Description
Description
ATI’s Model Q46F/D Fluoride Monitor provides continuous measurement of free fluoride concentration in potable water. The system employs a fluoride sensitive ion selective electrode (ISE), which provides reliable measurements down to 0.1 ppm and as high as 1,000 ppm. A chemistry module provides sample conditioning for the sensor and the measured fluoride concentration is displayed on a separate electronics module that also provides alarm and analog output functions.
Fluoride is widely added to drinking water systems to help prevent tooth decay. It is normally added in the form of liquid hydrofluorosilicic acid, which can be easily handled and applied using standard metering pumps. While control of the fluoridation process is easily handled by simple flow proportional feed, monitoring of final fluoride concentrations is useful in providing an alarm in the case of overfeed problems. Optimum fluoride levels of around 1 ppm are safe, but control system problems resulting in concentrations above 2 ppm are considered excessive and need to be detected as early as possible. Loss of chemical feed can also be detected quickly and reliably with on-line fluoride monitoring.
Fluoride ISE sensors measure F-Ion in solution the same way that a pH sensor measures hydrogen ions. A lanthanam fluoride crystal on the tip of the sensor develops a voltage that is proportional to fluoride ion activity. An integral reference electrode is used as a comparator to measure the developed voltage, with the measurement made at a differential input amplifier. Since the activity of fluoride ions in solution is a function of pH and ionic strength, a small amount of buffer solution is added to the measured sample. This creates a stable condition in which the concentration of fluoride ion and the activity of fluoride ion are directly proportional.
In operation, a small amount of sample is pumped into the system and mixed with the buffer solution. The treated sample then flows to a chamber where the combination fluoride ISE is mounted. The continuous flow of sample is measured in this chamber with changes in fluoride concentration immediately reflected at the monitor. The sample chamber drains back to the waste side of the sample inlet overflow chamber.
Fluoride monitors require very little maintenance. One gallon of buffer will operate the system for about 25 days and sensor fill solution level should be checked weekly.
Ion selective electrodes are subject to small changes in offset voltage, which can be reflected as a slow measurement drift. The Q46F provides an automatic calibration function that can be used to maintain long term accuracy without the need for manual adjustments. The Auto-Cal function can be programmed for either a single point or a two point calibration. Fluoride ISE sensor slope changes relatively slowly, so a single point Auto-Cal is often sufficient, but a 2 point Auto-Cal provides optimum long term accuracy.
The Auto-Cal system will periodically stop normal sample flow and option the inlet for calibration standards, normally 1 and 10 ppm fluoride. After the first standard has been read, and the mV value stored, the calibration standard valve switches to the second standard solution. Once the two standards have been read, the monitor automatically adjusts the zero offset and slope in the monitor and normal measurement resumes. During the calibration cycle of about 5 minutes, the 4-020 MA output is held at the value measured just before starting the cycle. At the end of the cycle, the output withhold for a short period to allow sample to stabilize again and then the output is released to update.
The frequency of the Auto-Cal cycle is user programmable, from every 24 hours to every 999 hours. Every 1-3 days is normally sufficient to maintain good measurement accuracy. each cycle uses about 30 cc of calibration standard so 1 liter of standard generally will provide about 33 calibrations.
Model Q46F/D Fluoride Monitor monitors allow for interface to digital communication systems. Monitors currently provide for Profibus-DP, Modbus-TRU or Ethernet-IP interface. Communication cards plug into the main power supply assembly and can be added at a later date is required.
ATI is now a Badger Meter Brand
For pricing, please call AFC International at 1-800-952-3293, 219-987-6825 or fax 219-987-6826 or email sales@afcintl.com
