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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.
Recent Posts
2
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.
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.
3
Test Equipment / Re: Choosing between entry-level 12-bit DSOs
« Last post by Mechatrommer on Today at 03:42:23 pm »comical or not, professional or not, sds800x cannot see 400-500MHz even on one channel active, prove me wrong.Difference is that "the other" scope actually does work as 4ch 200MHz BW scope.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.
At all times, no special conditions..
4
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.
DIY your own DDS:
Back in the day, before low cost microcontroller platforms and social media 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), some counters (74LS590 i think) and an AD669 (still available) with a REF01 10v reference. That was 16 bits of rock solid 10v pp waveform! No control loop rubbish to worry about. For your puposes a very simple antialias filter is needed to polish off any clock residues. Of course you can easily tune it up using the counter's clocks. Add your own precsion attenuators and gain. Feels good....
I think a pwm source driven by code or from a lookup table could do just as well. Precision clamp the PWM amplitude, nice lowpass filter, job done. The Arduio can create 16 bit PWM using its internal timers. Sine dump here www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml
DIY your own DDS:
Back in the day, before low cost microcontroller platforms and social media 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), some counters (74LS590 i think) and an AD669 (still available) with a REF01 10v reference. That was 16 bits of rock solid 10v pp waveform! No control loop rubbish to worry about. For your puposes a very simple antialias filter is needed to polish off any clock residues. Of course you can easily tune it up using the counter's clocks. Add your own precsion attenuators and gain. Feels good....
I think a pwm source driven by code or from a lookup table could do just as well. Precision clamp the PWM amplitude, nice lowpass filter, job done. The Arduio can create 16 bit PWM using its internal timers. Sine dump here www.daycounter.com/Calculators/Sine-Generator-Calculator.phtml
5
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,
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,
6
Other Equipment & Products / Re: Lets see your Nixie Tube equipment
« Last post by Dave Wise on Today at 03:38:11 pm »My Monsanto model 2000 Digital Voltmeter. DC Volts only. Easy on the eyes 20000-count non-multiplexed display required many many RTL integrated circuits for counters and latches. As far as I can tell, this is Monsanto's only DVM ever. I never found any advertisements for it, just an oblique mention of "a digital voltmeter" in an article from Chemical Engineering News January 1966 edition... which I can't find anymore. Gift from the late noted Tektronix collector Stan Griffiths.
It uses a single-slope converter with an electromechanical "Synchroverter" chopper. Communication across Guard is two pulse transformers with interesting signal timing. The automatic polarity switching is awkward and went through significant mods that appear to be from the factory, and it was still flawed - to measure a guarded negative voltage you had to manually connect GUARD to the IN terminal instead of the COMMON terminal. I fixed that by changing the circuit yet again. Other changes I made ended up inserting two microcontrollers to correct some timing glitches. It's kind of a Frankenstein but it works.
It uses a single-slope converter with an electromechanical "Synchroverter" chopper. Communication across Guard is two pulse transformers with interesting signal timing. The automatic polarity switching is awkward and went through significant mods that appear to be from the factory, and it was still flawed - to measure a guarded negative voltage you had to manually connect GUARD to the IN terminal instead of the COMMON terminal. I fixed that by changing the circuit yet again. Other changes I made ended up inserting two microcontrollers to correct some timing glitches. It's kind of a Frankenstein but it works.
7
Repair / Re: Laser Level Charger PCB ID
« Last post by Shaky on Today at 03:36:24 pm »Well, all I can say is WOW ! Thanks for the comprehensive reply @globoy but unfortunately, it looks like repair is way above my pay grade 
All I have available to me is a mid-range digi multimeter, no scopes or anything like that. It was basically an attempt at trying to save a mate (who doesn't do anything electrical at all, let alone electronics) a few quid
If it helps, the wall-wart outputs 5v, the battery is showing 3.6v but there is 0 volts on the + & - brass pins on the pack. Funnily enough, there is 3.6v between the - & the Y pin, which made me think it was just a simple charger/bms.
Ah well, I'll let him know that he'll have to wait for the packs to come back in stock.
Thanks again for the reply, it's appreciated.
All I have available to me is a mid-range digi multimeter, no scopes or anything like that. It was basically an attempt at trying to save a mate (who doesn't do anything electrical at all, let alone electronics) a few quid
If it helps, the wall-wart outputs 5v, the battery is showing 3.6v but there is 0 volts on the + & - brass pins on the pack. Funnily enough, there is 3.6v between the - & the Y pin, which made me think it was just a simple charger/bms.
Ah well, I'll let him know that he'll have to wait for the packs to come back in stock.
Thanks again for the reply, it's appreciated.
8
Test Equipment / Re: Choosing between entry-level 12-bit DSOs
« Last post by Fungus on Today at 03:33:43 pm »Simply put, Rigol hit a Home Run with the DHO800 introduction, then Siglent hit a Grand Slam with the SDS800 introduction
Yep, there's no way the Siglent boys will ever make me regret buying mine or that it's in any way insufficient for my work.
As good as the Rigol DHO800 is, and it's good, really good is every aspect, the Siglent SDS800 is just overall better IMO.
On paper, sure, but my question is how much of that translates into an advantage in practice.
Sure, there's some people who need 4 channels at 200Mhz over 50 Ohm coax that but I'm not buying that every single EEVBLOG member does.
I'm also not buying that those people wouldn't be far better off with a 2000-series 'scope at 350MHz. which seems to be an area where Siglent is supreme. "200Mhz" seems like a very arbitrary number to me.
So let's list the advantages of each and not try to say one is "better". Numbers aren't everything, one size doesn't fit all.
So when we reach for a DSO, now we reach for the SDS800, usually with the Rigol probes tho (these are really good, better than the Siglent IMO)
Rigol has their own ASICS so Siglent's margins are probably a lot thinner to be able to be sell at the same price point. Things like the probes will be the first to suffer.
9
Test Equipment / Re: Enabling options on Agilent ESA series E4402B E4404B E4405B E4407B
« Last post by Larry_Bridge on Today at 03:30:31 pm »Thank you very much.
I will check and let you know.
I will check and let you know.
10
Beginners / Re: How Current Limitation is happening in the circuit???
« Last post by ommsiva on Today at 03:29:16 pm »Mam,
Sorry, absolutely you are correct. It's my mistake, each picture were nearly 6mb and our site allows maximum of 8mb totally for a reply.so i reduced the image size .Now I have disconnected power transistor from heat sink out of frustration.
Sorry, absolutely you are correct. It's my mistake, each picture were nearly 6mb and our site allows maximum of 8mb totally for a reply.so i reduced the image size .Now I have disconnected power transistor from heat sink out of frustration.