TT-CL
2
Free Chlorine Sensor
SAFETY PRECAUTIONS
• Before attempting to unpack, set up, or operate this instrument, please read this entire manual.
• Make certain the unit is disconnected from the power source before attempting to service or remove any
component.
Make certain the unit is disconnected from other sources of force or pressure (for example, pneumatic or hydrau-
lic), before attempting to service or remove any component.
• Failure to follow these precautions could result in personal injury and damage to the equipment.
1.
THEORY OF OPERATION
The free chlorine sensor has been designed to measure the concentration of dissolved free residual chlorine.
It does this using a Potentiastatic 3-electrode chronoamperometric sensor insulated from the water supply
by a hydrophilic membrane. The free chlorine diffuses through the membrane and is reduced at the cathode
generating a small current that is proportional to the concentration of free chlorine. In potable, process, or
swimming pool water this means HOCl (hypochlorous acid) and OCl- (hypochlorite ion). The relative amount of
these two species is dependent on the pH of the solution. At low pH’s the predominant species will be HOCl.
At higher pH's the predominant species will be OCl-. Traditional amperometric measurement systems need to
be buffered to an exact pH in order that changes in the pH of the sample water do not affect the Free Chlorine
measurement. The probe supplied for Free Chlorine measurement with this instrument is not affected by changes
in pH to the same degree. This means that on many plants it will not be necessary to buffer the sample water at
all. If it is necessary to buffer the sample water, because the pH is both high and variable it will only be necessary
to reduce the pH to below 6.5. This is best done using the CO2 Buffer accessory. The probes are available for a
variety of ranges which are specified at the time of purchase.
The sensor incorporates automatic temperature compensation (ATC).
3
TURTLE TOUGH
IPM19 HaloSense Free Chlorine Probe
Manual date 12/1/2011
Page 4 of 29
1.0
Theory of Operation
The free chlorine sensor has been designed to measure the concentration of dissolved free residual
chlorine. It does this using a Potentiastatic 3-electrode chronoamperometric sensor insulated from the water
supply by a hydrophilic membrane. The free chlorine diffuses through the membrane and is reduced at the
cathode generating a small current that is proportional to the concentration of free chlorine. In potable,
process, or swimming pool water this means HOCl (hypochlorous acid) and OCl
-
(hypochlorite ion). The
relative amount of these two species is dependent on the pH of the solution. At low pH’s the predominant
species will be HOCl. At higher pH's the predominant species will be OCl
-
. Traditional amperometric
measurement systems need to be buffered to an exact pH in order that changes in the pH of the sample
water do not affect the Free Chlorine measurement. The probe supplied for Free Chlorine measurement
with this instrument is not affected by changes in pH to the same degree. This means that on many plants it
will not be necessary to buffer the sample water at all. If it is necessary to buffer the sample water, because
the pH is both high and variable it will only be necessary to reduce the pH to below 6.5. This is best done
using the
CO
2
Buffer
accessory. The probes are available for a variety of ranges which are specified at the
time of purchase.
The sensor incorporates automatic temperature compensation (ATC).
Typical Probe Response to pH
(Unbuffered)
0
20
40
60
80
100
120
6
6.5
7
7.5
8
8.5
9
9.5
10
Chlorine Probe Response
Typical Amperometric Probe Response
