KROHNE OPTISENS PAM 2080 EN - Manual (Page 30)

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6.2 2-Point-Calibration
2-point calibration takes place with two separate measuring solutions (standards) with known
concentrations.
pH- Redox electrodes:
To calibrate pH / Redox electrodes use ready-made standard buffer solutions that can also be procured via
the chemical / laboratory market.
Ion-sensitive probes (ISE):
To calibrate ion-sensitive probes do not use ready-made standard solutions from the laboratory market.
These are of no use for calibration, since as a synthetic measuring solution they never correspond to the
water matrix in which the online measurement is subsequently used. In practice, the resulting calibration
data are only utilisable to a limited extent and may sometimes lead to considerable deviations in
measurement.
Produce your own calibration standards . This is not difficult, but the mistakes described above can be
avoided by doing so. Production of a customised standard solution is described below.
If possible, calibration solutions should be used that are within the prescribed measuring range for online
measuring. The use of concentrations at approx. 10-20% and approx. 80-90% of the expected measuring
range has proved effective (see example).
Example:
0 .. 50 mg/ NO3-N measuring range set on PAM2080 (= mA output)
ca. 5 mg/l NO3-N = 1st standard solution (10% measuring range)
ca. 45 mg/l NO3-N = 2nd standard solution (90% measuring range)
Produce calibration standards with “your” specific water matrix.
For this you use the actual measuring water in which the online measurement is to function later.