Re: HV Measurement - Back to Basics

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Sharpe by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

Rick

Several questions concerning your HV monitor (nice design BTW)...
1.  How is accuracy when compared to a known voltage source
      like a PT under no load conditions?
2.  Have you used with an operating TC?  If so, can you distinguish
      in utility wave where the SG is firing relative to position on AC
      waveform?

Reason I'm asking is look at using similar instrumentation op-amp
front end driving an analog opto-isolator to drive HV meter and SG
"synchroscope", I need negative notches in AC waveform when
gap fires for operating my display.  Also need to include a +Voffset
that is removed on opposite side of opto-coupler for linear monopolar
operation.  I'm passing HV through a current limiting resistor, then a
bridge rectifier of 1N4148's to load resistor.  Input to bridge has
zener, neon, and varistor protection.  The instrument amp and
optocoupler now is mono-polar.  Any differences in diode conduction
are swamped by vast resistances of circuit (current limiter is 30, 330K
2W 5% carbon film on each side as your 495MegOhm).  Safety
factor thermal is better then 500%, 200-250% for HV BIL..

Looking at a different approach for opto then simple circuit for much
improved accuracy (IL300 or TIL300 LOC).  Cheap, much higher
performance, bandpass>200Khz, 2.5kVAC isolation.  Was looking at
other circuit because I needed no active components on the "high side".
Since I need them now to establish a LED '0' baseline, and have to
design and build a isolated PS anyway... Might as well design as
much precision as possible into circuit.

Best Regards
Dave Sharpe, TCBOR
Chestefield, VA. USA

Tesla list wrote:

 > Original poster: "Richard W. by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <potluck-at-xmission-dot-com>
 >
 > Hi all,
 >
 > Here's the schematic of a high voltage buffer I've been using for quite some
 > time now. Works great. You can use either a voltmeter or O-scope.
 > Calibration is done with a known voltage source and a good meter. And as
 > mentioned elsewhere I employ the "No-Touch" method when in use.
 >
 > ftp://ftp.xmission-dot-com/pub/users/p/potluck/pics/HV-buffer.jpg
 >
 > Here is a pic of the actual project.
 >
 > ftp://ftp.xmission-dot-com/pub/users/p/potluck/pics/HV-Buffer.jpg
 >
 > Rick W.
 > Salt Lake
 >
 > -<<SNIPPO>>