Author Topic: Teardown: Standard Resistors  (Read 142086 times)

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Offline plesa

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Re: Teardown: Standard Resistors
« Reply #150 on: September 04, 2017, 08:44:34 pm »
The initial accuracy of 20ppm on the untrimmed decades would be difficult to match. The 0.1 ohm decade on my RS925D has signs of filing/sanding where they adjusted each step by hand. Not sure about the 0.01 decade but it was probably done the same way.

In HARSX series the 0,01 and 0,1 Ohm ranges looks like trimmed by solder joints inside bend area. I can post some pictures. On TiN picture the solder has been evaporated :-)
I like the shadows on front panel. RIP \$\Omega\$
« Last Edit: September 04, 2017, 10:31:26 pm by plesa »
 

Offline manganin

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Re: Teardown: Standard Resistors
« Reply #151 on: September 05, 2017, 08:40:20 am »
0.1 ohm decade is cooked to coal condition. Other decades "seem" to work, but I'd be very surprised if whole box is any good other than metal enclosure and binding posts.

Luckily the lowest decade resistive elements are identical to the ESI DB series decade boxes, which are very cheap. Especially the low resistance ones.

Note that the DB series has only two parallel switch sections while the 924D has four.

By extending the spindle you can parallel all six sections, there is plenty of space. Better than the original...

 
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Offline Edwin G. Pettis

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Re: Teardown: Standard Resistors
« Reply #152 on: September 05, 2017, 05:20:36 pm »
Hello TiN,

It is really aggravating when someone abuses precision equipment like this, I hope they got fired for it, no excuse.  You could have a case for a refund given the condition it is in, definitely not in working condition by any definition.  That decade was severely overloaded, the resistors are definitely ruined, the switch might be recoverable hard to tell from the photo.  The blackening on the panel indicates severe stupidity.  If the switch could be recovered, it would be possible to rebuild the resistor chain since it is of Manganin alloy.  However, given the design of the 925D, the 0.1? decade has to calibrated to the 925D's 'zero' ohm value which is different for every unit, just 'plugging in' another decade will result in higher error.
 

Offline TiN

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Re: Teardown: Standard Resistors
« Reply #153 on: September 05, 2017, 06:55:08 pm »
Just got the message from seller, with promise to honor my partial refund requestGot the agreed partial refund, leaving me which what it is.
So eventually I'll be looking on ways to restore this unit, however at this point it likely to collect dust on the shelf, until I get decade element for replacement.

In the end whole thing must be calibrated, so I'd expect current "zero ohm value" doesn't mean anything anymore. What puzzles me a bit, how the other decades are not damaged (at least visually) as per my understanding they all in series? Maybe operator had all higher decades set to zero, and was trying to use RS925D as a 0.x ohm shunt?? That would be the only possible explanation.
« Last Edit: September 06, 2017, 12:31:27 am by TiN »
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Offline Edwin G. Pettis

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Re: Teardown: Standard Resistors
« Reply #154 on: September 05, 2017, 07:51:38 pm »
The .01? minimum value consists of the interconnect wiring between the decades (at 'zero' setting of course) plus the minimal error contributed by the vernier resistance which is not quite 'zero' either.  The 1st decade setting of the .01? bank is adjusted to correct (as best possible) for that total 'zero' resistance, the subsequent settings on the .01? decade are accordingly adjusted at each step and so on.  The 0.1? decade resistors are adjusted to the .01? bank.  The 1? and 10? banks are wound and either selected or adjusted to also account for the lower bank's error to stay within the required accuracy spec.

Since your 0.1? decade is destroyed and possibly the switch as well, the only compensation required to the total 'zero ohm' net resistance is if a new switch has a significantly different 'zero' resistance that the original switch if replaced.  If the resistance of the new switch is sufficiently different to throw the accuracy of the other low ohm banks off of spec, then you would indeed have to re-calibrate the lower decks.  This is a cascade failure in that one low end bank could cause the entire low end to require re-calibration and the upper adjustable banks need to be re-calibrated anyhow after traveling and obviously being mishandled, its accuracy/calibration is unknown.  I would also verify that the .01? resistors are okay, that black on them may be just blow back from the 0.1? resistors but then....maybe not.  There is no public copy of the calibration procedure for a newly made RSxxx standard.

