[Dsg-hallb_magnets] cernox sensor issue

[grenoble]

Hi Brian,
I appreciate you looking at the algorithm.  The algorithm you suggest 
was used for a time.  It caused the current to be recalculated every 
loop and made the temperature less stable.  One of the engineers asked 
that the current only be changed when the power dissipation was out of 
the range that Lakeshore recommends for Cernox operation.  I am curious 
as to why the existing algorithm only works when temperature is 
increased.  Could it be that more power is dissipated and the current is 
recalculated?  Why does it not work when temperature is decreased?  
Could it be that power dissipated is within range and current stays 
constant.

I will need Rubens permission to make the change.

As for additional power checks, the algorithm below matches the latest 
flowchart see attachment v1.  I do not see additional power checks.  I 
may have sent you an older copy of the flow chart which did have 
additional power checks see attachment v0.  The engineers asked me to 
change the code to what you see below.

I can apply your suggested algorithm, but everyone will need to be aware 
that the temperatures will not be as stable as they are now with the 
fixed currents.

I think we need to look at another parameter before recalculating the 
current, maybe voltage?  Lakeshore recommends that the voltage across 
the RTD be 10mV or less for the full range of temperatures that the 
Torus operates.

What are your thoughts on this?
Christiana


On 10/14/2016 12:27 PM, Brian Eng wrote:
> Instead of explaining with text, which could be confusing, I've 
> attached a few screenshots of the various VI block diagrams.
>
> For reference here's a PDF for the 
> algorithm: M:\hallb_eng\CLAS12\Magnets\Torus\JLab 
> Torus\C&I_Torus\Controls_&_Wiring\Fast DAQ\Cernox Algorithm\TR 
> Algorithm.pdf
>
> Here's what the VI looks like now (attached as current.png):
>
>
> The issue I've found with the current algorithm is that it will 
> increase the current as the temperature increases, but it won't 
> decrease the current as it goes down.
>
> After noticing that the logic doesn't exactly match the reference 
> algorithm (namely the additional checks on power dissipation) I 
> modified the VI to look like the following (attached as updated.png):
>
>
> This version properly increased and decreased the current with my 
> admittedly limited testing of using a single potentiometer in place of 
> a cernox sensor and varying it up and down between 4K and 325K.
>
> Finally I removed some of the terminals that weren't being used and 
> changed the code to use more LabVIEW primitives in my process of 
> upgrading to 2016 (attached as simplified.png):
>
> Hopefully the images make sense and get sent through to the mailing 
> list okay.
>
> --
> Brian Eng
> Detector Support Group
> 757-269-6018
>
>> On Oct 12, 2016, at 6:44 PM, Amrit Yegneswaran <yeg at jlab.org 
>> <mailto:yeg at jlab.org>> wrote:
>>
>> hello brian,
>>
>> today you and i had a discussion about the cernox sensor problem.
>> at the dsg meeting we further discussed the matter.
>> you mentioned that there were some errors in the main program VIs, 
>> which i'vent seen.
>> when you mentioned that you had e-mailed christians (author of the 
>> code) and nick i mentioned you to post a few words regarding this 
>> issue, so that rather than a select few, all of us including i might 
>> be aware of the source and cure.
>> perhaps it slipped your mind that i requested you the source and the 
>> cure for the problem.
>> i am documenting all these issues so that newcomers like pablo and 
>> tyler understand these issues and can provide
>> effective support.
>>
>> so when you come back on friday please do so.
>> amrit
>
>
> _______________________________________________
> Dsg-hallb_magnets mailing list
> Dsg-hallb_magnets at jlab.org
> https://mailman.jlab.org/mailman/listinfo/dsg-hallb_magnets

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