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MeasurementBlues
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Re: Rogowski Coil
MeasurementBlues   12/2/2013 11:25:07 PM
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"The interaction between the magnetic fields of the V/I coils and the eddy current in the disc causes it to rotate."

Which changes the speed of rotation, the fileds, the eddy currents, or both?

antedeluvian
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Re: Rogowski Coil
antedeluvian   11/27/2013 9:07:21 AM
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David

were you thinking of Eddy Currents?

yes I was- thanks. I must say though that "Ferraris motor" sounds much swankier.

 

David Ashton
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Re: Rogowski Coil
David Ashton   11/27/2013 4:42:02 AM
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@antedeluvian - were you thinking of Eddy Currents?   Electricty meters have a voltage coil and a current coil acting on the disc, which gets eddy currents induced in it.  The interaction between the magnetic fields of the V/I coils and the eddy current in the disc causes it to rotate.

Here's the english Wiki article

http://en.wikipedia.org/wiki/Electricity_meter

I work for an electricity utility and any disc meters that go wrong are replaced with electronic ones.  Divider on the voltage, CT on the current and the rest is done by the processor, displayed on an LCD and downloaded to the meter reader via IR LEDs used as an isolated data link.  Usually a backup battery in case of power failure.  But they rarely fix them when they go wrong, just chuck 'em.  

MeasurementBlues
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Current probes
MeasurementBlues   11/23/2013 6:25:59 PM
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EMC engineers love to use current probes with oscilloscopes. take a look at Doug Smith's Current Probes, More Useful Than You Think.

You can also use current probles to inject pulses into wires and cables


current probe

Caleb Kraft
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Re: Rogowski Coil
Caleb Kraft   11/22/2013 10:19:41 AM
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ooh, that is a cool piece of trivia right there! I'll have to file that in my "knowledge for no purpose" folder. Thanks!

antedeluvian
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Re: Rogowski Coil
antedeluvian   11/21/2013 3:02:51 PM
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monle

The rotating disc motor used in those kWh meters is the so called Ferraris motor

Thank you. I thought I had known the name, but that doesn't ring any bells. I will try to remember it next time my trivia knowledge is challenged.

pmoyle111
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Re: Rogowski Coil
pmoyle111   11/21/2013 2:59:18 PM
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Maybe that idea could be reduced to a mems device???

salbayeng
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Re: Current Sensor Magneto Resistive
salbayeng   11/21/2013 4:29:50 AM
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Used a MR sensor a decade ago in a compass chip ,  absolutely awful for anything analog, the scale factor, linearity and offset would change all the time, so needed to reset all the time .

One advantage of MR (for on/off applications), is that the magnetic field sensitivity is in the plane of the chip, where as hall effect is perpendicular to chip. More useful being oriented this way with SMD sensors for shaft encoders,  or current sensors when placed over a conductor. In both these applications a hall sensor would read nominally zero as its aligned with the null in the field.

monle
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Re: Rogowski Coil
monle   11/21/2013 3:59:15 AM
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The rotating disc motor used in those kWh meters is the so called Ferraris motor (Galileo Ferraris, italian physicist, 1847-1897, was the inventor). Not to be confused with a Ferrari engine ;-)

A good description can be found on the dutch Wikipedia site:http://nl.wikipedia.org/wiki/Kilowattuurmeter

 

ArcsSparks
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Current Sensor Magneto Resistive
ArcsSparks   11/15/2013 8:14:47 PM
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Need more bandwidht than a hall sensor or 1-5 Mhz consider magneto resistive.  Same techology used in many harddrive read heads.  Works like a hall sensor in that they need a bias current to read the restance change typicly aranged in a bridge.  Due to the fast response time you can pulse the current to save power.  Use two in oposition to cancel stray magnetic fields.  Note they can be magntized by large fields most have a reset winding.   Made by a number of outfits.  Have fun.

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