Author Topic: Are there any countries that use siemens instead of ohms?  (Read 5564 times)

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Offline XOIIO

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Are there any countries that use siemens instead of ohms?
« on: July 14, 2014, 10:02:17 pm »
Pretty simple, but I started wondering, is there any country or region that still does, or used to, use siemens instead of ohms in electronics? It would be interesting to find a schematic or parts list that called for resistors of x many siemens instead of ohms

Offline FrankBuss

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Re: Are there any countries that use siemens instead of ohms?
« Reply #1 on: July 14, 2014, 11:19:44 pm »
I don't think it is limited to a country. It is nothing special or old and often used in MOSFET datasheets (see e.g. http://www.fairchildsemi.com/ds/FD/FDS6680A.pdf and look for "forward transconductance") or in science. But looks like it is not used for resistors, where usually milliohm is used.
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Offline dannyf

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Re: Are there any countries that use siemens instead of ohms?
« Reply #2 on: July 14, 2014, 11:25:18 pm »
As widely used as 212.77mS vs. 4.7ohm.
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Offline T3sl4co1l

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Re: Are there any countries that use siemens instead of ohms?
« Reply #3 on: July 14, 2014, 11:34:43 pm »
As a dead resistor, usually only in analysis when doing series-parallel transformations.  Resistors in series add; conductances in parallel add.  The reciprocal of the sum of the reciprocals is...

And yes, transconductance amplifiers (that is, current out, voltage in) are rated in Gm.  A BJT's small signal transconductance is gm = Ic / Vth, for example.

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« Last Edit: July 14, 2014, 11:36:55 pm by T3sl4co1l »
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Offline rolycat

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Re: Are there any countries that use siemens instead of ohms?
« Reply #4 on: July 15, 2014, 12:09:41 am »
Werner von Siemens himself used siemens instead of ohms; it was a unit of resistance equal to about 0.95 ohms which he introduced in 1860, based on a standard column of mercury.

The siemens mercury unit of resistance was still in use by telegraphy and telephone engineers until World War II, despite siemens having been adopted as the unit of conductivity in 1881.



 

Offline T3sl4co1l

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Re: Are there any countries that use siemens instead of ohms?
« Reply #5 on: July 15, 2014, 12:30:51 am »
That's not confusing at all.  :-DD

Never heard of that one before..

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Offline VK3DRB

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Re: Are there any countries that use siemens instead of ohms?
« Reply #6 on: July 15, 2014, 01:35:20 pm »
I have not used siemens, but I have used Siemens capacitors :)

Actually at university we were told a mho was 1/R in ohms. Hence 0.5 ohms = 2 mhos.  Maybe I'll ask one of my colleagues for a 1 millimho resistor.

I have NEVER used mhos. Has anyone else used mhos? (pronounced like Moe in the Three Stooges).
 

Offline N2IXK

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Re: Are there any countries that use siemens instead of ohms?
« Reply #7 on: July 15, 2014, 03:34:12 pm »
Mhos (micromhos, actually) were the standard unit for measuring the transconductance (Gm) of vacuum tubes here in the US.  Given by dividing the mu (gain) of the tube by the plate resistance, Rp).

The UK and most other countries usually used the more intuitive units of mA/V to directly designate the change in plate current per volt of change in grid signal.
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Offline SeanB

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Re: Are there any countries that use siemens instead of ohms?
« Reply #8 on: July 15, 2014, 05:17:32 pm »
Used to measure water conductivity in desalination and RO and DI water plants. Easy to use as you aim for the lowest number.
 

Online HighVoltage

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Re: Are there any countries that use siemens instead of ohms?
« Reply #9 on: July 15, 2014, 06:48:09 pm »
In high voltage insulation testing for components, we sometimes have to use a salt water bath for the DUT.
Then the requirements in the specific ISO standard or DIN standard is given in "Siemens" for the water conductivity.

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Offline DaveW

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Re: Are there any countries that use siemens instead of ohms?
« Reply #10 on: July 16, 2014, 12:04:13 pm »
I was designing safety equipment designed to activate in water and all the measurements there are in Siemens/cm-20mS/cm is typical seawater, 40uS/cm is about the lowest conductivity freshwater lake, 500uS/cm is tapwater here. Doesn't seem to have much advantage over ohms, but still seems to be the standard for everythign related to that
 

Offline rob77

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Re: Are there any countries that use siemens instead of ohms?
« Reply #11 on: July 16, 2014, 12:22:34 pm »
IMHO it makes no sense to discuss the advantages or disadvantages of Siemens vs. Ohm.... one is unit for conductivity and a second is a unit of resistance... sure the one is the inverse of the other.. but is more natural to use Ohms when you think about limiting the current and it's more natural to use Siemens when you measure how conductive is something (e.g. conductivity of water mentioned above).
 

Online nctnico

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Re: Are there any countries that use siemens instead of ohms?
« Reply #12 on: July 16, 2014, 07:51:00 pm »
As a dead resistor, usually only in analysis when doing series-parallel transformations.  Resistors in series add; conductances in parallel add.
I agree. A while ago I used Siemens (conductivity) in some RF impedance math to make the formula easier.
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Offline DonRon

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Re: Are there any countries that use siemens instead of ohms?
« Reply #13 on: July 16, 2014, 08:02:48 pm »
.. but is more natural to use Ohms when you think about limiting the current and it's more natural to use Siemens when you measure how conductive is something ...
Agree!
Working in the field of material science and analytical chemistry it's usual to handle it this way.
 


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