Metrohm 796 Titroprocessor - Manual (Page 115)

7. Titration and measuring modes
796 Titroprocessor, Instructions for use 109 109
Observation Possible causes and remedies
"Overshoots". Titration
is not settled,
i.e. single pulses
are not added at
the end.
• Reduce 'Max. Rate'.
• Set a larger control range.
• Set a much smaller 'Min. Rate'.
• Optimize the arrangement of the electrode and buret tip and improve the
stirring. This is particularly important for very rapid titration reactions and
for steep curves.
Titration time
is too long.
• Set higher 'Min. Rate'.
• Set higher 'Max. Rate'.
• Reduce 'Control range'.
Titration results
scattered too
much.
• Set lower 'Min. Rate'.
7.5 SEC Endpoint conditioning
Application:
SEC modes are independent titration modes which can be used in the
preparation of a
SET mode. They are suitable for rapidly bringing a titration
sample to a certain measuring value (endpoint).
Their typical feature is controlled reagent dosing depending on the control
difference (actual value – endpoint) with the aim of reaching the preset value
as quickly and accurately as possible. Overshooting is virtually eliminated.
No provision is made for the representation of curves or carrying out calcu-
lations.
Reagent addition and switch-off criteria correspond to those of the SET
modes.
7.5.1 Control of the conditioning mode
Conditioning is normally carried out in the background, i.e. as soon as a
conditioning mode has been started the 796 Titroprocessor can carry out
other commands (i. e.
ASK, ADD_A etc.). A conditioning process also re-
mains active even when a determination has been finished, provided that it
has not been explicitly terminated; see below.
A conditioning mode carried out in the background is controlled by the
WAIT_C command (see page 209f). This checks whether the conditioned
state has been achieved and, if necessary, switches the conditioning mode
off.