Re: 453 calibrator

Fabio Trevisan
 

Hey Jeff,

Thanks for the heads up on my hunch about the possible construction of the actual current probes...
I tend to concur with you, that being solid state-devices, there should be at least some devices that can handle some high frequency.
But, as a a matter of fact, my knowledge in this area is an absolute zero.
The closest I was to a current scope probe was some 30 years ago in my first job, but it belonged to the switching power supply folks (and I was on the personal computer R&D dept) so, I had it in my hands and found it beautiful how the clamp would slide open / close and how precise and smooth the movement was, and how polished the matching surfaces of the clamp were.
I suppose that one really need to make sure the gap of the clamp is consistent day in day out, for it not to interfere with the picked signal.
But as I read your message it got me curious. I googled a little bit on it and got to these pages from TI:
http://www.ti.com/sensing-products/magnetic-sensors/hall-effect/digital/products.html
http://www.ti.com/sensing-products/magnetic-sensors/hall-effect/analog/products.html
At least from TI, the fastest ones are 30kHz and those are the digital ones... the faster Linear ones (analog) are 20kHz... so it seems they're not that fast after all (Granted... it may be only the TI range that is narrow).
Anyway, I think it's conceivable to implement a hybrid design, mixing Hall-Effect for DC response and DC stability, and magnetic pickup for frequencies - say - above 10kHz, but I`m sure this is already invented wheel and it can be probably seen on the service manuals of those probes.
By the way, since you mentioned Opto-Couplers... Not to counter your thinking, but coincidentally supporting mine, I remember of having seen once on eBay an Galvanically Isolated Tek probe (one that would allow up to some 1200V isolation IIRC), that would split the signal in two paths... the DC isolation path using optos up to some frequency and the AC isolation path using a capacitive coupling, to allow the probe's claimed bandwidth (I think it was 20Mhz).
I can't recall what probe that was...

Rgrds,
Fabio

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