81
New Brunswick Scientific
User’s Guide
1
1
0
0
C
C
A
A
S
S
C
C
A
A
D
D
E
E
C
C
O
O
N
N
T
T
R
R
O
O
L
L
A cascade is a control scheme in which the output of one control loop influences the setpoint
of one or more other loops. In other words, it uses one or more parameter(s) to influence
others. For example, if the DO control loop is cascaded to Agitation, whenever the DO
process variable drops below its setpoint causing an increase in DO control loop output, the
agitation setpoint will increase. This is effective, because agitation strongly influences DO.
With this type of cascade, errors in DO are corrected by changes in agitation RPM.
The BioFlo/CelliGen 115 controller allows cascading from the DO loop to as many as three
other loops, usually agitation, gas flow and oxygen (each complete loops with their own
probes and actuators).
When more than one loop is configured as the recipient of a cascaded loop, they respond
sequentially: as one maxes out, the next begins to ramp up.
Depending on the options installed in your system you will have the ability to select one of the
following cascades. Those unavailable will be greyed out and not selectable.
•
None
, which means that dissolved oxygen will not be controlled by means of a cascade
•
Agitation
controls dissolved oxygen through automatically controlled agitation speed.
When the actual DO2 value drops below the setpoint, the system will increases the
agitation speed up to as much as the high limit to meet the culture demands. Once the DO
setpoint is reached or exceeded, the agitation will fall back down to the low limit.
•
Oxygen
controls dissolved oxygen by automatically adjusting the mix of air and oxygen.
(This is not available without the Automatic Gas Mix Option.) When the actual DO2 value
drops below the setpoint, the system will increases the percentage of O2 to as much as the
high limit to meet the culture demands.
•
Agitation/Oxygen
controls dissolved oxygen by first increasing Agitation to the high
limit, then, if DO still has not reached the setpoint, increasing the oxygen percentage being
entered through the sparger to as much as the high limit. This cascade is most frequently
used in fermentation. (This is not available without the Automatic Gas Mix Option.)
•
Agitation/GasFlo
controls dissolved oxygen by first increasing Agitation to the high limit,
then, if DO still has not reached the setpoint, increasing the GasFlo entering through the
sparger to as much as the high limit. This cascade is most frequently used in fermentation.
(This is not available without the Automatic GasFlo Option.)
