Re: funky voltage readings [solved]

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader by way of Terry Fritz <teslalist-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Sent: Saturday, June 14, 2003 6:09 PM
Subject: Re: funky voltage readings [solved]


 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Ken,
 >
 > I had never used the HP34401 with the HV probe before...  120VAC reads
 > 61.536mVAC on the HP and 115.37mVAC on a cheap China meter.

Ha! HP tried too hard on this meter.

 > R301 and R302 going into U301 (buffer) are 500K each and that is where the
 > 1M comes from.  The impedance would be "high" without those resistors.
But
 > they need to have that low impedance to get the frequency response up into
 > the 100kHz region.  They actually use programmable variable caps to

Eek. That stuff should be some option you need to enable in programming. The
34401 is basically a computer that looks like a meter.

 > compensate the meter for higher frequencies and apparently mix in a 50kHz
 > calibration signal too.  Page 100 of the 34401A service guide tells about
 > it.  somebody spent a lot of time (too much) thinking about this
circuitry!

The best part is it's defeated by any cheap-o meter, at least at low
voltages and frequencies. The other ranges in the meter are great, and the
math features are handy too. I guess if you're not dealing with just a few
uA, the AC ranges are excellent.

 > I guess if you wanted a "normal" meter, you would not use the HP 34401
 > ;-))  Low-level high-frequency AC readings on the HP are also weird
 > too.  You can probably just go to 1 digit of precision in that case
 > :o)  Otherwise it is a super meter but it does have some odd moments.

I just found a used Leader RMS analog meter to take care of strange signals
I need to measure. Digital stuff is really obnoxious for many sorts of
measurements.

 > The probes sheet at:
 >
 >
http://we.home.agilent-dot-com/cgi-bin/bvpub/agilent/Product/cp_Product.jsp?LANGUAGE_CODE=eng&ID=1000003703%3aepsg%3apro&COUNTRY_CODE=ZZ&CT=0
 >
 > States: "The Agilent 34136A is only compatible with the Agilent
 > 34401A.".  I bet they blew it and that was supposed to say "NOT"
compatible!!

I got this probe because it can be used for simple (maybe not so simple)
60Hz measurements. My other probes are the TV flyback tester with stick and
tiny meter built in units, which is fine for DC, but you're still out of
luck fo AC.

KEN