Metrohm 796 Titroprocessor - Manual (Page 152)

8.3 MET
796 Titroprocessor, Instructions for use 146 146
Signal drift
Limits for signal drift
with MET_PH/U/IPOL: 0,5…50…999 mV/Min | off
with MET_UPOL: 0,1…50…100 µA/Min | off
After adding a volume step, the next addition of reagent
is not made until the change in the measured value of
the sensor falls below the indicated value for the signal
drift. If this is delayed, dosing is continued irrespective
on expiry of the pre-set equilibration time (see be-
low).This signal drift control can be switched off ('off’).
When the drift control is switched off, the pre-set waiting
time (see below) is strictly adhered to. This can be use-
ful if the titration reaction proceeds slowly or the sensor
takes a long time to respond.
Equilibr.time
max. waiting time before next volume step
0,1…9999 s | auto | off
The full waiting time between one volume increment and
the next volume step takes effect when, with the drift
control switched on (see signal drift, above), the signal
drift does not fall below the pre-set value. Otherwise,
dosing is continued after attainment of the signal drift.
The full waiting time also takes effect if the drift control is
switched off.
The equilibration time function can be switched off. In
this mode, the only decisive factor is the signal drift for
the titration procedure.
In the 'auto' mode the Titroprocessor selects an appro-
priate equilibration time in line with the pre-set signal
drift value. It is calculated using the following formula:
Equilibration time in s
drift mV
( )
/ ( / min) ,
=
+
+
150
0 01
5
For the standard 50 mV setting this results in a 26 sec-
ond equilibration time.
8.3.3 EP Recognition
If there is a possibility of several equivalence points occurring in one titra-
tion, it is essential for a correct evaluation that the criteria for recognizing the
EPs be correctly set.
The parameters of EP recognition for the montonic titration modes coincide
with those of the
DET modes, see page 139ff.
As the ERC is calculated differently for a monotonic titration, this results in a
different range of validity for the EP criterion, see next page.