Leeds and Northrup resistance standards - oil bath? General maintenance. - Page 1
Forum section: electronics / general

author: Rax
author_rank: Super Contributor
timestamp: December 29, 2022, 02:52:10 pm
content: Hi all,As I'm going to be receiving a set of these shortly, I am trying to figure what's needed for this.For instance, they seem to shine when provided with a proper oil bath. Has anyone having taken this road before have pictures, or some indication as to how to handle it? I assume they all have oil inside, but that it's likely this will need to be replaced for continued duty.With that in mind, what exact oil is considered to be appropriate? All I could find is "good quality mineral oil," which doesn't really say anything. Is there a known specific oil last recommended for these resistors, when they were still supported?In terms of what reference temperature they're trimmed for value (assuming that's part of the fabrication process) - it seems to me this is 25C. Is that true? I am thinking of it separately from the measured and attached to the resistor (if one's lucky) value post-fabrication. I am not sure I have all this nailed down in my head.What about conditioning of the terminals? I assume no one's messing with mercury on these, so what would work well? I read on some "silver dip" stuff but would be curious hearing more on this.(the specific L&N resistors I am getting is a set of 40XY-B types)Thank you.

author: Villain
author_rank: Regular Contributor
timestamp: December 29, 2022, 03:26:20 pm
content: Some info can be found here:https://xdevs.com/review/ln4040b/Basically without temperature controlled oil bath these resistors are quite useless due to high tempco.So not very friendly for hobby-use. Long term stability is quite good though.Can not say much about the oil. Also don't really understand the following:"In terms of what reference temperature they're trimmed for value (assuming that's part of the fabrication process) - it seems to me this is 25C. Is that true? I am thinking of it separately from the measured and attached to the resistor (if one's lucky) value post-fabrication. I am not sure I have all this nailed down in my head."Why would one care how the resistor was characterized 30 years ago. Absolute value, tempco and long term stability need to be characterized by you anyway if you are serious about it. All these parameters can change over life span of the resistor if abused. Absolute value of the resistor does not matter anyway, only that the value is known is important.Tempco curve does not seem to be trimmed for 25 C if you look at the xdevs data. Which does not matter if you have temp controlled oil bath.

author: Bud
author_rank: Super Contributor
timestamp: December 29, 2022, 04:19:13 pm
content: Quote from: Rax on December 29, 2022, 02:52:10 pmFor filling RF 50 Ohm dummy load cans people use clear mineral oil from drug stores. It is sold as laxative and as such is clean and safe for even human consumption. I used it for my Bird dummy load and once i put it in, I scanned the dummy load with a VNA and the impedance was bang on aganst the specs, meaning the oil's dielectric constant was very close to the original oil.

author: Gyro
author_rank: Super Contributor
timestamp: December 29, 2022, 04:52:07 pm
content: There was a discussion on suitable mineral oil (yes, pharmaceutical) here...https://www.eevblog.com/forum/metrology/oil-for-a-leaking-tinsley-standard-resistor/

author: Rax
author_rank: Super Contributor
timestamp: December 29, 2022, 06:34:36 pm
content: Thank you, Villain, Bud, Gyro.Another tricky thing with these is the potential mercury contamination of the terminals. As far as I know, mercury is volatile, so in my mind, any traces should be long gone - I assume any recent reconditioning of the terminals must have been done with other materials than mercury-based - but would appreciate other thoughts and input.

author: Gyro
author_rank: Super Contributor
timestamp: December 29, 2022, 08:49:51 pm
content: Metalic Mercury evaporatesveryslowly at room temperature, Mercury amalgams - can bewaayslower. Taking Silver/Mercury amalgam tooth fillings for example, I saw a demonstration of how it is possible to liberate traces of Mercury vapour by rubbing the surface with a swab, decades after they were inserted.If there are traces of amalgam on the surfaces, then they should be treated with caution, hand washing etc. Maybe covering the tips in some way. For a precision resistor, you clearly can't use high temperatures to drive off the Mercury.

author: bdunham7
author_rank: Super Contributor
timestamp: December 29, 2022, 09:11:32 pm
content: Quote from: Rax on December 29, 2022, 02:52:10 pmI'm not 100% sure, but I would think that mineral-based transformer oil would be more appropriate than food-grade because transformer oil is specifically processed to be very dry, <10ppm moisture.As for the external bath, they could use either water or oil. I'd think water would be the easiest to deal with, perhaps with some additives. However, if the resistor is filled with oil you can use a thermometer in the center well to keep it to a range of +/- 1C or better without any bath. The TCs aren't going to bethatbad, at least if the resistor is still in good condition.https://us.flukecal.com/products/temperature-calibration/calibration-baths/special-application-baths/700971087015-resistor-0

author: Bud
author_rank: Super Contributor
timestamp: December 29, 2022, 10:10:20 pm
content: Transformer oil sure, the problem is it is not easily obtainable. You cant go to a Home Depot and get a quart.

author: Vgkid
author_rank: Super Contributor
timestamp: December 30, 2022, 12:37:02 am
content: Here is a short piece of info on the manganin used.

author: jonpaul
author_rank: Super Contributor
timestamp: December 30, 2022, 01:54:38 am
content: Bonjour cher MonsieurAs an undergraduate, worked for Loebe Julie at Julie Research Laboratoire in NYC 1967Résistance wires like Maginin were from Driver Harris and Wilbur B Driver, we added series winding of temp comp eg Balco to get near zero TC.I believe oil baths were mineral oil, transformer oil is spec éd for other properties at hot spot terms 85..125 C, and high voltage standoff, viscosity vs temp.Most JRL voltage std cells used oil bath, very few resistance. The important reason of the oil was is isothermal throughout the element..Some were " air bath" well insulated enclosure, no oil.I still have some JRL resistance,.005% 10 ohm...100k etc, all molded dry axial, some 4 terminal, still in spec.My L&N standard 1k is the cylinder, bus bar termination 4 wire, also still in spec!I would check it in an oven with fan circulation, the oil may not be needed.Bon chanceJon

author: bdunham7
author_rank: Super Contributor
timestamp: December 30, 2022, 02:08:22 am
content: Quote from: Villain on December 29, 2022, 03:26:20 pmThis is true within reasonable limits. However, if you are using these to calibrate meters, some closed-case calibration models don't allow you to enter specific values. You need to provide it with the exact value specified during calibration. Most such meters will have tolerances much larger than the deviation from nominal of a reasonable standard resistor, but if you have more than 0.01% (100ppm) variance, you may run into this issue.

author: Villain
author_rank: Regular Contributor
timestamp: December 30, 2022, 04:23:16 am
content: Quote from: bdunham7 on December 30, 2022, 02:08:22 amIn such case you can always use the resistor to mathematically calculate the error of the dmm and account for that after the measurement.