Free Chlorine

04/05/04

IC Controls 875 Free Available Chlorine System

pH / ORPConductivityDissolved OxygenChlorineStandards

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R1.0 © 2004 IC CONTROLS

Free Residual Chlorine Measurement

Why measure residual chlorine in drinking water?

?

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Chlorine Chemistry

= HOCl + OCl--

= NH2Cl + NHCl2 + NCl3

= Combined Chlorine +

Free Chlorine

Free Chlorine

Combined Chlorine

Total Chlorine

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Chlorine Chemistry

HOCl + H+ + Cl-

H+ + OCl--

Cl2 + H2O

HOCl

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% Distribution HOCl vs. pH

7

100

pH4 5 6 8 9 10

% HOCI

90

80

70

60

50

40

30

20

10

0

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Measurement Methods

Colorimetric

Open /Electrode Buffered

Amperometric/Polarographic

High Resolution Redox

pH/ORP Method

Galvanic Sensor

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Colorimetric Systems

Operating Principle

Add buffer and indicator solution to a known volume of water.

After mixing, measure wavelength of light transmitted through sample to determine color change and thus, amount of free residual chlorine in the sample.

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Colorimetric Systems

AdvantagesPrice.High pH is not a limiting factor.EPA approved DPD measurement.

DisadvantagesUses reagents.Must use pumps, valves and capillary tubes.Can only generate a new residual reading every 2 1/2 minutes.High maintenance.No pH or temperature output.

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Open Electrode/Buffered Systems

Operating PrincipleA known volume of sample water is pumped into a chamber and buffered to a pH of 4.

Two bare electrodes are in contact with the sample inside the chamber and based upon mV readings, a free residual chlorine value is derived.

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Open Electrode/Buffered Systems

AdvantagesHigh pH is not a limiting factor.

DisadvantagesUse of buffers.Must use pumps and valves.High maintenance.Difficult start-up.No pH or temperature output.

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Amperometric/Polarographic

Membrane Sensor

Operating Principle A sensor consisting of a membrane (which allows HOCL to migrate through it), two dissimilar metal electrodes, and an electrolyte are submersed into the water sample.

A free residual chlorine reading is derived based on mV changes experienced by the sensor.

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Amperometric/Polarographic Membrane Sensor

AdvantagesEase of useNo reagents or buffers added

DisadvantagesNo pH or temperature compensation (OPTIONAL)No flow regulationNo pH or temperature output (OPTIONAL)

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Operating PrincipleCharacterize free residual chlorine demand based upon ORP values of the water sample.

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AdvantagesIn some instances, does a better job of determining residual chlorine demand.

DisadvantagesDoes not measure free residual chlorine directly.Any oxidant present in water sample will be read as an increase in free residual chlorine.

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Operating PrincipleWater flows through a Dual Flow Cell consisting of an ORP and a PH sensor.

Microprocessor in the analyzer calculates the free residual chlorine (HOCL+OCL-) concentration by using a polynomial formula. This calculation requires the analyzer to know the measured ORP, PH and temperature values.

IC Controls - pH/ORP Method

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AdvantagesNo reagents or buffers added.

No moving parts.

pH and temperature compensated.

Easy to set up and calibrate.

Multiple measurement readouts/outputs.

Dedicated relay control for residual chlorine and pH.

DisadvantagesDoes not measure free residual chlorine directly.

Any oxidant present in water sample will be read as an increase in free residual chlorine.

IC Controls - pH/ORP Method

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Operating Principle

A sensor consisting of a membrane (which allows Cl

2 to migrate through it), two

dissimilar metal electrodes, and an electrolyte are submersed into the water sample.

A free residual chlorine reading is derived based on mV changes experienced by the sensor.

Model 875 Galvanic Free Chlorine

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AdvantagesEase of useNo reagents or buffers addedAbsolute ZeroPretensioned Membrane CapGalvanic Technology

DisadvantagesManual pH compensation (now Available in 876)


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Polarographic vs

IC Controls Galvanic

What's the difference?

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Applied voltage from the Cathode to the Anode.Reaction of Chlorine at Cathode generates a current.Output can go below zero; a value that does not exist.

Therefore, decreased accuracy in calibration and measurement

Polarographic

VO2

O2

O2

O2

Cl2 Cl

2Cl

2

Anode

CathodeMembrane

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No applied Voltage. Chlorine is the fuel for the battery.Therefore, absolute zero and better accuracy.

Galvanic

O2

O2

O2

O2

Cl2 Cl

2Cl

2

Anode

CathodeMembrane

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Recharging the Sensor

Over time the sensor internal will deplete and the membrane and fill solution will need replacement. Historically, this was a difficult process with creases being formed in the membrane and air bubbles in the fill solution which cause inaccurate readings. At times the process could take up to 1 hour to replace a membrane and put a sensor back on line.

The model 835 sensor provides ease of use which includes fast, reliable and simple maintenance.

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Maintenance is made easywith the Pre-TensionedMembrane cap.

This system ensures thereare no air bubbles or creasesin the membrane cap whichwill cause false inaccuratereadings.

An easy process that allows recharging and re-installationin less than 5 minutes.

MembraneModule

TipRetainer

Pre-Tensioned Membrane Cap

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Galvanic Technology

Absolute Zero

No Reagents Required

Pre-Tensioned Membrane CapProven Technology

Superior DesignBetter Results


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875 Panel

875 Analyzer

835 Galvanic Sensor

Free Chlorine

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