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 the fluoridation process is often controlled 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.

ATI's Model A15/82 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 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 45 days. The system also performs an automatic calibration routine to correct for electrode "zero" drift. The fluoride standard is automatically pumped into the chemistry module and the analyzer zero is automatically adjusted. The frequency of this calibration is user selectable from every 1 to 999 hours. Calibration standards are easily mixed from a stock solution supplied with the unit and the buffer is easily prepared using common vinegar.

Specifications - Electronic Monitor

Range	0-1.00 ppm minimum, 0-1,000 ppm maximum
Accuracy	±5% of span
Repeatability	±2% of span
Drift	< 0.1 ppm per month
Display	16 character alphanumeric backlit LCD
Control Relays	Two SPDT relays, 5A @ 220 VAC resistive, programmable deadband and time delay
Control Mode	On/Off with variable deadband and time delay
Alarm Output	Independent alarm relay (SPDT) with dual setpoint
Analog Output	Isolated 4-20 mA, 600 ohm maximum load, programmable output span, output may be inverted
Power	110/220 VAC ±10%, 50/60 Hz
Enclosure	Panel mount standard, NEMA 4X wall mount optional

Specifications - Chemistry Module

Fluoride Sensor	Fluoride ion selective electrode sensor
Sensor Cable	10' standard
Response Time	T90 in 90 seconds
Sample Pump	Internal tubing pump, 5 cc/min
Buffer Pump	Internal tubing pump, 0.05 cc/min
Measurement Chamber	Cast acrylic
Temperature Limits	0 -50°C
Sample Rate	2-10 GPH at inlet overflow assembly
Sample Inlet	¼" id hose barb
Sample Drain	½" id hose barb
Power	120 VAC, 60 Hz, 220 VAC, 50 Hz optional

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.

Description	Catalog No.
Series A15/82 Fluoride Monitor, Panel Mount, 120 VAC	A15/82-1-1
Series A15/82 Fluoride Monitor, NEMA 4X Wall Mount, 120 VAC	A15/82-2-1

Downloads

Model A15/82 Fluoride monitor datasheet