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 ATF eLog Not logged in  Mon Jun 21 20:46:40 2010, Dmass, Computing, General, Oven interfacing Tue Jun 22 19:17:27 2010, Dmass, Computing, General, Oven interfacing Tue Jun 22 21:53:24 2010, Dmass, Computing, General, Oven interfacing Wed Jun 23 15:59:13 2010, Dmass, Computing, General, Oven interfacing  Wed Jun 23 21:53:50 2010, Dmass, Computing, General, Oven interfacing Thu Jun 24 21:18:49 2010, Dmass, Computing, General, Oven interfacing  Sun Jun 27 18:02:51 2010, Dmass, Computing, General, Oven interfacing
Message ID: 834     Entry time: Sun Jun 27 18:02:51 2010     In reply to: 833
 Author: Dmass Type: Computing Category: General Subject: Oven interfacing

 Quote: Here is the in loop temperature for various loop settings. Legend: The first number is proportional gain, the F is integral gain ("fast" as called by the 3040) To note: I don't know why the loop oscillates for lower gain settings The loop seems most stable for the highest possible gain settings ("300 Fast"), so I will use this. This is actually Kelvin/rtHz

Making sense of this - I spent a couple minutes sitting down and writing down the right equation for the complete open loop transfer function. Assuming an integral gain of "fast", we have:

OLTF = 3.68e-3*Kp*(s+8.5/Kp)/s/(s+0.0167)

Where Kp is the proportional gain. When we make Kp 50, we put the zero from the PI loop at 0.17, where the pole is at 0.0167. This makes a nice long chunk of f^-2 in the loop, murdering the phase. As we crank the gain up to 300, we push this zero down, and shorten the stretch of f^-2.

Ideally with an integral gain of "fast" we would have a proportional gain of ~500.

If we go to "slow", then we have for our complete open loop transfer function:

OLTF = 3.68e-3*Kp*(s+1.6/Kp)/s/(s+0.0167)

For a gain of "1 slow", as in the plot, we find the zero is 2 orders higher than the pole, which is consistent with this setting ringing way more than the others. A gain of "100 slow" would work for balancing the zero and pole. Our highest proportional gain available with a "slow" setting is 50, which is similar to the situation above, where the zero is about a factor of 2 before the pole, thought with a lower UGF than above.

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