Electronics > Metrology

Yet Another Hammon Divider (YAHD)

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rockstedy40:
Dave,

   Thank you for sharing your test results.  I'm still a little new to the Hammon Divider nomenclature, so I'm not following the configurations you tested.  Would you please explain in more detail, or possibly a sketch/schematic?  (I used to love Bob Pease's sketches.  Zero time creating, and 100% info)

  I like the idea of a fan to minimize self heating.  That had crossed my mind but was thinking that it might introduce more problems than it solves, but maybe not.

Thanks
Bob
p.s.  I'm still working through some final trim configurations for my divider, after "aging" the resistors for several days at 115 deg C.

bastl_r:
What is the key advantage of a Hammon divider?
When switching 10 to 1, due to the changing input impedance, there is a changing load on the input voltage.
And I have already noticed in my Solartron 7065 when measuring at its reference that the standard impedance of 10M of a 34401 is much too low and causes a change.

regards

Kleinstein:
For precision measurements it is standard to have more then 10 M input impedance at the meter. The 34401 also supports this for the lower ranges (up to 10 V).

The point is a relatively simple circuit to get a divider quite close to 1:10. The loading on the input side would not be an issue for a proper voltage source with driven and sense lines. Just a simpel 2 wire connection may not be good enough.

bastl_r:
In the meantime I know that too and had also found out how to activate the 10G mode on the 34401.

From the knowledge of these measurements, I am somewhat surprised that the Hammon divider is given so much importance in the dimensioning of the resistors.
After all, the input resistance is reduced by a factor of 100 in the example of the start article. Therefore, I wonder why such "small" resistors are used at all.
In the end, it might be cheaper and more practical to use a small Kelvin-Varley divider. These are available again and again with four decades for small money on ebay.  I had toyed with the idea of building a Hammon divider with 0.01% resistors. But since I have a small decade from Muirhead I will spare myself that....

Gyro:
The thing about a Hamon divider is that you can make it 'self-calibrating'. Having an accurate 10:1 ratio divider is very useful for calibration purposes. With ebay purchased KVDs etc, you are relying on their last-calibrated accuracy, they can drift over time, might have been overloaded etc. without your knowledge, unless you get them re-calibrated.


P.S. I built my own Hamon divider too, and also have a Muirhead potentiometric (non-KVD) constant resistance 4 decade voltage divider. I use both. The Muirhead is pretty close, but only trust the calibration of the Hamon.

https://www.eevblog.com/forum/metrology/anyone-else-built-a-hamon-divider/

https://www.eevblog.com/forum/testgear/kelvin-varley-reistor-porn/msg773770/#msg773770

It's also worth reading the manual for the Fluke 752A (self calibrating Hamon)

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