Metrohm 840 PC Control 5.0 / Touch Control - Manual (Page 236)

4.1 Titrations
224
PC Control / Touch Control
At the start of the titration the validity of the titer and the expiry date
of the selected titrant will be checked as well as the GLP test inter-
val for the exchange or dosing unit. The titer (Variable TITER) and
the concentration (Variable CONC) are also available for calculation
(CALC command, see Section 4.5.1).
STAT , ADD, DOS only: A second dosing device can be defined under
Tandem dosing in order to enable continuous dosing. Dosing is carried
out with a combination of two dosing devices so that the second dos-
ing device is dosing while the first one is being filled and vice versa.
• Dosing device: Select the second dosing device.
• Titrant: See above. The concentration, the validity of the titer and
the working life are ignored in contrast to the titrant of the first dos-
ing device.
• Filling rate: Rate at which the dosing cylinder of the second
dosing device is filled. The maximum filling rate depends on the cyl-
inder volume of the exchange or dosing unit used (see Sec-
tion 3.8.6 ).
However, in order to ensure continuous dosing, the following points
must be taken into account:
• Use the highest possible filling rate in order to keep the filling times
as short as possible. Please note the viscosity and density of the
liquid.
• When you use two dosing devices with different cylinder volumes
the filling rate of the larger cylinder must be at the minimum:
1 . cyl . Dos
2 . cyl . Dos
V
V
1 rate Filling 2 rate illing F ⋅ ≥
Example:
Dosing device 1: Volume = 20 mL, Filling rate = 50 mL/min
Dosing device 2: Volume = 50 mL
Filling rate 2 ≥ 50 mL/min ⋅ 50 mL/20 mL ≥ 125 mL/min
• The dosing rate must not exceed 75 % of the filling rate of the
smaller cylinder. This corresponds to the following values (at the
maximum filling rate):