USA Cal Club Round 2 Data Analysis - Page 1
Forum section: electronics / general

author: rhb
author_rank: Super Contributor
timestamp: August 11, 2019, 04:34:52 pm
content: I think I'm reasonably satisfied with the initial displays for the PX and FX reference runs. There was a *lot* of noise on the PX/FX ratio run which I don't understand yet. So I've got a good bit of research and experimentation to do before I post that run.All of my figures are generated using the standard Unix command line and gnuplot except for one program, trend(1), which bins the data in X & Y and then picks points on the cumulate distribution to allow testing to see if data are Gaussian distributed. That program has a dependency on and is available the Seismic Unix package. However, the version there is single precision which is not adequate for computing the standard deviation. And it may well have another name. I don't recall now if Stockwell renamed that program or not.SU is very useful for time series analysis, data filtering, etc. It does have a strong reflection seismology flavor, but I used it quite heavily for a major rock properties project. It has some very good display tools.The input for my scripts is the CSV files I posted to the Round 2 list. I strip the commas and reformat the 34401A output for convenience using trend(1). I discovered that gnuplot was not happy with the defualt HP notation and so I reformatted it rather than sort out how to make gnuplot happy.The plotting program and scripts are attached here. I had to add ".txt" to the file names to keep the forum software happy, so you'll need to make adjustments for that if you want to use them.

author: TiN
author_rank: Super Contributor
timestamp: August 11, 2019, 04:43:55 pm
content: Do you plan to post actual plots/results as well? Scripts are little help, as I don't have environment to run them, and many others might be in same boat.

author: rhb
author_rank: Super Contributor
timestamp: August 11, 2019, 04:48:58 pm
content: Here are the plots from the FX reference. The "lab" is a 7 ft x 10 ft utility closet with a 6000 BTU window unit for cooling.I neglected to make any provision for air currents other than to point the vents at the ceiling.The humidity spikes are from when I was in the roomThese next two are just probability density functions for the 2 meters. Notice that the Closet Queen has a missing code every 5th value. I *think* this is because we are over the maximum value for the range, but have not absolutely verified that yet. But we don't see it on the PX data.These next two require some explanation. The solid lines are the mean and the -1, -2, +1 and +2 sigma values. The small squares are the picks on the cumulate distribution at the appropriate points. So if the squares match the lines then it is proof that the data are Gaussian distributed.I've got another batch of plots for the PX, so hold off for a moment.

author: rhb
author_rank: Super Contributor
timestamp: August 11, 2019, 04:50:40 pm
content: Notice that we do not see the missing codes as we did with the FX reference.Not quite sure what is going on with the Closet Queen at under 20 C.

author: rhb
author_rank: Super Contributor
timestamp: August 11, 2019, 05:14:44 pm
content: These are plots from the PX/FX ratio run. I don't understand what is going on. They are extremely noisy. There is a short segment which is not noisy which is approximately at the time I turned off the A/C.To get the mean and standard deviation plots I had to reject any values greater than 0.72. The cumulate distributions were so spread out as to be completely useless, so I did not plot them.I added a zoom on the central portion of the probability density function to show that is approximately Gaussian.The noise is approximately time synchronous on both meters which makes me suspect either EMI or bad connections at the references. I plan to investigate as soon as I have an AR488 GPIB-USB interface put together.This is also the run in which I got goofy values for the temperature from the Tempduino, e.g. 2020.368 instead of 20.368.The data are obviously not usable for anything, but I'm hoping someone can suggest what the problem was.

author: Andreas
author_rank: Super Contributor
timestamp: August 12, 2019, 06:59:19 am
content: Hello,I think this is simply a common mode / GND wiring issue.I had also problems with ratio mode instabilities in the beginning.Both battery supplied references were connected floating to the 34401A.In the handbook I found that the maximum voltage difference has to be within 2V for both negative terminals on the 34401A.With my battery supplied references I simply connected the both negative terminals on the 34401A together to solve the issue.With external power supplies and a actively buffered negative terminal of the reference the wiring might be more demanding.with best regardsAndreas

author: rhb
author_rank: Super Contributor
timestamp: August 12, 2019, 12:41:19 pm
content: Andreas,Thanks for the comments on the ratio run. While I'm disappointed that I screwed that run up, it's rather to be expected when you're doing something for the very first time. Theory covers the big stuff, but the devil is in the little details. I see a pair of sealed lead acid batteries in an old fashioned oak box with nice knurled brass posts in my future.At the moment I need to build a GPIB-USB adaptor. For the runs I used one that vindoline supplied with the kit. I'm merging the GPIB-USB and Tempduino functions with an RTC as an option for WaveyDipole's AR488 FW. General idea is that it can be anything from just a GPIB-USB interface or you can go as far as a complete data logging solution just by setting the proper #defines.I have all the parts I need except the 2 x 36 PCB edge connector for the 44421A relay board.With a group trigger command I should be able to read the two 34401As and my spectrum analyzers at the same instant. Probably don't need the 22 GHz span of the 8566B, but it's available if I can't sort it out using the 3 GHz span of the 8560A.The 44421A relays are specified at < 1 uV EMF. That's more than good enough for anything I'm going to be doing with the 34401As, but I am curious about the possibility of reducing that. Mostly just as an engineering exercise.Basic idea is to fit a 3-5 mm aluminum plate pressed against the relays with silicone thermal pads and monitor the temperature of the plate for use in applying a software correction term. Any comments? I'd be very interested in prior work along those lines.My only real interest in the volt nut area is investigating the aging and hysteresis issues. I spent several years dealing with the continuum mechanics of rocks and fluids professionally. But to do that I need to be able to scan 20-40 channels of references. I plan to start with AD584JH references because they are cheap and I can afford to ruin a few by putting them in a lab oven to test the effect of high temperature annealing, etc. If I'm successful with those I'll move to higher grade references.I'm sure that the OEMs have spent a lot of time on the problem, but several hours of searching IEEE Xplore and google scholar didn't turn up any publications. Not too surprising given the competitive value of knowing how to better stabilize your references.Beyond that I just want to be able to cal my test bench from DC to 22 GHz. That's hard enough with a complete bench including an 8753B VNA to cal.Have Fun!Reg

author: SilverSolder
author_rank: Super Contributor
timestamp: August 14, 2019, 07:52:25 am
content: In theory, the difference between theory and practice is small.In practice, the difference between theory and practice is large.