Omega Products FCLTX-100 Installation Manual
Percent of free chlorine in protonated form (HClO)
0
10
20
30
40
50
60
70
80
90
100
5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
pH
percent
FCLTX-100 Series
SECTION 1.0
THEORY OF OPERATION
1.0 FREE CHLORINE DEFINED. Free Chlorine or "freely active chlorine"
is defined as the sum of molecular chlorine (Cl2), hypochlorous acid
(HOCl) and hypochlorite ions (OCl-). Molecular chlorine occurs at
pH values <pH4. Hypochlorus acid and hypochlorite ions are in pH
dependent equilibrium with one another as shown in FIG 1.
The graph shows % hypochlorous acid on the left of the curve.
Hypochlorous acid is a much stronger disinfecting agent (oxidizer) as
compared to hypochlorite ions.
1.2 SENSOR OPERATING PRINCIPLE. Both hypochlorous acid (HOCl)
and hypochlorite ion (OCl-) diffuse through the membrane between
the cathode and sample solution, even though the diffusion coefficients for each are different. At the applied potential, only hyphochlorous acid is electrochemically reduced. HOCl is reduced to chloride
ion at the gold cathode. At the same time, the silver anode is oxidized
to form silver chloride (AgCl). When the concentration of HOCl at
the cathode is dramatically decreased by electrochemical reduction,
hypochlorite ion will be transformed into hypochlorous acid , to some
extent, by proton transfer. The release of electrons at the cathode
and acceptance at the anode creates a current flow, which under
constant conditions, is proportional to the free chlorine concentration
in the medium outside the sensor. The resulting low current output
is then conditioned to 4-20mA current by the sensor's onboard electronic circuitry.
PRODUCT INSTRUCTION SHEET
SECTION 2.0
FACTORS INFLUENCING THE SENSOR
2.1 pH. Free Chlorine (FCL) exists as hypochlorous acid and hypochlorite anion (FIG 1). The acid-base dissociation of FCL has a pKa
of approximately 7.5. The FCL sensor responds to hypochlorous
acid and hypochlorite anion with different sensitivity. In combination, an increase in pH reduces the measured FCL and decrease in pH
increases the measured FCL. The need for automatic pH compensation depends on the pH value and the variation range of pH (Table
1). If pH variation of your sample is more than that listed in the table,
automatic pH compensation is required. pH compensation for the
sensors current (mA) reading is:
(sensor output in mA – 4)/(-0.0502pH3 + 0.867pH2 – 5.051pH + 12.43) + 4
2.2 Chemical Interferences. The sensors should not be used in water
containing surfactants, organic chlorine or stabilizers such as cyanuric
acid.
2.2 FLOW. The membrance covered free chlorine sensors (FCL series)
functions at any flow rate. To acheive reproducible measurements,
these free chlorine sensors require a specified constant flow rate. To
avoid complications (such as bubbles), it is best to operate the sensors at a flow rate of 0.2-0.6 gpm if using flow cell FC72 or FC70 (old
version).
Parts covered by this product instruction sheet include: FCLTX-100 Series
FIG. 1
-
HOCl
OCl
TABLE 1
pH Range <6.5 6.5-7.5 7.5-8.3 8.3-9.0
pH Variation N/A + 0.35 + 0.20 + 0.05
M4679/0708 page 1 of 6
PRODUCT INSTRUCTION SHEET
SECTION 3.0
SENSOR PREPARATION
3.0 FREE CHLORINE SENSOR ASSEMBLY. The Free Chlorine
Sensor is shipped with the membrane cap pre-installed and
covered with a cap with water inside to keep the membrane
wet. Make sure to keep sensor cap, anode and cathode inside
the sensor body, away oily or greasy materials. Contact with oil
or grease will result in inaccurate measurements.
NOTE: IF SENSOR WILL BE STORED DRY OUT OF FLOW
CELL, SHAKE BODY DOWNWARD INTO A SINK TO REMOVE THE
FILL SOLUTION. TAKE THE MEMBRANE CAP AND IMMERSE IN A
CUP OF TAP WATER UNTILL READY TO REUSE. SEE
SECTION 9. REPLACE CAP AND ELECTROLYTE BEFORE INSTALLING INTO FLOW CELL (see SECTION 10 for cap and electrolyte
change. See SECTION 5 for sensor installation into flow cell).
SECTION 4.0
FLOW CELL INSTALLATION
4.0 FLOW CELL. To obtain accurate Free Chlorine reading,
the Sensor must be installed into the Flow Cell to prevent air
bubbles formation on the membrane, proper spacing between
the sensor and the installation wall, and laminar flow across
the membrane.
FIG. 2
SENSOR
SNAP RING
GROOVE
THREADED FITTING
SNAP RING (INSTAL L S
INTO PROBE GROOVE)
O-RING
BARBED TUBE
FITTING
FLOW CELL
4.1. Using two 1/4” NPT Tube fittings, connect the FC72 Flow
Cell into your system, noting the inlet (bottom) and outlet
(side) orientation. (see FIGURE 2)
4.2. Install clamp with rubber backing as shown in FIG. 2A.
4.3 Drill 3/8" diameter hole on the panel.
4.4 Insert bolt as shown in FIG 2A
4.5 On back of panel attach lock washer and nut to secure
clamp and flow cell to panel.
SECTION 5.0
SENSOR INSTALLATION
5.0 SENSOR INSTALLATION INTO FLOW CELL.
a. First install threaded fitting onto sensor body
(remove fitting if pre-installed in flow cell)
b. Install snap-ring into groove on sensor body
c. Next, slide o-ring onto body of sensor until it
reaches bottom of threaded fitting.
d. Thread sensor assembly into top of flow cell as
shown in FIGURE 2.
d. Turn on flow and verify the flow through the Flow
Cell is at least 0.2gpm (45 liters/hour and no
more than 0.6gpm (135 liters/hour).
FC72 Flow cell
BARBED TUBE
FITTING
FIG. 2A
Parts covered by this product instruction sheet include: FCLTX-100 Series
M4679/0708 page 2 of 6
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