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RE: Primary Scoping
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To: "tesla-at-objinc-dot-com (postings)" <tesla-at-objinc-dot-com>
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Subject: RE: Primary Scoping
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From: "Zublin, Bryan (SD-MS)" <BZUBLIN-at-gi-dot-com>
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Date: Tue, 27 Feb 1996 18:36:00 -0800 (PST)
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>I have thought about using a 1000:1 divider ratio using 4 of the dale
>100Megohm resistors in series to a 5 parallel combination of 2megohm
carbon
>comp resistors. I'll then put some transorbs to ground before the scope
>connection. All components will be physically well mounted to prevent
>circuit disconnection.
>BTW, transorbs can be thought of as a 5ps.(thats not a typo: 5*10^-12
>second) zener with a many thousand Amp ratting. By using 2 of the
>unidirectional devices in antiparallel I can get any clamp voltage between
5
>and 500 volts with only a 200pF capacitance penality.
You've just built a lowpass filter with a cutoff frequency of 2 Hz! So you
won't see too much of the signal you are trying to measure (100's KHz).
Fc = 1/(2*pi*R*C) = 1/(2*3.14*400e6*200e-12) = 2 Hz.
With such large resistors, any capacitance is going to severely reduce the
frequency response. This includes the cables and scope input capacitance.
Bryan Zublin
bzublin-at-gi-dot-com