement chamber.
The measurement chamber consists of a sample inlet, a purge drain, and an overflow. The
reagent is added from the check valves integrated into the lower portion. 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 an overflow drain. This flow is used to both fill the cuvette and flush the system.
The reagents are dispensed from 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 also displayed on the screen. To
prevent interference, the white LED is turned off during measurements.
During normal operation the CLX will run through a timed cycle. A simplified cycle will
consist of the following sequences:
• Flushing – continuous sample flow
• Purging – PURGE valve opens
• Zeroing – no flow with cuvette full
• 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 is simplified and 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 on the LCD screen.
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. During
PRIME 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 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.