Teardown: Standard Resistors

[Vgkid]

I look forward to reading about your 242 endeavors.
I have a feeling E.G. Pettis will chime in.  

[Edwin G. Pettis]

The SR-1010 10K does not need to be trimmable, it is directly compared to the SR-104 for each step and the readings noted, the trimmable SR-1010 is optional.

Okay, I chimed in......

[CalMachine]

The SR1010 I picked up a few months ago is the MTS version, and I've already trimmed each step to our Ohm Labs 10k standard resistor.  If I remember correctly (I'm not at the lab), but I think our Ohm Labs 10k standard has drifted about 2ppm over the last 5 years.  So it's holding pretty strong!   I plan on shifting it to our working standard once I can get a SR104 in our hands with sufficient data to use as our lab's primary standard.

I tore it down, slightly, and posted pics on page 4 for those interested!   

[ManateeMafia]

I thought you partially tore down your Ohm Labs 10k standard. I was disappointed they weren't there.   

Which model do you have? Is it the 104 or 204?

[CalMachine]

I thought you partially tore down your Ohm Labs 10k standard. I was disappointed they weren't there.   

   No way I'm opening up our current, freshly cal'd, 10k standard.

Which model do you have? Is it the 104 or 204?

We have the 100 (1 amp version) and 104.  I wish we had the 200 series!  We were really small back then when they picked them up, before I was around. 

[ManateeMafia]

A couple of years ago I got a quote on the 200 1 ohm model and the price was $3400.00

[PartialDischarge]

Very interesting thread.

However I noticed that very few resistance standards use an oil bath ( the Leeds Northrup and another potted resistor If I recall did use it), and none have heated ovens, something common in voltage standards.
Why is that? any guesses?

[TiN]

Elevated temperature accelerate aging drift.
Same apply to voltage references, but with them it's "lesser evil" and in the end result is better. Not so much for passive resistor though.

[PartialDischarge]

Elevated temperature accelerate aging drift.
Same apply to voltage references, but with them it's "lesser evil" and in the end result is better. Not so much for passive resistor though.

Hmm, well since voltage standards use resistors too, to set currents, and as voltage dividers, heat would be evil too in that sense.
I've been reading for example about the HP 735A, its basically a selected and ovenized (at 80ºC) 6.3V zener, whose output is divided to 1V via resistors, ie no op-amp feedback or similar. Two
of those resistors are inside the oven. If those resistors drift fast its game over for it. But these little things were pretty stable over time.

More about it here https://www.eevblog.com/forum/testgear/hp-735a-dc-transfer-standard/

[PartialDischarge]

Earlier this year I was too busy and missed this one, how is it not referenced here??

https://www.eevblog.com/forum/metrology/fsl-project/
https://xdevs.com/article/fsl935/

[Echo88]

Well, its a prototype, not a standard resistor. Regarding the HP 735A-post: The necessary resistors have to be inside the ovenized compartment together with the voltage reference, otherwise the temperature difference between voltage ref and resistor junctions would create drifting parasitic thermal emf voltages.

[PartialDischarge]

Regarding the HP 735A-post: The necessary resistors have to be inside the ovenized compartment together with the voltage reference, otherwise the temperature difference between voltage ref and resistor junctions would create drifting parasitic thermal emf voltages.

Oh, the HP735A was just an example to see that resistors are heated in voltage standards. The Fluke 732B also does the same. Thus my question of why we see no resistance standards with heating, but well Fluke also thought of that in the SL935

[ap]

There absolutely are resistance standards that are heated. E.g. Measurements International offers them. Price is steep though.
You can also diy for your labs, using oild filled precision resistors and a precision heater device.

[schmitt trigger]

Well... I'm back at it   This time the magical RS925D!   

Watching these images, I'm completely in awe, no, actually speechless, at the top-level workmanship of these units.

I'm pretty sure that this level of craftsmanship was obtained in a shop which employed only a very few, very skilled workers.
Ran by managers which were technically very competent.

Back then when the label: MADE IN USA actually meant something special.

[Echo88]

Interesting ap! A few standard resistors to check your equipment? Are they more suitable for some jobs than your 5720A?

[ap]

Actually I use 4808s as sources (which, btw, in many areas have better uncertainty specs than a 5720), but resistors uncertainties of calibrators are usually pretty high. The 5720 10kOhms spec is e.g. 9ppm for 90 days, +/-5K and 3ppm at +/-1K (plus factory calibration). A hermetic, thermo-regulated resistor has <0.5ppm/a uncertainty (plus calibration uncertainty). The temperature stability can easily be made better than 0.1K.

[Vgkid]

There absolutely are resistance standards that are heated. E.g. Measurements International offers them. Price is steep though.
You can also diy for your labs, using oild filled precision resistors and a precision heater device.

Do you have a build thread for your resistance standard. I feel like I have seen it before.

[ap]

There was some mentioning earlier, but no real build thread, just one or two more pictures.

[TiN]

It was unavoidable, at rate I'm lurking and buying stuff of evilbay. RS925D ESI arrived today. Great deal at 600$ huh?

Hmm, what is that rattling sound... 





Ah... those are bits of coal from the switch... ... 

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.
Oh well, don't go shoppin unprepared, dear precision-nuts. 

P.S. was listed as "used".

[cellularmitosis]

Thanks for the cautionary tale!  That's a bummer.

[Vgkid]

Damn, interesting things always happen when TiN spends money...

[CalMachine]

That is most unfortunate =(  I was hoping the RS925 you picked up was going to be a good one, so we can get some international transfers going     

We will have to resort to other plans.

Perhaps, now, you might have a donor unit for fellow precision-nutt hobbyists who might have faulty parts. (I don't know.. perhaps $50 or so per dial?  ) 

How does the µOhm vernier feel as you make complete revolutions?

[alm]

P.S. was listed as "used".

At least that gives you a shot at returning and/or receiving a (partial) refund. Ebay's description of used is "fully functional, but possibly some sings of wear that are described in the pictures and/or item description". So based on that, any non-described defect is a reason to consider the object not as described. Severe undisclosed defects make it significantly not as described.

[ManateeMafia]

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.

[TheSteve]

It was unavoidable, at rate I'm lurking and buying stuff of evilbay. RS925D ESI arrived today. Great deal at 600$ huh?

Hmm, what is that rattling sound... 

Crispy sadness.