Noninvasive current sensing.

[kellym]

I have a single cable with 24vdc pos/neg within that switches a load of approx 200ma. Is it possible to determine when that line is active (switched on and running the load) by any noninvasive means currently available? Whether Hall Effect or other transducer/transformer?

Ideally, I'd like to be able to monitor such a line for on/off status without having to open the line and separate the conductors. I've been told that this is impossible - that any (noninvasive) attempt to detect a load will be cancelled out by the balanced lines.

Is this true?

 

[kellym]

ahh my life is a nightmare sometimes. Everything I find is over 200USD and still not quite capable. Last thing that I found was this

http://www.veris.com/file_uploads/h600_800_d.pdf

and the sales guy said that 300amps would certainly break it.

I'm finding diy sheets on how to physically split round iron cores and jimmy in hall effect sensors to do this stuff. Am I really ruduced to that? Is this such a theoretically esoteric thing to do that I can't find a <20USD fixed point low amperage sensor/gaussmeter/etc to do this?

I've had a few engineers tell me that it's impossible to measure low current (by magnetic field) in a #2 copper cable. I've had a few others tell me this is nonsense... that one amp is one amp through any sized cable and will eminate the same measurable field around that cable.

AAAAAARRRRRGGGGGG!

 

[kellym]

Skogsgurra,
No, I did actually mention that in the previous post. I went to that website. There are no international/U.S. contacts. Prices look right. The circuit descriptions give little clue (to me anyway) as to how the devices might be used for cable current sensing.

I googled "flux gate" and "flux gate switch" and was unable to find any manufacturers/suppliers other than the link you provided. Is it a question of nomenclature? Are these available under varying descriptions? Perhaps Digikey even stocks this animal, but under a different description.

Can you cite any more links that might describe the use of these in the sort of application I'm involved with?

 

[Skogsgurra]

I think we cross-posted.

OK. I will try and find some more stuff. Stand by a couple of hours

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[VEBill]

I think that any ham radio operator within 30m could probably tell you if the arc was established, or not, using a shortwave radio. I can only assume that the intial waveform mentioned by OperaHouse must be vastly lower in amplitude.

Experiment: wire loop and oscilloscope.

 

[Skogsgurra]

Googling "flux gate" results in around 500 000 hits. Googling "fluxgate" is more selective. I got around 180 000 hits there. Finally, +"fluxgate" +"current detection" resulted in 149 hits.

But, you are right. There are not many products available. I think that is beacause it is so simple to roll one's own. There are many practical and theoretical papers in the 149 hits and I think that a winder could make you the magnetic circuit (copper wire and high-permeability iron). The electronics is simple.

Not exactly what you may want to pursue. But a way out if nothing else works.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[kellym]

VE1BLL, I agree with the ham radio point. Seems like there would be a few detectable things going on here that I could utilize non-contact. I just have to turn over the right rock.

I believe that for the time being I'm going to order this

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=620-1213-ND

and epoxy it into a gap in a split iron core. I'll clamp that around the output lead to the torch and start experimenting.