42
6
Dosing accuracy
Air bubbles in the system are the main cause of inaccuracy. It is absolutely decisive to keep the cylinder
free from air bubbles. The air bubbles are mainly adhering to the piston. The air bubbles can be removed
from the piston by knocking, and in the course of the subsequent dosing, or during rinsing, they will escape
outwards. Direct sun exposure and temperature fluctuations promote the formation of air bubbles in the
cylinder, since there is always (physically dissolved) air in the dosing or titration liquids.
If the system contains air bubbles which cannot be removed easily, one should predose a small volume,
e.g. 0.5 ml. Subsequently, use a double click of the grey key of the manual key button to reset the display
to zero. The burette is now ready for accurate dosing and titration.
7
Replacing the dosing unit (disassembly and installation)
As a rule, the need for replacing the dosing unit occurs only rarely. The dosing unit has to be re-
placed, if such a replacement becomes necessary as a result of a defect or of an inspection of the
TITRONIC
â
â
â
â
universal
Piston Burette.
! Caution! Please wear protective glasses!
Prior to starting working, screw off the hose from
the cylinder!
!
Chemicals might leak out!
The dosing unit is equipped with lateral ribs around its circumference, with one of these ribs being in dou-
ble design. This double rib serves as a mark for the correct placement of the dosing unit (
&
Fig. 29,
item 2, or Fig. 9, item 2).
Important note: The disassembly of the dosing unit as such is only possible using a special tool (TZ 3630)
and should only be done by experienced persons. The sealing lip of the PTFE piston and the sealings of
the liquid system may be damaged or incorrectly positioned in the course of such a disassembly. As a re-
sult, titration liquid would leak in unwanted places.
7.1 Detaching and placement of the dosing unit
!
Caution, place a receptable under the titration tip!
!
Ü
Press the <FILL/F1> key for five seconds, and keep it depressed until the display shows <<change of
the dosing unit>>.
When the piston moves upwards, titration solution will be dosed out of the burette tip.
Ü
If <<unlock unit !!>> is displayed, the dosing unit has to be unlocked by rotating it by 90° to the left
(counter-clockwise Fig. 27).
Ü
Press <START>. The motor of the TITRONIC
â
â
â
â
universal
Piston Burette will now automatically move
the dosing unit upwards. After the display shows <<remove unit / set on new unit>> remove the dosing
unit (
&
Fig. 28). The process is completed.
Detaching the dosing unit :
Placement of the dosing unit:
Fig. 27 Unlocking
Fig. 28 Removal
Fig. 29 Placement
Fig. 30 Locking
Pos. 1
Pos. 2
Pos. 1
Pos. 2
Pos. 1
Pos. 2
M
Pos. 1
Pos. 2
Ü
Set on new (inspected, if necessary repaired) dosing unit vertically (
&
Fig. 29), then press the <FILL>
key. The running motor will now pull the dosing unit downwards, while the display requests to align the
unit, „M“ mark to position 2. If any noise should become audible at this point, please stop the process
immediately by pressing the <START/STOP> key. The cause of this „rattling noise“ will be eliminated
by setting the dosing unit
vertically
on again!
