Automation Tech-Tips
Date Issued: 12/15/2014
Title: Guidelines to Sell and Install a Chlorine Analyzer for a Successful Operation
The Signet 4630 Chlorine Analyzer System utilizes an amperometric sensor designed to measure
residual chlorine species known as hypochlorous acid (HOCl). When selling this technology the
following guidelines should be observed.
1.The sensor utilizes a PTFE hydrophobic membrane. This membrane is temperature sensitive
and has an operating window of 0 °C to 45 °C (32 °F to 113 °F).
a. The colder the water the slower the diffusion of HOCl.
b.
Never use solvents or soap to clean the membrane.
c. DI water or 5% HCl solution should be used.
2.HOCl concentration is pH dependent.
a. The operating range of the 4630 Free Chlorine system is 5.0 pH to 8.5 pH.
b. The higher the pH, the lower the concentration of HOCl molecules.
3.The sensor generates an internal current, based on the level of HOCl that passes through
the membrane.
The range of the sensors are:
a. 2630-1:
0.02 to 2.00 ppm
b. 2630-2:
0.05 to 5.0 ppm
c. 2630-3:
0.1 to 20 ppm
The sensor technology has wide temperature, pH and chlorine concentration ranges. The system
can be installed in a variety of applications to accurately and reliably measure free residual chlorine.
However, try to avoid applications that have:
a. Low temperatures (below 5 °C, 41 °F)
b. High pH (above 8.2)
c. Low chlorine levels and low temperatures
d. Low chlorine levels and high pH
e.Low chlorine levels with low temperatures and high pH
Chlorine sensor maintenance
Chlorine sensors can achieve a 2 to 4 year life. The sensor is a 2-electrode system consisting of a
gold cathode and a silver/silver chloride (Ag/AgCl) anode. The HOCl molecules get reduced at the
surface of the gold cathode as they pass through the membrane. The silver/silver chloride anode gets
oxidized in the reaction and is considered a sacrificial electrode, which is consumed over time. There
is a potential difference of +200 mV between the 2 electrodes. It is the polarizing voltage that drives
the reduction of HOCl at the gold surface.
The 4630 is EPA 334.0 compliant. This means that the sensor maintains its accuracy for more than
14 days between drifting to the point of required calibration.
The two metal electrodes are electrically connected via an electrolyte solution containing potassium
chloride (KCl). The electrolyte conducts electricity and maintains charge neutrality in solution during the
reduction-oxidation reaction.
1.The membrane should have a life span of 1 year as long as it is clean and free from damage.
2.The electrolyte should be changed every 6 months.
Dull
Polished
3.If the calibration drifts and requires calibration every 14 days
or sooner this is an indication the gold cathode needs to be
polished. Polish the gold electrode surface to a mirror-like
finish as often as required (see Figures 1 and 2).
Curved Surface
4.When calibrating the system, verify the chlorine concentration
by testing the process water with a DPD test kit. Take three
samples and average the samples to find the in-process
Figure 1
calibration point.
5.The free chlorine sensor should develop a 20 to 85 nA signal per every 1 ppm of free chlorine,
depending on pH and temperature of the process water.
Figure 2
Polishing the Electrode Surface
1. Remove the membrane cap.
2. Place the sensor on a firm flat surface with the gold
cathode pointing upward.
3. Apply a small amount of water to the Blue (Course)
polishing paper (dull side).
4. Polish the gold electrode by moving the paper in
a circular pattern for 10 seconds. The course paper
removes the accumulated material and absorbed
species from the surface. DO NOT go back and forth
in a single direction.
5. Rinse the sensor tip with DI water.
6. Apply a small amount of DI water to the White
(Fine) polishing paper (dull side) and polish the
gold electrode by moving the paper in a circular
pattern for 40 to 60 seconds. The goal is to achieve
a mirror-shine surface finish. DO NOT go back and
forth in a single direction.
7. Rinse the sensor tip with DI water.
8. Top off the sensor with electrolyte and inspect
membrane for dirt or damage. Clean or replace
if necessary.
9. Insert the sensor into the 2650 electronics and
apply power.
Curved Surface
Please refer to the 2630 manual for additional information.
If you have any questions or need further information on this or other GF Signet products, please contact
your local Georg Fischer Sales Office or visit us on the web at www.gfsignet.com | www.gfps.com