EEVblog #210 - Krohn-Hite DC Voltage Standard Teardown & Calibration

[jacekpaw1]

Dave please take us for the trip to this metrology lab. I'm sure that many peoples (including me) are very curious  how does the lab work's.

[schimpl94]

Can you sent me the circuit diagramm of the MV106J ?

That would be great :-)

[daafies2]

Nice find!

[bejius]

17:30 what is the name or brand-name of this transparent plastic insulator ? I've seen it before many many times but I never knew what they are called besides "plastic insulator"

[criscros7]

The whole thing looks DIY, especially the PCB. I've never seen anything like this sold commercially (then again, I haven't seen a lot of gear from the inside). I'm not saying that that's a bad thing, just that it looks as if a hobbyist like myself had done it. Charming. :)

[TrueBlueAustralian]

mmm nice

[besaid00]

Dave, wouldn't the voltage change when you put an actual load on the output?

[thewii552]

Am I the only one that noticed the Bob Pease reference in the description? I like how you put that in. RIP legend Bob Pease

[rapsod1911]

Thank you very much for very informative video. I have watch it 5 times. What a surprise!!! Big box, small board and no vodoo magic.

[nebuchadnedzzar]

@ivaneduardo I think I can answer your question, at least in the case of a voltage source. You can get a very accurate voltage reference directly linked to QM using a Josephson Junction Reference. This is superconductive though so you have to have low temps. But absolutely stable and very accurate. You calibrate that using a Watt balance to measure planks constant..... but those get doen to the ppb range. exotic stuff

[nebuchadnedzzar]

@ivaneduardo I think I can answer your question, at least in the case of a voltage source. You can get a very accurate voltage reference directly linked to QM using a Josephson Junction. This is superconductive though so you have to have low temps. But absolutely stable and very accurate. You calibrate that using a Watt balance to measure planks constant.....

[TedRobotBuilder]

10? Mine goes up to 11! XD

[MichelDeSarcelles]

The final tempco is not only caused by the Zener tempco but mainly by the resistors. Like all Zener diode there is a specific forward current which causes the tempco to be closed to zero. I guess that each diode is tested in an oven to determine this particular current, and the source current is set to this specific current.

[EEVblog]

@MichelDeSarcelles Yes, they would have individually tested and selected I'm sure. "Close to zero" ain't zero though, so it still matters. You can get special "zero tempco" foil resistors too, once again, close to zero, but not zero :-> The exact parts used in this instrument aren't known though.

[TheAdambee7]

handy piece of gear. very surprised at the simple board design. great vid again mate.

[heroineworshipper]

Xena diodes are the best.

[CampKohler]

The insulated spade terminals leading to the output binding posts don't look like they have been crimped by a pair of insulated-terminal crimpers. Were they crimped with uninsulated crimpers, soldered on or what?

[aptsys]

@CampKohler They look to be using uninsulated crimps then a sleeve slid over the end, but only Dave can confirm that.

[CampKohler]

@aptsys Now that you mention it, that is what it looks like, but I can't tell for sure. OK, Dave, satisfy my curiosity, please.

[keenantims]

Great video dave! What an amazing instrument, it really is incredible how good this stuff is just being made from careful design and parts selection. Aside from the switches and resistors nothing amazing or incredible expensive.

What did that odd 4-load component turn out to be? I thought I caught it on the schematic with a symbol like a TVS diode, but I'd be curious to know what its purpose is.

Also I'd like to see a similar vid for the HP 3478 when you calibrate it with your new standard!

[cantankerousbhr]

our dividers go to eleven....

[samgab]

Nice ebay find, and cool review! I wish I had access to something like that to test my Chinese-made Fluke DMM's DC voltage accuracy. Speaking of which... I would LOVE to see a Dave review/teardown of the China domestic market Fluke 17B... I suspect that it's one of the better <US$100 DMM's out there. Also, what is zener voltage and who was Clarence Zener?

[mikeselectricstuff]

Your simplified diagram is slightly wrong - the unit produces a negative reference, which is converted to positive via the inverting amplifier.

I knew a UK company that made stuff like this- a big test rig held a couple of hundred zeners to age over several weeks & they then picked the best ones.

They designed an amp module in the 1970s which was a chopper built from many 741's and discretes, used up til ~2000 when I redesigned it for them with a modern chopamp & reference IC.

[ivaneduardo747]

By the way, how do you calibrate standard calibration equipment? It's not like calibrating weight scales, where you just use a copy of the kilogram prototype, as far as I can tell.

