43
Ü
As soon as the dosing unit moving downwards has reached the edge of the casing, the display requests
you to lock the dosing unit manually by rotating it by 90° to the right (clockwise,
&
Fig. 30).
Ü
After locking it, start the rinsing and initial-filling process using the <FILL/F1> (Rinsing/F1) key.
Ü
Select cylinder of 20 or 50 ml.
The following image will be shown:
Setting
cylinder volume
Cylinder volume:
20 ml
Change digits:
<
↑↓
>
OK:<F1>
ESC:<F4>
Use the <
↑
>, <
↓
> arrow keys to change for the software the cylinder volume from 20 to 50 ml or vice
versa. Acknowledge your selection using the <FILL> key, and it will be permanently store in the EEPROM.
Please note:
An incorrect input can only be changed by repeating the entire procedure of replacing the dosing unit!
If the input cylinder volume is incorrect, the volume being displayed will not match the one!
7.2 Replacing the titration solution
If titration solutions are to be changed, since differing analysis methods are used, one should first consider
whether the time required for frequent changes is not more expensive than the acquisition of another dos-
ing unit or piston burette.
As a principle and in the case of all piston-burette systems, a substitution of the titration solution by another
one involves mixing and carry-over processes. The reason for this is the dead volume above the piston in
the cylinder and in the hoses. The disturbances to be anticipated are the greater, the more the new solu-
tion differs from the previous type and concentration. In the case of highly different solutions, the first sub-
stitution liquid should be distilled water (rinsing), and the new titration solution should be used only after-
wards.
The possible disturbances are very much different in the individual cases and cannot be predicted without
knowledge of the specific case. Therefore the replacement of titration solutions must always be performed
under the supervision of experts who ensure the correctness of the future analyses.
If the decision to change the titration solution has been made, the first thing to do is to remove the dosing
unit as is described in “Detaching and placement of dosing unit” chapter. If possible, the residue of the
titration solution should be removed manually by carefully pushing the projecting piston rod towards the
hose. When doing so, more liquid will leak out of the titration tip, and the residual volume is furthermore
reduced. Removing the old titration solution can be accelerated by moving the piston rod with the dosing
unit being held top down. The suction hose is then immersed in the new solution or in distilled water
serving as a rinsing liquid. By moving the piston several times in both directions (pumping) the previous
liquid is gradually replaced by new liquid. Subsequently, the dosing unit is set on again according to the
description in “Detaching and placement of dosing unit” chapter.
