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projects:stm:log [2025/06/15 15:33] – [Day 2025-06-15 (rahix)] rahixprojects:stm:log [2025/06/16 07:51] (current) – [Day 2025-06-15 (rahix)] rahix
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 ==== Day 2025-06-15 (rahix) ==== ==== Day 2025-06-15 (rahix) ====
  
-TBD+Tried reproducing the results from yesterday -> achieving tunneling was quickly done.  The goal today is to tune the control loop better. 
 + 
 +Achieved control for short periods of time, but the control behavior looks way too slow: 
 + 
 +{{:projects:stm:control-2025-06-15_17-06.png?400|}} 
 + 
 +Assuming that the proportional control is not doing its job right now. 
 + 
 +Added back an ''R8'' of 100k to shut up the I-controller, to just look at the P-controller.  It shows its familiar ringing when giving a factor using the potentiometer.  This even couples back into the probe current, as can be seen below (at this time, the tip is very far away): 
 + 
 +{{:projects:stm:p-ringing-2025-06-15_19-01.png?400|}} 
 + 
 +Frequency of the ringing is 1.47kHz. 
 + 
 +Added another 1µF capacitor across C7. **This gets rid of the ringing across the whole range of the ''P'' potentiometer.** 
 + 
 +With this, we are now able to see actual stable control over long periods of time with fast response from the control loop: 
 + 
 +{{:projects:stm:control-2025-06-15_20-11.png?400|}} 
 +{{:projects:stm:control-2025-06-15_20-12.png?400|}} 
 + 
 +You can also see the piezo sweep using the I-controller until it finds the tunneling point. 
 + 
 +{{:projects:stm:sweep-then-find-2025-06-15_20-10.png?400}} 
 + 
 +What's still a bit unclear is how there can be situations like in the image above where tunneling stops again as the Z piezo moves even closer? 
 + 
 +Part of a very stable tunneling over a very long period today: 
 + 
 +{{:projects:stm:2025-06-15_20-23.png?400|}} 
 + 
 +During mechanical adjustment, the controller now sweeps until it finds something (left side of the picture below).  On the right, it has gone into control. 
 + 
 +{{:projects:stm:2025-06-15_20-28.png?400|}} 
 + 
 +Settings during the experiments above: 
 + 
 +  * ''Probenvorspannung'': Maximum 
 +  * ''Sollstrom'': 0.322V (= 322pA) 
 +  * ''I'': Minimum 
 +  * ''P'': Maximum 
 + 
 +Now changing the settings somewhat in hopes of getting the control loop more tight: 
 + 
 +  * ''Probenvorspannung'': Maximum 
 +  * ''Sollstrom'': 0.144V (= 144pA) 
 +  * ''I'': 9 turns up (out of 10) 
 +  * ''P'': 9 1/8 turns up (out of 10) 
 + 
 +You can see the faster I-response at least: 
 + 
 +{{:projects:stm:2025-06-15_20-50.png?400|}} 
 + 
 +It seems the noise has increased since yesterday.  We don't have values from before, but right now, seeing ~80mV of noise overlayed over the tunneling current signal. 
 + 
 +After some time, the control loop settled down quite a bit, assumingly because process disturbances decreased for some unknown reason: 
 + 
 +{{:projects:stm:2025-06-15_20-56.png?400|}} 
 +{{:projects:stm:2025-06-15_21-00.png?400|}} 
 +{{:projects:stm:2025-06-15_21-01.png?400|}} 
 + 
 +Managed to increase the setpoint current to 456pA: 
 + 
 +{{:projects:stm:2025-06-15_21-05_1.png?400|}} 
 + 
 +Finally tried putting the lid onto the STM for noise shielding, but I think I crashed the tip way too hard during the process as I couldn't achieve stable tunneling again afterwards... 
 + 
 +Should create a new tip next time and then retry more gently.  Also X/Y control is probably a good next step.
 ==== Day 2025-06-14 (rahix, k8ik, hugo, q3k, ln, zoe) ==== ==== Day 2025-06-14 (rahix, k8ik, hugo, q3k, ln, zoe) ====