[laharl2k]

@ivaneduardo747 i second that question, and now that i think of it, how do they calibrate the equipment used to calibrate calibration equipment? Where do they get the ABSOLUTE reference?

i can imagine some scientists un a penta layered faraday cage, 50 meters under the ground in the south pole XD (just kidding, but a good question though, i too would like to know the answer, or even better, a video by dave :P)

[ivaneduardo747]

Wow, I love this kind of teardown / explanation videos, I always learn about a couple of new topics at least. Same with the "obscure stuff" tutorials, like the burden voltage one tutorial.

[CNCAddict]

1lb of electronics in a 10lb box !!  What were they thinking when they made the case that huge? Does bigger sell better in measurement instruments?

[nemoDaedalus]

That would be Cromwell Fleetwood Varley (C. F. Varley on Wikipedia) (1828-1883). Worked on the telegraph.

[fingerboy18]

Boston, yeah! That's the closest large city to me. Boston is a huge engineering city, but I don't think many companies do all out electronics products such as this.

[aerofart]

I enjoyed this video very much, Dave. HOWEVER, we still have a MYSTERY 4-PIN DEVICE that needs some explaining . . . ;)

[bfestevao]

@EEVblog Hi Dave!!. great video!. I was thinking if it's a good idea do some modification to obtain that temperature compensation, that LM you showed have a heater, is it viable to wrap the MV106J's diode and design a temperature control circuit?.. maybe with galvanic insulation to avoid some problems..

Thanks!

[EEVblog]

@bfestevao Yeah, possible, but you'd have to weigh up how much improvement you'd get. The tempco is already more than low enough for my use at least.

[skonkfactory]

@bfestevao You could just air condition your lab. 

[annekelive]

Nice one! Love it when you explain the datasheets, good to follow, since my day job only allows me to swap modules and not component level. Sign of the times!

[Kankki1]

Woah, that thing looks homemade :D

[Zed1967]

I've thought about buying dated but great quality test gear off ebay like the Fluke bench multimeters that have the old style mechanical push buttons, you push one button and the previous one pops out, as I'm sure you can get a bargain, when I used to calibrate them they were really accurate but by todays standard the look quite dated. Could you do a video about things to look out for on ebay i.e. test gear, components, electronics in general etc that go for pennies due to age but are gems.

[oqla2000]

old is gold

[Zed1967]

I used to work as an instrument technician for a cal lab in the mid 90's and I'm pretty sure they had the same HP multimeter but the main Fluke calibrator was a 5700 sat on top of a Fluke transconductance amp, they also had the Fluke calibrator that preceded the 5700 with a transconductance amp as well but I can't remember the model numbers. Watching this brought back memories. :)

[DanFrederiksen]

interesting video but I really don't like devices that look like they were made in 1930 : ) are those decadic dials some Forbidden Planet fetish Dave? : )

I'd want some ipod nano looking switch mode supply that is not only accurate but can also supply current.

[MewesK]

I like all your videos. I don't mind if you mix them up. Tutorials, teardowns, interviews, etc. Keep them coming!

[P55CxE9]

that's precision!

[TheCrazyInventor]

That is an awesome bit of gear you have there, Dave. How much did it cost you? :)

[msylvain59]

If someday you happen to find a soviet-russian made instrument, jump on the opportunity, you will have fun tinkering weirdish electronics and it will give one more great video !

[Gameboygenius]

Why didn't you go all the way out and use sense return in the cal lab? Also, why did you cut out the audio near the end? Dirty talk in this pornographic setting? ;)

[EEVblog]

@Gameboygenius For such a short run, with high input impedance, there is no benefit in 4 wire in this instance.

The silence, I meant to cut out more of that, looks like my edit failed. Charles's phone rung with an important call :->

[slaithen]

I like the teardowns, but as a novice electronics hobbyist, I would love to see more videos focusing on tutorials and design ideas.

Having said that, this video went into more detail of the reasons and considerations put into the design of this source. Very nice explanation of the schematic!

Thanks for all the stuff you do Dave, we love it.

[JumperOneTV]

Nice video! Thanks, Dave!

Will you do video on your HP meter calibration?

[hoppes9]

@slaithen You don't think this is a tutorial?

[slaithen]

@hoppes9 This started out as a "good buy review"/"teardown", but like I said in my comment, "... this video went into more detail of the reasons and considerations put into the design of this source. Very nice explanation of the schematic!"

So, yes, this video turned into more of a tutorial than it started out as, but I would like to see more tutorials from Dave. Things starting with a project/circuit in mind, explaining it and different considerations associated with it.

[thomasey2]

That is cool



[prayag123456789]

can you do some more tutorials ?