6.1 Calibration
Calibration at a higher water tem‐
perature
In contrast to chlorine, chlorine dioxide
can only be physically dissolved in
water.
At high temperatures (> 30 °C),
chlorine dioxide gasses out of the water
very quickly. It is therefore essential
that DPD measurements are performed
quickly. Never leave more than 1
minute between taking the sample and
mixing it with reagents. The red dye
should be generated by the addition of
the reagent directly at the sampling
point. Then use a suitable photometer
to perform the measurement as quickly
as possible at the sampling point.
CAUTION!
–
Perform slope calibration following
the replacement of a diaphragm
cap or electrolyte.
–
Repeat slope calibration at regular
intervals to ensure correct opera‐
tion of the sensor. The calibration
intervals are 3 ... 4 weeks,
depending on the quality of the
water.
–
Avoid air bubbles in the sample
water. Air bubbles can result in
incorrect metering. Air bubbles
that adhere to the diaphragm of
the sensor may cause too low a
measured value and thus lead to
over-metering.
–
Please note the applicable
national guidelines for calibration
intervals.
Requirements:
–
Constant flow in the bypass fitting.
–
Constant temperature of the
sample water.
–
Identical temperature of sample
water and sensor (wait approx. 15
minutes).
–
The sensor has been run in.
–
Constant pH value.
Commissioning
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