Hi, It's time to talk about one of the handiest bits of test gear you can have in any lab. It's a Decade Resistance Box. now. This particular one I've got from I Labs is the Rs21 W It's a nine Decade box.

You can tell because it's got nine, uh, different switches on there from 0 to 9. so it's called a Nine Decade Box. It goes from 0.1 ohms up to 100 Megga Ohms 0.1% uh basic tolerance and uses thumb wheel switches instead of the instead of the traditional style uh rodor ones. Really quite nice.

Not exactly the hobbiest affordable level though. it's 539 us bucks. Woohoo! Okay, but they're supposed to be pretty darn good quality, manufactured with top quality parts and we'll get into that and uh, uh, you can get, uh, cheaper ones from starting from $174 but yeah, not quite the do- it yourself hobby level. But anyway, I Think it's very nice and here it is.

It's a nice small compact unit I Rather like it, but you can get that using these, uh, thumb wheel switches. You can actually, uh, manufacture quite a small unit. There's going to be a bit of uh Dead Space inside this thing, but it's you know, generally speaking it is a very small nine deade resistance box I Love it! Nice tough, tough polycarbonate Case by the looks of it. and uh, it's got two standard 4mm banana terminals on here, a binding posts, and uh, it's 9 decad and we can dial in any value up to here it is 99.999999 9 Megga Ohms Crazy! Now this one is actually uh, calibrated.

so it comes with a calibration certificate that's an extra 74 bucks if you want to get it uh, calibrated. but they give you a full test report we'll take a look at. and uh, here's the Um specs. uh, from zero to uh, basically 99.9 Megga Ohms.

As we said, in 0.1 Ohm steps, it's a uh 0.5 watt uh rating. so each resistor inside would be 0.5 Watts. But because they're in series um, that will actually uh, rise up to a maximum of 2.5 Watts Um, if you actually dial it in to uh a value of nine basically and the accuracy is uh, plus - 0.1% Plus 0. 36 owns because it will have when you're dialing zero, it will have that fixed uh, offset value there.

So it's nice that they've actually included that um, and if and but that accuracy only applies if you're between Uh 9 Ohms and Uh 10 Meg Ohms. If you're outside of that, it's going to be Plus -2% instead of Uh 0.1 and the zero resistance is less than Uh .5 OHS but it's manufactured by IET Labs I Haven't looked at any of their gear before, but uh, based on outside side, it's quite nice. And the best part about taking anything apart is of course breaking the calibration. Seal Recalibrating Seal Broken my ass.

Let's crack this thing open and here we go. Let's have a look inside. Tada Thumb wheel switches. No surprises there whatsoever.

That's exactly what I expected. A whole bunch of, uh, whole bunch of precision resistors mounted on the thumb wheel switches. Now, if you take a look, there's only five resistors per decade and that's not what I was expecting at all. Uh, I Was expecting the more traditional uh, 10 resistors per decade and having a 10 position thumb wheel switch, but they haven't.

They've gone for the reduced resistor count here and uh I you know I don't know why they've actually done that. It's rather curious. I Guess it's uh, you know it's simpler. It takes up less room, and when you custom designing um, these switches, if you're getting them custom made, well, why not? Uh, actually reduce your resistor count.

It's not a problem. So they've obviously gone in a configuration of um, like a one and then 2, two, two, two. So if you add them all up, 2, 4, 6, 8, and then nine, so you can dial in any value from 0 to 9 and that's what the values in there look like if you read the resistor color codes in there. Um, they've gone for the 12222 arrangement with um, some sort of, you know, um, multipole, uh switch Arrangement inside the thumb wheel switches.

Now here's the switch for the 0.1 ohm uh decade. As you can see, they haven't used traditional axial resistors they as they have on the other decades. Here, they've used. uh, they've used a resistance wire here and you can see they're slightly different lengths getting down.

well there. these are all the same cuz it's 2, two, two two and then that one down there is a different is a shorter length or half the length of the other one, so they've just tweaked those to get their 0.1 Ohms I'm not not sure why they've done that instead of using a Precision through hole resistor. Who knows now? I Really don't like this at all. Look, they've bodged on I Don't know why they've used, you know, nice formed uh leads on the resistors here and this one has just been bodged and hacksold it it like it's like they actually broke the lead on it or something and they extended it with a crappy bit of wire I don't know what's going on with there, that's that's really unacceptable.

I Don't like it and on the Uh 10 Meg oh Decco range here. of course they've got a single 10m resistor there on the back and then to get their 20 Megs instead of using a 20 meg resistor, you know, buying a custom 20 meg resistor, they've just whacked two of them in series are granted they're You know they've Twisted the leads here and they're sold of them, You know? No, no problems at all. but gee, I Don't know why couldn't they just order a bunch of Uh 20 meg resistors to order? I Don't know and you can see that these are actually Uh switches custom made by or for IET Labs uh ink and I actually uh, confirmed that with them And they do say that they are that they are actually custom designed top quality Uh switches specifically made uh for them. to the they basically claim that they are the most uh, one of the most reliable thumb wall switches uh, on the market.

