EEVblog #1017 - Enter The World Of Atto Amps

hi this is the Keithley DMM 7510 it's a pretty schmick seven and a half digit multimeter one of the best you can get so if we can have a look at what can measure in terms of low current well of its lowest range here our decimal point is here on the micro amps range move the decimal place three spots over and that's nano amps move at three spots over again and that's Pico amps so it basically has one Pico amp resolution pretty schmick but yeah this is amateur hour this is what you want when you're measuring low currents thirty-five-year-old technology the Keithley six one seven programmable electronic from the early 1980s this is a fantastic bit of kit not only can it measure voltage it can measure owns thank you very much Giga ohms hundreds of Giga ohms if you want to go that high it can measure coulombs for those playing along at home everyone loves cool loans and it can measure current how low can it go well how high can it go well look at this milliamps no worries micro amps no worries keep going ah keep going ha nano answer that's very mature speak OS that's for amateurs - let's have a look its lowest range is a 2 Pico amp range and that's Pico amps that's puff so there's our decimal point if you move oh sorry you can't really black pointers hopeless in there there's a decimal place three places over that digit there is femto amps this one here is 100 800 amps at Oh most people don't even learn what a doe is in engineering it's like her what prefix is that a hundred at Oh amps resolution now pretty much there's only a couple of instruments that can well that like mainstream instruments that I'm aware of that can beat this these days there are a couple of modern ones that can go down to ten at AU amps resolution but this one can 200 @o amps absolutely amazing thirty-five-year-old better technology for those playing along at home that is 62.5 electrons per second for a hundred at AU amps whoa this is heavy so what do you need something like this for well basic our physics and material research new nano tube research new polymers and various other like you know real low current electrochemical type applications we pretty much down to the level of counting electrons it's ridiculous anyway a hundred at of's resolution and please excuse me for turning it on before I take it apart but I just have to show you that how low this thing could actually go and yeah we can this is the actual I haven't got nothing plugged into it at the moment and we can actually do well there we go I had it on zero there but there we go it's actually counting if you fart on the other side of the room this thing's going to change by like a hundred counts so I'm clenching my butt cheeks just I've been not breathe either more anyway look we can zero check that and it's got an internal - an internal one femto ab offset there and we can zero it well we can zero correct that before we take our measurement unbelievable now it's actually got a voltage source output as well voltage generator 103 volts maximum very nice for are powering stuff under test that allows a higher resistance mode as well using the building voltage source and also it's got awesome monitor outputs as well so you can actually we'll have a closer look at the schematic up there but it's got the obligatory i triple e 4w g p ib interface and it's also got outputs which tell you that the the completion of the measurement has done an external trigger as well so you can trigger it and then it gives a response when it's taken that measurements so good for our system integration so you can see that you can actually get a preamp put here and also an amplified analog output as well and that might be handy for once again system integration stuff now of course you can't just use a regular B and C or banana Jack inputs for this sort of thing you've got to use a special low noise tri-axial connector it's called it's called tri-axial because it looks like a regular BNC which is basically a biaxial and this is actually got a third contact in there that goal one around there if you can see that closely so don't just go plug in a regular BNC cable into a tri-axial connector you'll bugger it up so this actually provides a separate internal shield in there as like different for like internal guard different from the external output here and that's critical for really lows noise measurements but you'll also find them on very high resistance meters as well once designed and once again they're ultra low carb but like thousand very high voltage system high resistance meters for example will actually use these tri-axial connectors for testing at a thousand volts and you know you can pay like a thousand dollars for a test cable that comes with this instrument but considering that one of these modern instruments is like seven thousand dollars for the base model unit and like fifteen thousand dollars for the for the top-of-the-range model then you know people are used to paying a thousand bucks for a special low noise tri-axial cable oh manufactured by nude virgins now unfortunately I don't have a tri-axial connector here in the lab handily I could all have to order one so they can done you know do some better experiment so I'll just plug some shop probes up as quacker and I'll see if it's being on let's have a look here we go hung at the right angle like that being on that is the least significant digit awesome so I'm not going to go to the effort at the moment to measure all the other ranges that you require specialized our setups to do but suffice to say that if it's being on on the 1 million odds of it being good on the other Rangers our high confidence is high and check it out the building voltage generator it works as well so let's set it to 5 volts shall we there you go it's only a smidgen out but this can actually go up to as I said a hundred odd volts is I actually will have an adjustable velocity thing so should get there reasonably quick tada there it is under 0.45 not bad at all so basic functionality seems to be there awesome and I love gear that has the instructions on the top look at that beautiful why can't they