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7.0 Instrument Calibration
The instrument was tested prior to leaving the factory. The instrument
operates from a pre-determined calibration curve for high accuracy
of residual oxidant concentration. It is not necessary to recalibrate to
maintain accuracy specifications.
If re-calibration is required by a regulatory authority, this can easily be
performed if required. The method is by comparison against another
instrument, such as a laboratory or hand held photometer (such as HF
scientific’s Chlorine Pocket Photometer).
There are two points of calibration. The slope or gain and the zero
(offset). To perform the zero calibration, the instrument must be
plumbed to a sample of known chlorine free water, such as de-ionized
water for a zero adjustment.
7.1 Slope (gain) Calibration Procedure
It is important that the chlorine level be quite stable to use this method.
The comparison will be made against a trusted measurement such as a
chlorine photometer, spectrophotometer, or an amperometric titration.
1. Obtain a grab sample of the flow prior entering the instrument.
2. Measure the value of the sample with one of the methods shown above.
3. On the CLX-Ex, press the
MODE/EXIT
button once. The screen is
shown below.
4. Press
to enter the calibration adjustment.
5. The screen will show the current reading on the CLX-Ex. Using the
and
buttons adjust the reading to agree with the laboratory
method or portable photometer.
6. Press
to accept the calibration adjustment and return to
AUTO
measurement mode.
NOTICE
There is a limit to the size of the change that can be made to a
current reading. The upper limit is the current reading times 1.5.
The lower limit is the current reading divided by 1.5.
Ensure a reading is posted to the display before calibrating to
avoid a nOnE error.
7.2 Zero (offset) Calibration Procedure
Generally this calibration is only required if readings are expected to be
below 1 mg/L or if it is required by a regulatory authority. To perform
this calibration, the water supply to the CLX-Ex must be changed to
chlorine free water such as de-ionized water. This chlorine free water
must be run through the instrument for at least 5 minutes prior to using
the following procedure.
1. On the CLX-Ex, press the
MODE/EXIT
button once. The screen is
shown below.
2. Press either the
or
buttons to get the following screen.
3. Press
to enter the zero calibration screen.
4. The screen will show the current reading on the CLX-Ex. Since
there is no chlorine, the only reading may be a slight offset due
to the absorbance of the reagents. There should be no pink
color developed.
5. Press
to perform a Zero calibration. When the calibration has
completed the instrument will return to
AUTO
measurement
mode automatically.
NOTICE
There is a limit of ±0.20 mg/L total adjustment available. A ZERO
Cal. greater than this will cause a CAL warning and no calibration
will have occurred. Enter SERVICE mode to clear this error.
7.3 Restore Factory Settings
If the CLX-Ex displays a CAL error or the calibration was incorrectly
performed, it may be preferred to restore the factory calibration. All
factory defaults settings including the factory calibration can be reset
by holding down the
button and then pressing and releasing the
button then releasing the
button.
