Re: New Chat: Question: Understanding a scope probe #chat-notice


Tom Lee
 

In a word, bandwidth. VTVM's don't need it, scopes do.

If you want the nitty-gritty, email me off list and I'll send you a writeup with more detail than anyone wants.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/18/2021 23:03, TekScopes@groups.io Notification wrote:

A new chat has been created:

New

I would like to better understand the components in a scope probe. But first I should clarify my beliefs about a VTVM. As I understand it, most VTVM's have a plain ordinary wire with a pointed probe tip. Any wire would do. The probe runs into the VTVM, where the first thing the signal goes through is an 11Mohm resistor, before going on to an amplifier to run the meter that reads out the voltage. The purpose of the amplifier being to amplify the signal by an amount that compensates for the gigantic drop in strength from the 11Mohm resistor, so that the meter reads actual voltage. The purpose being to sample a very tiny amount of "water running through a pipe" to give a pressure reading. Compared to a regular VOM which would require such a large amount of "water in a pipe", that it would actually cause a drop in "water pressure" just to run the meter, that the reading would be useless. Have I made a good analogy? If so, why does an oscilloscope probe utilize a capacitor in parallel with the 11Mohm resistor, when the VTVM doesn't? What is the purpose of that capacitor? Thank you.

*By:* henryfinley <tomsradio@gmx.com>

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