AC and DC Current Sensing

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I'm interested in sensing AC and DC currents, 0-8A nominally, but up to 160
A for 10msec current surges from both AC and DC sources... I'm after the be
st resolution I can get... I don't know if it's possible to do this for bot
h AC and DC off the same current sense circuit... I was thinking a shunt th
rough a current sense amplifier then to an RMS to DC converter IC... but I'
m not sure if this is the best approach... any suggestions?

much thanks!

Re: AC and DC Current Sensing

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The Danfysik DCCTs are fantastic.  



--  

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

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Re: AC and DC Current Sensing
If it's at a convenient common mode (like connected to GND), a shunt can  
work.  You need a small enough resistance of course.

Hall effect sensors are also useful in that range.

Tim

--  
Seven Transistor Labs
Electrical Engineering Consultation
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Re: AC and DC Current Sensing
On a sunny day (Mon, 14 Apr 2014 20:57:11 -0700 (PDT)) it happened panfilero

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I have some nice Hall sensor based DC sensors....
No shunt losses.
 http://nl.farnell.com/lem/hx-10-p-sp2/current-transducer/dp/1617421
There are lower current models too.

Re: AC and DC Current Sensing
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 I have a couple of current clamps for scopes or DMM coming that can  
do like 20mA up to 65 or 650 Amps scaled to mV.  

  These only have 20khz response time but close enough for what I want  
them for and the price is acceptable since the upper units can't seem to  
do much better, so why pay for them?

Jamie


Re: AC and DC Current Sensing
On a sunny day (Tue, 15 Apr 2014 18:14:08 -0400) it happened "Maynard A.

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Yea, that would work too, size?
I payed 4 Euro for these...  


Re: AC and DC Current Sensing
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" No shunt losses".   OK, since we all know that TANSTAAFL, would anyone
care to estimate what the additional impedance of running a wire past a
Hall effect sensor is? It takes real force to push those electrons and
holes around, you know. Just the thought of calculating the answer makes my
brain hurt.

Re: AC and DC Current Sensing
On a sunny day (Wed, 16 Apr 2014 02:19:59 GMT) it happened Ralph Barone

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You could avoid that pain by spending 6 dolars and measuring it?
Or is measuring no longer of this age, and is slimulation required?

Re: AC and DC Current Sensing
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My suspicion is that the increased burden in the primary circuit from
adding a Hall effect sensor is probably unmeasurable, which is why I asked
about a theoretical solution. And it is just out of curiosity, but I
thought that somebody else with better analytical chops than me and better
knowledge of Hall effect device design might take up the challenge.

Re: AC and DC Current Sensing
On Wednesday, April 16, 2014 6:12:40 PM UTC-7, Ralph Barone wrote:

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I'm pretty sure the Hall effect is due to electron drift velocity
and deflection of the moving electrons by a magnetic field.  There's
no work whatever done by the magnetic field on such a moving charge.
No work, zero power, zero resistive-like energy losses.

Magnetic force on a moving charge is perpendicular to velocity,  
the power is zero because F-vector and V-vector are orthogonal.

Re: AC and DC Current Sensing
On Thursday, 17 April 2014 17:09:15 UTC+10, whit3rd  wrote:
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ked
  
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ter  
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IIRR Hall-effect sensors depend on having roughly equal currents being carr
ied by positive and negative charge-carriers.

The work being done by those charge carriers is supplied by your measuring  
circuit and has no effect on the load.

Getting a magnetic field for the Hall effect sensor to detect could involve
 forming the current carrying conductor into a loop, which would add induct
ance to the circuit being measured, but you can just measure the magnetic f
ield being created around a straight wire, and the inductance of a straight
 wire is around 5nH per cm, which isn't much.  

http://www.k7mem.com/Electronic_Notebook/inductors/straight_wire.html
  
<snip>

--  
Bill Sloman, Sydney

Re: AC and DC Current Sensing
On Thursday, April 17, 2014 10:56:18 AM UTC-4, Bill Sloman wrote:
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asked
  
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etter  
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rried by positive and negative charge-carriers.

I don't think so.. OK I'm not hall effect expert.  But I have been measurin
g it recently in Si and Ge wafers.  (I need to start a thread about that...
later.)
So if you had equal pos. and neg. charge carriers (each with the same mobil
ity*)
then in theory you'd get no Hall voltage.  The sign of the Hall voltage giv
es you the sign of the charge carriers.  

As far as the load of a Hall effect on the line... If I'm allowed to specul
ate wildly.  I'd guess the load will only be on changing magnetic fileds...
Any nearby conductor will have induced eddy current, and that will be some  
sort of "load" (loss).  Since Hall effect devices are pretty darn small, an
d also will be fairly poor conductors**, I'm thinking this is a pretty smal
l effect.

George H.
*the Hall mobility is different from the normal electric field mobility.  
  
by somethng like a factor of 1.2 to a factor of almost 2. (Sze sec 1.5.2)
  
** the Hall signal is proportional to the carrier velocity, so all other th
ings being equal you get a bigger signal with fewer carriers.    
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g circuit and has no effect on the load.
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ve forming the current carrying conductor into a loop, which would add indu
ctance to the circuit being measured, but you can just measure the magnetic
 field being created around a straight wire, and the inductance of a straig
ht wire is around 5nH per cm, which isn't much.  
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Re: AC and DC Current Sensing
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Well, so much for my intuitive conclusion that Hall effect sensors have
burden. I suppose if that were true, one could cool a permanent magnet by
surrounding it with Hall effect sensors. Thanks all. That's one more small
piece of ignorance removed.

Re: AC and DC Current Sensing
wrote:

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asked
better

Stuff and nonsense.  If you change the path of a particle you have
accelerated it.  That takes work.  However the amount involved in a hall
effect sensor is mighty low.

?-)
  

Re: AC and DC Current Sensing
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Only if the applied force is in the direction of the motion, which is
never the case in Hall-effect cells.

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--  
umop apisdn



Re: AC and DC Current Sensing

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Sounds like you need some remedial work in vector mathematics (and the
"right-hand rule" :-)
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: AC and DC Current Sensing
On 4/18/2014 12:14 PM, Jim Thompson wrote:
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No, he's quite right.  Work is a dot product, viz. force dot distance,  
whereas Lorentz (magnetic) force goes as v cross B.

The dot product v dot (v cross B) is identically zero.

Otherwise, the Sun would be doing work on the Earth by bending its path  
into an ellipse.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: AC and DC Current Sensing
On Fri, 18 Apr 2014 16:10:34 -0400, Phil Hobbs

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So you get something for nothing?
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: AC and DC Current Sensing
On 4/18/2014 4:50 PM, Jim Thompson wrote:
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No.  If you try drawing current from a Hall sensor, it does work because  
there's a component of the current in the direction of the E field.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: AC and DC Current Sensing
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No. Immagine a hall sensor with a permanent magnet.



--  
umop apisdn



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