47
When a double point calibration is performed the S.P..C value is forced to 0.00.
500
400
300
200
100
0
-100
-200
-300
-400
-500
2
0
4
6
8
10
12
14
o
C urve relative to the initial
calibration
C urve relative to electrode
ageing
C urve corrected w ith a
single point calibration
Fig. 14 - pH Calibration curves examples
NOTE :
Single point calibration corrects the sensitivity in the zone where the correction is made. It is therefore
necessary to operate single point calibration as near as possible to the process fluid pH value.
IMPORTANT : THESE CURVES ARE ONLY A THEORETICAL REPRESENTATION, NOT BASED ON
EXPERIMENTAL VALUES.
6.1.4
ORP Sensor Calibration
The calibration procedure is necessary to standardise the sensor sensitivity. The double point calibration gives
the maximum accuracy because it allows to set both the slope and the offset of the curve giving displayed
ORP value as a function of the mV from the probe (sensitivity).
The calibration of ORP Monitor is not usually required, however the two point calibration procedure is
foreseen in the transmitter software.
NOTE:
Calibration procedures are different if the arrangement “oxidation potential with negative value”
or “oxidation potential with positive value“ is used. Both are described in the following pages.
The calibration procedures involve both the electronic transmitter and the sensor. The following description
indicates step by step the double point calibration procedure:
To operate the calibration the following material is necessary:
- two plastic or glass beakers
- standard ORP solutions.
Pour the two standard ORP solutions in two beakers in a sufficient amount to cover the sensor. Wash the
probe with de-mineralised water, dry it and dip it in the first buffer solution. Stir softly but continuously the
probe : in this way a shorter stabilisation time will be required.
Summary of Contents for AW400 Series
Page 1: ...Instruction Manual IM AW4TX Issue 5 Chlorine Transmitter AW400 Series ...
Page 69: ...67 Notes ...
Page 70: ...68 ...
