Description And Specifications; Features - Emerson Rosemount Analytical FCLi Instruction Manual

MODEL FCLi

DESCRIPTION AND SPECIFICATIONS

• COMPLETE SYSTEM INCLUDES sensor, connecting cable, analyzer, and flow controller
• SENSOR RESPONSE IS PRACTICALLY INDEPENDENT of pH between pH 6 and 10
• NO REAGENTS
• NO AUXILIARY pH ELECTRODE
• VARIOPOL QUICK-DISCONNECT FITTINGS makes sensor replacement easy
1.1 APPLICATIONS AND FEATURES
The FCLi free chlorine system is intended for the determina-
tion of free chlorine (hypochlorous acid plus hypochlorite
ion) in fresh water. Unlike free chlorine analyzers from other
manufacturers, the FCLi does not use expensive sample
conditioning systems or messy reagents to control pH. Nor,
does it require an auxiliary pH sensor for pH correction.
Instead, the pH adjustment takes place inside the sensor,
producing a signal that changes less than 4% per unit
change in pH between pH 6 and 10. Below pH 6.5 the
change is less than 1%. The linear range of the sensor is 0
to 20 ppm (mg/L).
The FCLi is not intended for the determination of total or
combined chlorine (like monochloramine). Nor, can the FCLi
be used for the determination of chlorine in seawater.
The FCLi uses a three electrode, membrane-covered
amperometric sensor. The sensor consists of a hydrophilic
membrane stretched over a gold mesh cathode. A silver/sil-
ver chloride reference electrode and an external copper
auxiliary electrode complete the circuit. The fill solution is
saturated succinic acid slurry. During operation, an electro-
chemical reaction, driven by the polarizing voltage, con-
sumes free chlorine at the cathode surface. The auxiliary
electrode provides the electrons for the cathode reaction,
and a current proportional to the reaction rate flows between
the electrodes. Because the concentration of chlorine at the
cathode is zero, free chlorine in the sample continuously dif-
fuses through the membrane and is destroyed at the cath-
ode. Thus, the cathode current is proportional to the
diffusion rate, which is proportional to the concentration of
free chlorine in the sample.
Unlike other free chlorine sensors, the FCLi sensor requires
neither sample pretreatment nor pH correction. All ampero-
metric free chlorine sensors generate a raw current that
depends primarily on the concentration of hypochlorous
SECTION 1.0.
1.1 APPLICATIONS AND FEATURES
1.2 SPECIFICATIONS
1.3 ORDERING INFORMATION AND ACCESSORIES
DESCRIPTION AND SPECIFICATIONS
acid. Because the fraction of free chlorine present as
hypochlorous acid is a function of pH, readings will be in
error if the sample pH changes from the value it had during
calibration. To correct for pH changes, some manufacturers
treat the sample with acid to convert hypochlorite to
hypochlorous acid. Others continuously measure the pH and
use the pH value to correct the chlorine sensor reading. The
FCLi is different. The sensor uses a highly buffered acidic fill
solution for internal pH adjustment. The fill solution converts
all the free chlorine entering the sensor as well as much of
the free chlorine at the outside surface of the membrane into
hypochlorous acid. Thus, the sensor response is practically
independent of pH.
For customers who wish to measure pH, an option that
includes a pH sensor and flow cell is available.
Maintenance is fast and easy. Replacing a membrane
requires no special tools or fixtures. A screw cap holds the
pre-tensioned membrane in place. Replacing the membrane
and fill slurry takes only a few minutes.
The FCLi includes the easy-to-use Model 1055 analyzer.
The analyzer features two fully programmable 4-20 mA ana-
log outputs and three fully programmable alarm relays.
Programming and calibration is simple and intuitive. The
backlit, two-line display allows the user to read chlorine (and
pH) at a single glance.
Valves, rotameters, and pressure regulators to control sam-
ple flow are things of the past with the the Model FCLi. A
constant head overflow sampler ensures the correct flow to
the sensor no matter how much the sample flow or pressure
changes. To eliminate wiring hassles, quick disconnect
Variopol cable is standard.
Stable free chlorine standards do not exist. The chlorine sen-
sor must be calibrated using the results of a laboratory test
on a grab sample.
SECTION 1.0
1