Re: Metering my x-ray supply (fwd)

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---------- Forwarded message ----------
Date: Wed, 10 Nov 2004 16:46:27 -0500
From: David Speck <dave@xxxxxxxxxxxxxxxx>
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: Metering my x-ray supply (fwd)

Dave,
High voltage probes come up all the time on eBay.  B&K makes nice ones 
rated for 40 or 80 KV, and you can usually score them for under $50.00, 
all ready made, and compensated. 

Best way to measure high DC currents without making contact with any 
potentially high voltages is to use LEM current transducers.  These look 
like current transformers, but can sense both AC and DC current 
simultaneously.  I've seen units rated 100 to 500 amps go on eBay for 
3/$10.00.  They require +/- 15 volts DC input, and a burden resistor, 
just like a current transformer, but then you look at the voltage across 
the resistor with a scope or meter, just like you would with an iron 
core current transformer (which can see AC only).  Nice thing about the 
LEM units is that they do not produce high output voltages if you pass 
current through their sense openings without a burden resistor, and they 
are not damaged if left in circuit without being powered.  The tech 
support at LEM is very friendly to deal with.  If the 100 amp sensor is 
too low a sensitivity for you, then pass the primary wire through the 
core for 5 turns, and you'll have a 20 amp full scale unit, or twice for 
a 50 amp full scale unit. 

HTH,

Dave

>Hi all, I am interested in making or possibly buying a high voltage probe,
>so I am interested if anyone has any tried designs. Also where would I get
>the mega-OHM resistors cheaply? On the other hand if I could find a 40KV
>probe for less then ~$50 I would love to trade or purchase it! ;-)
>
>I also need to find a reliable way to measure the tube filament DC current.
>Anyone have a reliable method using easily obtained parts?
>
>Thanks, David Trimmell
>