Solartron 7081 - Mods & More for 8.5 Digit Voltmeter

this video has been supported by Skillshare hey there are cnc friends this is not a cnc machine but it's full of chips and it's very accurate so maybe you'll like it too I'm currently repairing it that'll take a bit more time so I thought today we could start gently by doing something similar with volts ohms PP m/s and so forth for that a quick look back to 2018 I repaired a solar Tron 70 81 eight-and-a-half digit precision voltmeter and I thought about modifying it a little bit but I didn't dare it was the best voltmeter in my arsenal until now and that says something being surrounded by all those key flees but now not a CNC machine has moved in and effortlessly took the prestigious position of highest end instrument that doesn't mean that the good life is over for so Letran quite the contrary it's finally getting some dignified playmates and the chance to do what it's good at that's right it's actually not just a decorative backdrop for silly YouTube videos oh no I'm also measuring voltage references with it once a year or so remember these beauties I remember the LTC swear part on permanently since I made their video so they should be ripe now and that's precisely what solar Tron is good at determining it can measure the infamous 7.1 something output voltage all the way down to nano vault you just got to give it a minute for one of those eight-and-a-half digit readings that's not a problem though because usually you're not hand-holding probes while eagerly waiting for a result as a matter of fact no holding hands necessary at all 70 81 is not the youngest voltmeter anymore but still perfectly capable of working alone for a few hours thank you very much preferably in a calm and temperature stable environment you can let it take measurements all day long and recall the statistics program afterwards in terms of variance and standard deviation it mockingly told me that oh you did your best son and you made an okay voltage reference maybe again when it has aged for 40 years like mine hey does anybody else feel that my inner clock says it's almost had on time so we've got an 11 micro volt standard deviation that's great for a voltage reference but other builders of this pretty much maxed out multi-hundred dollar insanity module are reporting much better results so where's the problem well I got too close and caught the highly infectious vault nut disease that's where it all started to go wrong but I just configured a similar long term experiment with an even more trustworthy voltage source one that I didn't DIY that gave me an even worse reading so now I've got a pretty good idea on whose fault that is first of all it's not a big deal these are not first world problems these are absolutely esoteric ivory tower problems so no hard feelings towards this absolutely esoteric ivory tower voltmeter that somehow managed to be this awesome in the 1980s I love the enclosure even though it's not metal I think this thick fiber reinforced molded plastic provides better thermal insulation for the insights than sheet metal could it also doesn't have grills or even cooling fans further improving thermal stability and letting absolutely no dust in the lid is coated conductive ly and connected to mains earth when closed that doesn't seem to be enough because for the sensitive analog area there's an extra shielding PCB that gets connected to a floating guard note in a similar way the front panel is a piece of art absolutely no sign of yellowing in the high-quality plastic and have you ever seen a foil membrane keypad that still works like new after 40 years it's a miracle but it's got to come off there's one little thing I'd like to change for that I've got to unplug a few connectors and D solder a let go mr. speaker then only the main input connect is left it's attached to the front rear switch with fancy Teflon isolated cables Teflon alone being great against leakage current and high-voltage breakdown not at all against triboelectric noise as I thought before but internal cables are supposed to be stationary so that's all perfect every metal junction in the signal path is a potential source of unwanted nano volt so if we were completely dead serious we could eliminate the front rear switch in favor of the truest possible signal but that would be a butchery I'm aiming for something nicer you can guess if you've seen my last video about this thing this connector area is just an insert a very lucky I only just realized that I've shown this exact same measurement before in the Keithley one at one video so chances are that some of you may have forgotten to here's a quick refresher so Letran original input cable unwanted micro volt offset in spite of luxury swiss-made fischer connector not very good these are Pomona three seven seven zero low thermal EMF binding posts directly gold-plated tellurium copper no evil nickel layer in between those would be a perfect match for this instrument I only have to find a way to fabricate a new insert [Music] hey good news Darin have just sent over not a 1281 eight-and-a-half digit voltmeter they are not making those anymore sadly but some of their futuristic balanced single flute and Milt's those are absolutely deadly razor sharp so a little band-aid dispenser is also a very thoughtful thing to include I'm not going to hijack this array attests key a video to turn it into a C&C episode halfway through so here are just a few impressions this is a surprisingly non easy part because it has two planes and it needs three or four separate operations with the high MA 3d probe re clamping is not a problem though and with a dart Ron and mill aluminum stock effortlessly turns into a nice and uniform stream of chips with good chip load and surface speed settings I'm also having fewer problems with powdery chips this should have been a single pass with a pot clamped at an angle but I chose the lazy way and it took like 15 minutes of machine time to make this micrometer staircase and so forth it's an exciting when everything just goes according to plan time for yours truly to truly mess it up maybe pull the pot out of the vise with cutting forces know maybe drill too deeply and break through the front nope still came out flawlessly well the way I see it I only have one option left I'm going to try it anodized it without ever having anodized anything before that's an almost guaranteed disaster for that I'm suspending it on aluminium wire in diluted sulfuric acid I'm researching time and current parameters in YouTube tutorials while the thing is already cooking after collecting a lot of contradicting data for an arbitrary amount of time and watching someone built a directional Wi-Fi antenna out of jar lids I'm just plopping it into a preheated energizing dye solution there we go finally it's nice and ugly but at least it's got a very hard surface and golden violet go well together kind of like a click spring project I'll try this again later for the purposes of this video it's good enough that I got the dimensions right the original connector has only five pins high low resistance high and low and guard for the sake of symmetry and maybe a shielding box later I've added another hole for mains earth but I wouldn't want to waste another lower thermal EMF connector on that one okay that was kind of the intro what I actually wanted to talk about in this video are the insides a lot has happened since this thing was designed how can it still be relevant well it's