Author Topic: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]  (Read 26721 times)

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Offline Cerebus

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Well, I've decided to build zombie 5700A out of nothing  :)

You're just a glutton for punishment aren't you? Any reasonable man would have been adequately chastised by that 3458A.  :)
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline Echo88

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"Reasonable"...yeah, not a word you would use to describe a voltnut. Did you stop developing your own backplane-pcb for the PWM-DAC TiN?
 

Online TiN

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I still might need to do it, as it's unlikely that backplane will be for sale on fleabay. But it will have ports for all boards instead of DAC only. :) oh well.


« Last Edit: April 13, 2017, 01:01:14 am by TiN »
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Offline TheSteve

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If TiN gets anymore out of control we're going to have to start a GoFundMe account to just pitch in and get him a 5700A.
VE7FM
 

Offline ManateeMafia

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Maybe an airline ticket to Everett so he can go dumpster diving?
 

Online TiN

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I can soon have own dumpster, thank you.  :P

Schematics for backplane board in progress :)
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Online TiN

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Initial schematics and PCB placement - check  :)

Original 5700 board is 6-layer, I'll see if I can do in four. Need figure out some guarding and grounding connections. Also need to decide what relays to use instead of customized COTO 7003-5065 and COTO 7004-5071 which Fluke has.
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Online TiN

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Revive, revive...

I've finally got some vapourware relays (every single relay manufacturer ceased production of dual-coil 4PDT low-signal relays due to lack of demand), as abovementioned DS4E-ML2-DC5V-C-H239 relay on one of my Fluke 5700A boards (A8 switch matrix PCBA) have damaged housing.



While it was still working, I've replaced it now with standard DS4E-ML2-DC5V, bought from fleabay. Not to waste a chance, I've finished the desctruction of the housing, so ya'll can enjoy "teardown" photos of internal construction.



There are many relays of this type in 57xxA's , as well as DPDT version DS2E-ML2-DC5V-C's. So I've bought plenty till there is such chance.



To be continued...
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Online TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #58 on: August 30, 2017, 04:15:52 am »
Perhaps somebody may be interested in little stability study of above-mentioned 5700A.
Unit was calibrated in beginning of the year, against SR104 and Fluke 732B (both in <6 months from subppm standards lab cal).

Since that time we run calcheck's on various periods, storing all data. Lab temperatures were kept around 24-26°C. Unit was mostly 24/7 online till summer time.
Last few months it was turned off, and powered on just couple days ago before 8/29 calcheck.

Here's snapshot on resistance function:



I'd say not too shabby at all for 26-year old calibrator. Ohm board was replaced at some point with one made in 2005, according to IC datecodes.

Here's how it look like, in case you forget:



Given that lab was not controlled very well, no humidity control, I'd say numbers are very nice, well under 3ppm for all resistances except 100Meg.
Major 1K, 10K, 100K resistors are better than 1ppm stable over this 8 months period.
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Offline Kleinstein

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #59 on: August 30, 2017, 05:06:07 pm »
For a reference / stable resistors an age of 26 or 12 years is not a problem at all. If handled proper, they get better with time. Not sure a brand new one would be that stable - unless Fluke keeps them for 1 year before delivery.
 

Online TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #60 on: August 30, 2017, 05:15:43 pm »
I was more concerned of impact with all those relays. There are many in the signal path with different configuration, which all may have different contact resistance, rather than hermetical ceramic resistors themselves.  There are at least 3 relays on each resistance tap before they reach the internal MFC output bus.

Worth to note, that table above is stability versus own's 5700A "reference" 10K resistor (network Z5 on OHM CAL board), not the absolute deviation.
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Offline chinapp

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #61 on: September 19, 2017, 08:33:41 am »
I think the relay should be noticed and test if the machine has been used for heavy duty,the fluke 5100 calibrator has much faults caused by  relays
 

Offline Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #62 on: December 12, 2017, 02:34:56 pm »
Attached you find the ltspice-simulation (change from .txt to .asc) for the 5700A PWM-DAC, which greatly aided me in understanding the various circuit-tricks used in this schematic.

I only use Channel A PWM (V5) and added an additional R42/C12 lowpass behind the 190Hz-Filter. I didnt use this simulation since a while, but i think the rest of the component-values should be all according to the schematic.
 
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Offline Henrik_V

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #63 on: December 14, 2017, 10:45:22 am »
About 5700 relays...
I was told by an old 5700 cal lab spezi  that I even if my 5700 is not in use /standby regulary do the autozero to ativate the relays, to avoid oxide between contacts.
Watching the snails,cars,....  :D
Greetings from Germany
Henrik

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