Recent Posts

21

Buy/Sell/Wanted / WTB (US/NA) Battery and Charger for Flir Ext (compatible with E4, E5, E6, E8)

« Last post by ZGoode on Today at 03:54:29 pm »

I'm looking to buy one battery and one charger for the Flir Ext family to replace charging over micro-USB.  If anyone has any extras, especially of the charger, I would be happy to buy one off you.

22

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by mawyatt on Today at 03:52:54 pm »

On paper, sure, but my question is how much of that translates into an advantage in practice.

That's the point we don't "practice", we performed in real time, no backups, or woops, or awe sh*its, missed that, our career and reputation were/are on the line in everything we did/do.

Today things are a little less stressful as we are semi-retired, but still adhere to the "no excuses" policy wrt to electronics design, and the Siglent is simply our more Pro Level instrument IMO.

Please remember we have both Rigol & Siglent, and don't need to defend nor exaggerate the performance of either

Of course YMMV

Best,

23

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by wasedadoc on Today at 03:51:28 pm »

No, it does not have to be periodic. "Perfect reconstruction" only requires that the original signal sampled by the ADC sampled was bandwidth-limited.

Nope.

The signal in this image is bandwidth limited (5Hz signal, 11Hz sample rate) but sin(x)/x won't reconstruct it unless the filter is infinitely wide and the signal is periodic (which can't happen in practice).

That signal has components above 5.5 Hz.

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Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by KungFuJosh on Today at 03:48:44 pm »

comical or not, professional or not, sds800x cannot see 400-500MHz even on one channel active, prove me wrong.

🤣🤣🤣 I don't need to. The FACT of REALITY is that if you're trying to measure outside of the scopes designed bandwidth, then the results simply won't be accepted by any professional. The results shapirus showed of his DHO800 measuring 500MHz were TERRIBLE. If you think that's something to be proud about, I don't know what to tell you.

Do you need to measure a 500MHz signal? Your scope better be CERTIFIED to do so, or you could be subject to legal action when the product you're trying to sell doesn't meet specs, or the device you certified as functional isn't. Standards and reality matter, unless you're talking about a toy.

Are you looking for a toy or a tool?

25

Projects, Designs, and Technical Stuff / Re: PCB humidity measurement circuit design

« Last post by strawberry on Today at 03:47:01 pm »

5X5 mm PCB sensor area and feature size 0.1mm
pure water = 1.8E9 /m
A=12.5^2mm
l=0.1mm
R=~8E9 (100% humidity)
resistivity measurement will be hard
maybe capacitative

are commercial sensors reliable(>100kh)? some say, need to dry them to make them operable again

26

Beginners / Re: Any off-the-shelf clock using DS3231?

« Last post by hap2001 on Today at 03:44:24 pm »

Thank you, I'm aware there are sync methods other than NTP, like WWVB and GPS, but their signal reception is a big problem.

27

Metrology / Re: Remote controlled DMM DCV INL tester based on voltage divider idea

« Last post by CurtisSeizert on Today at 03:43:57 pm »

First off, I got to the bottom of the anomalously high turnover error for the center tap voltages. I had unwittingly connected circuit GND to the shield of the USB cable via the SMA jack and the case. Things are much better behaved after using some polyimide tape to insulate the jack and connecting the USB cable through an isolator.

To address Kleinstein's comments, the "corrected sum error" values came out to near zero seemingly by coincidence for that test. It is an interesting sum because it ends up cancelling out the even-order errors from the data. However, with the source actually floating now, it is noisier than the regular sum error. There is no option to short the meter at a common mode potential relative to circuit ground other than that of the center tap because the output switching is handled by four SPDT switches (a TMUX 7234). The relays on the board are actually range switching for the Howland current source. The short nulls out the TEMF-related offsets back to the common terminal of the first switches. It is not clear to me that anything would be gained by taking short readings at multiple bias voltages unless there is considerable noise from the center tap buffer. The meter would be seeing the exact same impedance between its terminals for a short at any tap, and there is no effect from bias voltage on the short voltage in the data I have captured. The range for the tests was set manually, and it is the 10V range the whole way through.

