EEVblog #709 - EDC 4601 AC Voltage Standard Teardown

hi welcome to tear down Tuesday we haven't had an interesting bit enough calibration kit for a while so I thought we'd take a look at this this is one is scored recently we've seen this brand before EDC electronic development corporation from Boston Massachusetts in the United States of America who are now owned by Cronkite and hence khcom Cronkite ADC and this is the model 4601 AC voltage standard I'll link in the cron hi DC voltage standard that I've done videos on in the past and what the eevblog lab has lacked here as most labs would is an AC voltage standard like this and then not that common there's not actually a lot of these sorts of things on the market but this is a really nice bit of kit look at this six decades here 1ppm resolution you could dial it in so you can dial in one point that's what that LEDs for not lead sorry light bulb one point zero zero zero zero zero a C fault it's not quite that absolute accurate of course but their resolution is there and you can end the ranges go anywhere from a hundred millivolts up to a full 1000 volts and it can deliver up to 25 watts as well it's a bit of a beast and you can choose your AC frequency as well one kilohertz 400 oh it's 60 Hertz or 50 Hertz test frequency a built in or you can supply your own external frequency here if you have an oddball requirement so let's take a look at it and this one was last mistress oblique calibrated back in 2000 so it's 2015 now so it was 15 years ago but this is it looks like a you know like a really vintage model but this is actually um I believe were first released in 1998 according to the manual which in scheme of things you know isn't that long ago and the manual was often last I plated in 2000 one but Cronkite EDC they still made standards like this and I think they probably still make them today a really old-school looking and like any good reference standard of course it must have the sense lines here and by the way I have to be extremely careful this could be potentially be a very dangerous instrument because it is capable of a thousand volts as I said up to I think it's a maximum of 25 watts even a thousand volts we'll take a look at the grass for that in a minute but yeah we've got the shunts in there too I just connect across the load of course the four terminal current scents very important if you are driving any significant load then of course you have to account for the drop in your cables here now I know we're violating now don't turn on take it apart rule but I just wanted to show because people will want to see just it's a spot accuracy check so I've had it go in for I don't know 20 minutes or so it's taken eighteen thousand samples as you can see here I've got it producing one volt precisely dialed in at one kilohertz and this is what I'm getting don't worry about that what we need to do is have a look at the average here look at this one point zero zero zero zero seven nine whack that into your calculator and it's point double O seven percent high woohoo well within spec and by the way though is just continuing to track down as well so I'm not sure what it's eventually going to go to you know like really actually tracking these things and it can take you know weeks to actually track and verify the performance of this thing and I off hand I'm not sure of the a sieve already spec of the Agilent 3 double for six one a but it's one of the best meters I've got here in the lab so we're going to assume that it's bang on and off we turn on the trend chart here you can just see it tracking like that I don't know why it just suddenly shot up they're not sure what's going on there but we could see a few Wiggles in there it's really quite interesting and if you got into the you know the thermals of this thing and everything else maybe if I like blow into it or something we might see some hang on I've no idea haven't done this probably not but you never know never know you like until you try it all over that big excursions there let's try that again I have no idea where the reference in this thing is haven't taken it apart yet but are those big scourgings aren't an accident I don't think this makes for great video and of course this looks like huge variations here but if you actually have a look at the scale here and actually calculate as a percentage what's happening there it's still well within spec it's just that this agilent bench meter at 6.5 digit bench meter is capable of quite high resolution here so you get to see all the little Wiggles I love it and what's really interesting with this is that it gives you an indication here whether or not it's actually set ie it's locked and presumably you know gonna be within tolerance whether or not you know it's high or low outside of the boundary is going to give you a red LED there you might actually show up if we change the frequency or the range here and it's a rather interestingly got electronic buttons here for the standby and operate mode so you can work it in a standby mode but you can just do that just by changing the range like that there we go it's gone into standby mode it's still in set so I have yet there we go it just went to low so it's going to take some time to go up yep you see it just that it's sort of like overshot to high and then came back within tolerance there so by the way yet this thing appears to be fully working the guy I bought it from has verified it against much better year than what I've got here and that says everything is within tolerance so it's pretty sweet let's actually turn this sucker up to a thousand volts and see what we can do