Author Topic: MX Reference  (Read 16817 times)

0 Members and 1 Guest are viewing this topic.

Offline Dr. Frank

  • Super Contributor
  • ***
  • Posts: 1697
  • Country: de
Re: MX Reference
« Reply #100 on: September 11, 2017, 01:57:19 pm »
Similar, but I wanted separate 3458A-like ref module, so I could use that elsewhere (I want to build a variable resistance standard, based on Valhalla 2724A, like Mickle T did) and separate step-up/10k standard in the oven.

I have parts to build 4 (and 1 extra ref-module), so the final version will be a DIY Fluke 734A. I need to find a suitable case that would fit a toroidal transformer for charging and PCB slots to slide the modules in.

We obviously had the same idea, and I also have 4+1 sets.

So my layout allows to cut off the amplifier part, and get a 57 x 50mm PCB, similar size like in the 3458A (48x41, I think), but with space for PWW resistors.
Direct pinning for the 3458A is not available, of course.

But a pinning for the 34465A would be interesting, to improve its noise and stability to 34470A level.
Had already begun to reverse engineer the 34470A reference .. but did not figure out, how LM399 and LTZ1000 are merged on these 8 pins.

Anyhow, the design of an isolated, silent, 4 fold PSU would be great.. much more important than YaRM - yet another reference module..  :-DD

Frank
« Last Edit: September 11, 2017, 02:05:01 pm by Dr. Frank »
 

Offline lukier

  • Supporter
  • ****
  • Posts: 614
  • Country: gb
    • Homepage
Re: MX Reference
« Reply #101 on: September 11, 2017, 02:08:08 pm »
So my layout allows to cut off the amplifier part, and get a 57 x 50mm PCB, similar size like in the 3458A (48x41, I think), but with space for PWW resistors.
I was thinking about something like that, I think at seeedstudio they call it self-panelization, but because of the many mechanical components involved in the mini-module covers (steel sheet, spacetherm, kapton, nylon standoffs) or oven (heater - TBD, some resistive foil to test on order) I think I'll have 2 separate designs.

Anyhow, the design of an isolated, silent, 4 fold PSU would be great.. much more important than YaRM - yet another reference module..
Yeah, I was thinking about that initially, some form of Royer followed by low noise LDO and a lot of ferrites everywhere. My analog foo is probably not good enough for that and it is a lot of work.

Now I'm not as ambitious as that, there will be one linear supply in the chassis for all the 4 modules, just for charging the 18650 cells in the modules and when I need to use the module I isolate its charging supply (i.e. turning off the charger IC and floating the module) with a rocker switch on the front of the module, thus running the module from the LiPo cells.
 

Offline 3roomlab

  • Frequent Contributor
  • **
  • Posts: 936
  • Country: 00
  • can you tell me how to cal sesame street meter?
Re: MX Reference
« Reply #102 on: September 15, 2017, 12:09:29 am »
Yes, 1mm ~ 3mm would be a good place to start.  We use .05 or .0625" as a starting place if you're on imperial measurements.  The inner box can be slightly thinner, and maybe a single box is all you need.  We normally go for a 1/4" spacing between inner and outer but 1/8" would probably be OK.  It depends on what you're shielding from.  Aluminum will help some against E-fields but not much for mag field issues.

Also note:  If you're using PWW resistors it's important to at least have some minimal shielding around your circuit if you're near stronger H-fields - say an industrial area where you've got power mains in conduits, motors, ovens, etc.  Those resistors are wound with balanced windings but they will see some magnetic interference effects in a strong field unless you give them at least some protection - otherwise they will give you low noise performance.

ive been looking up more info on the net about the why and what, not much info until i saw this
http://www.compliance-club.com/archive/keitharmstrong/design_techniques4.html

i assume the 1-3mm being indicated have a correlation with skin effect vs frequency? esp for steel?


*edit : there are many TAOBAO shops offering 1J85 (permalloy equiv?) have anyone used these?
« Last Edit: September 15, 2017, 11:41:44 am by 3roomlab »
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 

Offline MisterDiodes

  • Frequent Contributor
  • **
  • Posts: 454
  • Country: us
Re: MX Reference
« Reply #103 on: September 16, 2017, 05:54:34 pm »
That's related more to induced current effects in the shielding material, and is more of a concern at higher freqs.  For low freq and DC circuits we worry about lower freq mag field problems, say at 100kHz and under...although noise injection can come from anywhere.

You use steel and / or MuMetal or whatever material you've got that has high permeability -without saturation- to protect your circuit from external mag fields.  In other words you need to steer the magnetic field -around- your circuit, so you give it a very easy path to follow in its own contained path around your device.  If the material is too thin it is likely to saturate if the mag field is strong enough, and then it's not doing much.  Once that shield material saturates, it's not steering the mag field anywhere in particular.

Depending on the local field strength and frequency you use the combination of shielding materials that works the best for best profit and effect - For instance you might find that a small steel box (a few dollars at the hardware store for a junction box for instance is a simple test, much heavier gauge than a candy tin) might give you enough noise attenuation for your lab situation.  Or a double shield box design.  Or you might need an annealed deep drawn MuMetal can that will shield your circuit all the way down to DC.  Copper and Aluminum can shield at higher freqs. and more for RF issues.  Sometimes a simple steel box with an overwrap of MuMetal foil works well enough at low freqs.  If you don't kink the foil in a really sharp bend that MuMetal will still work surprisingly well without any heat treatment at all - and is miles better than nothing.

