Data transitions from noisy to smooth

I was wondering if you know what might be causing the behavior shown in the OD graphs below. In the graphs from last night, you can see that the Normalized OD had large spikes every ~20 minutes (in chemostat mode, exchanging 0.5 mL every 20 minutes). Looking at the OD chart, you can see the data was pretty noisy until ~9:45 PM, but then the noise just seemed to disappear.

Looking at the graph from today, the noise did not return and the graph is much more smooth. I did not handle/or change the pioreactor around 9:45PM last night. Do you know what might be causing this behavior?

Last night:

This morning:

hmmm a few things come to mind.

  • Was the stir bar “skipping” in that time period? (it would be an audible noise)
  • It’s possible there was a mass of something large, and it was diluted out.

Yeah, it may have been both those things.

I do remember hearing an audible noise that I thought was the stir bar skipping, but that fixed itself and is not audible any more.

What’s your RPM? I usually recommend ~400. Are you higher than that?

I usually leave it at 450 rpm (current default), but if the stirring isn’t working, I sometimes try and go up to 500 or 600 to see if that fixes the issue.

if the stirring isn’t working

Can you describe this situation more?

Back to your original problem: one trick we use is to open up the Pioreactor’s “window” to look inside the vial when something strange is going on.

Can you describe this situation more?

Sometimes I’ll get an error that the stirring rate is zero and the reactor is attempting to restart stirring. It’s an occasional issue that I’m usually able to resolve. It tends to happen at the beginning of experiments, but once it starts working properly, I usually don’t notice the issue re-occurring.

I think it might have several causes. One time I had some large particulates in the culture chamber that sunk to the bottom and were blocking it. Sometimes I’m not sure the reason. I think this time may have been due to a loose (home-made) wire connection and I plan on fixing that when my new pioreactors arrive.

From using bigger magnetic stir bars, reducing RPMs usually fixes skipping, rather than increasing. Going faster just makes it bump faster.