ATI
Model A15/82 Fluoride Monitor with Auto-Calibration
25
O&M Manual
Rev-G (6/10)
AUTOMATIC CALIBRATION
The A15/82 Fluoride Monitor performs an automatic calibration adjustment as often as the user desires.
This automatic calibration routine corrects the monitor for small changes caused by electrode drift. Fluoride ISE
sensors are quite stable over long periods of time when used in buffered samples, but electrode drift could cause
errors of 0.1 – 0.2 PPM if not adjusted every week or two. The automatic calibration routine delivers a fluoride
standard into the system and corrects the analyzer zero offset to correct for drift. As a default, the monitor is
programmed to provide this function every 48 hours. This is actually more often than necessary, but will insure
that the analyzer operates at optimum accuracy on a continuous basis. The frequency of this calibration is
adjustable by the operator.
The automatic calibration routine takes about 4 minutes. During this time, the 4-20 mA signal is locked
at the output value just before the routine activates. The user may start this routine manually at any time to
verify that the calibration routine is functioning properly. To do so, press the MODE key on the monitor until the
display reads “AUTO CAL”. Press CAL and the display will read “NEXT CYCLE: XXX h”, which tells you the
number of hours until the next automatic cycle begins. Press ENTER and the display indicates “CAL CYC.:
WAITING”. Press the DOWN arrow and the display reads “CAL CYC.: START”. Press ENTER and the
calibration cycle will activate. The display will flash back and forth between the fluoride concentration display
and a display of “CALIBRAT. CYCLE”. This will continue for 3 minutes (assuming no change in the default
timing for calibration) and then will switch to “ “. If the calibration should fail due to excessive drift of the
sensor (which could be caused by buffer feed failure, calibration standard feed failure, or sensor drift), a
“CALFAIL Z –XXXmV”, which indicates that the zero offset is beyond the 10 mv. limit set in the Configuration.
Should you encounter a calibration fail error, perform the manual 2-point calibration procedure on page 23. If
this is not successful, polish the fluoride sensor as described on page 28 (Sensor Maintenance). If this does not
resolve the problem, replace the fluoride ISE.
To program the frequency for the automatic calibration, press MODE until the display reads “AUTO
CAL”. Press CAL and the display will read “NEXT CYCLE: XXX h”, which tells you the number of hours until the
next automatic cycle begins. Press ENTER and the display indicates “CAL CYC.: WAITING”. Press ENTER
again and the display indicates “AC REPETIT.: XXh”, with XX indicating the current frequency setting. Use the
UP or DOWN keys to adjust this setting to the number of hours desired between automatic calibration routines.
The frequency can be set to any number of hours between 1 and 999. When you have adjusted the frequency,
press ENTER and the new frequency will be stored.
MIXING FLUORIDE BUFFER SOLUTION
The buffer solution used in the A15/82 Fluoride Monitor is designed to adjust the sample pH to about 5.3
and to provide a relatively stable ionic strength in the sample to allow stable fluoride measurement. The buffer
solution can be purchased from ATI or can be mixed by the user if desired.
To prepare the buffer solution, you will need sodium acetate and white vinegar. Place 1000 grams of
sodium acetate trihydrate (Fisher Scientific #S207-10) in a gallon reagent container. Fill the container with pure
white vinegar and allow to sit for a few hours until the acetate has completely dissolved.
