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I have a Fluke 87V and I can see lots of EEVBlog videos were Dave measure high resistance values, and instead of using the Ohms range, he goes to the Siemens range (nS actually).

My question than is, why the multimeter shows this big values in Siemens instead of Ohms? Is it a standard or something? Or there is more to it, like speacial math?

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up vote 5 down vote accepted

Think about the resolution and range. My trusty (non-yellow-brown) classic Fluke 8026B has a 200nS range. The resolution is 0.1nS.

enter image description here

That means that I can read resistance to a resolution of 10% up to \$1\over 1nS\$ = 1G\$\Omega\$, and see leakage in the 5~10G\$\Omega\$ range.

You could have a 10G\$\Omega\$ range on the meter, either directly measured or calculated, but the number of significant digits at the higher values would probably be only one or two unless the meter was made significantly more expensive.

So it just makes sense to offer a conductance range for making coarse high-resistance measurements. The resistance ranges on the meter go up to 19.9M ohms, so it's mostly useful for the 20M ohm to 10G ohm range.

The resolution of conductance goes down as the accuracy deteriorates (at very high resistance values) but the meter never goes off scale, even for an open circuit, as shown in the photo. Resistance does the opposite, so it will go off-scale for a resistance of more than 19.99M ohms.

Similarly, conductance wouldn't be ideal for very low resistances- the resolution would go up as the resistance approaches zero. It's better to start losing significant digits in the display as a hint to the user, and to allow the meter to not go over-range even if the leads are shorted together.

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That's what I thought at first too...but then I think the digit count will be the same...for a 4 digit display it will just show 4 digits, so whats the difference if it is a float number 4 digit in siemens or an integer in ohms? – mFeinstein Apr 6 '14 at 23:00
@mFeinstein They're both 3-1/2 digit integers, no floats. I've edited to expound a bit more. – Spehro Pefhany Apr 6 '14 at 23:14
I got it now, the "secret" is the screen size...but 3-1/2 digit wont give you 19.99M ohm instead of 19.9M ohm as you said? – mFeinstein Apr 7 '14 at 3:31
@mFeinstein 19.99M ohm. – Spehro Pefhany Apr 7 '14 at 3:35
yes, but in your answer u said 19.9M ohm... – mFeinstein Apr 7 '14 at 4:30

Siemens is a unit of conductance, the reciprocal of resistance. It is more suited for some types of high resistance measurements.

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Your reply resembles more of a comment than an actual answer, it just states what Siemens is without answering the OP questions. – alexan_e Apr 6 '14 at 22:27
Thanks Colin...but that I already knew haha as Alexan_e said, I am more interested to why use it instead of ohms...as you said "It is more suited for some types of high resistance measurements"...but the thing is: Why?! – mFeinstein Apr 6 '14 at 22:31

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