actually we better not take it to a thousand because my edgelet meter here is actually if you have a look at the input it says that 750 volts AC maximum so I've got it set to 700 there and we can reset the trend on there to get the average now I've had it there for a couple of minutes and it looks like it's a little bit out but if you think about it this is 700 volts ac what's point zero five percent art spec of that well it's not point three five volts so actually it's well within the point O five percent full-scale speaker this thing and just down at us 70 volts AC here just left it there but drop to by a decade yeah we're within 0.01 percent once again well within the point O five percent normal spec of this I'm not sure if you can hear this but there's no audible noise on it at the lower frequencies but you wake it up to the hundred kilohertz and you start hearing some hum there let me turn up the mic level never trust an instrument that doesn't harm and down to 100 millivolts it's kicking some serious ass to look at that and I just love this the light weight of the unit makes it a desirable laboratory instrument yeah or eighteen bloody kilos of it there you go it looks like the hundred millivolt range here is attained by a divider network so really it's like a one volt minimum range and here we go we've got the basic specs here for about twenty three degree art nominal plus minus five so it looks like it's a SPECT over that not including night drift and noise of course so on the thousand volt down to 10 volt ranges as I said point zero five percent in fact it's point zero five percent of both of them the only difference is the range there of course you've got a decade worse range figure on the one volt and 100 millivolt ranges and as far as the stability goes look at it's very impressive eighty hours of course you'd expect it to be pretty good point double O at 75 percent of setting plus almost a bugger all half Abi's dick of the range but the six-month stability so if you left it on for six months how much would you expect it to drift by maximum well 0.01 five percent of the set in plus you know I don't know quarters of obese dick of the range and also load regulation very impressive point double oh five percent and of course it can go up to 25 watts delivery on this thing so of course you've got to use the yacht for terminal light sense to actually get that and if you care about the frequency stability and accuracy there you go it's pretty good but most people don't care about that unless you have a precise need for an exact frequency and recommended calibration cycle twelve months this poor puppy hasn't been touched in 15 years but it's still bang on eighteen fifty pound for you Yanks got bugger all on the back here it looks like it does have some sort of options maybe for some sort of you know a couple of banana plug terminals or something like that couple of the cutouts here which has then got plastic inserts in them we've got the lion fuse and yes it is selectable between 230 volt and 110 volt operation as well handy if you're buying these internationally so yeah just flick the switch and Bob's your uncle there you go at maximum of 25 watts here only at a hundred percent of the range of course if that loses some of that and for the thousand volt range there's just start three different diagrams here one hundred to three hundred and three hundred twelve hundred watts but even at the full thousand volt output can still deliver 25 watts and give you a point oh five percent accuracy in point double O seven five percent stability on that awesome all right let's have a squiz inside this puppy there is a screw missing on the back here so I'm not sure what the deal is there there are no calibration seals on the thing so let's lift up the skirt slides off oops move the camera and Mike Flynn wants to transform up to huge caps a bunch of our precision resistors and switches on the front and some old-school through-hole stuff now first of all take a squiz at the decade-- switches down here and as you can imagine they're very very nice they look a bit crusty because well they're old but you know you can these things are pretty much self clean very nicely although if you do have to and the rare occasions you do have to clean them at EDC Cronkite have some recommendations for that you don't use a silicon-based lubricant or oil so you've got to use it like a dioxide brand switch cleaner or something like that so yeah you really need the proper stuff and just like on my previous side DC voltage standard we find a trimmer board like this on the high range of switch so that's the first decade so that's to bring the thing into calibration don't want to touch those and you'll notice that they're the only adjustments all the other ranges here they've just got those fixed precision resistors on them and they just decrease in value as you go along right down there and they're going to be I don't know an ohm each or something like that and as far as the rest of it goes in here and we haven't seen it all by the way there is some more on the bottom which we'll check out shortly but very classic EDC Chron height type very old-school construction we've got ourselves a just a very old school tin plate PCB in there yes it is fr4 it's not like phenolic base or anything but yeah it's all through-hole parts they're all socketed and very very like reminiscent of like this thing was designed and built in the 70s or 80s or something like that but get in there and look at some of the chips in a second but it needs to be like a weird combination like they had the board's left over from a previous