When time permits, I would first remove the damaged resistors and then clean up the switch decks and see what condition they are in before doing anything else,  the question of whether or not the switch requires replacement is the first step, we already know the resistors are toast (literally!).

Personally I have never seen an RS925D is such bad condition, sometimes I've seen dec boxes with damaged resistors (DB series or even SR-1010s) but usually standards of the RS725 or RS925 series are treated with kid glove care, they are worth too much for such tomfoolery.

May I inquire what country this came from?
 

Offline TiN

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Re: Teardown: Standard Resistors
« Reply #155 on: September 06, 2017, 12:35:11 am »
I've also got a word that decade from new IET RS925 are not compatible with this older ESI unit. It came from USA as most of my stuff :)
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Offline Edwin G. Pettis

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Re: Teardown: Standard Resistors
« Reply #156 on: September 06, 2017, 01:42:33 am »
Well, I'm not too surprised, IET has been busy trying to cut costs some as those older ESI switch decks were of very high quality and weren't too cheap back when ESI  was buying them.  I'd say if you want to try and save this unit, start by cleaning and checking the switch, if that is still in good shape, that is one less hurdle, next would be replacing the resistors and re-calibrating it, could be worth the trouble.

Argh, it appears that this website doesn't support standard special character coding, it changed my Omegas into '?'....tsk, tsk.
 

Offline TiN

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Re: Teardown: Standard Resistors
« Reply #157 on: September 06, 2017, 04:54:28 am »
Will do, Edwin, thanks for suggestions. I might also first test higher decades by bypassing the lower side connection, just to check if whole thing worth the efforts.
Based on smoke marks it would look like there was open fire of spacer at 0.1 decade, which could very well caused PWW's above it to be cooked as well.
I'd expect resistance wire stability may be affected by that.

And yea, none of Ω ° ± stuff working here. Another reason why I maintain own site :D.
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Offline alm

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Re: Teardown: Standard Resistors
« Reply #158 on: September 06, 2017, 06:08:44 am »
\$ 1 \Omega \$ (Mathjax) works on the desktop version.

Offline sarel.wagner

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Re: Teardown: Standard Resistors
« Reply #159 on: September 06, 2017, 09:53:39 am »
My lesson also learned on the DB788, burnt  :palm:  but not quite as bad as Tin's unit.... Managed to get some NOS resistors to repair. Also talking to Edwin about that first decade resistors.

Rgrds

Offline manganin

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Re: Teardown: Standard Resistors
« Reply #160 on: September 06, 2017, 10:15:38 am »
What puzzles me a bit, how the other decades are not damaged (at least visually) as per my understanding they all in series?

I = U/R and P = U*I

Low voltage / high current supply will damage the lower decades. In case of high voltage / low current supply the higher decades will suffer.

Higher decade switches are probably just fine. The switch current carrying capacity is much larger than the switching capacity.

The ESI 801 source is not able to damage the 925D, even if directly connected. Must have been something with output current much higher than 2A.

 

Offline manganin

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Re: Teardown: Standard Resistors
« Reply #161 on: September 06, 2017, 10:21:14 am »
IET has been busy trying to cut costs some as those older ESI switch decks were of very high quality and weren't too cheap back when ESI was buying them.

