Terry's DRSSTC

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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