design back in the 80s or something and they just rehash them and just whacked in some new chips and sold these things because I'd saw these in high quantities I mean they might even make them to order pretty much so maybe they've got like tons of old stock you know hanging around and things like that of various parts and chezy's and whatnot and yeah they just put one together a hat sort of like a hand build each particular one anyway over here we've got our mains in what transformer pretty much this wouldn't pass our modern wiring standards and things like that there's no insulation on any of the mains input over here walk some heat-shrink over there on the on the Krusty 240 volt the voltage mains voltage selection switch up the back that's a bit how you're doing and the up fuse on the back and well yeah anyway this is the big-ass primary transformer it's only just got to send a single center tapped arm output here and that's it this other big beast over here this is why it weighs so much with the combination of two of these this is the big output transformer with the multiple taps on there we've got some heat sinks up here with some either bipolar transistors or Fezzik probably bipolar transistors now this field modern field effect rubbish and then we've got some more big reservoir caps here we'll see those on the bottom they're just filtering the the main output supply here that's it you'd have one for the positive and the negative for your split rail and then curiously we've got a plug-in board here we'll take a look at it's the gonna be the oscillator board and a couple of relays on there for switching and if we take the bottom cover off here this is a rather interesting as well here we go the caps protrude down through the bottom here we've got ourselves some bleeder resistors across there so they discharge those caps these are 70 volt rated Nippon chemi cons might show you that in a minute we've got our bridge rectifier here mounted down to the shade down there so we're just getting the split supply the wiring that comes through I believe there and it goes into the bridge rectifier so it's just a classic arrangement it looks like this chassis has punched for something else I mean look at these holes here and here and they've got to cut out here for these two terminals but I think they maybe put them there this it doesn't look like this chassis was designed for this particular model so they've probably reused it although it does have the cutouts for the dual transformers but there's lots of unused holes and things around here anyway they've got a bit of art folded up metal here so they've got pennant the wire in penetrating this is looks like an output relay down here which switches the airport got some shielded cable going back up there so we'd have the output line play whether this sense line going back to another relay that's protruding through the board in there I'll show you a close-up of that now check out that they've got this relay sort of just like it's almost like this cutout in the board is like hand cut it doesn't look like it's routed out so it's very much how you're doing and it's what it makes me think that they just you know manufacture some old balls that they've got around and hack these things together I don't know but jeez it's it's not pretty is it oh sorry I was a bit wrong on that mains input transformer on the front it actually has a couple of more our supplies as well the main supply here comes out but as I said it's just a split supply there and you'll notice that the centre tap for that look going all the way up here through this penetrator and over to this star point over here so they've got another wire running off there which then connects this base down here which then grounds a whole bunch of other stuff if you follow it around and then they've got like another wire going up there from that ground point so there you know tying a lot of stuff back to that central star point there that'll be for the power because this is all the power supply side of things but of course you would have different star point arrangements if you want to take a look around here for the various so for the voltage reference stuff and there's a hack down in there look at that goodness so that's the flyback diode on the relay there so there's the screw holding in the relay and that's just oh man they use sockets for all the other side ICS why couldn't they include a soccer for the relay I don't know and over here we're clearly got a high voltage resistor arrangement this is coming from this shielded cable which as I said goes down to the looks like an output relay down here so this is probably the sense terminal and of course when you're sent in a thousand volts output well you don't want to tap off directly a thousand volts you can't feed that India you know you're up here feedback or whatever so you've got this up will see the resistors on the top side but it's basically a high voltage resistive divider here it looks like this cable pair comes from the switch on the front that selects your test frequency you can see that going up to these various traces here going up to this vertical board which is our oscillator board so that selects your oscillator frequency there's more hackery going on in here look they've got this jumper going across there and there's our Jersey reference point they have actually tied that in they're going over to there wow this thing is like you know all hand-built and hacked together and there's the mains input I was telling you about it all looks really quite crusty have a look at the board down in here it's got all sorts of weird it's