Are there any countries that use siemens instead of ohms? - Page 1
Forum section: electronics / general

author: XOIIO
author_rank: Super Contributor
timestamp: July 14, 2014, 10:02:17 pm
content: 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

author: FrankBuss
author_rank: Unknown
timestamp: July 14, 2014, 11:19:44 pm
content: 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.pdfand look for "forward transconductance") or in science. But looks like it is not used for resistors, where usually milliohm is used.

author: dannyf
author_rank: Super Contributor
timestamp: July 14, 2014, 11:25:18 pm
content: As widely used as 212.77mS vs. 4.7ohm.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 14, 2014, 11:34:43 pm
content: 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.Tim

author: rolycat
author_rank: Super Contributor
timestamp: July 15, 2014, 12:09:41 am
content: 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.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 15, 2014, 12:30:51 am
content: That's not confusing at all.Never heard of that one before..Tim

author: VK3DRB
author_rank: Super Contributor
timestamp: July 15, 2014, 01:35:20 pm
content: I have not used siemens, but I have used Siemens capacitorsActually 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).

author: N2IXK
author_rank: Frequent Contributor
timestamp: July 15, 2014, 03:34:12 pm
content: 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.

author: SeanB
author_rank: Super Contributor
timestamp: July 15, 2014, 05:17:32 pm
content: Used to measure water conductivity in desalination and RO and DI water plants. Easy to use as you aim for the lowest number.

author: HighVoltage
author_rank: Super Contributor
timestamp: July 15, 2014, 06:48:09 pm
content: 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.

author: DaveW
author_rank: Frequent Contributor
timestamp: July 16, 2014, 12:04:13 pm
content: 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

author: rob77
author_rank: Super Contributor
timestamp: July 16, 2014, 12:22:34 pm
content: 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).

author: nctnico
author_rank: Super Contributor
timestamp: July 16, 2014, 07:51:00 pm
content: Quote from: T3sl4co1l on July 14, 2014, 11:34:43 pmI agree. A while ago I used Siemens (conductivity) in some RF impedance math to make the formula easier.

author: DonRon
author_rank: Regular Contributor
timestamp: July 16, 2014, 08:02:48 pm
content: Quote from: rob77 on July 16, 2014, 12:22:34 pmAgree!Working in the field of material science and analytical chemistry it's usual to handle it this way.