AquaMetrix AM-FCL Specifications
AM-FCL Operation Manual
AM-FCL Free Chlorine Sensor Manual, Rev. 1.1, July 2016
AquaMetrix AM-FCL
Free Chlorine Sensor
Installation and Operation Guide
AM-FCL Operation Manual
AM-FCL Free Chlorine Sensor Manual
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1. Introduction ................................................................................................................... 3
2. Specifications.................................................................................................................. 3
3. Principle of Operation ..................................................................................................... 3
3.1. Free Chlorine ................................................................................................................................................................ 3
3.2. Probe Operation .......................................................................................................................................................... 5
4. Installation ..................................................................................................................... 5
4.1. Sensor Preparation..................................................................................................................................................... 5
4.2. Flow Cell ......................................................................................................................................................................... 6
4.3. Flow Meter ..................................................................................................................................................................... 7
4.4. Installing the AM-FCL Probe .................................................................................................................................. 7
4.5. Electrical Connections............................................................................................................................................... 8
5. Sensor Maintenance ....................................................................................................... 8
5.1. Cleaning the cathode ................................................................................................................................................. 8
6. Calibration .................................................................................................................... 10
6.1. Span/Slope Calibration ........................................................................................................................................... 10
7. Maintenance ................................................................................................................ 10
7.1. Sensor Storage ............................................................................................................................................................ 10
7.2. Membrane Cap Replacement ............................................................................................................................... 10
8. Troubleshooting ........................................................................................................... 11
9. Appendix ...................................................................................................................... 12
9.1. Dimensions .................................................................................................................................................................. 12
9.2. Order Information .................................................................................................................................................... 12
9.3. Warranty and Customer Support ....................................................................................................................... 13
AM-FCL Operation Manual
AM-FCL Free Chlorine Sensor Manual
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1. Introduction
The AM-FCl is a compact, rugged free chlorine sensor that is primarily targeted toward clean water
applications. The AM-FCL outputs a 4-20 mA signal and can be connected directly to a PLC or the
AquaMetrix 2300. However it is typically bought as a replacement probe that is part of a chlorine
analyzer system. Such a system consists of a flow cell and analyzer. The flow cell insures a constant
pressure against the membrane and the analyzer combines the probe reading and the pH into a free
chlorine signal.
2. Specifications
Wetted Materials
PVC
Membrane Material
PVDF
O-Ring Material
Viton
Anode
Silver-Silver Chloride
Cathode
Gold
Cable
2-conductor shielded, 10 ft. (3 m)
Measurement Range
AM-FCL-2: 0 to 2 ppm
AM-FCL-5: 0 to 5 ppm
AM-FCL-10: 0 to 10 ppm
Temperature Compensation
Pt 100 RTD
Operating Temperature Range
O to 45 °C
Maximum Pressure
14.7 psi at 40 °C
Flow Range
0.2 to 0.6 gpm (0.8 to 2.4 l/min)
Supply Voltage
12-24 VDC, 250 mA
Cross Sensitivity
Monochloramine, chlorine dioxide, ozone, bromine, iodine
Chemical Compatibility
Up to 50% ethanol/water or glycerol/water.
Dimensions
8.2” length x 1” diameter
Mounting
Optional constant pressure flow cell recommended
Environmental Ratings
NEMA 4X, IP67, CE certified
3. Principle of Operation
3.1. Free Chlorine
Free chlorine is a frequently misunderstood term. When chlorine (Cl2) dissolves in water it creates
hypochlorous acid (HOCl):
AM-FCL Operation Manual
AM-FCL Free Chlorine Sensor Manual
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Eq. 3-1
HOCl is a very strong oxidizing agent and disinfectant. However it partitions into H+ and hypochlorite
(OCl-) to some degree:
Eq. 3-2
The degree to which this dissociation takes place depends on pH. When the pH is low, i.e. the
concentration of H+ ions is high, then the equilibrium in this relationship is driven to the left and HOCl is
the predominant species. Conversely, under basic conditions the equilibrium shifts to the right and OClis the predominant species. Figure 1 shows the ratio of the one species to another. At pH values less
than 7 the mixture is mostly HOCl. At pH values greater than 8.5 the mixture is mostly OCl-.
Figure 1 - Concentration of HOCl vs. pH. As the pH increases, more HOCl converts to OCl-.
Free chlorine is defined as the sum of HOCl and OCl-. Since most regulations refer to free chlorine
concentrations any measuring device must measure this sum of species. Colorimetric test kits, based on
the reaction of DPD with chlorine, measure the total free chlorine concentration. However
amperometric chlorine sensors only measure the concentration of HOCl. Therefore, the output of the
free chlorine sensor must be corrected to give the sum of HOCl and OCl- using the relationship
displayed in Figure 1.
Most regulations call for free chlorine without specification of the percentage of HOCl. Unfortunately,
specifying the free chlorine concentration without specifying the pH does not give an unambiguous
measure of the oxidation or disinfection power of the chlorine solution. A 4 ppm free chlorine solution
at pH 6 will have about 100 times the disinfection power of a 4 ppm free chlorine solution at pH 9.
Therefore it’s vital that all free chlorine measurements are accompanied by pH measurements.
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