got like weird deposit on it yeah look at that so I don't know where all that's all that sort of almost like soot or something has come from really quite strange so that seems to all be in this part which is the power supply of course that's a flat power supply section and then this is where all the magic happens over on this side and as we saw in our previous side DC voltage stand and all the magic happens in their hands selected by somebody with a gray beard and tongue at the right angle then a voltage reference so they aged these things and they've got special zeners which are super super stable and they've obviously hand selected it at a particular arc current there and they've measured that six point one five one seven volts and then the whole thing is tweaked and calibrated and yeah you know touch it from that point because these are zeners are specifically i aged and tested been to be extremely low drift and that's what you need in a precision reference like this whether it's AC or DC doesn't matter the the Zener diode itself could be like plus minus 5 percent absolute tolerance doesn't matter it's all about the drift but you can just calibrate that out later as long as it doesn't drift you can tweak the pots to your heart's content do whatever the other pots we saw on the front panel and once the thing is tweaked to a specific calibration then it's all about the drift so if we have a look in here we've got some Oppo sevens Opie 177 yep and op1 seven so we've got some precision offence as you'd expect and some date codes on there about 1993 if you have a look over here look we've got a CD 401 3 4000 series CMOS it's got a date code of the 18th week 99 so and all the chips on here seem to have quite you know widely varying day code so it makes me think yeah they just had you know old stock of parts or whatever lying around cuz as I said the manual says this is a 1998 model so that 99 there does make sense so you know unless they've changed it unless this has been replaced post manufacture then yeah this date then that dates this to you know and past 1999 so you know into the 2000s but a lot of other chips on there 93 vintage anyway we've got ourselves a uln to double-o for our they'd be using that to drive the realise we're gonna go old school our tale over 7 for up here it wouldn't be doing anything not critical at all it just been doing some miscellaneous stuff we've got some trim ports around this TL o 707 one is it um yeah just you know once again that's not a precision op-amp that's just a J fit job and there's our high voltage resistant at work here so it's come in there and they just tap it off at the point so they got like you know a hundred to one division ratio or something like that but they stagger them just to get a voltage rating on each one so that yeah they're just gilding the lily they're good engineering practice then just rely on one resistor why not have a bunch of them in series yeah over around the voltage reference around presumably around here somewhere I don't know which one is the precision Zenit reference yeah I probably one of those I'd be guessing I don't know I unfortunately do not have the schematic for this puppy so I can't see if I do I get it then all oh I eventually get it I'll definitely ask Cronkite to see if they can still get it for us but at this stage they're just pissing in the wind we've got ourselves a little probably a coaxial koto relay down in there you can see that's three terminals on one side one on the other so the center is actually the relay contacts with the two outer ones being the coil contact so that would be like a you know a really low thermal EMF real aegis for you know precision applications like this yeah a really super modern part in here is this precision metal film package down in there there you go that's a point oh one percenter 10k resistor a precision resistor that you get from vishay by the looks of it also got this very interesting part here and well we'll find out what that is it's more obvious when we get over to the main oscillator board but that is what's called a VAT all hmm go Google that one what do you know that does look like a MOSFET I believe that's a 2sj 162 peach annum job and please excuse the crudity of the light source here this is a to SK 105 8 matching N channel MOSFET and of course that's where we're dissipating all the power in these two MOSFETs here and they fuse those that's a nice little touch there got a separate board for that and you know why they didn't integrate that with the main board you know who knows there's not much on it there's a couple of links to resistors and two fuses jeez and the cap on here seems like a bit of an afterthought perhaps hmm Hey Bruce this thing's not quite stable under maximum load on this range let me fix it just work a cap on there she'll be right Oh check out that spared no expense on the mains power switch oh goodness and over on the oscillator board here's what I told you about before this is a vac troll and you're probably wondering what the hell is that well it is a photo resistive opto isolator like a photo resistive opto couple it's like an old-school 1960s opto coupler trademarked the VAT roll our name is trademarked by our vac tech I don't know if they still exist or not so unlike a regular opto coupler which has a photo transistor on one side this has a lid on one side and a photocell like a CD SR photocell on the other side so there you go so that allows isolation and used in oscillator stable oscillators and things like that you know very sort of you know hp-200 old-school using a light bulb as the you know as the main arc