Re: Terry's DRSSTC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Greg Leyh <lod@xxxxxxxxxxx>

Hi Terry,

Looks like a lot of very clean design work.  What PCB capture are you using?


> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> Lots of busy work these days but it is getting there...
>
> I have the fiber-optic link working and got the current measurement 
> figured out now:
>
> http://drsstc.com/~terrell/pictures/CTs-FiberRec.JPG
>
> The fiber optic link works perfectly but it was unexpectedly inverted:
>
> http://drsstc.com/~terrell/pictures/Fiber-Optic-Output.gif
>
> http://drsstc.com/~terrell/schematics/CurrentMeasurement.gif
>
> No problem since I have extra inverter gates...  I did switch to Agilent 
> HFBR-2412T receivers since they have a perfect open collector digital 
> output with no fuss...
>
> The analog and digital current signals are fine be a bit delayed:
>
> http://drsstc.com/~terrell/pictures/CurrentMeasurementAnalogCT.gif
>
> http://drsstc.com/~terrell/pictures/CurrentMeasurementDigitalCT-clipped.gif
>
> Seems the CTs have about 400nS of lag.  Have to work on that...  I used 
> 1N5819s in series with 4.7V 5W Zeners.  The capacitance of the Zenors acts 
> like nice rail power supplies and charges very fast:
>
> http://drsstc.com/~terrell/pictures/CurrentMeasurementDigitalCT-startup.gif
>
> That eliminates a lot of silly circuitry while giving super fast low-Z 
> signals.  A simple resistor and 1N4148 clips the negative side on the 
> controller to feed the digital stuff:
>
> http://drsstc.com/~terrell/schematics/Controller.gif
>
>
> We are always asking about what to use as RF and AC ground.  We like to 
> hook them together but we don't want the RF to get into the AC 
> grounding...  I really like the blocking inductor for that:
>
> http://drsstc.com/~terrell/schematics/PowerFilter.gif
>
> Mine is 7.5uH now:
>
> http://drsstc.com/~terrell/pictures/GroundInductor.jpg
>
> Just a simple 10 turn inductor on a Delrin form.  At 60 Hz AC its 
> resistance is only 0.003 ohms allowing the AC ground to keep everything 
> safe.  But at say 100kHz it's resistance is 5 ohms so RF currents should 
> be pushed into the RF grounding and not the AC grounding.
>
> The protection board gets here monday so that will be interesting to see 
> how badly I screwed that all up :o))
>
> http://drsstc.com/~terrell/pcbart/ProtectionCard.gif
>
> Mostly testing circuits these days...
>
> Cheers,
>
>     Terry