Fast, Reliable Fluoride Monitoring!

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, water quality 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.

The Q46F provides continuous water quality monitoring of free fluoride concentration in potable water. The system employs a fluoride sensitive ion selective electrode (ISE) which provides reliable measurement down to 0.1 PPM and as high as 1000 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.

Applications

- Potable Water Systems
- Semi-Conductor Wastewater Systems

OPERATION

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. A reference electrode, which is part of the fluoride sensor, provides the other half of the sensing system, with the measurement made at a differential input amplifier. Since the activity of fluoride ions in solution are 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 and reference electrode is mounted. The fluoride ion concentration is measured in this chamber with changes in fluoride immediately reflected at the monitor. The treated sample is pumped back out of the measuring cell and into the drain side of the inlet overflow chamber. Fluoride monitors require very little maintenance. One gallon of buffer will operate the system for 25 days and sensor fill solution level should be checked weekly.

PRODUCT FEATURES

Analog Output Options

Two isolated 4-20 mA outputs are standard. Default setting provides analog outputs for fluoride and temperature.

PID Output

Standard PID control function assignable to one analog output.

Digital Communications

Communication options for Profibus-DP, Modbus-RTU, or Ethernet-IP.

Sensor Preamp

A sensor preamplifier module in the Auto-Chem enclosure allows separation between the monitor and chemistry unit by up to 300 feet.

Relay Outputs

Three SPDT relays are standard, with relay functions programmable for alarm, control, or trouble indication.

Flexible Mounting

NEMA 4X (IP-66) enclosure is suitable for wall, pipe or panel mounting.

Clear Display

Back-lit large LCD display provides clear visibility in any lighting condition. A scrolling second line on the display provides additional information and programming prompts.