right there at the beginning of their manual DC voltage stability r6 ppm per year while not universally accepted these meters are known to be a bit noisy for example one doesn't make such a claim without foundation considered by many to be the gold standard today even a 3458 a can only guarantee to be better than that with a special high stability option although much better results are reported for this meter routinely and it gets even better literally when treated right metallic resistors and zener voltage references have a tendency to get more and more stable over time the solar Tron Schlumberger 70 81 in front of me uses this property better than any other voltmeter out there probably not really but as far as I know to make sure that nothing can interfere with a nice square root shaped aging process this thing is absolutely full of hermetically sealed components and I'm not talking about these no doubt fancy molded plastic resistors Oh No tío metal cans all hermetic quarto reed relays this one looks a bit like a jb weld botch but it's actually an original they all have at least a glass tube in them only the magnetic coil and optional shielding and guarding are outside even these guys when first I opened the meter I asked you if I should replace all the caps that have survived for 40 years with modern planned obsolescence parts that will start leaking in 10 while I almost did it but then I realized what they are military and aerospace solid tantalum hermetic caps absolutely not preventive maintenance replacement candidates they even used some of them on the logic boards the highlight on this board are a great barrels of those are hermetic nitrogen-filled precision wire wounds made by men components in the UK shortly before being acquired by vishay absolutely incredible parts with multiple glass to metal seals and a few interesting advantages over today's thin film technology lock forum members lie max has accumulated quite a fascinating collection of standard resistor photos including something very similar to my gray barrels I'll link that down below that entire bot on the right is called printed circuit board six may be analog front-end would be a more modern name if you are curious about this kind of thing the service manual is public complete and very well written in short this pot is a variable voltage divider that turns a maximum 1k V input voltage into something a little bit more manageable for smaller signals there is a variable gain amplifier that is actually built discreetly but summarized on this sheet then the signal is handed over to printed circuit board v where a fully discrete analog to digital converter is waiting it's actually based on a shockingly simple integrator that measures how many clock pulses it takes for a certain capacitor voltage to surpass a reference voltage not the reference voltage however they are using that to bias the signal to be measured so that there is some safety distance to zero then it can just be calibrated out because it's always the same or is it d 301 on this sheet is the main voltage reference and it's looking a bit lonely there isn't it the ad 590 right next to it is a temperature sensor on the basis of which they are adjusting the Zener current ever so slightly that way they are apparently counteracting thermal effects successfully but come on it's just freely standing there out in the open they haven't even coiled the leads as was good practice to absorb my new tectonic forces from the board after learning a bit about subsurface organized LTC 1000s I'm not so sure about this arrangement anymore it's not like somebody is going to release a cold draft inside your instrument during a critical measurement or at any other time but you know the difference is kind of huge as in a hundred fifty micro volt versus immeasurable again if you're interested in that kind of thing check out the entire article on x desc um and everything else too for that matter in short this thing is an absolute monument to stability except for a so-called LT flu which we are going to meet shortly and $100,000 Josephson voltage standard there is no better voltage reference out there it's that good because on the same die in the same hermetic package there's a buried Zener diode two transistors and a heater resistor one of the transistors is actually used as a temperature sensor inside the metal can whereas the other one controls the Zener current external configuration resistors have little influence over the performance and since even those have been fitted with fish ice high and dizzy foil technology the mythical 1 ppm per year drift should be doable okay here's the plan I'm going to implant this module into a solar Tron to replace its lonely little Zener diode 70-80 one expert Michael has documented what a seamless almost effortless motor that can be here it could even be reversed if it doesn't work out well enough but before judging it'll need some more time to acclimate it would have been wise to test to the influence of the binding posts and the voltage reference separately but then again this video was meant to be nothing but a fun little diversion while I was waiting for parts for not a CNC machine I should probably finish repairing that before letting it participate in these long-term experiments after only an hour it was clearly not done warming up but the increased standard deviation from 20 to over 500 was still a bit of a shocker it would also be interesting to try and change the ref amps that turned the reference voltage into plus minus 10 they are all POS Evans now nice op amps but there are numerous better candidates today another hour later and we are down to 84 micro what do you think will we get better than the initial 21 micro I'll keep you up to date until then take a look at Skillshare Skillshare is an online learning community that offers a membership with meaning there is a lot to explore there real projects to create and a community to be a part of Skillshare offers classes designed for real life so you can move your creative journey forward without putting life on hold you can learn and grow with short classes that fit even the busiest of routines like DSLR photography with Justin bridges most of these skills not only apply to DSLR cameras so in less than one hour and a half you're getting better pictures out of virtually all cameras with an annual subscription costing less than $10 a month Skillshare is also incredibly affordable especially when compared to pricey in-person classes and workshops the first 500 to sign up with a link in the video description are getting two months of premium membership for free so give it a try and explore your creativity that's it for now thank you for watching and don't do this on a desk by the way I've got little specks of sulfuric acid everywhere now

Channel: Marco Reps

Views: 82,011

Keywords: cnc, marco, reps, engineering, mechanical, electronic, metrology, ppm, volt, ohm, resistance, standard, reference, voltage, modification, solartron, precision, instrument, 7081, digit, resolution, keithley, fluke, calibrator, calibration, ltz1000a, nanovolt, teflon, circuit, vishay, wire, wound, hermetic, arduino, raspberry, statistics, teardown, schematic, time, pcb, voltnut, insulation, enclosure, guard, shielding, multimeter, oscilloscope, soldering, hack, noise, emf, copper, thermal, machining, datron, aluminium, anodizing, josephson, zener, diode

Id: -4hikkIJ_YI

Length: 17min 44sec (1064 seconds)

Published: Wed Feb 19 2020