do that these days and you wait let's do a teardown on this puppy and into the world of ASO and I this is going to be interesting so what we're going to see inside here is I'm guessing this isn't just going to be running Virant the cow acts just across the cable over to the PCB it's going to be going into a nice big shielded block or something like that there's two screws on the back the rest of its of course all going to be regular our stuff there's just going to be some magic on the on the front end and look yep we're in like Flynn and tada there it is there's our magic block that's where the magic is going to happen and for the external power supply over here that's hilarious in fact all that transformer is it it's bent that is not camera angle that's not my I got a wonky but transformers do these things can I bend it back geez check out down in the mains input down here look at this it's right near these signal outputs look not a single toss was given about making it you know aesthetically physically separate from the rest of it but you know as long as you've got your clearance on the PCB it's all hunky-dory so what they're doing is running the mains traces down here's little common mode choke they're running them right down the edge of the board right past all the active circuitry once again if the clearances there okay but you know it's not exactly modern design technique and then they've got the the mains real clunker mains power switch on the front they're not sure that puppy's doing there it's not labeled you have to read the manual on that one hmm anyway so I've got our mains input and then our line fuses next to that oh and the Motorola 6800 five fanboys go wild there it is in socketed thank you very much and then we've got the obligatory SRAM next to that I can't read that what is over yeah it's six double one six of course it is absolutely classic and then we've just got our basic rom so of course 65 a 60 805 processor and the TMS 99 one four up here this is actually the GPIB interface chip and you can can't have tell because it's plugged into all the micro on the bus and then they all bugger off up here got some drivers and then it goes over to the GPIB connector sorry I Triple E fault I'm late so we've got our decode there 85 there it is and yet some of the other chips down there 85 I'm not going to give any cares about all the digital stuff not me I want to see what's inside the can and we've got some AC coupling to the chassis of course for a raft system noise reasons just a couple on there look at the braids they've got in there by the way little pro tip when you're using your solder wick don't throw away you use solder wick actually I keep them in you're paying off cuts from those keeping your pass drawer they're very useful for really low impedance are straps like this one it probably doesn't need the low impedance somebody's put the strap in there but yeah it can be useful keep them know some of the glue is starting to peel off there look at that that's they've got a shield all the way you know the entire box is are shielded as you'd expect on an instrument of this class and it looks like the board in here it's all going to be you know through-hole stuff just like this but it looks like they got it on the one board with the power supply over here this is of course a dedicated analog power supply for this analog section the other transformer down year has got its own stuff for all the digital thing that makes sense to what separate those but again it looks like they've got it all on the one board and calibrated by 1065 good on your 1065 and inspected by 1300 some of the unsung heroes of Keithley wonder where they are now all right let's reveal the magic here a couple of tremor holes up there you're going to trim those at the riot right angle you're not allowed to probe through there unless you've got your tongue at the right angle and you've got a gray beard so let's check in today whoa got some Jersey stuff going on here with this care we'll take a closer look but of course what you expect to find in one of these things is exactly what we see standoffs here there is too much leakage on PCBs for this sort of stuff to be going into PCBs so we've got ridiculously low leakage relays here we'll have to check that amp let's see if I can can't even get a brand et phone home anyway what'd you expect PCBs have too much leakage they get crap contaminants oil dust and condensation all sorts of crap on them so you want point-to-point wiring on this sort of stuff Teflon standoffs oh maybe no maybe they're not Teflon because Teflon can actually build up a static charge and that can be a trap for young players but ya can see our input is going directly over here over to the standoff there into these transform into these relays which are doing the range switching and have you ever seen a 250 gig on not mega and Giga ohm resister before well you have now that's the impedance of this thing by the looks of it now on a quick search I didn't find anything for these relays here but I'll have a better look if I can I'll include it these are going to be ridiculously low leakage hermetically sealed relays now I've actually done a video on talking about one of the designs I did back in the day for a company I worked out where it was a once again measuring high resistances and high voltages and we required a relay matrix in like a massive relay Matrix hundreds and hundreds of relays and all the problems involved in actually designing one of those things it's one of my very old videos from most seven eight years ago I'll link it in down below and at the end of this video check it out and whatever that little metal can there is it's very important because they didn't want the metal can just flapping around in the breeze so they had to actually have a strap tying that down to some sort of a guard point it's probably not going to be ground it's going to be a guard point there is a difference between ground and guide point I might have to do a separate video on that because that's kind of an interesting topic in its own right now you might be able to notice down in there oh maybe not might