I have been collecting slopes from the data points for each measurement in the test, and I noticed that with a randomized code order, there is a relationship between slope and code. Moreover, when I use bipolar references for the DAC and take readings on either side of zero sequentially, the second of these has a smaller standard deviation. To try to keep the settling better behaved, I started running the codes in sequence. This does help reduce the standard deviation a bit, but it is now impossible to separate drift in time from code-dependent drift, so I may look at some alternatives.

The weakest point in this strategy is probably the reliance on polynomial regression. With a dataset I gathered at 10 NPLC with 50 points and 8 replicates each, going above fifth order fits was dicey. Seven was possibly OK except at the edges, but nine was not well behaved. I have been experimenting with fitting cubic splines, and this is definitely better near the edges. I don't know if it is possible to analytically derive the transfer function from such a fit, but I have been testing some algorithmic approaches to converge on a transfer function that minimizes deviation from the turnover error fit spline and the sum error fit spline. This is doable, but it tends to be poorly behaved around zero, which has significant effects on the other points in the curve. I may also try fitting a polynomial to the data near zero, as high order terms will not be important, and calculating out from the fitted curve. The sum error formula is agnostic about what happens on the other side of the origin, and the turnover error data do not constrain the difference between two points on opposite sides of the y axis. That means just trying to derive the transfer function through recursion is subject to compounding errors. The effect of fitting errors on the slope of the transfer function is greatest near zero because the sum error is effectively the slope of the error of the transfer function between the total voltage and the center tap voltage (assuming a ratio of 1/2). As the function approaches zero, the divisor defining this slope gets small, so the impact of the errors gets large. This is a work in progress, and the results would need to be validated against simulated data with various polynomial and non-polynomial transfer functions to gain confidence in the technique. I expect that this general approach will ultimately yield the best way of processing the data.

28

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by Mechatrommer on Today at 03:42:23 pm »

Difference is that "the other" scope actually does work as 4ch 200MHz BW scope.
At all times, no special conditions..

The argument that it's not that hard to disable 3 of the channels on the Rigol to get higher bandwidth is comical, not professional.

comical or not, professional or not, sds800x cannot see 400-500MHz even on one channel active, prove me wrong.

29

Projects, Designs, and Technical Stuff / Re: Accurate sine wave in terms of amplitude

« Last post by Terry Bites on Today at 03:39:24 pm »

That DDS chip has an output stabilty quoted as "200  ppm/°C" not great, but then DDS is aimed at RF where no one cares much about precise amplitudes.

Brew up your own DDS, you don't need all that parameter register nonsense or a micro doodad to control it.

Back in the day, before low cost microcontroller platforms had been dreamt of, I made a sine source for an LVDT sensor using a lookup table on a M27C1024 eprom (still to be found on ebay and in my 90's junk box). I used a TCXO and some counters to create the address lines, 74LS590s but dont quote me on that. Driving an AD669 bolted to a REF01 10v reference. A fat buffer amp on the end and I had a 16 bit rock solid 10v pp waveform. It was overkill for my LVDT but fun to make. There's none of that control loop rubbish to worry about here.  A proud day in Terryland, no pay riase though.  Of course, you can easily tune it using the counter's clocks. Add your own precsion attenuators and gain. A very simple antialias filter might be needed to polish off remaining clock residue.

Calculate a Sine LUT here www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml

30

Test Equipment / Re: SDS800X HD Wanted Features

« Last post by mawyatt on Today at 03:38:14 pm »

Can one imagine what we would end up with if all the wants, don't likes, stuff this and that in, make it do this and that, and so on, would create?  Designed by Committee seems to fit, but Complete Cluster F**K seems better

The old HP and Tektronix didn't yield to all this type of BS, they had a group of knowledgable engineers/scientist, were actual in-house users, that decided how the instrument would be configured and built.

If a potential user didn't like what HP and Tek offered, wanted this and that, tuff then user could go somewhere else, or fly a kite!! We the users learned to use and operate the HP and Tek equipment like it was intended for, and generally for the better!!

Why, simply because HP and Tek engineers were more knowledgeable about their own instruments than any users, and we the end users learned and benefited from these Masters. Folks that didn't learn from this user experience unfortunately ended up being managers/excutives, and later this trickled up into HP and Tek pyramid which lead to their own demise

Hopefully Siglent will have limited BW and only listen to the very few knowledgable folks, which we know who they are!!

Best,