Operators Handbook DCU3 – System
6., Main function „Control Loops“
BAEDCU3 - Rev. 4.6 - 0504 6 - 19
6.13 pO
2
- Gasflow Ratio Controller
To improve the control quality, the pO
2
can also be controlled by means of continuously mixing of two
gases, e.g. O
2
and air, via an external massflow controller. The DCU3 - system realizes such a control
strategy by a cascade control with a pO
2
gasflow controller as the master controller and a gasflow ratio
controller as the servo controller. The pO
2
gasflow controller is a PID controller and controls the gas-
flow ratio controller, which is the servo controller.
The gasflow ratio controller acts as a ratio controller and can be used in two modes:
Control of the total gas flow (TOTAL): The setpoint for the total flow is manually adjusted.
The pO
2
gasflow controller provides a setpoint for the portion of Gas 1 (RATIO) in relation to
the total flow.
Connection of specific gasses to the massflow controller, depending on the oxygen con-
sumption of the culture and the available gasses. The following gasses can be connected:
– Air (GAS 1) and N2 (GAS 2) for low O
2
requirements
– O
2
(GAS 1) and air (GAS 2) for high O
2
requirements
– O
2
-(GAS 1) and N
2
(GAS 2) for processes with considerably varying O
2
requirements
6.13.1 Operating Display Master Controller (pO
2
-Gasflow Controller)
For a description of the tags, the physical units or entries, the displayed value or function
and of the required inputs see the table in section 6.3, Controller Operation in General.
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