leeds northrup resistor box - Page 1
Forum section: electronics / general

author: NANOJOLTS
author_rank: Contributor
timestamp: June 24, 2024, 01:49:39 pm
content: Hey, anyone have information on this Leeds & Northrup 4790 resistance box?10 Ohms fixed with +1.11111 -0.111111 Ohms resolution? Waidner Wolff.Thanks Norm

author: ch_scr
author_rank: Frequent Contributor
timestamp: June 24, 2024, 02:01:01 pm
content: Explanation of the "Waidner-Wolff" from NIST:https://nvlpubs.nist.gov/nistpubs/jres/15/jresv15n5p477_A1b.pdfTL;DR: "It consists essentially of a relatively small fixed resistance shunted by another larger resistance, the latter variable by means of a dial switch,in 10 unequal steps, so chosen that the resultant resistance is variable in 10 equal steps, and for the highest step the resistance of the shunt is infinite."

author: NANOJOLTS
author_rank: Contributor
timestamp: June 24, 2024, 07:13:58 pm
content: Just a odd-ball resistance box I thought I'd share. I was thinking more along the lines of what practical application?I've never encountered of a 10 Ohm resistance box with steps of 10.000001 9.999999.Limit of Error Specs +/- 0.05% +10uOhm. I wonder about the Tempco of this box?I found a RTD resistance box (General Resistance) that claims to utilize the Waider-Wolff Shunt type circuit.I'll have to do some measurements/comparisons to other resistances.

author: Vgkid
author_rank: Super Contributor
timestamp: June 25, 2024, 07:49:36 am
content: Wow , you found the L&N decade box I have been searching for.Regarding specs that is the only other information I can find. A guess for the temperature coefficient is that it would be rather high, as there will be alot of wiring I did recall seeing an "S" variant that had the milliohm division as its smallest.For modern use these are used for rtd/strain gauge simulators.Historically they form one of the arms of a mueller temperature bridge.I own the general resistance rtd simulator. Even with a 34420a , it is hard to measure milliohm changes in a 10ohm circuit then again it is a noise issue.Edit: here are some links to a microhm decade other than the nbs ones.https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.osti.gov/servlets/purl/4479228&ved=2ahUKEwjA9rrpovaGAxX9HUQIHduZBJcQFnoECBgQAQ&usg=AOvVaw1-V4UWq3Wslg178uzCSbTh

author: NANOJOLTS
author_rank: Contributor
timestamp: June 25, 2024, 06:42:59 pm
content: Hey, here's some pics of a comparison of a (RTD-100X 10.000 Ohm 0.005% General Resistance) and the (L&N 4790 resistor box). appox. 23 degrees.I used a couple PXI-4071's DMM'S that I calibrated awhile back. Chart runs about 20min.Sorry about the mess.

author: Poroit
author_rank: Frequent Contributor
timestamp: June 26, 2024, 02:41:22 am
content: Leeds & Northrup were a large Process Instrumentation Company who manufactured Chart Recorders, Thermocouples, RTD,s etc and also a range of supporting calibration equipment like Potentiometers, Decade Boxes etc.They were very strong in Temperature Measurement and developed lots of gear for Foundries.One application I can think of for your decade box would be for calibrating Analogue Temperature Indicators where you need an accurate decade box to substitute the lead resistance of Thermocouple Compensation cable. You would use the decade box to substitute the lead resistance and a potentiometer as the voltage source. There were handbooks of Reference Table for all the common thermocouples and RTD's which gave you mV versus Temperature or Resistance versus Temperature with 0.1°C resolution.Showing my age here

author: donlisms
author_rank: Frequent Contributor
timestamp: June 27, 2024, 03:19:22 am
content: Resistance decades like this were used as the adjustable arm of a Wheatstone or Kelvin bridge. An important one was used in the Wenner bridge at the National Bureau of Standards.With 1ppm resolution at 1:1, it becomes 0.1ppm with a 90 ohm resistor in series, or 0.01 with 990 ohms. Linearity also improves.The absolute value of the 10 ohm nominal would not be a big deal, as a bridge is a relative device. The absolute value for the measurement is in the standard resistor being compared to.

author: NANOJOLTS
author_rank: Contributor
timestamp: June 28, 2024, 01:15:51 am
content: Yes I attached a RTD box set at 990 Ohm to this 4790 box. Now that makes it 1000.000001 or 999.999999 Range 1001.11111 or 999.888889.I'll post a pic if I get get some good readings.