Now this is a resistor substitution box! - Page 1
Forum section: electronics / general

author: FenderBender
author_rank: Super Contributor
timestamp: October 21, 2012, 07:26:41 pm
content: I was visiting NJIT today. College visit..I was in their power distribution lab. This is a real man's resistor substitution box. 1/4W? 1W? 10W? 100W?. Nah. 3kW!Just wanted to share.

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2012, 07:32:36 pm
content: Also doubles as a room heater and pie warmer if needed.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 21, 2012, 07:37:03 pm
content: I'd love to make a resistor subsititution box, but have no idea where to start , I noticed dave has a good one he built, something I'd like to make and should , like power supplies, that another item I'd like to build.

author: Monkeh
author_rank: Super Contributor
timestamp: October 21, 2012, 07:38:14 pm
content: Quote from: M0BSW on October 21, 2012, 07:37:03 pmA box, some binding posts, thumbwheel switches, and 1% 0.5W resistors. Start and finish.

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2012, 08:11:42 pm
content: Robenz has made some really good ones, very nice looking and very functional. My solution is a big box of assorted resistors, if not the right value then pretty close, or good enough.

author: PA4TIM
author_rank: Super Contributor
timestamp: October 21, 2012, 08:52:32 pm
content: Some 10 position switches, 1, 10, 100, 1000, 10000 Ohm resistors, ten each. You can make it as good as your budget allows. I had to buy a 0.01 % 1 ppm tempco resistor for the repair of a bridge. 15 euro for one resistor. But if you need 50 of those...1% resistors are not expensive and if you only want it as a substitution box it is even more easy. Just for intance a two deck 6 position switch and a switch to change between decks. For instance 10, 47, 100, 220, 470, 1K, 2K2, 5K6, 10K, 47K, 100K, 470K, 1M resistors. A second switch with some caps is also handy.http://www.pa4tim.nl/?p=2400http://www.pa4tim.nl/?p=3163some examplesFred

author: kripton2035
author_rank: Super Contributor
timestamp: October 21, 2012, 09:05:03 pm
content: Quote from: M0BSW on October 21, 2012, 07:37:03 pmhere you have a bunch of step by step tutorials to do it easy.hope this helps.http://kripton2035.free.fr/LabTools/lbt-resistordeca.html

author: notsob
author_rank: Frequent Contributor
timestamp: October 21, 2012, 10:49:56 pm
content: Here's the axial resistor versionhttp://www.digitalunderpants.com/?p=219

author: FenderBender
author_rank: Super Contributor
timestamp: October 21, 2012, 11:26:50 pm
content: I gotta say I don't see what the point of these sub boxes are...I mean shouldn't a potentiometer do the same trick?

author: Monkeh
author_rank: Super Contributor
timestamp: October 21, 2012, 11:31:49 pm
content: Quote from: FenderBender on October 21, 2012, 11:26:50 pmAnd can you achieve an accurate resistance from your pot faster than I can dial the number in?

author: FenderBender
author_rank: Super Contributor
timestamp: October 22, 2012, 12:03:44 am
content: Quote from: Monkeh on October 21, 2012, 11:31:49 pmOhm meter and a ten turn, I would think I could.Not against the substitution box, just trying to think of what application it would have.

author: Monkeh
author_rank: Super Contributor
timestamp: October 22, 2012, 12:04:42 am
content: Quote from: FenderBender on October 22, 2012, 12:03:44 amI really doubt you can do it faster than I can dial it in. And I don't have to hook up a meter to check it.Also, a worthwhile ten turn pot costs more than my entire box, and only goes up to what, 50k?

author: FenderBender
author_rank: Super Contributor
timestamp: October 22, 2012, 12:24:11 am
content: again not saying it's a bad thing to have. just don't go spending a million dollars on one of those IET GenRad ones...unless it's someone else's money of course.

author: Unknown
author_rank: Unknown
timestamp: October 22, 2012, 12:50:25 am
content: If I was going to put the time and effort in it might as well build a Kelvin Varley Divider instead. Add a precision voltage reference and Bob's your uncle.edit: Seems like the robenz substitution box can be used as a KVD, not sure though.

