Builded a 50-turn coil

[Zermalmer]

Hi,

I have in access 10, 20 and 30turn coils... but they are produced a long time ago by the need of them and no one ever really
asked about them... and as long as the calibrators or aplifiers are not tripping... who cares?
The specification of such a coil and the uncertainity of a coil exist, but is much smaller than the usual current clamp specification.

I also have access to a nice "selfmade" current source up to 1200 A at 50Hz. without coil... but this also have it's disadvantages.

Some month ago I thought about the need of a 50 turn coil...
A coil from a manufacturer... all well calculated... fitting to the needs... theoretically no calibration is needed,
because the specification and the uncertainity is normally small enough to fit nearly all clamps.

I readed posts, links, artikels, whitepapers aso. and got an idea how more complaiced it is to make one by myself without any knowledge which I maybe collected while study at an university.

I asked for the prices of the existing coils you can buy from Fluke, Transmille and maybe some others.
You have to throw in a good bunch of moneys to get them.
But you can be sure that they work at related calibrators.

After long thoughts I tried to get 'biggest' paint wire in company.. but unfortunatly I ended up with 1,5mm (thought I will find also 2, 2.5 or 3mm... but had no luck)

So I decided to simply make a 50 turn with 1,5mm (with some overhead to add wrong counted turn or to connect it to binding posts aso.)

I grabbed a existing pipe and wounded up 50 turns to a 75mm diameter pipe.
After that I put it off the pipe and measured it with an LCR Meter.
Tied toghether it ended up at 200uH.
oh wait... .200uH ?! that is eactly the maximum impendance of the Fluke 5500A.
I made a short test and ended up very disappointed with a tripped calibrator. 

One big difference is... my coil was still tighted together and Fluke coil was spread over >180"
More spreading = less inductance... could be an good idea
So I spreaded my coil and...oh wonder... the inductance dramatically shrink.

I "played" a little bit with the angle of the spreading and tried to separate the coils as regular as possible without any fix mount.

After revisiting the removing the point from the wire and the spreading of the coil I ended up at some inductance between 90 and 120uH.

With this info I started testing the coil with a Fluke 5500A and a Yokogawa 2858.

DC in general is less the problem.. .for this I have a 100 turn coil which bring me easy up to 1000 A.

But I wanted to know if this 50 turns of copper wire will do the right job before I mechanical fix it in some way.

After reaching <120 uH at first tests, the calibrators do their job and I got no tripping in the most usual sections.

Design was decided after a discussion with our mechanical departement.

After the creation of the basic frame with screen printing plates I fixed the coil into the upper frame and then it was filled with industrial "plastic".
(unfortunatly some air bubbles still exist, but that doesn't matter)

I added also some foam to the construction, so the DUU normally will not get any scratches.

After the mechanical fixing part I ended up with the folloing numbers:

50 turns
diameter of paint wire 1,5mm
iameter of turns = 75 mm

measured inductance with LCR meter @ 100 Hz ~ 100,4 uH
measured inductance with LCR meter @ 1 kHz  ~ 100,1 uH

measured resistance with LCR meter @ 100 Hz ~ 0,185 Ohm
measured resistance with LCR meter @ 1 kHz  ~ 0,183 Ohm

This coil works for me at a:
Fluke 5500A : DC A 550A and AC A 550A up to 65 Hz
Yokogawa 2858 : AC A 1000A at 50 Hz and 60 Hz

That will fit commonly a lot of current clamps.
Maybe I will also have a look to the flexclamp section... but only if time allows it.

Maybe I also have forgot a lot of parameters or oversee a lot of critical informations...
But I am sure that the coil will meet commonly the needs.

Feel free to ask.

ADD:No gurantee for everything. I am not responsible for harmson your devices. You have to check if the specifications fit to your needs and to your devices!

[ArthurDent]

I'm assuming this is what you are talking about but it isn't very clear.

https://youtu.be/cyVTFnjFYes

[dl1640]

Your build is lovely. I have Fluke 5502A calibrator and 5500/COIL (50-turn) on workbench, I think it is useful to calibrate some Fluke clamp meters but is not fit for some others such as a Hioki 3275 current probe (https://www.hioki.com/en/products/detail/?product_key=5755) whose clamp diameter is relatively small e.g. 20mm. In my experience the 5500/COIL has about 100uH inductance, IIRC the calibrator can drive up to about 400uH. So, to calibrate up to 500A (50Hz) for 3275 I need to make own coil tool, I was considering to use 1.0mm diameter coated copper wire for 50~60 turns thus the calibrator would be sourcing 10A or less, it is compromise between loading inductance, current capacity of the wire and tool form factor etc. Unfortunately I never build a prototype yet.

[Zermalmer]

Hi,
you are right, for such a small diameter this coil doesn't work.

For that I use our smaller "free turned" coil with 10 to 30 turns with smaller wire diameter.

[HighVoltage]

I made a 10 turns amplifier before and it works well for large current clamps

[HighVoltage]

And for small current clamps I made this 50 turns coil amplifier.
I had posted details somewhere on the forum before.

[Zermalmer]

Thanks for the pics HighVoltage.

Very nice designed.

[dl1640]

And for small current clamps I made this 50 turns coil amplifier.
I had posted details somewhere on the forum before.

I've seen your design on this forum, it's really good for those small thru-hole current probes.
But I wonder is this capable to carry large current e.g. 10A from calibrator?