Got extra thick gold plating inside designed for ultra low contact resistance, over age and stuff like that and well, that's what you'd expect in a um, you know, in a in a in sort of a professional level uh, decade resistance box that cost uh, many hundreds of dollars. You at least expect Uh custom switches like that and pretty much uh, that's what it comes down to is the reliability of the switches in these things because the actual resistors themselves they don't age too much. Although they do say I Labs do uh say that they do use Uh custom uh Precision resistors in here designed for long STM long-term stability they're 25 PPM so they're not setting the world Al light there. That's pretty standard, but um, they do actually manufacture these things for long-term reliability.

So the bottom line is if you go, uh, buy those thumb whe switches you can get you know 10 for 10 bucks on eBay or something like that from the one hung low Factory in China well there I you know, they might work um first go, but in 5 or 10 years time, they're probably not going to be uh working as well as these ones will. And here's the back of the Uh switches here. and as you you know it's it's fairly simple. All this all the stuff happens inside the switch of course, all the uh, complicated multipole uh switching arrangements so that you can actually use uh five resistors instead of Uh 10 and um, uh, basically this is the highest.

This is the 10 Meg position and look, the other ones are soldered just fine, but this particular one has solder in flux residue left over between the contacts and well, that's not what you want to see on the especially on the 10 Meg range. It's not going to matter right down in the Ohms range down here. but when you're up at 10 Megs stuff like that might matter and of course I wouldn't be happy unless I at least attempted to, uh crack one of them open. but they are um, heat uh state in there so I won't actually uh, physically, um, cut those out.

but uh, as you can see, that looks like the model number there of the uh of the particular switch in there and they are um IET uh lab, uh I Labs branded again there we go on the side there and uh, you can see the contacts in there and they look like dual wipe ones. It's going to be really hard to see in there, but uh, that would be a really thick high quality uh gold pla in with uh, very uh, top quality? uh dual wipe contacts? I'm sure see might think 500 bucks for a box like this is fairly expensive and well, you know if you're an individual, uh, it is. you can make one yourself for a lot cheaper. But you know if you use top quality uh, thumb wheel switches and they cost you, you know, 10 20 bucks each not the cheap one, hung low ones and you've got uh, you know, nine almost 10 decades there.

you know that could add up to a couple hundred bucks right there just for uh, good quality, uh switches so you know you have to look at that aspect of it really. But yeah, apart from, but, um, I'm quite disappointed by a few. Um, you know, bodgy aspects of the construction inside this, you know, a bit of residue left over they're using the um, you know, two series resistors down here. they should just cut it to one and that bodge solder joint there.

I Don't know what's going on, but I Have no doubt though, um, that this will, um, be a, um, quite a stable box over a long period of time. and uh, the I uh ones are quite well, uh, actually proven in the industry. So I Have no doubt it's going to work quite well and will be stable for quite a long time. Let's still a quick little check on this thing, shall we? now? I'm using the Ulent u1272a today because it's got a 1 Milli Ohm resolution on Ohms and that's excellent.

So let's uh, zero the leads out here and uh, there we go .37 that'll do and we'll null that out. There we go. and uh, let's see if we can measure the Box on all zeros here. What? What do we get? and Bingo 0.361 And of course that is well under the claimed uh 0.

5 Ohms. Zero resistance there. and uh, as I said, you know, in 5 or 10 years time, I' I'd expect this still to have a pretty good uh, close Tolerance on the uh, low ohms, they nice stability and you know it doesn't have dodgy contacts and things like that. So I expect it to be reasonably reliable and let's just dial it up here.

We' got 0.36 Uh 367 there. Let's dial it up by 1 1365. So there you go, bang, it goes up and then that one's going to go up by .1 each time. Now that's a disadvantage with these boxes that you got 0.1 Ohms.

You know you're down into the switch, uh, contact resistance, and the wiring and solder joints and stuff like that. So you know, really, you know your absolute accuracy down at your 0 uh 1 Ohms is not that great, But your resolution. As you can see, if you put in, say uh 10 Ohms, it's going to go up by 0.1 There it is. 36 2 46 Bang.

And if we dial in our 1K there, then the Um 0.1 Ohms here actually represents the least significant digit. So let's dial that up Bang It goes. Yep, there we go. 0.1 Ohms Resolution: Not a problem.

So even though the accuracy at Uh 1K at the accuracy of 0.1% at 1K here is only uh, this, uh, particular, Uh digit here, the third Uh digit there, we can get greater resolution to that and we talked about that before. The difference between accuracy and resolution. They're two entirely different concepts. Now, just check for Uh Dicky switches here if you go along and you sort of give them a give them a little flicking.

a little bit of a wobble, does it? uh, does it change? And no, because you'd expect those switches to have you know good quality uh, spring contacts in them that uh, actually retain a good low resistance over the range. And if I wiggle that one back and forth just a little bit then it doesn't change at all. unless we actually flick it over bang to the next one. Now if you put it smack in the middle there bang, it's just jumped up to 9k as you can see.

