IM 12B06J07-02E-E
16
6.3 Calibration of ORP and rH
measurements
For calibration of ORP and rH, the procedure
for MANUAL CALIBRATION can be used as
described in the Instruction Manual of the
analyzer.
The rH value is a function of the reference
system and the pH value of the buffer solution.
The SC24V sensor has a reference system
of 1molal Silver/Silver Chloride (Ag/AgCl).
The commonly used standards for ORP and
rH calibration are made from Chinhydron
(Quinhydrone) powder dissolved in pH
buffer solutions (1 g / 200 ml). In Table 5 the
measurement values are given as function of
the used pH buffer solution with Chinhydron
powder. The accuracy of the standards is
approximately ± 10 mV.
Table 5:
ORP, pH compensated ORP and
rH as function of pH buffer solution with
Chinhydron powder.
pH
ORP (mV) Na
ORP (mV) pH rH (mV)
buffer compensated compensated
4.00 228
51
23.6
7.00 51
51
23.6
9.00 -67
51
23.6
The accuracy of the standard values is
approxi/- 10 mV.
6.4 Maintenance of the SC24V sensor
A pH sensor requires routine maintenance
to keep the measuring elements clean and
functioning. Because the SC24V sensor does
not have an open reference junction and is
hermetically sealed from the process, it does
not suffer from poisoning, diffusion and fouling.
This means the SC24V sensor requires very
little maintenance.
In most cases cleaning with water, iso-propanol
or methanol is sufficient. In other cases the
measuring elements of the sensor have to be
cleaned with specific solutions. Examples:
1. Deposits of limes, hydroxides or carbonates
can be removed by immersing the
bottom part of the sensor in a solution
containing dilute hydrochloric acid (5% is
recommended). Afterwards rinse the sensor
with water.
2. Deposits of oil and fat can be removed with
hot water with a detergent. When the results
are unsatisfactory, a mild (carbonate based)
abrasive can be used.
3. Protein deposits should be removed with
a protein enzymatic solution, for instance
a solution containing 8.5 ml concentrated
hydrochloric acid and 10 grams of pepsin in
1 liter of water.
A soft toothbrush may be used to accelerate
the cleaning process.
Note:
Avoid cleaning with non-polar solvent like
tri-chloro ethylene, toluene or hexane.
The non-polar solvents will break up
the gel-layer on the measuring glass
elements and requires that the sensor
has to be soaked in water for at least
12 hours before it will function again.
IM12B06J07-02E-E_ed05.indd 16
14/01/16 09:47
