Ph And Mv Calibration - HACH LANGE sensION+ PH 3 Bedienungsanleitung

4. Operation

4.4. pH and mV calibration

pH Calibration
To measure pH correctly, the electrode and the instrument set
needs to be calibrated regularly with buffer solutions. This
compensates deviations of asymmetry potential and slope of the
electrode over time i.e. the calibration corrects variations in the
electrode response.
The instrument allows one-, two- and three- point calibration.
The calibration parameters remain in memory until a new calibra-
tion is performed.
One-point calibration
This type of calibration is acceptable when measuring pH values
similar to those of the buffer solution.
It corrects the asymmetry potential of the electrode.
Two-point calibration
This is the most common calibration.
It is recommended to start with pH 7 as first buffer. pH 4 or pH 9
buffers can be used as a second buffer, depending on the meas-
ured zone (acid or alkaline).
The two-point calibration compensates the asymmetry potential
and the electrode's sensitivity (slope).
Three-point calibration
This type of calibration is recommended when measurements are
made across the whole pH scale.
As a first point pH 7 is recommended.
For the second and third points, two of the remaining values
must be chosen (2.00, 4.01, 9.21, 10.00 at 25ºC (77 ºF)).
The three-point calibration compensates the asymmetry
potential and electrode's sensitivity in the acid (a) and alkaline
zone (b).
mV calibration
The metallic electrodes do not suffer significant variation in their
potentials, for this reason normally they are not calibrated.
Nevertheless, some potential deviations can be produced due to
the continuous use of the electrode.
+
The sensION ™
PH 3
trodes, with platinum or gold indicator metal, using redox
standard of 220 mV (value at 25ºC (77 ºF)).
Calibration data
They can be viewed at any moment. See diagram.
Calibration frequency
Select between 0 h and 7 days. The instrument by default is
programmed for daily calibration and indicates the remaining
time to the new calibration. Selecting 0 h the automatic re-cali-
bration warning is deactivated.
The calibration frequency depends on the required accuracy and
the effect of the samples on the electrode. Hach recommends
daily calibration, but users should decide on the right time based
on their own experience.
sensION+ PH3 HACH_LANGE 0710.indd ANG:7 sensION+ PH3 HACH_LANGE 0710.indd ANG:7
All manuals and user guides at all-guides.com
allows calibration of the metallic elec-
Theoretical calibration
Selecting "theoretical calibration" the calibration data of the elec-
trode in use are replaced by the theoretical values at 25ºC (77 ºF).
This step is prior to the obtention of a calibration certificate.
Preparation
Fill the flasks with the corresponding buffer solution (40 ml.)
These buffers can be used to perform between 5 and 10 calibrations.
Every calibration flask is supplied with a magnetic bar.
Diagram for calibration
10-04-2010
New CAL. in 12 h
CALIBRATION
pH, Press pH
mV, Press mV
CAL. data , Press
CALIBRATION mV CALIBRATION pH
Use standard 220 mV Use first buffer
Press Press
CALIBRATION mV CALIBRATION
235 mV 23˚C pH 7.15
Time 23 s
CALIBRATION OK 1st buffer OK
223 mV 23˚C pH 7.01
Time 40 s
3s
CALIBRATION pH
Use second buffer
Press
CALIBRATION
pH 4.12
2nd buffer OK
pH 4.01
CALIBRATION pH
Use third buffer
Press
17:15
23˚C
CALIBRATION DATA pH
17-03-07 17:15
Buffers: pH 7, 4 & 9
Asym: a) 8mV, b) 8mV
Sens: a) 97% b) 94%
t: 7s T: 25°C
CALIBRATION DATA mV
1st buffer
23˚C
21-04-07 08:23
Compensation: -15 mV
Time 23 s T: 15.7°C t: 6s
CAL. FREQUENCY pH
23˚C
Every: 1 day
Time 30 s Automatic warning.
Press
3s
2s
For
THEORETICAL CAL.
pH, asymmetry 0mV
pH, sensitivity 100%
mV, compensatión 0mV
3s
2nd buffer
23˚C
Time 19 s
23˚C
Time 19 s
7
8/7/10 16:39:53 8/7/10 16:39:53