Calibration
ISEmax CAS40D
14
Hauser
Single-point calibration
If you use the sensor in the inlet to the sludge activation, you have to use a higher standard
concentration for the calibration, e.g. 50 mg/l.
Preparing to calibrate
1.
Take 3 l (0.79 US gal.) of sample from the sewage treatment plant outlet.
2.
Have some of the sample analyzed in the laboratory for the parameter to the calibrated.
3.
Add 2 ml (0.068 fl.oz.) standard (1 mol/l
i
14 g/l) to 2 l (0.52 US gal.) of the sample.
Concentration of the sample with standard added [mg/l] = laboratory measured value [mg/l]
+ 14 mg/l.
4.
Transfer the sample with the standard to a suitable container and immerse the sensor into it.
--> The measured value display increases.
Standard addition
Standard addition is particularly useful if it is not possible to determine reference values in the
laboratory.
For this purpose, place the sensor in a container with approx. 1 l of sample.
Potassium and chloride compensation
Depending on the selectivity of the ion-selective electrode vis-à-vis other ions (interference ions),
and the concentration of these ions, such ions could also be interpreted as part of the measuring
signal and thus cause measuring errors.
When measuring in wastewater, the potassium ion which is chemically similar to the ammonium
ion can cause higher measured values.
The measured values for nitrate may turn out to be too high due to high concentrations of chloride.
To reduce measuring errors resulting from such cross-interference, the concentration of the
potassium or chloride interference ion can be measured and compensated for with a suitable
additional electrode.
5.3
Calibration
For calibration guidelines, see the Operating Instructions for the transmitter.
5.4
Checking the calibration
1.
Immerse the sensor in a suitable container of drinking water (to check the ammonium value)
or discharge water (to check the nitrate value).
2.
Compare the measured value with the specifications for
a. Drinking water (ammonium)
--> The measured value must drop to the local concentration for drinking water (e.g. in
Germany: < 0.1 mg/l.)
b. Discharge water (nitrate)
--> The measured value must equal that of a reference measurement.
3.
If the measured value does not meet expectations:
a. Repeat the single-point calibration.
b. Carry out a two-point calibration.
c. Enter a manual offset at the transmitter. Use the measured value from a comparison
measurement to calculate the offset.
