[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: [TCML] ocilloscope: Yep, I blew mine, too



For measuring the high voltage on Geiger counters, which run between 550 and 1500 volts, we use a divider with a 1 Gigohm resistor inline with a DMM (and a few trimmer resistors to even it out and increase accuracy).  The HV power supplies in them for the Geiger-Mueller tubes and photomultipliers produce very little current, and even a 100MOhm network loads down the supply too much, resulting in erroneous readings.  Good DMMs are around 10 Meg input impedance, whereas the el cheapo Harbor Freight Chinese specials are only around 1 meg!  But for measuring real high voltage, like others have said, using multiple single resistors will help prevent flashover.  You can add them up to make a 1-Gig divider.  Incidentally, in those old yellow CDV-715 survey meters (ion chamber units, NOT Geiger counters, as the liars on ebay call them) are some very high-value resistors in the range switch setup.

Nick A





> From: william_b_noble@xxxxxxx
> To: tesla@xxxxxxxxxx
> Subject: Re: [TCML] ocilloscope: Yep, I blew mine, too
> Date: Sun, 1 Nov 2009 07:36:22 -0800
> 
> 1. you will find that a vacuum tube scope is much more tolerant of 
> overvoltages with low current
> 2. you can make an HV resistor by putting many LV resistors in series - make 
> your 100 meg (10 is way too low) resistor out of 100 1 meg resistors in 
> series, put it in a plastic sleeve and fill sleeve with HV grease
> 
> --------------------------------------------------
> From: <Davetracer@xxxxxxx>
> Sent: Saturday, October 31, 2009 10:00 AM
> To: <tesla@xxxxxxxxxx>
> Subject: Re: [TCML] ocilloscope: Yep, I blew mine, too
> 

 		 	   		  
_________________________________________________________________
Hotmail: Trusted email with powerful SPAM protection.
http://clk.atdmt.com/GBL/go/177141665/direct/01/_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla