Q46H/79S Total Chlorine Monitor from ATI


Wastewater disinfection helps to ensure that receiving streams are safe for recreational use and cooling water chlorination reduces biofouling that can degrade heat transfer efficiency. This wide use of chlorination for disinfection purposes results in the need for a reliable “residual chlorine” analyzer that can operate in a wide variety of applications.

Residual chlorine is found in many chemical forms in water systems. Residuals in clean water are often predominantly free chlorine while wastewater and cooling water can contain mixtures of free chlorine, combined chlorine and organochlorine species. Measurement of residual chlorine in applications where only free chlorine (potable water) or only combined chlorine (chloraminated water) exist can often be monitored with direct sensor measurement. However, applications where a variety of chlorine forms can exist (wastewater effluent and some cooling water) require a more complicated measurement method. These application generally require a “Total Chlorine” measurement and involve chemically converting all chlorine species into a single chemical form. This is normally done by reacting the sample with pH 4 buffer and potassium iodide, where the various chlorine compounds convert iodine ion into molecular iodine.

Many on-line monitors for total chlorine use this iodometric method, often measuring the current between two exposed electrodes to determine iodine concentration. ATI’s Model Q46H/79S uses this same standard iodometric chemistry, but with a unique sensing technique for measuring the released iodine. The system takes the reacted sample containing iodine and uses an air-stripping system to remove molecular iodine from solution. The gas-phase iodine from the water sample is channeled through a conditioning module and then directly to an iodine gas sensor. The result is that the iodine measurement is made without any contact between the water sample and the sensor. Contaminants in the sample that cause fouling and contamination of standard electrodes do not affect the Q46 system, providing greater optional reliability.

The Q46H/79S Total Chlorine Monitor employs ATI’s Auto-Chem chemistry module to provide chemical treatment of the sample, air stripping of the released iodine, gas sample conditioning and iodine gas measurement. In operation a mall amount of sample is pumped from an overflow assembly into the chemistry systems and mixed with pH 4 buffer and potassium iodide (K) solution. At pH, chlorine compounds in solution react as follows (equation shown for one chlorine compound only)

HOCl + 2Kl + H+ = 2KCl + I2 + H2O

The treated sample flows into an air-stripping chamber where a controlled amount of air removes the iodine from the water sample. The air coming from the top of the stripping chamber is directed to a gas conditioning module which removes any excess water and then to a flowcell containing the iodine gas sensor. The iodine gas sensor is an amperometric membraned sensor that generates current in proportion to the amount of iodine in the gas stream. Since the gas sensor is only in contact with clean air containing iodine, sensor fouling due to contaminants in the sample if eliminated.


  • Measurement is made without contact between sample and sensor, eliminating the potential for sensor fouling
  • Total Chlorine is measured using EPA recommended iodometric measurement after reaction of the sample with buffer and potassium iodide.
  • Two isolated 4-20 mA outputs are standard. One output is programmable for PID function
  • Power options include 115 or 230 VAC, 50/60 Hz
  • Relays are programmable for setpoint, deadband and time delay
  • Communication options for Profibus-DP, Modbus-RTU or Ethernet-IP
  • Back lit large LCD display provides clear visibility in any lighting conditions. A scrolling second line on the display provides additional and programming prompts.

Specifications – Electronic Monitor

Range  0-2.000 or 0-20.000 ppm
Accuracy ±0.005 ppm
Repeatability ±0.002 ppm
Linearity 0.5% of FS
Zero Drift < 0.005 ppm per month
Display Large 4 digit LCD main display, 0.75″ characters, 12 digit alpha-numeric second line display
Control Relays Two SPDT relays, 6A @ 250 VAC
5A @ 24 VDC, resistive
Analog Output Two isolated 4-20 mA, 500 Ohms max load, assignable
Temperature -20-60°C
Power 110/240 VAC, 50/60 Hz
Enclosure NEMA 4X (IP-66) Polycarbonate, V-0 flammability

Specifications – Chemistry Module

Sensor Membraned I2 gas sensor
Sensor Cable 25′ standard, 100′ maximum
Response Time 95% in 3 minutes
Sample Pump Internal tubing pump, 7 cc/min
Acid Pump Internal tubing pump, 0.1 cc/min
Air Supply Diaphragm air pump with precision flow control
Air Stripping Chamber Teflon
Inlet Sample Flow Rate 5-20 GPH at inlet overflow assembly
Sample Inlet ¼” ID hose barb
Sample Drain ¼” ID hose barb
Power 115 or 230 VAC (customer specified)
Operating Temperature 2 to 50°C
Enclosure Kydex with acrylic cover, V-0 flammability
Weight 15 pounds

Ordering Information

For pricing please call AFC International at 800-952-3293, 219-987-6825 or fax 219-987-6826 or email sales@afcintl.com.

Catalog No.
Series Q45H/79S Residual Chlorine Monitor, 120 VAC
Series Q45H/79S Residual Chlorine Monitor, 120 VAC, Profibus-DP Output


Model Q46H/79S Total Chlorine Monitor Literature

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