Teardown: Standard Resistors

[LorenzoDL]

May be a little off topic because for now I didn't tear them down, but here are some photos of two standard resistor, one 10Ohm and one 100Ohm that I bought in a fair for 20 Euros each last week.
There is not much documentation available online, and especially the one from Tettex seems quite good construction quality with silver plated terminal.
If you have some info on the resistor I would like to get them, I would also search  for more info and post some better hi res photos on my blog delucalabs.com

This is my first post in this thread (and in the metrology section actually) but I was a fervid reader of all the sections and expect more posts from me because I have an Advantest R6581T coming and a Fluke 5440B/AF on the repair.

Lorenzo

[Alex Nikitin]

I was fortunate to obtain four ESI SR-1 Standard Resistors recently, from my measurements they are much better than the specification suggests (perhaps ageing helps?). For this thread the most interesting is the 10M standard as it is internally very different from the rest (the other three internally about the same as shown at the very beginning of this thread). After it has stabilized in my lab it comes very close to my local understanding of what 10 MOhm is  (inside 10ppm).

Cheers

Alex

P.S. - only on the 10 Ohm unit the date of the original calibration is (barely) readable - 6/15/83 . 41 years old.

P.S. - I've added the label from 10M unit. The date is not readable but the original value 9,999,900 Ohm is clear. My current measurement shows 10.00003 MOhm (OK, +/- 20ppm) .

[Victorman222]

A teardown of decade resistor box R4002 (Р4002 in cyrillic) made by the Mikroprovod factory in Chisinau. The box features 4 decades: 10k, 100k, 1M, 10M and an accuracy class of 0.05%. When i got the box, two resistors were broken (open), some resistors had their end caps touching since they are held in place only by their leads. On further inspection i discovered that all resistors drifted up about +0.03%...+0.07%.

At the top of the box we can see the binding posts. Interestingly there is a tap point before the last resistor on the 3 higher decades.

After removing the front panel we can see the decade switches mounted on a rubber gasket. At the back there  is a small hatch also mounted on a rubber gasket. After removing the rear hatch the decades can be desoldered, unscrewed at the front and pulled out.

[Victorman222]

Now onto the pictures of resistors and decade switches. The resistor assemblies are made in an interesting way - resistors soldered to brass posts screwed into brass switch contacts. The switch wiper is also interesting, bent copper piece melted into the rotating part of the switch.

[Kosmic]

Fluke 720A hermetically sealed & oil filled resistors







P.S: I found those online. I'm not responsible for the disassembly.

[trobbins]

Those pen markings are likely pos and neg ppm levels, and used to suppress total tempco.  Perhaps the individual tempcos were measured beforehand, rather than on the final pcb assembly.

[baltersice]

Happy World Metrology Day! Here are some scandalous ESI SR104 x-rays. This is SN 307129 with an unknown date of manufacture (white box, black top plate, classic orange black gold ESI badges)

[zlymex]

X-Ray of IET SRL-10k

[Overspeed]

Hello

I link some pictures of AOIP ( french made ) standard resistor

Two type are available the std and the h type h for haute precision

the original doc is readable but the quality is poor

Regards
OS

[felixd]

How is your reference behaving after 9 years? 

Im intrigued to see how the trim the srx to 10k, as the vishay is 9.995k. I will need to look at the pics,for the possible series resistor.

I updated to include the schematic of the trim part.

I knew it's true, they have mislead me before. Although didn't  order a few thousand, but a few hundred is more than enough. When my first order of 50 VHP101 came, it arrived in one plastic bag.

Ohh please do tell - what's your experience with respect to the 'typical' 2ppm/6 years claim? Even a few weeks worth of data could be very interesting.

I didn't test the aging in a systematic way for all, but I made a standard resistor out of them in 2008 and the result is superb. Have a look at photos below, the value is virtually unchanged in five and half years time.

[zlymex]

How is your reference behaving after 9 years? 

Very good, but there is sign of acceleration.

[DB4UCH]

Here are some pictures of a Hartmann & Braun (H&B) 100 Ohm “Normalwiederstand” (reference resistor):

I recently acquired this one on eBay for 33€ (including shipping). I sadly wasn’t able to find any information about this resistor other than that the manufacturer has built standard resistors since the late 19th century. (The company is now part of ABB.)

It seems to be based on a coil of Manganin wire that is wound around a metal (brass maybe?) cylinder. This cylinder is mounted to the (seemingly Bakelite) base plate while the resistance element itself is connected in between two big bus bars that the connect the force and sense screw terminals to one another.

