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Q45H Training Handout 4.05
Page 7 of 11
allow for stabilization of the pH probe. An independent pH meter, lab test or colorimeter is required to get this
reading for the 1 point cal, if you do not have a portable pH monitor or a method of measuring pH, you will need to
continue using the 2 point cal with buffers for future calibration. If you feel that the application you are using has a
different pH to that of the water you are measuring, complete the 1 point cal and leave.
Maintenance of the pH probe (replacing the saltbridge and refill solution)
If FAIL appears when calibrating the pH probe, give the bulb a wipe with white vinegar and see if it will pass. If it
remains to fail and the pH sensor is 2 years old or more, it may require maintenance in the form of a replacement
saltbridge and refill solution. These are low cost consumables. Simply clean the bulb with white vinegar, unscrew
the old saltbridge (brown plastic piece around the bulb), turn the probe up so that the bulb is facing up, pipette the
refill into the horseshoe gap until filled. Fill with a bit more to make sure that there are no air bubbles in the sensor.
Now screw on the new salt bridge and screw in fully and tight. Connect back onto the cable and calibrate.
Do not zero the monitor unless you are expecting zero chlorine
There is absolutely no need to zero the sensor. Once you leave to polorize it will (in most cases) come to the correct
reading of chlorine if left. The zero does not move. If you zero in error (calibrating by using 2…zero instead of
1…span) You WILL need to zero. Do this by disconnecting the sensor from the cable. The reading will come to
0.000. Go into MEASURE and look at nA reading. This should also get to 0nA. Once it has, go to CAL menu and
zero by changing the number to 2…zero. Press ENTER and it will zero. If you are using the free chlorine monitor as
a ‘break through’ monitor when using ammonia or sulphite, etc. You can zero the monitor by completing the above
if you are certain that there is no chlorine at all.
I am losing electrolyte? Why?
If the sensor has been built and tightened correctly with the o rings in place, there should not be any loss in
electrolyte. Please rebuild and check that the o rings are in place and are not broken. If after time this happens again,
it may be due to ‘micro cavitation’ created by the pump you are using, drawing the electrolyte out of the membrane
(vacuum created). This may happen in < 1% of all chlorine applications. If this does happen, ATi make an
electrolyte gel that can be used. It is best not used if helped due to the decrease in sensitivity after calibration.
How often should I check and/or calibrate the chlorine monitor?
You can check the calibration as often as you would like. The difference between ‘check’ and ‘calibration’ is simply
pressing a few buttons. Simply perform a dpd test and compare with the reading of the ATi chlorine monitor. If it is
> +/- 0.1ppm, calibrate. If it is /- 0.1ppm, leave. Remember to check the pH with standards OR with a
portable pH monitor before you check the chlorine if the compensation is turned on. Calibration can be anywhere
between every 1 month, 2 months (up to 18 months) in some cases! Please make sure you are 100% confident with
the method of checking before you calibrate because the ATi monitor will only be as accurate as this method.
How often do I change the membrane? When do I know when this will be?
You should only change the membrane when you attempt to calibrate and it fails with messages; ‘slope too high’ or
‘slope too low’. This means that you are trying to change the reading (and of course the sensitivity of the membrane)
at a stage where the unit cannot compensate for the change. This could be <20% or >600% slope. Best to check the
slope% (in MEASURE) prior to making the change as this would prove to be helpful when estimating when the
membrane should be changed. The slope can be anywhere between 20% and 600%. It will only change when you
calibrate the unit. If you change the reading UP, the slope will come DOWN and vica versa. Once you get close to
the low or high slope and need to change it so it increases/decreases further, it can fail.
My pH is very high and varies a lot. It is making my chlorine unstable due to dissociation of HOCL
with the pH?
Contact ATi to assist with the settings of the curve within the electronics. The old 3 point compensation has now
been changed for the user to alter the curve to accept higher pH readings. This will assist in the overall reduction in
error due to the high pH.
I don’t believe that my portable can be +/- 0.1ppm! Show me proof from the manufacturer! My Hach
says +/- 0.02ppm! Why shouldn’t this be the case! Please see fig below for Palin test explanation.
