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Current Measurement, Part 2

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antedeluvian
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Rogowski Coil
antedeluvian   11/15/2013 5:15:02 PM
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I must apologize for not mentioning the Rogowski coil for AC current measurement. I have never had the opportunity to use one, so there is not much that I can add.

For completeness, I guess I should mention the rotating disc that used to be on all power meters. For the life of me I can't remember that name of the effect that produces the rotation and I don't know of any modern application that uses this approach.

antedeluvian
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Like the MAX4211, but digital
antedeluvian   11/15/2013 5:23:55 PM
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Like the Maxim MAX4211 TI produces a (low side) current and voltage monitor with an SPI output, the LMP92064. Your processor will have to do the multiplication to get to power, but that's what processors are good for!

 

I believe TI has one or two others, but it will have to wait untll I get back to work on Monday.

MeasurementBlues
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Re: Rogowski Coil
MeasurementBlues   11/15/2013 6:07:56 PM
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I think there is a Rogowski coil at NIST.

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.

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

 

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.

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???

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.

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!

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

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