Hello,
I've been gradually automating my fermentation chamber, particularly the mechanisms I use for pressurized fermentation. I use a mass flow controller to gently bleed pressure off of my fermentor in response to measurements from an in-line transducer. I use the PID library on an Arduino to keep my setpoint, and so far it has been working very well.
After a fair bit of trial and error, I've found PID coefficients that seem to keep me steady (Kp = 200, Ki = 1, Kd = 5). These keep me reasonably tight on my setpoint, and even during the height of fermentation I rarely drift more than a tenth of a PSI away.
But, in the course of keeping things steady, my control output (valve position) races around like a jackrabbit. At peak fermentation, I'll see something like 300 SCCM average, but at any given moment it will be anywhere from 200-400. I stay very close to my target pressure, but the flow rate oscillates on about a 90 second period.
Any suggestions for convincing my output to settle down? My instinct is that I should lower my Kp and increase my Ki, but I wasn't able to make this work immediately. Before futzing with it more extensively, I thought I'd put the question to the many here who understand this stuff far better than I ever will.
Thanks!
I've been gradually automating my fermentation chamber, particularly the mechanisms I use for pressurized fermentation. I use a mass flow controller to gently bleed pressure off of my fermentor in response to measurements from an in-line transducer. I use the PID library on an Arduino to keep my setpoint, and so far it has been working very well.
After a fair bit of trial and error, I've found PID coefficients that seem to keep me steady (Kp = 200, Ki = 1, Kd = 5). These keep me reasonably tight on my setpoint, and even during the height of fermentation I rarely drift more than a tenth of a PSI away.
But, in the course of keeping things steady, my control output (valve position) races around like a jackrabbit. At peak fermentation, I'll see something like 300 SCCM average, but at any given moment it will be anywhere from 200-400. I stay very close to my target pressure, but the flow rate oscillates on about a 90 second period.
Any suggestions for convincing my output to settle down? My instinct is that I should lower my Kp and increase my Ki, but I wasn't able to make this work immediately. Before futzing with it more extensively, I thought I'd put the question to the many here who understand this stuff far better than I ever will.
Thanks!