Re: Time Domain Reflectometer (was Re: internet outages)
- Date: Mon, 24 Dec 2018 07:12:37 -0500
- From: Gene Heskett <gheskett@xxxxxxxxxxx>
- Subject: Re: Time Domain Reflectometer (was Re: internet outages)
On Sunday 23 December 2018 23:54:20 John Hasler wrote:
> rhkramer writes:
> > Yeah, but I wasn't thinking about actually using a CRT to display
> > the signal in real time, but, instead, collect samples (at maybe 4
> > GHz??), store them, and then display them as a static display.
> At that sort of frequency sampling scopes (including the old crt ones)
> sample at far below the signal repitition rate.
And depend on being out of synch with a repetitive signal, so they in
effect build up an image that covers enough time samples to assemble the
waveform. So you do not see it in real time. But the glitch is still
caught, and you will see a full brightness dot or pulse thats out of
place. 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.
Probably also true of servo-motors today since they are often driven at
full power with pwm signals. Much more efficient to make the motors
inductance work for you instead of against you. The drivers will heat at
1% or less compared to an analogue drive with the same effective gain
and power. They heat only during the transition, with very little heat
when on, and no heat when off. So the faster you can make that
transition, the cooler it stays. I use such an amplifier thats not much
bigger than a pack of camel cigarettes, to run a 1hp at 90 volts at 9.7
amps rated spindle motor on a 127 volt, 20+ amp capable supply, so it
can do in a short 1/2 second surge, around 2 hp. I've never scanned the
heat sink with an IR thermometer and found it above 85F in a 75F room.
The only time I hear it is when this amplifier regulates the current,
which I've set at 17 amps, makeing the motor iron "chirp". I figure
thats enough considering that the gear train its driving is plastic.
Cheers, Gene Heskett
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