author: robrenz
author_rank: Super Contributor
timestamp: October 22, 2012, 01:43:05 am
content: Quote from: SeanB on October 21, 2012, 08:11:42 pmThanks SeanB, I am just finishing some of the final details of my decade box and then I will be posting a video of all its features.2.25" x 3.4" x .88" 1/4W thin film precision resistorsEach decade is 10 resistors in series with a pin socket at each resistor. Any number in series can be selected by where you place the supplied precision calibrated jumpers. 4 banana jack sockets provided that you can jumper to.Twofull 8 decade 0.1 to 1meg in one box. multiple resistances can be used simultaneously. You can get 4 resistances at one time like 1k or 10k or 100k or 1M for op amp circuits plus use any other resistors available at the same time.0.1% for the 10 Ohm thru 1 Meg decades. 1% resistors on 1 Ohm and 0.1 Ohm decades.0.1 thru 1k decade resistors are heat sinked.Any resistance selected can be a 4 wire kelvin connection if desired.Fan forced air thru the heatsinks when using it for higher wattages.No unknown residual resistances. All jumpers are calibrated values.Parallel attachment allows Paralleling 2 thru 20 resistors to get many intermediate reistances down to 5mOhm at 5W with kelvin connection. More to comeAlso seen at the beginning of this videohttps://www.eevblog.com/forum/projects-designs-and-technical-stuff/video-of-design-and-build-of-precision-kelvin-banana-jacks-and-header-pins/msg148204/#msg148204

author: PA4TIM
author_rank: Super Contributor
timestamp: October 22, 2012, 07:17:39 am
content: Nice made.A Kelvin Varley devider is a total different animal als a resistor box or decade box.Building one yourself is not a simple thing.You use a resistor box or resistor decade just like you could use a potentiometer but with more resolution ( getting a 1M potentiometer at 1 Ohm step is not possible, even using a 10K ) and if saves the trouble of disconnecting it and then measure it. What in many cases is not a problem but in others it is. Like using it as an D/Q extention in bridge measurements. It is also more save, you can not so easy by accident zero it or get a to low resistance,A KV is used as voltage divider for ratio measurements. You feed it with, or instance 10V and you can dial the output. Its an inginius system of switching while bridging resistors to keep a constant impedance. They are also terrible expensive, in the order of 15K dollar or so. You can not use them as resistorbox.The ESI resistor decades or IET, or GenRad ( GR) are precision boxes, they are used for bridge measurements, precision measurements, calibration ect, not to hook it up in a schematic as feedback resistor to find the right value ( allthoug you can use them for that too)I have bought a GR at a HAM fair for 10 euro that is from the 30's. Massive switched, wirewound resistors. Whitout a cabinet. Made one for it. Put a metal liner in it a few weeks a go to hield it. At home after the fair, I hooked it up to a 7,5 digit meter and it was after 80 years still within specs.Allmost creepySince I have one, i must say, i use it a lot. More then my two KV dividers ( a fluke and a ESI). They are coupled to Vrefs ( a Fluke 332, homebrew 10V, a Philips and 3 other Flukes) i use two as a test. If i get strange results i can test the deviders, reference or meter to calibrate. Like last time I found a common mode problem. The meter to clibrate looked non lineair, but it also could be the monitor-meter or KV. Then as test it showed excact the same prolem using the other KV. Also using an other monitor or other Vref.So the problem was in the meter or something else. But a monitor meter on the output showed the same roblem. Switched of all power exect the reference, monitor and meter to calibrate and the problem was gone. Still must fin the source of the prolem. So by having things double you can check and anlyse problems.But that had nothing to do with a resistorbox or the "real men resistor box" from the first pos that , i think, is just a passive dummyload. Replaced today by electronic loads.

author: kripton2035
author_rank: Super Contributor
timestamp: October 22, 2012, 09:56:13 am
content: yep - the nice cambridge micro ohmmeter at the back of the KV divider is some hundreds $ ... more than the 10$ of my decade box ...but robrenz as always very nice tool !can't wait to see another instructive video as you already did for the kelvin probes !

author: PA4TIM
author_rank: Super Contributor
timestamp: October 22, 2012, 12:08:34 pm
content: I do not think Roberts box is a KV devider.A 4 wire measurement is named after Lord Kelvin. Like temperature in Kelvin a KV devider has noting in common with 4 wire resistance measurements.Kelvin worked together for a while with Varley. Together they developed the Kelvin Varley devider. And that is not a 4 wire device. ( ok it has 4 or more terminals but 2 are Vref input en two are V-out. It is just a ( very) special kind of voltage-divider.But Varley has also more inventions on his name. Like the varely bridge measurement, used to find resistance faults in cable-wire.

author: robrenz
author_rank: Super Contributor
timestamp: October 22, 2012, 01:37:08 pm
content: Quote from: PA4TIM on October 22, 2012, 12:08:34 pmIt is not a Kelvin Varley but it can be jumpered in Kelvin Varley fashion. The decades are not 1/5 increments as in a KV they are 1/10. Since it is a double decade it can divide a voltage to .01ppm resolution (not accuracy)

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 22, 2012, 03:41:02 pm
content: Quote from: kripton2035 on October 21, 2012, 09:05:03 pmKripton you are a star thank you