I've added resistors in series with R1008 and R1044 to bring the resistance
for those parts of the A divider to a value that it would calibrate OK (two
of the resistor sets in the oil bath very low in value). I also had to
remove five turns (about 1.3 Ohms) from R1051 as the combined value of R31
Hi Dave,
I think you need to review how to calibrate the 720A and Kelvin Varley
dividers in general. The loading you need to worry about is the load
you put on the output terminals, irrespective of the particular decade.
I do not know how you are measuring the output, but it would appear,
f
David:
First suggestion would be to see what the output measures, with the
input still set to 100.0014 volts (same as before), when setting the dials
to:
0.9X(equivalent to setting the "A" decade to "0.1")
1.9X(equivalent to setting the "A" decade to "0
David:
Ignore my previous post. In thinking about this while out shopping this
morning I know the answer.
The output resistance of the 720A is about 66k ohms. Your voltmeter has
an input resistance of 10 megohms. You are simply loading the output of the
720A. The reason that the 0.1 r
Drats! That was most of the problem! Moving down to 10V where the 3458A has
an input impedance of >10GOhm, and I see much more sensible results.
Thank you
Dave
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of wb6bnq
Sent: 07 August 2017 11:19
To: Disc
Thanks
Dave
-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Bill Gold
Sent: 07 August 2017 19:22
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Update on 720A
David:
Ignore my previous post. In thinking about this while ou
Update: After changing the resistor I added in series with R1008 (A decade
position 1.0) from 204.8 to 202.4 Ohms (I wonder if this means that R302 is
slowly increasing in value back towards nominal) and re-calibrating again, the
A decade is now within 1ppm of linear (using the 10V range and no
