I was trying to set up the auto approach while I noticed this unexpected behaviour.
In short, when the scanner is fully retracted (according to the probe HUB) the output is 10V and at -10V is fully extended.
However, as you can see from the attached picture, when the Zs output (yellow) reaches -10V the stepping signal (blue) is sent. Shouldn't it be the other way around?
Lastly, could I ask some more clarification on the "Retract CI" parameter (reasoning behind the choice of its value, so far seems to change the ratio between retraction and approaching speed ) and the Z polarity parameter in the hardware settings (generally I didn't see any change of the Zs output when switching this parameter and I can't find it in the manual)
A) make sure you Z-Polarity is set correctly, this is what determines if + or -10V is fully extended. (Gxsm3 -> preferences) Must restart Gxsm after adjusting. Then it will ask you to confirm to reconfigure the DSP (MK2/3) accordingly. (DO NOT RESTART THE DSP!)
B) All CP, CI must be positive. Else you cause internal "confusions"... only for vert special purposes or testing they may be negative in linear transfer mode.
C) "Retract CI" is a "speedup" using negative CI (CP=0) temporary to force a retract for this phase of auto-approach.. Where are you looks at?? This is normally not user exposed... (DSP internal)
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I have changed the Z-polarity settings (in preferences\Inst-SPM) without restarting the DSP, only Gxsm. However after restart of Gxsm it doesn't ask to reconfigure the DSP and the output when retracted remains the same.
However, even in reversed polarity, shouldn't it step only when fully retracted?
I found Retract CI on the Mover control window\auto.
If any other information is needed let me know and again, many thanks for your help
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Oh OK that Retract CI value. Leave that positive, some where 100..300.
Q: Is your Z-Scan going the direction as required when you simple test the feedback?
Do this test:
1) Just connect Bias (OUT6) -> Tunnel Input Signal (IN0) to simple emulate a current via Bias.
2) Put Current Setpoint to 1nA or so (assuming simple 1nA / Volt for testing)
3) Put Bias = 0V => This should move Z-Scan all the way to fully extended (+10V for positive polarity)
4) Put Bias > "1V", say 2V -- what is > 1nA, this should fully retract (-10V for positive polarity)
If that works the auto approach will work.
Anyways, please make sure:
** you never exceed +/-10V (not even 10.001) for the current input IN0! To be save if your amplifier can go beyond 10V, limit the range via a suitable analog limiter circuit (Z-Diode+resistor., etc) -- I am saying this as a precaution as if you over saturate the analog inputs I may read undefined/false values what can be dangerous... plus the hardware does not like that either and may cause damage. (out of specs)
** noise level on Current is reasonable small...
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hi everyone,
I was trying to set up the auto approach while I noticed this unexpected behaviour.
In short, when the scanner is fully retracted (according to the probe HUB) the output is 10V and at -10V is fully extended.
However, as you can see from the attached picture, when the Zs output (yellow) reaches -10V the stepping signal (blue) is sent. Shouldn't it be the other way around?
Lastly, could I ask some more clarification on the "Retract CI" parameter (reasoning behind the choice of its value, so far seems to change the ratio between retraction and approaching speed ) and the Z polarity parameter in the hardware settings (generally I didn't see any change of the Zs output when switching this parameter and I can't find it in the manual)
Thank you all for your attention,
Cheers
A few points:
A) make sure you Z-Polarity is set correctly, this is what determines if + or -10V is fully extended. (Gxsm3 -> preferences) Must restart Gxsm after adjusting. Then it will ask you to confirm to reconfigure the DSP (MK2/3) accordingly. (DO NOT RESTART THE DSP!)
B) All CP, CI must be positive. Else you cause internal "confusions"... only for vert special purposes or testing they may be negative in linear transfer mode.
C) "Retract CI" is a "speedup" using negative CI (CP=0) temporary to force a retract for this phase of auto-approach.. Where are you looks at?? This is normally not user exposed... (DSP internal)
Thank you Percy for your answer!
I have changed the Z-polarity settings (in preferences\Inst-SPM) without restarting the DSP, only Gxsm. However after restart of Gxsm it doesn't ask to reconfigure the DSP and the output when retracted remains the same.
However, even in reversed polarity, shouldn't it step only when fully retracted?
I found Retract CI on the Mover control window\auto.
If any other information is needed let me know and again, many thanks for your help
Oh OK that Retract CI value. Leave that positive, some where 100..300.
Q: Is your Z-Scan going the direction as required when you simple test the feedback?
Do this test:
1) Just connect Bias (OUT6) -> Tunnel Input Signal (IN0) to simple emulate a current via Bias.
2) Put Current Setpoint to 1nA or so (assuming simple 1nA / Volt for testing)
3) Put Bias = 0V => This should move Z-Scan all the way to fully extended (+10V for positive polarity)
4) Put Bias > "1V", say 2V -- what is > 1nA, this should fully retract (-10V for positive polarity)
If that works the auto approach will work.
Anyways, please make sure:
** you never exceed +/-10V (not even 10.001) for the current input IN0! To be save if your amplifier can go beyond 10V, limit the range via a suitable analog limiter circuit (Z-Diode+resistor., etc) -- I am saying this as a precaution as if you over saturate the analog inputs I may read undefined/false values what can be dangerous... plus the hardware does not like that either and may cause damage. (out of specs)
** noise level on Current is reasonable small...