From: Spehro Pefhany
Subject: Re: Current Sensing Schematic
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Date: Thu, 28 Nov 2002 22:27:44 GMT
NNTP-Posting-Date: Thu, 28 Nov 2002 17:27:44 EST
On Thu, 28 Nov 2002 18:57:50 +0000, the renowned John Woodgate
>I read in sci.electronics.design that Spehro Pefhany
> wrote (in <firstname.lastname@example.org
>om>) about 'Current Sensing Schematic', on Thu, 28 Nov 2002:
>>On Thu, 28 Nov 2002 17:33:15 GMT, the renowned "Marc H.Popek"
>>>Yes! Think about rogowski coil as the traditional solution to this problem.
>What an extremely helpful response!
>>Wouldn't get much output, would you, unless you separate the
>>conductors of the line cord?
>Not even then. Winding one wire round another does NOT produce a
>transformer, which is what you need to construct. You need a toroidal
>magnetic iron core. You wind about 100 turns around the core. Depending
>on the current you want to measure, you may just be able to run ONE of
>the load conductors through the hole in the middle, otherwise you need
>to wind a few turns round the core. The you put a LOW value resistor
>across the 100 turn winding, like 100 ohms, and measure the 60 Hz
>voltage across it. That voltage is proportional to the load current. 1
>volt corresponds to 1 A if you have just the load conductor threaded
>through the central hole.
I'd call *that* the traditional solution, and probably more suitable
for the OP's request.
Rogowski coils are interesting. Essentially an air-core toroidal
transformer, when loaded they output a voltage proportional to di/dt,
so they need an integrator to measure current.
Being air-core, they don't suffer from linearity errors due to core
saturation, even at very high currents. They could also potentially
be made quite cheaply. For example, check out US 5,414,400 assigned
to GEC. AD supports Rogowski coils in addition to conventional
CTs and resistive shunts in their silicon offerings.
"it's the network..." "The Journey is the reward"
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