From: nojunk@knology.net   
      
   On 9/25/2018 10:06 AM, Tom Gardner wrote:   
   > On 25/09/18 15:34, George Herold wrote:   
   >> I was thinking of making a DC (slow) x100 'scope probe by adding a   
   >> series 100 meg ohm resistor.  Any thing I should look out for?   
   >>   
   >> George H.   
   >>   
   >   
   > Don't forget the point David Hess frequently makes...   
   >   
   > If you are relying on the scope's 10Mohm input resistance   
   > to form the lower leg of the potential divider, then consider   
   > what happens if you turn the scope to AC input coupling. The   
   > *entire* input voltage appears across the scope's AC coupling   
   > capacitor.   
   >   
   > That can and should be avoided by having a probe with the   
   > potential divider made from two resistors, one for the upper   
   > leg and the other is (in parallel with the scope/s input)   
   > the lower leg.   
      
   I described this in a later post, but I adjusted the resistor divider   
   to make up for the loading of the probe, so it will be 100X with the   
   the probe attached.   
      
   >   
   >  ... how about an on board voltage divider.   
   > 10meg from your source to a 1.39meg to ground. Place your 10meg scope probe   
   at the junction.   
   >This is will display as a 10 to 1 ratio of the initial HV. This assumes your   
   HV source will   
   >drive an 11.22 Meg load without appreciable sag and that your probe is 10meg   
   at the frequency   
   > of interest.   
      
                                       Mikek   
      
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