Rogowski current probes?
Rogowski current probes?
(OP)
And on a totally related note to my other post... anyone home-brewed their own Rogowski current probe? I got really excited about the CWT series from PEM - you can uncouple the loop and slip it in between the legs of a TO-220 part to measure, eg., drain current! - but wasn't too excited about the price: $1445?!?! Since that is clearly not in the budget this year (or next, etc., and so on) I was thinking of rolling my own with some thin (2mm?) teflon tubing for the coil form... Or if someone knows of another supplier of a similar style Rogowski probe that *isn't* smoking crack, I'd love to hear of it (yes, I've done a lot of Google searching... coming up a bit short).





RE: Rogowski current probes?
Have you contacted Rocoil in the UK? This is a small company making custom and semi-custom Rogowski coils and associated electronics. The guy to speak to is the owner, David Ward. He is very knowledgable on the subject and has done some unusual applications for ultra-high accuracy and for measuring some outrageously large currents. Highly recommended!
www.rocoil.co.uk
BTW, I have no association other than being a satisfied customer.
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If we learn from our mistakes I'm getting a great education!
RE: Rogowski current probes?
The problem is that they get destroyed when you measure rotating shafts on motors and other machinery. I lost two that way.
I also made myself a few when the conductors (heavy tubing in this case) were too wide for standard coils. Picture attached.
I have used these with passive integrators (RC filter with around 1 ms time constant) and active integrators. Lately, I have used the integrating function in USB scopes. That gives a great flexibility but also a problem with the DC offset, which drives the integrator into saturation. It can be overcome in many ways, but you have to take care of it if you measure over several seconds.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Rogowski current probes?
Gunnar - Interesting observations. I'm going to need to measure current rise times in the 50-300nS range so it would seem the PEM integrator is not up to the task for me anyway.
The most common solution to integrator saturation is to short out the integrator capacitor with a FET either periodically, on demand by the operator or, ideally, at every zero-crossing. Frankly, trying to pull off the latter without sampling the voltage of the circuit under test seems a bit difficult, though.
Thanks for the picture of your home-brewed coil!
FYI - Athena Energy, LLC, is willing to sell the probe only - everything but the integrator, that is - for $150! That's definitely well within the budget. Also, for larger industrial applications I found out that Fluke sells Rogowski current probes. Check out the i3000S, for example. It's totally useless for my application - measuring the individual collector currents of a bank of IGBTs - but it looks perfect for buss bar monitoring, VFDs, etc... and the price is definitely right: $400US!
RE: Rogowski current probes?
I have also used an FCC HF clamp-on transformer. Goes to hundreds of MHz. But has a definitive influence on the impedance. Which a Rogowski doesn't have. Or very slightly so.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Rogowski current probes?
As a former try some of the medical PTFE tubing which is occasionally used to insulate compenent leads. The joint doesn't matter too much and overlap is preferable to a butt joint with a gap. For coil as small as you are trying to make the connections to the outside world will need to be simimilarly small. The ideal would be shielded twisted pair but I don't think you'll find it in very small sizes. Enamelled wire twisted will probably be ok. Wire gauge is fairly arbitrary but you need a reasonable number of turns in the length available and you need to be able to work with it. Anything below 40AWG is going to be too fragile - 40 breaks if you breathe heavily - but I would guess you are looking at 40 AWG on a 1.0mm former.
Are the TO-220 leads splayed at all or staggered? Might be easier to drill a pair of holes straddling a PCB track to the IGBT and thread the coil through them rather than trying to get around the device itself. You then have the chance to anchor the wiring etc securely to the PCB.
How many of these are you looking for?
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If we learn from our mistakes I'm getting a great education!
RE: Rogowski current probes?
At any rate, I definitely can't justify making my own probe when his price is $150US; making my own integrator for his probe, though, is definitely compelling as the combo costs $950. Yeah, I'll definitely spend half a day to make an integrator and calibrate it with my IGBT pulse tester to save $800. I mean, How Hard Can It Be??? (Famous last words...) :)
RE: Rogowski current probes?
Thanks.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Rogowski current probes?
http://www
Update: Dimos Katsis of Athena Energy was extremely helpful when I talked to him on the phone and even managed to convince me that rolling my own integrator would probably cost more time than I expected, and I'd still never be sure it was perfectly calibrated. So, I bought the complete probe package - coil + integrator, rather than just the coil as I had intended. When it arrived I was not terribly impressed with the way it looks - a lot like a ham radio tinkerer's weekend project - but man did I get a big ol' grin the first time I used it. Being able to thread the probe coil around the source (emitter) of a To-247 part in-circuit will make power circuit design (and the troubleshooting thereof) infinitely easier. Really, folks, if you are at all involved in switching high currents around at high speeds a Rogowski probe is damn near indispensable. Yeah, I know it sounds like I've definitely been drinking the Kool-Aid here but for good reason.
RE: Rogowski current probes?
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If we learn from our mistakes I'm getting a great education!