Kelvin Varley Divider design - one little question

[cape zoloh]

I've seen KVDs following the rule of 10k-2k-400r-80r-16r..... - each following resistor ladder uses resistors with a resistance 1/5th of the previous one.
I've also seen designs when they use several 10k ladders in a row, and that seems to work as well.
It would be very practical if one could use only 10k resistors for all ladders.

Is that possible? If not, why?

Thanks!

[MosherIV]

It would be very practical if one could use only 10k resistors for all ladders.

Is that possible? If not, why?

No it will not work.

Each stage of the kvd forms a voltage divider network with the previous stage.
If the resistor are all the same, the divider is all wrong for the next stage.

Design where they use a couple of 10K in a row have been carefully work out to make sure the ratios still work.

Hope I have explained it clearly enough.

[Dave]

No it will not work.

Yes, it will work.

The real reason why you wouldn't want to use all equal value resistors is that barely any current is going to flow through the lower digit circuits. This means that the output voltage is going to be very easily disturbed by any input bias currents that the null meter might be producing.
Having a KVD with progressively lower resistances towards the lower the digits means that the current is larger, mitigating this problem to some extent.

[The Soulman]

Conrad Hoffman did a nice write-up in part three of his mini-metrology-lab series:

http://www.conradhoffman.com/mini_metro_lab.html

[Kleinstein]

One can use equal value chains and extra compensation resistors. However there is a downside to this, somewhat related to less current flow: with equal resistors one adds more to the output resistance.

One can use a combination like:
1st chain switch with 50 K
2nd chain with 10 K
3rd chain with 2 K
4rd -6 chain with 2K + compensation resistor parallel to the chain.

This way the lower chains don't add that much to the output resistance an on can still use several equal ones.

[cape zoloh]

Very helpful answers. Reason for asking is that it is hard to get them Vishays in all values.

[Conrad Hoffman]

Remember that the top string is the most important. By the time you reach the lower two or three divider strings, you can use garden variety metal films, selected for value. Some units even use a wire wound pot for the last divider.

[cape zoloh]

Was just about to edit above text, when I realized i had forgotten this. Thanks for the heads up!