be a bit hard but all the magic of course is happening in our jewel fit matched fit pair here you can see that one of the leads just in there bugger go into the PCBU way too much leakage and whatnot so it goes they bent it out at right angles like that directly to the standoff so you can see that the signal path comes in here from the coax and then it goes through the various relays and then goes to you know various input impedances and stuff like that to get the current of course because we're measuring current we're going to transport it through a resistant measure the voltage across it basically so we've got the fixed and here's the fixed are 250 gig resistor here so that would be used for the two Pico ampere range there and that is directly on that no there so everything travels above the board's like you know manhattan-style above the board's Manhattan construction technique which is a technique of dead bugging components on copper clad board and then just point-to-point wiring might include a photo if there is one and yet so it all stays off the PCB and goes directly into our jewel matched fit there which of course is going to be a super duper special matched characterized one manufactured by nude virgins with gray beads see if we can get the part number on that it's got a one six eight then an eight-five to a on their hmm and T - TG on the front of that and it em so it's not doesn't look like the motor all a job anyway so I can pull up any data on that putt I doubt it like you know this could be a Keithley internal part number you may not know what that jewel fat input is anyway if you blow the ice out of that oh yeah good luck it the new one so are you young whippersnappers out there probably going here what's the big deal like it's got some realizing and jewel fit important bloody fancy pantsy tri-axial connected but whoop-dee-doo um will he go try and design something like this go try it design it test it and then get you know a proper controlled are characteristics in production environment and you'll find out very quickly how difficult this is to get right it's not rocket science its electron science and you'll notice that the grounds are going all over the shop not only did did the shield here for this matched fit bugger off to somewhere else over here to some guard ground but what some guide terminal doesn't have to be ground but the shielding for this case up here which is isolated from well supposed to be touching there isn't it did that cause an issue all right like that eventually touching there cause an issue it may it may do i don't know hmm anyway that like this ground is bearing off somewhere else a shield for this is Berggren or somewhere else the tri-axial i presume that that green wire in there is going into the tri-axial shield guard inside there so it's buggering off downstairs somewhere which we don't know about and it's getting all this stuff right is not easy anyway i'm got ourselves a kodak hybrid resistor network there so that's pretty nice but apart from that you know we've got what the 250 gig resistors they're not going to be cheetah hundred Megara no 100 then we've got 100 gig but 100 gig 50 gig resistor and other there's a hundred Meg one in there and various other yep there is special hundred Meg one there you go for the different ranges they're going down in decades of course to give you your different ranges there the shunt resistors just like on a micro current for example except it uses a fancy pantsy FET front end and really high value resistors it's simply the voltage cross and the foliage drop across a resistor but yeah it really is a super duper special huh if we get down in there having fully removed the board yet but check out yeah the tri-axial god is coming from that point down there as is the shield for the can so it looks like as are two different wires buggering off there buggering off somewhere else on the board we've got ourselves a star ground in point there so it's all referenced back to that one point so they certainly know what they're doing and here's the circuitry underneath there so that's actually all to do with like the 100 volt high-voltage power supply over here and take a look at this and notice something interesting look at this big strap over here this big crimp connector there's from the hundred volt output over here they've got that going through what looks like in our massive high current day lead it's not doing that it's going over to this capacitor here which then couples into the ground and that ground is on the output which straps into which has an optional strode to the earth ground which then straps optionally into the output ground over here and of course whether or not you include that ground guard strap there is all to do with your system implementation and how you do that so you have to really know what you're doing when you're playing around you know implementing this sort of stuff and taking serious measurements not in terms of using the instrument but your system setup and all your system grounding and things like that it's really important and huh looks like those are extra system ground wires that star grounding I told you about is going over here looks like one of them is going into the main ribbon cable which then goes back up to the main connector at the top of the main analog input board at the top and thankfully we have full access to the schematics for this thing and all the theory of operation the whole works I'll link in the manual down below the regular manual has the all this stuff in it it's not just the service manual that you know you used to be able to get it's all in the main manual fantastic that make them like this anymore anyway take a look at the notes that they've got for just assembling this PCB look free unclean the PCB flow and touch up using rosin flux wash immediately after this slower flow in freon sort of the polystyrene capacitors and polystyrene thumbs up love polystyrene this super are stable I super stable capacitors used for you know high precision circuits like this one after the freon you're going to do that after the freon wash and then remove flux locally with