Hall Current Sensor

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Hello all,

 

 This is an impressive device - has anyone used these before?  Have they been around for a while and I am just not aware? Seems like a lot of extra hardware is required for programming. 

 

http://www.melexis.com/Current-S...

 

I wonder how accurate they are compared to current sensing IC's with integral op-amps?

 

Thanks

John

 

 

Just some guy

Last Edited: Mon. Jan 5, 2015 - 03:47 AM
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Quote:
I wonder how accurate they are compared to current sensing IC's with integral op-amps?
As in with an inline current sense resistor?

 

I don't know how accurate they are (datasheet section on accuracy is a bit hard to unwind), but hall effect (and other magnetic-flux measurement methods) sensors have other benefits.  No need to route current through a sense resistor, no resulting voltage drop or power loss, no skewing of measurements as a result.  This is what makes clamp meters possible:

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

https://www.google.ca/search?q=dc+clamp+meter

Some hand-held devices can easily measure 1000 A.  This Fluke meter claims an accuracy of 2% + 0.5 A:

http://en-us.fluke.com/products/all-accessories/fluke-i1010.html

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

Last Edited: Mon. Jan 5, 2015 - 05:56 AM
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johnrk wrote:
Have they been around for a while

Yes.

 

eg, http://www.allegromicro.com/en/P...

 

You will find several "breakout" boards for these kinds of things on Sparkfun et al, ...

 

joeymorin wrote:
hall effect (and other magnetic-flux measurement methods) sensors have other benefits.  No need to route current through a sense resistor, no resulting voltage drop or power loss, no skewing of measurements as a result.  

Isolation is another.

 

 

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Thanks for the responses - it looks impressive, but the "calibration and programming" tools are $1300!! Ouch! Also, how great is it if you have to use torroids (or special PCB layouts with large footprints) for accurate measurements? 

 

This one on Sparkfuns site is not "exactly" what I was referring too. The current flows through the actual ACS712 chip which is very different that laying the chip over a PCB trace. It seemed to good to be true:)

 

https://www.sparkfun.com/product...

Just some guy

Last Edited: Mon. Jan 5, 2015 - 11:55 PM
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The current in the acs712 does not flow through the chip - it flows through a metal link. Place the chip over a track carrying current and it will measure it. Its hall effect. I could determine if a nearby relay was activated on one of my pcbs.

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"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Kartman wrote: 

The current in the acs712 does not flow through the chip - it flows through a metal link

OK, so the path of pin 1 & 2 and pin 3 & 4 does not pass through the chip? I mean I know the sensor is part of the die correct?  But unless I am missing something (admittedly possible) then the current must from in pins 1 and 2 and out pins 3 and 4...

 

Whereas in the Melexis I reference above there is not current flow pins on the chip at all. 

Just some guy

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Yes the path between pins 1,2 and 3,4 passes through the package, but it (I imagine) is not part of the die, and is electrically isolated from the rest of the device.  Rated for 2.1 kV isolation.

 

That conductor has a 1.2 milliohm resistance, so the 30 A variant of the device will drop at most 36 millivolts across that conductor, which would dissipate at most 1.08 W.

 

Yes the Melexis device is designed to measure the the current flowing through an adjacent conductor rather than an integrated one, but as you have noted this requires careful calibration.  The '712 is delivered fully calibrated.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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It is easy enough to prove my suggestion: get a acs712 device and place a wire with a known amount of current flowing on top of the chip - measure output. The datasheet warns you about nearby magnetic fields affecting the reading.