Author Topic: Using gold plated brass binding posts on a resistance reference box  (Read 4722 times)

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Offline MiDi

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #25 on: December 26, 2018, 05:50:45 pm »
Interesting build. Instead of paying big money for individual binding posts, you could find an old school 6.5 digit meter on ebay for less than $100 and scavenge them. An old Fluke 8502 has 7 posts and you can get them for less than $80 broken. Just a thought.

80$ for 7 old binding posts is more than 11$/post.
Sounds quite expensive for used brass posts, I do not think they are low EMF type.
You get Pomonas for ~8$ new and they are quite expensive too.
Low EMF TeCu Pomona 3770 are ~15$.
 

Offline Inverted18650

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #26 on: December 27, 2018, 02:56:56 am »
$15 is still > $11. ($4 x 7 = $28 saved). Plus you can/will probably resale the cards and/or everything else inside the unit. More importantly, I am imaginative and interested in scavenging what I can, and where I can. I have two Fluke 8000 series units that I am restoring to there previous glory...so its not just about how cheap I am.
« Last Edit: December 27, 2018, 02:59:03 am by Inverted18650 »
 

Online splin

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #27 on: December 30, 2018, 03:38:16 am »
$15 is still > $11. ($4 x 7 = $28 saved).

But how much of the original gold plating has been lost in the sockets of a well used instrument? I don't know but gold is relatively soft so this has to be a concern.
 

Offline voltlog

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #28 on: December 30, 2018, 07:16:55 am »
I am all for re-using so if I had an old instrument and the terminals were in good conditions, I would probably use them in a project. But if you don't already have the instrument I wouldn't buy a used one just to salvage the connectors because you can't possibly know their condition before purchase and the cost would be similar to buying new connectors.

Offline MiDi

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #29 on: January 03, 2019, 02:23:32 am »
the BIL 20 AU have a very "cheap" look.
Why don't you look at PKI 10A AU?

I thought about using the PKI 10 AU for my resistorbox, but they do not have soldering point and only give 2mm for case thickness.
So no good option for me as my chosen plastic case and metalbox (HF type) have around 3mm together.

For now I put an eye on the Keystone 4109 pair (brass, gold plated) for ~10$.
Btw what the hell is the difference between 4108 (20$) and 4109?

Finally I used SEB 2610 F4,8 gold-plated brass from SKS/Hirschmann (1.40€ @ reichelt) for my box - cheap and good enough for this purpose.

The resistors are Vishay Z201 and Ohmite Slim-Mox (1G) soldered on 1,2mm silver-plated copper wire.
Box is RND 455-00169 160x80x55mm IP65, hf-case is 100x64x40mm from junk box.
« Last Edit: January 03, 2019, 02:29:19 am by MiDi »
 

Offline TiN

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #30 on: January 03, 2019, 04:51:23 am »
1G looks out of whack in this box. Also 4-wire connection is pointless for high resistance like this.  :-//
But insulation and guarding on other side become very important.
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Offline 001

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #31 on: January 03, 2019, 10:19:22 am »
1G looks out of whack in this box. 

Do You mean leackage?

Also 4-wire connection is pointless for high resistance like this.  :-//

It is not actually 4W -- double posts only
Autor use it for simple gear connection probably


PS - What about RCA connector? Is it guard?
 

Offline SvanGool

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #32 on: January 03, 2019, 11:07:08 am »
If we assume that the isolation distance of your posts to the metal is app. 2mm and we assume that the Rho of the PVC of the binding posts is app. 1E+13 Ohm-cm and allow 20% max resolution influence then:
  • For a   6.5 digit 34401A multimeter you can measure up to 120 K without substantial influence (   1 ppm resolution)
  • For an 8.5 digit   3458A multimeter you can measure up to   12 K without substantial influence (0.1 ppm resolution)
Above these values, you need to put at least the binding posts (and apply guarding for the higher Giga values) onto an isolated PTFE (teflon) area. Teflon has a Rho of app. 1E+17 Ohm-cm.

If we assume two test leads of AWG16 stranded copper wire of 50 cm with a resistance of app. 15 mOhm per meter then:
  • For a   6.5 digit 34401A multimeter you can do a 2-wire measurement from higher than   12 K without substantial influence (   1 ppm resolution)
  • For an 8.5 digit   3458A multimeter you can do a 2-wire measurement from higher than 120 K without substantial influence (0.1 ppm resolution)
Below these values you need a 4-wire measurement.

I do like your 4-wire construction, it is a neat job !  :-+
« Last Edit: January 03, 2019, 11:12:55 am by SvanGool »
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Offline MiDi

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #33 on: January 03, 2019, 12:44:03 pm »
1G looks out of whack in this box. Also 4-wire connection is pointless for high resistance like this.  :-//
But insulation and guarding on other side become very important.

Yes it is, do not take the 1.21G as serious  :-DD
This happens when you have space left on final design and do not want to waste it, so there came 2 more posts and this is the result.

If we assume that the isolation distance of your posts to the metal is app. 2mm and we assume that the Rho of the PVC of the binding posts is app. 1E+13 Ohm-cm and allow 20% max resolution influence

There is ~1mm air gap between outer and inner isolation in parallel with ~1cm height of insulation from nut to conductor, so this is not that bad.
Besides the posts, the leads have major influence and proper way would be using triax cable, connectors and proper measurement system (not affordable).
Nevertheless you are right that this is not the correct way to build precision very high resistance standard, though I would not call the used 1G a very precision one  ;)

RCA is for temperature measurement with 10k NTC, guard/shield is blue post.
 

Offline voltlog

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #34 on: January 04, 2019, 08:55:44 am »
Really nice, clean construction. I like it  :-+
 
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Offline Inverted18650

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #35 on: January 07, 2019, 12:23:39 am »
Now I want one...T.E.A.!

Offline The Soulman

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Re: Using gold plated brass binding posts on a resistance reference box
« Reply #36 on: January 07, 2019, 12:49:44 am »
1G looks out of whack in this box. Also 4-wire connection is pointless for high resistance like this.  :-//
But insulation and guarding on other side become very important.

Yes it is, do not take the 1.21G as serious  :-DD
This happens when you have space left on final design and do not want to waste it, so there came 2 more posts and this is the result.

If we assume that the isolation distance of your posts to the metal is app. 2mm and we assume that the Rho of the PVC of the binding posts is app. 1E+13 Ohm-cm and allow 20% max resolution influence

There is ~1mm air gap between outer and inner isolation in parallel with ~1cm height of insulation from nut to conductor, so this is not that bad.
Besides the posts, the leads have major influence and proper way would be using triax cable, connectors and proper measurement system (not affordable).
Nevertheless you are right that this is not the correct way to build precision very high resistance standard, though I would not call the used 1G a very precision one  ;)

RCA is for temperature measurement with 10k NTC, guard/shield is blue post.

The 1G resistor should have just two terminals connected to it, this could have done without additional space or costs.
Now you have unnecessary leakage from all other terminals, probably not a problem in your application but my ocd told me I should mention this.  :scared: 

Otherwise nice construction with the box in a box.  :-+

But what about temperature rise with sustained sources and the stagnant air trapped inside the outer box?  :scared:
Probably time for medication.
 


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