freon and then clean thoroughly with methanol after a flow and touch-up in dust areas what components mounted on teflon so they are actually tap on standoffs that's interesting so our static mustn't be a problem case we know what they're doing and must not touch PC board or other components because if they have to be completely also isolated so here you go it's just like assembly steps that's just great and we have the schematic for the ad converter as well know it says they've rolled their own analog to digital converter it's a constant frequency charge balance single slope job and well you can do it's got theory of operation in the manual if you want to go into that but yeah that basically I roll their own it's not like they just bought metal devices a DC now bugger that and of course this is what everyone wants to see the front end how do they do this how do they get like a totally 100 at oh mmm to amp levels on this thing well let's take a look the input as you can see you can see that the guard they're the three inputs and the guard as I said goes down to mates down to the motherboard so it's all it goes around in you know various configurations for that star ground and all that if you we see that there are different symbols used for the different ground there and look over on the right-hand side near K 301 over there that relay you can see that that's actually a star ground point and that might go back to the main board that we actually saw back down the bottom that star ground point down on the bottom PCB so as we've seen in the teardown it doesn't go to the PCB at this point it's all off the board construction that input signal goes to those are those rows of standoffs and those relays that we actually saw there with the you know it's just up in free air so it's not touching the board so it's completely isolated air gapped isolated from everything goes into those special Squirrel relays which I still can't find any data on those but they'd be ridiculously low leakage and you can see that are if you go through our 3 3 4 3 5 5 & 3 3 2 there then you can see the 250 Giga ohm resistor permanently going down to ground so that's like 250 gig ohms as that permanent input resistance there and then the other ones at the top there right at the very top there's 100 Gig are 330 there and then 331 100 Meg then they'll go down in decades 100 K and so forth for the various ranges now of course this isn't those don't go down the ground they're part of the feedback loop part of the feedback amplifier and of course if you look at the theory of operation this is actually a feedback amplifier so the the shunt resistor in quote marks the resistor that the current needs to flow through converted to voltage is in the feedback loop of the op amp and the op amp here you can see it there you 309 is actually a linear technology LT 101 too and that's a pretty schmick op amp but it's only Pico amp level input right so it's not good not Pico ants for that's you know that's amateur hour so they use Q 308 the dual match J FET input as the high impedance and input required to get the at o amp level so this is a very special matched transistor can't probably hand-selected hand tested it hand graded everything else and I looked in the manual departs list for it and yet they don't actually give a part number so you know it's super special secret squirrel stuff presumably if anyone does know please tell us down below anyway that is what gives you your extremely ridiculously high input impedance the only thing they can do the job here is J fence now this MOSFET rubbish like really special matched J FETs there for the front end but apart from that that's where all the magic happens and physically as well where the magic happens it's all off the board choosing these components like the match J FET like the relays mounting them off the board but everything else is just pretty much off-the-shelf the LT 101 2 and u 304 up the top there whatever that is they've got to vote six point three fold voltage reference our Zener and you know like the rest of it's pretty ordinary stuff really so yeah all the special stuff transistor real a Manhattan construction that's the ticket lady so there you have it I hope you enjoyed that interesting look inside the Keithley six one seven electrometer and these things they're still available for all sorts of physics and materials research and all sorts of we in wonderful stuff don't have much use in the regular electronics of course they might be using our semiconductor you know fabs and other places for various things but you know you general-purpose electronic lab is not going to need to go down to a tow amps I like this thing can or even femto amps really so you know you might go Pico amps you know nano amps is quite common for low power stuff but you know even Pico answers like usually several orders of magnitude beyond what your regular electronics person ever needs to deal with but these things are very specialized it's a kit they have their place that's why they're so expensive you know having the matched FET front-end and all the special relays and everything else you know and they don't manufacture these in high volume which is why that they can charge you know seven eight ten fifteen thousand dollars for these sorts of things they are precision bits of kit lots of engineering goes into them but you might look it and go home you know me whatever but there's a try and do it I dare you try and measure you know hundreds of Giga ohms tera ohms and femto amps and @om so it's just crazy different world anyway if you liked it please be give it a big thumbs up as always they're high res are tear down photos on eevblog com LinkedIn down below if you want to discuss it comments all that sort of stuff link of the eevblog for him hope you liked it catch you next time you

Channel: EEVblog

Views: 144,628

Keywords: eevblog, video, attoamps, atto amps, pico amps, nano amps, femtoamps, low current measurement, measurement, electrometer, kiethley, keithly 617, resolution, low noise, electrons, electron counting

Id: LI_5ANmkVqo

Length: 27min 34sec (1654 seconds)

Published: Sat Aug 19 2017