GenRad 1433 by General Radio:




Genrad 1433 by IET Labs:




More IET photos:
http://www.edn.com/design/components-and-packaging/4421782/When-wires-become-components

 
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Offline CalMachine

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Re: Teardown: Standard Resistors
« Reply #162 on: September 06, 2017, 03:47:13 pm »
Quality and craftsmanship has hit a rock bottom, it seems...  Thanks IET!  :--
« Last Edit: March 09, 2018, 01:29:37 pm by CalMachine »
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Offline Macbeth

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Re: Teardown: Standard Resistors
« Reply #163 on: September 06, 2017, 08:11:35 pm »
Just look at the ludicrously overpriced relabeled IET DE-5000/6000 debacle compared with the Taiwan DER EE DE-5000 and all the bullshit that goes with it.

I've always wondered why Dave gave a glowing review and never used it since, he always uses his Agilent LCR like with the $7 AVR 328 Transistor Tester review that is so recent.

 

Offline cellularmitosis

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Re: Teardown: Standard Resistors
« Reply #164 on: April 12, 2018, 04:03:11 pm »
Just came across this powerpoint presentation about the history of the Ohm and resistance standards.  Great intro to the subject!

https://pdfs.semanticscholar.org/presentation/7395/d0272221da51ebe5b45970a3bb55c29d0f30.pdf
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Offline ManateeMafia

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Re: Teardown: Standard Resistors
« Reply #165 on: April 12, 2018, 04:19:54 pm »
nice find.  :-+

It is good to see some of my own standards covered and their history. There is an article out there that describes the method used to build a 4210 resistor and how the wire was annealed including temperatures. Have you come across that one?
 

Offline Dr. Frank

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Re: Teardown: Standard Resistors
« Reply #166 on: April 12, 2018, 05:48:16 pm »
Very nice presentation, thank you!

Resistance  \$\Omega\$ seems to be a typical German affair: Georg Ohm, Werner von Siemens, Wilhelm Eduard Weber, Otto Wolff, Reichsanstalt Ohm, von Klitzing QHR... great evolution story.

Next year, 20th May, this story will come to a finish, as the Ohm will have a zero definition uncertainty, and an extremely small realization uncertainty, due to being a quantum standard, finally.

Frank
 
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Offline Vgkid

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Re: Teardown: Standard Resistors
« Reply #167 on: April 12, 2018, 06:09:20 pm »
nice find.  :-+

It is good to see some of my own standards covered and their history. There is an article out there that describes the method used to build a 4210 resistor and how the wire was annealed including temperatures. Have you come across that one?
Here you go
Stability of double-walled manganin resistors - Nvlpubs.nist.gov…
PDFhttps://nvlpubs.nist.gov › nistpubs › jres

Another good one:

A new design of precision resistance standard - Nvlpubs.nist.gov…
PDFnvlpubs.nist.gov › jresv5n2p295_A2b


« Last Edit: April 12, 2018, 08:13:33 pm by Vgkid »
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Offline alm

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Re: Teardown: Standard Resistors
« Reply #168 on: April 13, 2018, 06:04:42 pm »

Offline Vgkid

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Re: Teardown: Standard Resistors
« Reply #169 on: April 13, 2018, 07:00:39 pm »
Thanks , my phone doesn't like to copy certain links for some reason.
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Offline ian.ameline

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Re: Teardown: Standard Resistors
« Reply #170 on: April 23, 2018, 05:02:22 pm »
I have recently acquired a General Radio 1433-M in very clean condition. I've tested it (as well as I can with an HP34401A with kelvin probes, and using recommended metrology practises.) All of the values on all of the decades are within 0.01% +- 2mOhms, with the exception of 3 of the values in the 100 Ohm/div decade -- 500 Ohms is high by 0.012% and 600 and 700 are high by 0.011%. Several other values in this decade are at 0.01% high.

The other decades are all closer -- the 1k/div has all values within 0.001% !!!. The highest decade is about 0.005% low, and the low three decades are between 0.004% and 0.009% high, with the exception of the 100 ohm/div decade which is 0.009% to 0.012% high.

Other than cleaning the contacts with deoxit (as recommended by IET Labs) is there anything else to be done? I don't think I can say with any confidence that the unit is in or out of spec without something with more precision and less uncertainty than an HP34401A.

