Metrohm 785 DMP Titrino - Manual (Page 34)

2.6 Parameters, key
785 DMP Titrino
31
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.