Playing with delta sigma converter, poor man's meter.

[joeqsmith]

Added an APEX reference to the evaluation board along with a liner supply.   Drift seems to have improved but it's not a controlled test.   The temperature is what it is.

Enabled the PGA's chopper to see if this would remove some of the noise or the wobbles but it doesn't appear to make a difference other than taking longer to collect.  If I normalize all the five data sets  and then remove the wobble, you can see how the noise compares.  Ignore the p-p, but look at the standard deviation.   Adding the reference increased the noise (shitty workmanship, board hacking). 

I think the next step is to blob the inputs.   

[joeqsmith]

Insulating the PCB enclosure. 

[joeqsmith]

All data with the DC removed (normalized to zero).   Most data sets were short, or off screen so for the most part, ignore the readouts. 


Purple: Showing the ADC's input shorted with jumper wire at screw terminal.   Then moved the 731B's guard from the PN to the ground which slightly improved the noise. 

Dark Blue: Decided to AC terminate the power leads with a poor mans feed through (cap + coax), to the chassis.  Also added braid to the reference signal's cable and terminated to the chassis.  Then tossed a towel over the mess.   

Light Blue:  Original data after adding the APEX reference without towel.   

Green: Original data of stock eval bd with shield + towel.

[joeqsmith]

The orange blob seen through the screen is one of the small disc caps going from the braid to each power lead.   

[joeqsmith]

Finally, I have the noise sorted out and things are working well enough to try and run a somewhat constant temperature test with it.  The meat packing box has the USB cable already routed.  I want to combine my software that collects data from the ADS126e evaluation board with my temperature controller. 

My linear regulator is inside the shielded box along with the APEX which dissipates a bit of power.   At lot more than the handheld meters I have been using for a load up till now.   

[joeqsmith]

Testing out the software now.   We've had USB for how many years now and the team designing this couldn't figure out how to make it work without a push button switch to reset the board. 

The linear regulator is located inside the screened box.  This dissipates a couple of Watts.  I was thinking to run the temps low but am concerned with humidity.  My plan is to use the regulator to heat the chamber and control it around 30C.   The Peltiers should have an easy time keeping up. 

While attempting to tune the loop, looks like I picked up a new troll.  I wonder why they bother.
   

[joeqsmith]

Tuning the controller then things go bad...   I wonder if I am pushing the evaluation board beyond it's limits.  I'll let it run and see if this trend continues. 

https://www.youtube.com/watch?v=n38-smUTLg8&feature=youtu.be

[joeqsmith]

I suspect the board has some sort of thermal oddity.  This is similar to what I had seen before when I thought something may have touched the case.  I had the towel over the unit and after some period, the reported value started to dramatically change.   

After reaching an offset of 12uV, I started bringing the temperatures back down.  What's strange is the reported value becomes stable but doesn't return to the original value, it seems no matter how low I bring the temperature down.   

I have a couple of K-type sensors to monitor the temperature and this appears fine.   The reference doesn't appear to be the cause.  There's only so much on the eval board.  Time for some sleep and then a fresh look at the data sheets and manuals.  I'm missing something.

[joeqsmith]

A few bone head things to report on this TI eval board.   

First, as it turns out there is no need to press the reset switch on the evaluation board.  As a matter of fact, had I read their popups, it states it.  Just power cycle the board.  This is far better than removing the board from the chamber.

Next, my software had a major structural flaw that was causing some really strange behaviors.  I was suspecting their under lying code and wrote TI today about it after I couldn't find anything in the datasheets.   This problem was there from the beginning and am now certain this was the problem I saw when I use using the towel to keep the air flow off the circuit board. 

I am very happy to say the system is finally working.   

Shown is updated software.  The chamber is programmed to run a sweep from 22 to 30C and back down where it will hold.   The dwell time at each temperature will be 60 minutes.  The reference's flat area is higher than this.  It's more of a sanity check. 

 

[joeqsmith]

After setting the chamber to 22, the profile holds for 2 hours.  Then 1 hour hold at each step.   Total time shown is over 11 hours.

Data was collected using SIN4, PGA 2 non-chopped, DRATE 2.5, APEX 0.6ppm external reference.   

Notice the second graph is showing the offset after the board was returned to 22.0 degrees.   This is roughly 200nV per division or shift of 600nV.   I suspect this shift is caused by parts outside the environmental chamber.   

I'm pretty much at the limit of what I have the ability to look at using my meat packing box and old modest equipment. I would have no way of cross checking anything.  It's a pretty impressive board by my standards which I will admit are pretty low. 

[joeqsmith]

Setting up to run one last test before putting the TI board away.  The next test will be at a fixed temperature with the chopper enabled.   I'll post one last video of it collecting data.

My troll buddy I mentioned above had posted one last time but I don't have their response.  It was basically something about Donald Trump and their loss of respect for me after each post.  They closed with something to the effect that they doubted I would leave the post, something about them making me look bad to my viewer's.   I did end up blocking them like I have done with most trolls.  I just don't have time for them and I doubt viewers do as well.  The real twist was I went to their channel and they had one video I assume they had made about saving on your home energy bill with their device.      No wonder they were so upset.    If you are into the free energy thing, you should check them out.  I did not watch it. 

[joeqsmith]

24 hours of a somewhat constant voltage and temperature.