The IET documentation says to lubricate using Synco Super-Lube with PTFE -- would not the PTFE particles suspended in the synthetic grease increase contact resistance? This unit at 0 measures at under 2.5 mOhm using kelvin probes on my HP34401A. The General Radio specs for these switches was  < 0.5 milli-Ohms of contact resistance. With the exception of the three values above, it is so precise, I'm reluctant to fuck with it.

Any advice?


 

Offline Edwin G. Pettis

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Re: Teardown: Standard Resistors
« Reply #171 on: April 23, 2018, 05:44:13 pm »
According to original General Radio specs, the 1433-M accuracy is ±0.01% + 2m \$\Omega\$, so it appears that most of the resistors are within tolerance, with a few of them close to the limits and some of the 100 ohm units a bit on the high side possibly.  The newer IET versions are using significantly lower quality switches and they appear to have began replacing mica card resistors with film/foil resulting in lessor specifications.  This is probably due to their inability to manufacture the mica card resistors.  Given the accuracy of the 34401A on low ohms range, a fair number of your readings are on the 'ragged' edge of being out of tolerance.

In my opinion, the older genuine GR units are of higher value than the new units.
 

Offline Vgkid

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Re: Teardown: Standard Resistors
« Reply #172 on: April 23, 2018, 06:45:25 pm »
Thr new IET 1433's appear to use the same switches as the ESI DB(the old ones , and probably new as well) series boxes.
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Offline ian.ameline

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Re: Teardown: Standard Resistors
« Reply #173 on: April 23, 2018, 07:18:28 pm »
According to original General Radio specs, the 1433-M accuracy is ±0.01% + 2m \$\Omega\$, so it appears that most of the resistors are within tolerance, with a few of them close to the limits and some of the 100 ohm units a bit on the high side possibly.  The newer IET versions are using significantly lower quality switches and they appear to have began replacing mica card resistors with film/foil resulting in lessor specifications.  This is probably due to their inability to manufacture the mica card resistors.  Given the accuracy of the 34401A on low ohms range, a fair number of your readings are on the 'ragged' edge of being out of tolerance.

In my opinion, the older genuine GR units are of higher value than the new units.

On the 1 Ohm/division all but one reading was within the 2 milliOhm uncertainty, and the single one that was more than 2 milliOhms was 2.2 milliOhms out. So I think those ranges are ok (within what a 34401 can say). Its the 100 Ohm/step decade that is on the "ragged edge".

I'm attaching the readings (the 0 offset has been subtracted from all readings on each scale of the 34401) The "corrected" column is the actual readings with up to 2 milliOhms of error subtracted. (The 34401 had been on and connected to the unit with kelvin probes for 24 hours no movement or touching other than turning the knobs and waiting for 30 seconds, temp is a constant 22C, with no gradients or breezes) The readings are very stable and very reproducible - to within 1 digit in the least place every time.

I agree that the older units seem to be much better built. I've ordered some deoxit -- I wonder if it can trim 10 milliOhms off the resistance of the 100 Ohm/Step decade...

Still, for $140, not too bad. IET wants $2300 for a new one.
 

Offline ian.ameline

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Re: Teardown: Standard Resistors
« Reply #174 on: April 23, 2018, 07:31:02 pm »
Given the accuracy of the 34401A on low ohms range, a fair number of your readings are on the 'ragged' edge of being out of tolerance.

For the low ohms range, the 34401 is 0.01% of reading + 0.004% of range (which is 100 Ohms.) For the 1K range it is 0.01% of reading + 0.001% of range.

So for 500 Ohms, it would be 50 milliOhms + 10 milliOhm -- 60 milliOhms of uncertainty. My reading for the 500 Ohm setting on the 1433-M is 500.062 Ohms. Just outside of the uncertainty of the meter -- So without a more accurate & precise meter, I don't know that I can say that the 1433 is out of spec. (Which should be +- 52 milliOhms for a setting of 500 Ohms.)

 


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