as the main stability element in your oscillator ah man you know we're talking nineteen sixties here so you know this EDC Cronkite stuff goes back a long way and they don't change their designs they just you know keep yeah they might have a few little modern refinements but G's to use vector oils unbelievable anyway if you're curious to take a look at this I'll actually link in the datasheet to this puppy down below check it out and here's the oscillator board in stark contrast to the board that we homemade hack that we saw before I mean you know it's a fairly modern I'm a compared to that sodomize silk-screened air hole the works you know so it really is you know amazing sort of difference anyway look an interesting element down in here one of these old XR brand triple two eights now that's a multiplier detector normally used in not PLL's of course so that's what they've got going on here so they've got a detector and they've got a that vac droll up there and anyway so this is the programmable oscillator it looks like they've got some diode iGate in down in here perhaps 401 six is really all just you know discrete old-school stuff in here but I'm a fairly ma at that na is real a wha and the most recent chip on this board 96 so well 1996 so 24 weeks so it's just it's so rather interesting all there's another one of those that koto coaxial relays in there as well yeah I don't know why they're using those for you know such low frequency stuff anyway it's pretty schmick but whoa what's that Epson part oh and that folks is an Epson crystal oscillator where's L where's our crystal I don't see it oh look there's a J fed over here by the looks of it but where's that crystal it's a crystal oscillator not a Fed over here but geez what's going on there really is quite interesting all this diode which is probably like diode like gating is actually goes into this Epson chip here fascinating and of course it's obvious when you take a look at the data sheet which I will link in down below um it's got a built in oscillator and I and it's got a digital programmable divider in there to select multiple frequencies hence all the ER diode gated and stuff like that it's just selecting the different frequencies so that is our main frequency element in there so yeah I'd really love to get us chimeric and our theory of operation of how they're doing this whole thing not just the oscillator side of things and the detector over here but you know just just the whole kit and kaboodle for this thing and over in this power supply section here you can see all that sorting or whatever it is down there check out that puppy it's an LM 39 1/4 dot bar display driver the hell are they using that for the only thing I can think of offhand is that they're using that for the output here which the low and set outputs because it's got built-in night comparators and you can get you can get the LED outputs based on you know is it in the center or not so that's my guess is that's actually driving something and it must be driving that I guess if you follow the wire in there you'll probably find out and sure enough I did follow the wiring which I takes off from these pins here down on the bottom of the board and then pops up up over here and there we go goes to our LEDs on the front panel there so it seems like they're just you know creating some sort of our DC offset voltage which then it gets compared with you know some set thresholds on this Krusty LM three nine one four dot bar display driver using it in dot mode obviously in this case and whether detect whether or not it's within thresholds I just assumed that would have been done with you know some comparators or something like that but whatever floats your boat it's gonna work so there you go I think I spent enough time on this thing I hope you enjoyed that look inside this our EDC kronkite 4601 AC voltage standard something that your average lab doesn't happen this is almost a metrology grade instrument it's amazing how they can get the performance out of this thing with as you saw the dodgy you know so like do-it-yourself homemade that construction in there but hey you know there's it doesn't have nothing has to look fancy or be you know what we would consider you know ultra professional construction to actually work and have the performance of this thing it's all about you know the little minor things about this star point grounding in your choosing the right components for the drift and you know testing it and everything else and calibrating it and well yeah it doesn't look the business from inside but well yeah things like the rain switches and all that are you know very quite nice and all your precision resistors low drift film resistors on there and you know it's stuff like that is all nice but all the other analog II type stuff in there as it really is quite how you doing but it does the job and it meets the spec and this is a pretty kick-ass instrument even today there's not too many AC voltage standards on the market so that's really quite fascinating if I came we don't have the schematic for it if I can get it I will eventually link it in or if anyone has it please leave it in the comments and as always there will be some high res that tear down photos of this thing on Evi blogger.com @ link is down below and the eevblog forum link is there to be had so I hope you enjoyed it catch you next time [Music] you

Channel: EEVblog

Views: 64,142

Keywords: voltage standard, ac voltage standard, voltage reference, calibration, calibration standard, dc, ac, teardown, zener diode

Id: pUXGQ7zQxkM

Length: 32min 5sec (1925 seconds)

Published: Tue Jan 27 2015