So going from 0 to 0 Ohms to 1 here. switching to one, it's actually switched to 9k in the middle there. so just be wary of that that when you're switching. uh well this particular box because of the switch Arrangement used.

Um, if your you know your circuit might suddenly jump for a little bit there for a split second could jump from 1K to 9k. It's not going to jump from zero or let's say from one, let's go 1K and let's try and jump to bang There We go. It jumps to 9k before it jumps to 2K something to be aware of. If you're doing your circuit you suddenly see a spike or something like that because these things, uh, some of them with the um, the traditional 10 resistors per decade.

they may actually uh, break before they make the next uh contact. If they got what's called break before, make uh, rotary switches in there. then your Whole Decade resistance box will become open for Split Second as it switches to the next one. And if you're using your circuit, live and switching in resistors like this and dialing them up, just be aware of that.

If you s suddenly see some sort of impulse in your circuit, you know that uh, you know it's not that exact value until it's actually um dialed right in like that. if it's halfway between, you could be in big trouble. There it is 9k again and let's check out the 10 Meg value here. There we go.

Pretty spot on according to the agilant I Can't remember the agilant spec on uh, this range right off the top of my head. but uh, there you go. It can uh, measure up to 99 n No problems at all. Now ordinarily though, you wouldn't need this sort of uh range.

You know from this nine decade one is, you know, Amazing. From 0.1 ohms up to you know, 100 uh megga ohms that's really outside of the you know, the normal range that you would need for just a general purpose decade box. So you're guilding the L A bit there. you really only need just the uh $174 one that goes from 1 ohm up to 10 Meg It's it's only got seven, uh, decades much.

Uh, you know it's much cheaper, much more usable. Granted, it's only 1% instead of .1% but you know once again, you may not need uh .1% either. So, but if you're building your own uh one 1% resistors and a seven 6 or 7 decade unit not a problem at all. And for the 74 bucks extra, you can get your cow certificate with your decade resistance box.

and well, you know I mean do you need a cow certificate for your decade resistance box? Well, some people might. Anyway, it's got all the individual uh marked values here for all the Rangers and if we have a look at, say, the middle of the range 1K uh range here, you know it's it's uh out by an absolute Um percentage. Are you know 0.06 0.08 You know, 0.05 .01 There in the middle, you know, 0075 it's You know it's um under. You know there's there's one range there which is close to its 0.1% tolerance range, but of course they were all going to pass.

They wouldn't sell it to you if it didn't um, meet. Its absolute spec of 0.1% but as you can see, a good majority of these uh figures are you know, around the 0 1.02 uh range so you know it's it's pretty good, but that's that's what you'd expect. You wouldn't expect them to actually or a good majority of them to be close to the 0.1% tolerance. And of course, if you're building your own box like this, you can actually hand match resistors as well, which we'll go into later.

but uh, they. I Don't know if they've hand selected the the resistors that went into this or whether they just, uh, um, you know, take them direct from the manufacturer as a random uh B or not. But yeah, it's um, certainly well within spec. Not a problem at all.

Even up on the Uh 10 Meg range up here, right? we're we're still only talking look 0.05% You know it's It's not too bad at all .02 and uh, on the Me range here, 0.02 0.01 Pretty darn good. And of course, as we mentioned down on the milliohm, hundreds of milliohm range. Here you know your percentage errors are quite, uh, a fair bit larger. You know, 3% down at 0.1 and you know, minus one and well, that one's way spot on.

There we go. Brilliant. Um, but you know, plus - 1% 2% 3% Those sort of figures down there. and then once you jump down to the you know, Ohms range, they start to jump, uh, back towards the Uh .1 uh% end of the spectrum and then they get better from there cuz their Um Figures were quoted from 10 Ohms up.

If you remember the figure on here, it tells you from, you know, um, from 10 Oh to 10 Meg is where it meets that 0.1% And sure enough, it jumps straight down to the Um 0.1% or lower on that range. So they've got a whole bunch of different models in the I range. They've got the, you know, from 174 bucks up to $847 Uh, they've got either um, a half watt which is the Box we've got here or they've got the Uh 2 watt Uh ones. This is the particular model, the Rs21 we got here 539 bucks.

Um, but the cheapest one is 174 at .1% or it jumps up to 324 if you want the .1% Ah, it's a bit rough, but these aren't designed for the individual hobbyist really. so they're sort of professional. prices. what do you expect? Um, they do capacitance boxes as well as inductance boxes.

Um, a capacitance box is really handy by the way. if you want to buy one or make one, Highly recommend it. Inductance box: Not as handy as the capacitance box, but some people do actually make them and uh, need them. and overall, it's It's quite a nice box.

I Really like it. Um, and just a few dodgy, uh construction things inside they need to fix up. Why do I always end up with the boxes that have problems? I Don't know the curse of the Eev blog anyway. I Rather like it so if you can afford it I recommend you pick one up.

See you.