Input RC Standardizers
John Doran <johnd@...>
Tektronix specifies the use of "input RC standardizers" in their
calibration procedures for vertical input attenuators. For example,
the procedure for their 1A2 plug-in unit specifies:
Tektronix part no. 011-0073-00, time constant 1 megohm
x 15 pF; attenuation 2X.
What sort of network lives inside the RC standardizer? I'd like to
build one; I imagine a few other folks need one too!
--- In TekScopes@yahoogroups.com, "John Doran" <johnd@e...> wrote:
It's a 1 Mohm resistor in parallell with one fixed and one variable
capacitor connected between the input and output of the box.
I placed a copy of the old data sheet at
Craig Sawyers <c.sawyers@...>
Tektronix part no. 011-0073-00, time constant 1 megohmThey are a parallel combination of a resistor, a fixed ceramic capacitor,
and a variable capacitor. I think the resistor is always 1M. The 15pF one
has a 12pF fixed capacitor, and a variable 1.5-7pF cap.
Of course, that begs the question - how to adjust the variable cap? Have a
look in the archives for Stan's suggested method...basically use a bridge to
set the input cap of a plug-in to nominal. Then plug in the standardiser,
and apply a square wave. Adjust the standardiser to give flat top.
You need to have the PI powered when setting using the bridge - the input C
is dependent on having bias on the input devices, particulaly if they are
JFETs. Then you have to get the bridge real close to the PI to reduce
parasitic C. Or use a 130LC. But that uses a UHF connector, and if you use
a UHF-BNC adaptor, that adds about 2pF - it is all a bit of a nightmare
Now use the standardiser to adjust all your PI's to the same nominal input
C. The idea is not to have to tweak a scope probe as you move from PI to
PI. So is it really worth it?
Stan & Patricia Griffiths <w7ni@...>
Hi John,toggle quoted messageShow quoted text
You can use a properly compensated probe instead of the RC "Standardizer" if
you want to . . .
----- Original Message -----
From: "John Doran" <firstname.lastname@example.org>
Sent: Wednesday, September 17, 2003 9:56 AM
Subject: [TekScopes] Input RC Standardizers