Re: Time Domain Reflectometer (was Re: internet outages)
- Date: Mon, 24 Dec 2018 08:42:31 -0500
- From: Gene Heskett <gheskett@xxxxxxxxxxx>
- Subject: Re: Time Domain Reflectometer (was Re: internet outages)
On Monday 24 December 2018 08:21:57 John Hasler wrote:
> Gene writes:
> > In a cnc machine running on stepper motors, the current regulating
> > of the drivers if the grounding is not truly single point, can
> > crosstalk at the regulating frequency, usually well above 20
> > kilohertz, at peak voltages well over what it takes to destroy an
> > fpga gate as the ringing in that event often peaks at over 100 MHz
> > and 30
> > volts. Trivial to see on the samplers display, but turn off the room
> > lights and really study what you see on a 100+ megahertz analogue
> > scope.
> For that sort of thing you want a storage scope. Old Nicolets are
> readily available for prices that even I can almost justify.
> I used Tektronix analog storage scopes when doing motor control design
> in the seventies but the digital ones are orders of magnitude better.
> Being able to trigger on things that already happened is cool.
> Before that it was cameras.
> As to TDRs, if you can get by without actually seeing pictures of all
> the impedence bumps you can get by with a fast counter, a high
> risetime pulse generator, and a couple of fast comparators. Maybe $20
> at Digikey.
I dunno if I could tolerate losing the pix, this old f--- has had a scope
probe in one hand since 1951.
Cheers, Gene Heskett
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