frank.stellmach at freenet.de
Tue Mar 8 18:47:01 EST 2016
yes, there has been a longer discussion on eevblog a few years ago..
Originally, the Weston Standard Cells had an odd value of 1.01865V. This
was transferred to other values by KV dividers. These dividers were
easily built in decades, but maybe that did not prefer 10V, yet.
Analog meters at that time also had no preference, as they had several
overlapping ranges, sequenced like 1-3-10, or 1-2-5-10.
When more precise DVMs with higher resolution were built in the
1960ties, like the Fluke Differential DVMs, as for example the 883A,
893A, and so on, they got decimal ranges, as a necessity for cascading.
HP also designed several standards and differential DVMs having 9.9999X
Also, digital counters and early digital DVM, being based on such
counters, naturally had a F.S. like 9.999.
You can often find in the catalogues of that era, that digital or
differential DVM with a F.S. of 11V or 12V were described as 10V
instruments with 10% or 20% of Overrange Capability, or so.
So there was a necessity to have as a reference these Cardinal Points
like 100mV, 1V, 10V, 100V, 1kV, with 10V being the most stable and
easiest one to realize.
And that lasts until today, although a direct calibration on the 6.9..
7.2V of zener elements like the LTZ1000 or LTFLU would be much more
stable and more precise than the 10V from a 732B.
More information about the volt-nuts