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Force curve shape at high ramp rate, how to interpret the retraction curve?

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BenSD posted on Wed, May 22 2013 2:11 PM

Hello,

I am trying to see the effect of various ramp rate at constant force. To do so I calibrated the trigger threshold at various ramp rate so I reach the same max force. When I measure the deformation from the approach curve at different ramp rate (after phase offset correction), I find comparable results, however the retract curve shape is very different showing important hysteresis at high ramp rate which make sense. What doesn't make sense is that at high ramp rate, it seems that when the force decrease, the deformation keep increasing (the retract curve is bended and go below the max deformation reach during approach).

I don't know how to interpret that, is it artefact due to high ramp rate or is it real deformation due to some weird behavior of my sample?

Below are 2 FC, one at 2Hz showing hysteresis and one at 19 Hz showing weird retract curve:

2Hz

 

 

19Hz

 

Thank you!

Benoit.

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Bruker Employee

Excellent!  Now I see what you are saying.  Which microscope are you using?  Multimode, Dimension, Catalyst? Are you using CLZ?  If so, I'm thinking that the feedback is not keeping up with the Z motion.

I would suggest switching to open loop, but collecting the Z sensor as a separate channel so that you can use that in the separation calculation.  Another possibility is to increase the gain for the Z feedback loop, but 20Hz is usually a bit on the fast side for ramping with CLZ.

--Bede

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Top 10 Contributor
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Can you repost your images?  They are not showing up, making it difficult to understand the "weird behavior"

--Bede

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BenSD replied on Thu, May 23 2013 11:01 AM

Hi Bede,

 

Here it is (hopefully) :

2Hz

 

19Hz

 

Thanks,

Benoit.

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replied on Thu, May 23 2013 3:58 PM

Hi Benoit,

It appears that the images are still not showing up. Did you try uploading them to your Nanoscaleworld media folder and then use the "insert media" function?

Stefan

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BenSD replied on Thu, May 23 2013 4:28 PM

Hi Stefan,

Thanks for the tip, now it should be there!!

Benoit.

 

 19Hz

2Hz

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Top 10 Contributor
280 Posts
Points 6,219
Bruker Employee

Excellent!  Now I see what you are saying.  Which microscope are you using?  Multimode, Dimension, Catalyst? Are you using CLZ?  If so, I'm thinking that the feedback is not keeping up with the Z motion.

I would suggest switching to open loop, but collecting the Z sensor as a separate channel so that you can use that in the separation calculation.  Another possibility is to increase the gain for the Z feedback loop, but 20Hz is usually a bit on the fast side for ramping with CLZ.

--Bede

Top 25 Contributor
35 Posts
Points 405
BenSD replied on Thu, May 23 2013 5:07 PM

Hi Bede,

It is a catalyst and yes I am using CLZ! I will try next time with open loop, thanks!


I am not sure to understand what you mean, should I use Z instead of Heigh sensor?

Where can I find the gain for the Z feedback loop?


For the FC I already acquired at 20Hz is it correct to measure the deformation from the approach curve or am I underestimating it?

Thanks,
Benoit.

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