[Dsg-hallb_magnets] cernox sensor issue

[Ruben Fair]

Christiana. 

We shall not be making any changes to the software that is presently being employed for the Torus unless it is a planned test and this will require input from Dave Kashy also. 

For now, as you have planned, see what conclusions you and Brian can draw from the bench testing that you are carrying out using the two LV chassis from the solenoid. 

Regards 

Ruben 


From: "Christiana Wilson" <grenoble at jlab.org> 
To: "dsg-hallb magnets" <dsg-hallb_magnets at jlab.org> 
Sent: Friday, October 14, 2016 1:59:01 PM 
Subject: Re: [Dsg-hallb_magnets] cernox sensor issue 

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 


BQ_BEGIN
On Oct 12, 2016, at 6:44 PM, Amrit Yegneswaran < 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 




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BQ_END


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