NEW BRUNSWICK SCIENTIFIC BioFlo 415 Manual To Operations page 82

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Figure 37 is an example of the setup for multiple loops being used to control one
source loop:
The cascade scheme shown above can be read as follows: as DO output% increases,
prompted by a need to increase DO, agitation will increase from 250 rpm to 1000 rpm
over the DO output range of -100% (see the following paragraphs for guidelines on
setting DO Start Out%) to 25%. If this response is not enough to correct the
deviation between setpoint and present value of DO, the system will then begin to
respond by increasing GasFlo. The setpoint will increase from 5 SLPM to 20 SLPM
over the DO output % range of 25% to 100%. If these two events are still not enough
to correct the error the system, will then respond by increasing the O2 percent of the
gas mix. The O2 percent will increase from 0% to 100% over a DO output% range of
50% to 100%
When to use -100 as DO Start Out% in a Cascade:
Commonly after calibrating DO probes, the system will have a DO present value
higher than the setpoint. This happens because of calibration methods and because the
culture has not had enough time or has not grown to a significant enough density to
start to consume the available DO. This difference, as described earlier, will cause the
DO output % to plummet to -100% because the system thinks it needs to decrease the
DO. When you set -100 as the DO Start Out%, the loop being cascaded to begins
increasing as soon as the PV dips below the setpoint. Once the PV dips below the
setpoint, the Output % will begin to increase.
When to use 0 as DO Start Out% in a Cascade:
Zero should be used as the DO Start Out% if the media is equilibrated to the desired
setpoints before inoculation or before the cascade is enabled. In other words, if the DO
setpoint and DO PV are close to equal at the start of a run, it will work best if the
cascade DO Start Out% is 0. When configured this way, any drop in DO below the
setpoint will be compensated by the cascade loop.
BioFlo 415 M1360-0050
Figure 37: Sample DO Cascade
User's Guide