Whole-Body Vitrification System (Technical Version)
During the on-going development of the perfusion process control system, we found it necessary to remove one of the controllers from the system. We found the particular controller to be providing unreliable signals at low RPM speeds, in particular the signal we were using to determine main pump flow rates. The inconsistency was due to frictional effects as the pump rollers hit the pump shoe and the rotation rate slowed. Because we use a linear look-up table to estimate the flow rates, addressing this inconsistency would require a non- linear look-up table to fix.
Because non-linear look-up tables are hard to maintain and because we had another alternative available, we decided to remove that particular controller. This, in turn, necessitated modifying the code to accommodate this change and some re- wiring of the system. Fortunately, this means that we have a reduced amount of third-party hardware and wiring, and the control functions are actually easier.
The main issue with this removal is that we needed a new way to calculate flow rates, but a solution was readily at hand. We were able to take the main pump control module, which still had seven open channels for future scalability, and use its analog output signal to make the flow calculations (once again using a linear lookup table). Changes were tested with the perfusate process controller driving the main pump, using the controller to cause pressure changes following a sinusoidal curve.