Metrohm 751 GPD Titrino - Manual (Page 35)

2.6. Parameters, key <PARAM>
751 GPD Titrino
32
Relation between the stop criteria "time" and "drift"
The stop criterion "time", t(delay), means that the end point must be exceeded for a
certain period of time. In other words, after the last dosed increment, time t is allowed to
elapse before the titration is stopped. The size of this last increment depends on the
volume of the Exchange Unit used. With a 20 mL Exchange Unit, the smallest possible
increment is 2 ul. With a t(delay) = 5 s, the last 2 ul reagent must thus suffice for 5 s or
longer. This results in a drift of ≤ 2 uL/5 s = 24 uL/min (the drift can be less than 24
uL/min as it is not known whether the last increment would also suffice for 10 s). If you
have been working up to this point with a 20 mL Exchange Unit and a t(delay) = 5 s, you
can set a value of ≤ 24 uL/min as stop drift. The following table shows several values for
the maximum stop drift.
t(delay)
min.incr. (Exchange Unit)
5 s 10 s 20 s
0.5 uL (5 ml) 6 uL/min 3 uL/min 1.5 uL/min
1 uL (10 ml) 12 uL/min 6 uL/min 3 uL/min
2 uL (20 ml) 24 uL/min 12 uL/min 6 uL/min
5 uL (50 ml) 60 uL/min 30 uL/min 15 uL/min
Same t(delay) with a range of extremely small volume increments means different switch-
off points. In case the stop criterion "drift" is used, the stopping point remains the same.