Sartorius DCU 3 - pO2 Cascade Control with 3 Servo Controllers

Operators Handbook DCU3 – System
6., Main function „Control Loops“
BAEDCU3 - Rev. 4.6 - 0504 6 - 12
6.9 pO
2
-Control Methods
Contrary to the other controls of fermentor systems (temperature, pH etc.) the pO
2
- control is adapted
to the specific process requirements. For this the DCU3 - system comprises different pO
2
- controllers
that can be implemented according to the selected process. These control strategies can be realized:
 pO
2
- cascade control with the following possible servo controllers:
– Stirrer
– Airflow (Massflow Controller)
– Substrate
– Pressure
– Gasmix (pulsed valves)
– Gasflow Ratio (two Massflow-Controllers with O
2
-enrichment)
The controller configuration can be especially matched to the fermentor system and process. Several
of the above controllers can be implemented. Besides the controllers mentioned above, customized
DCU configurations with other pO
2
- control strategies can be realized.
6.10 pO
2
- Cascade Controller with 3 Servo Controllers
In the cascade system the pO
2
-controller is the master controller. Its output directly triggers the set-
point input of the servo controller.
Optionally a sequential mode can be selected for the pO
2
-cascade control. Then the pO
2
- controller
triggers two or three servo controllers sequentially, in order of their priority. In the pO
2
- controller you
can define a specific „MIN/MAX“ range for the setpoint signal transmitted to each servo controller:
 When the pO
2
control is switched on, at first the output of the pO
2
controller operates the
setpoint input of the priority 1 - servo controller (CASC1). Optionally defined servo control-
lers 2 and 3 get the setpoint, which is defined as „MIN“ in the pO
2
controller.
 At increase of O
2
-consumption, when the setpoint output of the 1st servo controller reaches
its „MAX“ limit, the output of the pO
2
controller is automatically switched over to the priority 2
- servo controller (CASC2). The user can adjust the delay time for switching-over, default
delay time is 5 minutes. Then the outputs are controlled as follows:
– servo controller 1: the predefined „MAX“ - output
– servo controller 2: controlled output of the pO
2
-controller
– servo controller 3: the predefined „MIN“ - output
 After switching over to the 3rd servo controller, the outputs are controlled as follows:
– servo controller 1: the predefined „MAX“ - output
– servo controller 2: the predefined „MAX“ - output
– servo controller 3: controlled output of the pO
2
-controller
 If the O
2
-consumption decreases the controller setting is switched back in reverse order.
Such a control strategy allows to keep the pO
2
value constant over prolonged periods of the process
without further manual intervention. The PID parameters for servo controllers of priority 1, 2 and 3 can
be adjusted independently of each other in order to allow maximum adaptation to the process-
dependent behavior of the control system.