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Connect String Pots and Linear Pots to NI 9216


@rolfk wrote:

Sorry to ask this, but do you have any electrical engineering background? While the higher art of proper grounding is a topic one could write an entire book about and still not having covered everything, some of your questions are pretty basic EE stuff that you learn in the first year of any electrical engineering class. Learning on the job is an interesting principle but can be also an expensive exercise for whomever you are meant to do this!


Nope 😕

Learning on the job is kind of a pain in this field, especially regarding grounding (I've read several books and articles and papers about it, and I still don't understand properly...)

My PCBs seem to be doing OK though 😉

 

Do you have a preferred resource regarding grounding and loops and coupling problems? I quite enjoyed the demonstrations in the recent GDevCon #2 talk, but it doesn't exactly lead to big changes - just a few points to keep in mind.

Textbooks on electronics tend to cover other topics far more heavily, with just some brief mention of the effects of ground loops, and the guidance to avoid creating them, but often little mention of the potential unnoticed (except in the results) coupling effects (beyond just: I attached wires to two different "ground" locations and thought they'd magically all be the same).

Richard Jennings and Fab's new book had some interesting notes on it in their chapter on connecting to hardware - that was quite nice because it specifically references common NI configurations.

 

Think my next place to look might be this: Understanding, Finding and Eliminating Ground Loops (Bill Whitlock) but I'm not sure it will give me more than previous resources.


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I am a PhD student in the civil engineering field and this is a part of an experiment I am performing in the lab where the displacement sensors are these pots, I have no background in EE, yet I have to do the job. Sorry for bothering, but your help is appreciated.

 

Thanks

Ahmad

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Well there don't exist any books that cover this topic exhaustive. That is because the whole thing sometimes seems to defeat any logical explanation. There are common rules and good practices but when you end up in the field with the task to get everything working it can at some point turn into simple trial and error.

The main reason in my experience is that you can not always know for sure which devices may have a more or less hidden ground reference anyhow. Unless it is 100% stated, such as with the NI 9205 module that is specified to have a channel to ground isolation, you can't assume it is or isn't. And static electricity can be nasty depending on the environment you are in.A PT100 mounted in a metal block may or may not be ground referenced through that metal block. It al depends if the metal block has some earth connection somehow, and if the PT100 is explicitly isolated or not. And even if it is that isolation may be damaged over time, which won't cause a big problem in terms of temperature measurement but can be the source of a perfect ground loop.

On the other hand isolated PT100 can have nasty static charge build up if the housing AND the electric circuit input aren't both grounded.

So no matter what you do and what sensors you use you can end up with unwanted situations either from start or after some time from wear.

Rolf Kalbermatter
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I found this and other threads as I'm working the same problem now: How to wire up to 10x SP1/SP2 string pots using cDAQ.

 

I understand the Analog Input side for making the measurement, but am wondering if anyone can make some practical advice on how to power/excite these when up to 10x are needed in a single setup?

 

Ideally, I want a cDAQ solution but this seems impossible and I am thoroughly green when it comes to wiring these up, purchasing the right parts.

 

Can anyone help with some practical advice here?

- Do I need a programmable DC supply to get sufficiently clean power, or would a PS-14 or similar work?

- What's the easiest way to distribute power to these 10?  What terminal block or other method?d

 

And I saw another thread discussing the RTD NI-9216 which seems reasonable as well.  Could that be an all-in-one solution for the SP1/SP2 string pots?

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