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Projects, Designs, and Technical Stuff / Re: high voltage opamp?
« Last post by macboy on Today at 03:59:00 AM »
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What solutions do good multimeters use? They have a way more extreme job, they have to measure 10uA to 10A, in  mV to 750V range,

Multimeters measure the voltage across a switched current shunt and are floating so there is none of this high side and low side nonsense.  As far as the multimeter is concerned, it is just another low, typically 100s of milivolts, voltage measurement.  Duplicating this would be more expensive and complex; it means floating the analog to digital converter to the high voltage supply.
Exactly. All multimeters, even the cheapest ones, have an optically-isolated output! You look at the screen with your eyes, so the multimeter can sit happily at hundreds of volts above or below ground (and your body) without issue. You don't need a common ground connection to the multimeter to view its screen  :-DMM

The usual issue with high-side current measurement is that you need to shift that measurement result back down to ground/common for use by the circuitry which needs the current measurement in the first place. Unless of course that circuitry can reside on the high side as well.

Of course the OP didn't even say if the measured current is going to be used by anything other than human eyes. Maybe the best solution is a simple panel meter with a transformer-isolated floating supply? Too many assumptions.
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Test Equipment / Re: HP 5385A
« Last post by metrologist on Today at 03:58:19 AM »
I have not installed the oscillator shown, but that one will fit. I'll need to build it onto a daughter board with the tuning circuit, just have not had time. It was easier to use an external reference.
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General Chat / Re: Alien or Driftrock...
« Last post by brucehoult on Today at 03:57:08 AM »
Likewise, it's average speed of 26.3 km/s (58 kilo-miles per hourjust to make the imperial and metric fanboys cringe) isn't that fast in the scheme of things - though it does have the fasted inbound velocity at 200AU compared to other Oort cloud objects.

It seems to have not been going anywhere particularly fast with respect to our Galaxy, but has more or less been run down by our Sun as it tootles along in its galactic orbit.

It's going somewhere now! Got a pretty good slingshot.
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Beginners / Re: What kind of liquid flux?
« Last post by GreyWoolfe on Today at 03:56:17 AM »
I use MG Chemicals 835 liquid RMA flux.  I dispense from a small squeeze bottle with a needle tip.  It works well for me.
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Test Equipment / Re: Understanding what to read on this FFT Plot
« Last post by trys on Today at 03:56:01 AM »
I've really learnt a great deal from all your replies - thank you so much.

I've found the Blackman window to be the easiest to work with for finding harmonics. The strange thing is that FFT seems to literally work off the image of the scope signal itself (rather than the underlying signal) so if I alter period until until I get Moire patterns then the corresponding FFT display goes pretty silly too, (or say if I set a volts/div too low).

Not having much luck with FFT from the memory.

SO the good news is, that using your suggestions I've managed to get down to about 100dB on an USB soundcard (the oscillator and laptop both on batteries, short coax). Using ARTA at the moment, and also sampling into Audacity and using the spectrum analyzer option.

I have considered going in the middle of a field somewhere with it, but I'm not quite mad enough to have that level of dedication at the moment. It's also very cold.

Octave is very easy to use, though interpreting the results is a bit more difficult. 
Search on "Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon"
It's the title of  an article by Jim Williams which appears in his book "Analog Circuit Design".  It's a great article.

That's a very interesting article indeed - I thought I'd stumbled on the wrong one at first with it starting with an obituary.

As it turns out I've done FFT measurements on a wien bridge oscillator before: https://tinyurl.com/ybtjyqtk

TMM - you've really set me on the right path with your reply - just what I needed. Your article on your findings of the Wien bridge oscillator was very useful too. I'm now on my fourth bulb that I'm trying out and observing their effects. It also comes down to how much power the op amp can source (to feed the negative feedback) too it seems. I've observed very similar findings in substituting standard ceramics with metal foil types.

That's partly why it's taken me so long to reply!!

Thanks everybody again for the replies, very much appreciated as always. I've learnt a great deal over the last week or so.

Trys

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General Chat / Re: Bye bye FM
« Last post by JPortici on Today at 03:54:17 AM »
That is why even AM radio stations are not only hanging on but actually doing well.  Commuting hours are the coveted time slots for shows.  Some shows boast the millions of listeners they have.

Precisely. I also listen to the radio at work, because radio means that my eyes are free to do something else.

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Almost every car has an analog AM/FM radio, almost none has digital AM/FM radio.  So day one, you will go from thousands/millions to almost none.

That may be related to what james_s said, because from what i know here in italy (and i think in europe) every new car since 2010 or so has DAB+ compatible radios
I also prefer analog, though, because i used to commute/travel by train in areas with very poor reception (valleys) but i could hear the radio even if it was swamped with noise
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I  would get the scope out and look on the mains myself, but the boss won’t let me do this kind of investigation unless I provide some proof up front.
Does boss = wife? I really get the impression you are a cottage industry trying to make a buck off of the industry that has sprung up around people growing medicinal plants at home?  You've read enough to get a product out the door but are just now learning engineering has lots of quirks you haven't learned yet?
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Repair / Re: Agilent/HP E3646A Repair
« Last post by Ordinaryman1971 on Today at 03:51:49 AM »
Would you be willing to list the components you've found faulty.
One of mine developed the same problem few days ago. When I turn it on, the display comes to life but goes dead right after.
I've swapped control board from the other unit and the display as well as the power supply are fine.
So, the fault is on the control board. It looks like the same trouble you had.
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Test Equipment / Re: Strange signal shift on Siglent SDS1202X-E
« Last post by StillTrying on Today at 03:51:25 AM »
Have you tried all 3 probes on the same signal.

Tried finding the EXT/5 signal's center position by adjusting the trigger level up and down.

Some of the displayed X trigger positions don't make much sense to me, on the last one SDS00019.png (and others) the X trigger marker is nowhere near the CH1 signal's rising edge.

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KiCad / Re: Switches on Schematic Do not Create Ratwires on Board
« Last post by hermit on Today at 03:47:38 AM »
I was on the right track, wrong view. ;)  I'm so automatic about making those changes when I import the netlist I don't know what it looks and what problems it solves when you don't do it.
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