Electronics > Metrology

Beautiful precision from the golden age - Fluke 720 oil can teardown

<< < (5/6) > >>

RoadDog:
I suppose you’re right. I meant any other types of solvents that could react with the wire somehow. I figured alcohol was the safest bet. I used 99% isopropyl alcohol from the drug store.

RoadDog:
Also I let it dry for quite a while on top of my refrigerator which gets warm and a small fan blowing on the open port just to be safe before hitting it with the soldering iron.

RoadDog:

--- Quote from: xrunner on May 22, 2022, 07:02:05 pm ---
--- Quote from: guenthert on May 22, 2022, 05:52:30 pm ---
--- Quote from: MrYakimovYA on May 22, 2022, 02:09:42 am ---
--- Quote from: xrunner on May 22, 2022, 01:54:01 am ---
--- Quote from: MrYakimovYA on May 22, 2022, 01:29:43 am ---What is this? :o

--- End quote ---

Looks like precision resistance values created with wire-wound parts, hence the naming Rxxx ...

--- End quote ---
It's very interesting are those resistors bifilar wounded to minimize parasitic inductance?

--- End quote ---

I don't know, but I noticed that those 'coils' come in pairs, so they could be wound in alternating orientation for the same effect.

--- End quote ---

I found a few that were clear enough that I think I can see how they were wound. I believe every other one alternates the winding direction. I can see (starting at the left) the winding's exit wire, say this one was clockwise. Then I believe I see the next one's exit wire coming around in the counter-clockwise direction, then the next again clockwise. Can't see the last one for sure.

But I may be wrong ...

--- End quote ---

You are not wrong. Each section of the bobbin is wound the opposite way.

Also Kleinstein was right I think they are welded not soldered. I thought for sure they were so soldered but looking again at some I believe they were welded. They have a coating over them that looks like epoxy to hold the wire to the end of the bobbin. I think I need glasses soon. Eyes are getting old  :-//

MrYakimovYA:
So, the main advantages of those resisor set, if I understand it correctly:
1. Low tempco.
2. Low additional noise (not Johnson).
3. Very low parasitic inductance.
4. May be low ratio if the set can be used as resistor devider.
5. Good long time stability.

I can't see any trim section in the string/or each resistor to get very very very low initial tolerance. I could be wrong here.

I just tried to bring it all together) To sum it up...

RoadDog:

--- Quote from: MrYakimovYA on May 24, 2022, 12:43:47 am ---So, the main advantages of those resisor set, if I understand it correctly:
1. Low tempco.
2. Low additional noise (not Johnson).
3. Very low parasitic inductance.
4. May be low ratio if the set can be used as resistor devider.
5. Good long time stability.

I can't see any trim section in the string/or each resistor to get very very very low initial tolerance. I could be wrong here.

--- End quote ---

There is a trim circuit in the 720. It’s not inside the oil can. It’s a couple resistors and a 20 turn potentiometer in a series/parallel arrangement that allows very fine tuning when self calibrating it. You can take a look at the manual which includes a schematic towards the end.

https://download.flukecal.com/pub/literature/720A____imeng0200_0.pdf

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version