This resistor seems to have been calibrated in April of 2024 where the value was determined to be 100.0127 Ohms. As I don’t have any information on how exactly this value was measured (temperature, measurement current, thermal offsets) I can’t accurately verify this value. Using my “reference” 34401A I get a value of 100.0123 Ohms at 21.3 °C. Both values are slightly higher than allowed by the 0.01% specification.
The TC seems to be pretty poor at +20PPM/K. (my quick guesstimation)

Does anyone here know more about this reference resistor? (There also exists a 1 Ohm variant that was also sold on eBay at the same time although I was overbid there.)

Greetings,
Simon

Here is a translation of the label:

Reference Resistor
Manganin
Nominal Value ± 0.01%
From 0 to 0.1*Imax [0.3A]
Nominal Value ± 0.03%
From 0 to Imax [0.3A]
In air at 20 °C

[stijena1973]

Could You x-ray SR-104 ?   It will reveal internal construction without opening the oil can...

Just a visit to the dentist office and You'll have the answer we all await......

[negativ3]

I've never had to use these yet but it is fascinating none the less.
The solder used in the various construction, is it a special grade, 60/40 or something else?

[stijena1973]

Could You measure the dimensions?

I have the resistors, and want to make a replica of the whole unit.

(I need dimensions of the box also to be in line with the original...)

[Conrad Hoffman]

I've never had to use these yet but it is fascinating none the less.
The solder used in the various construction, is it a special grade, 60/40 or something else?

Some L&N standards used high cadmium solder for low thermal EMF. Frowned on today!

Also note that standards before 1948 will be 495 PPM higher than today because of a correction to the ohm at that time. So basically you'd expect a 1930s 100 ohm resistor to measure 100.05 ohms.

[Mickle T.]

Precision wire-wound resistors manufactured in the 1970s and 1980s by Takeda Riken for use in their own measurement equipment and standards (e.g., TR6120, TR6655, TR6877, and others). There are no datasheets online, nor are there any references to the existence of these resistors.
The TCR of several dozen resistors I tested was within +-5 ppm/K. The 100 ohm resistor (pictured) exhibited a monotonic drift upward in resistance at a rate of ~20 ppm/year (observed over 10,000 hours). Even simply bending the leads resulted in a resistance variation of +-5 ppm. After disassembling and re-soldering the wire-to-lead joint, the resistance decreased by 60 ppm.

[trobbins]

I've just checked the drift of a 33 year old SR1010-10k box.  1993 factory deviations ranged from +10 to +27ppm (ie. a span of 17ppm) for the twelve 10k resistors.  Whilst I can't confirm deviations from nominal, I was able to measure a deviation span of about 30ppm, with eight of the twelve resistors showing similar relative deviations, but four had noticeably drifted down in relative value.

The SR1010-1k in this post ( https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg4107907/#msg4107907 ) had been re-calibrated after 9 years, and showed worst-case drifts of +12ppm and -13ppm.

The ESI technique of using shorting bars, and series/parallel, and series connections, for 0.1x, 1x, and 10x transfer ratios is somewhat moot to lowish deviations between individual steps in a box.  Choosing a sequence of 9 steps for the 1x transfer, and 10 steps for the 0.1x and 10x transfers may need some selection of which end steps to avoid if they have  noticeably drifted away from the pack. 

In some of the teardown photos of ESI resistors, and in the photo below of my box, there appear to be 'scuff' patches on some sides.  Nothing consistent, and perhaps just blemishes of the enamel coating, but perhaps not.  I suppose its not implausible that they are related to a factory selection or testing or fitting procedure.

[Conrad Hoffman]

One technique for adjusting card resistors was to use a draftsman's electric eraser with an ink rubber, which is slightly abrasive, to abrade the wire and raise the value. This spot was then painted over with whatever they dipped the resistor in.

[Hydron]

I'm pretty sure this is value tweaking as suspected, it's more obvious in my ESI RV722

[trobbins]

Electric eraser - not for a fainthearted diyer trying to tweak their SR10xx box !!  Even the retrofitting of a 500Meg parallel resistor seems more achievable to do some tweaking. 

The SR10xx averaging of multiple paths still makes the 0.1, 1 and 10x transfer ratio's applicable as even significantly drifted end resistor steps may be able to be excluded from the transfer setup.  Maybe not quite the same outcome when using an SR10xx box for linearity testing (as per the RV722 calibration process), as I'd anticipate any additional deviation spread between box steps due to drift is not good.