It just depends on what you're shielding against, for your situation and budget.  You also look at protecting and shielding all leads (Chokes - ferrites usually) and equipment around the sensitive circuit - mag shielding is only part of it - you have to look at the noise delivered into your system from mains power and noisy high impedance grounds, noisy equipment in the lab etc.

The main thing is to keep your current loops with as small an area as practical, and try to minimize mag field interference as much as possible that way.  Twisted short & shielded connection leads, for instance.   Normally we'd never be using longer banana-plug and clip-lead style connections at low ppm for serious measures, but we see that all the time with the informal hobbyist setups - and those standard, separate red/black test lead assemblies are usually much too long and wind up acting as a pretty good loop antenna (transmit and receive) more than anything.

Do whatever works best for your situation, budget and measuring uncertainty goal. 
 
The following users thanked this post: lowimpedance, 3roomlab

Offline ManateeMafia

  • Frequent Contributor
  • **
  • Posts: 719
  • Country: us
Re: MX Reference
« Reply #104 on: September 30, 2017, 01:19:19 pm »
Received several sets of resistors from Edwin on Thursday. Thank you Edwin!
Most of them will be for building newer versions of the MX board but a few sets are earmarked for another project by a forum member.

These are the smaller body model 802 which is the same size that TiN had for the KX board here https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/700/
Coincidentally, these are the same size I used to create the original part library for my first board.  I have since created the larger version (805?) and the next rev can use either one.

I have vacation this week so I will be finishing the test chamber and will cycle it using my Keithley 2510. The tempco results from casual observation are not good but I will need a starting point.

Thanks again to everyone with suggestions. So far I am sticking with the datasheet for the components but will leave one or two unpopulated locations. I will need to sort out basic layout problems first. The next rev has all the PWW resistors closer together on one side of the board and the traces are shorter where possible.

Once we get tempco data, it will be posted hopefully later next week.
 
The following users thanked this post: dr.diesel

Offline TiN

  • Super Contributor
  • ***
  • Posts: 4045
  • Country: tw
  • xDevs.com/live - 24/7 lab feed
    • xDevs.com
Re: MX Reference
« Reply #105 on: September 30, 2017, 01:31:27 pm »
My Raspberry snakes are ready to run  >:D. Let's see some tempcurves!
YouTube | Chat room | Live-cam | Have documentation to share? Upload here! No size limit, firmware dumps, photos.
 

Offline ManateeMafia

  • Frequent Contributor
  • **
  • Posts: 719
  • Country: us
Re: MX Reference
« Reply #106 on: September 30, 2017, 01:35:27 pm »
I will need to mount the TEC and add a power connector. I think I will drill a small hole for the test cable. I have some STP and will use that instead of the CAT5. The pcb mounts are already done.

I have to work this weekend so maybe time late tonight or tomorrow. If not, I have staycation all next week. I just need to clear the bench, there is this large beast taking up room  :-X
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1474
  • Country: de
Re: MX Reference
« Reply #107 on: September 30, 2017, 03:13:28 pm »
Quote
Received several sets of resistors from Edwin on Thursday. Thank you Edwin!

I always wondered why they are not marked like any other resistor manufacturer does.

-branadic-
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15087
  • Country: za
Re: MX Reference
« Reply #108 on: October 01, 2017, 05:27:43 pm »
Pretty much every hand wound resistor is hand labelled, even the Vishay special order ones that start off as a regular glass slab and then are precision trimmed to an exact value or tempco.
 

Offline Echo88

  • Frequent Contributor
  • **
  • Posts: 567
  • Country: de
Re: MX Reference
« Reply #109 on: October 03, 2017, 09:27:28 pm »
@ ManateeMafia: Would you mind sharing your Eagle-Project on the MX-board or the LTZ1000-footprint-file? I plan on building a LTZ1000-bank and therefore would like to design a suitable pcb, which might divert a little bit from yours.
 

Offline branadic

  • Super Contributor
  • ***
  • Posts: 1474
  • Country: de
Re: MX Reference
« Reply #110 on: October 03, 2017, 09:35:42 pm »
I'm not ManateeMafia, but I can share my LinearTechnology library with you. You will find LTZ footprint in there.

-branadic-
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 
The following users thanked this post: ManateeMafia, Echo88, kj7e, CalMachine

Offline ManateeMafia

  • Frequent Contributor
  • **
  • Posts: 719
  • Country: us
Re: MX Reference
« Reply #111 on: October 03, 2017, 11:24:41 pm »
@branadic,

Thanks for sharing. My library had a small error on the last pcb run. I think it is fixed but I am concerned people will get boards made with problems. My issue involved a solder mask over one of the pads. Fortunately the pcb house caught it and manually removed it for me. You can see it in one of the photos.

I hope to have the thermal chamber going late tonight or early morning.
 

Offline 3roomlab

  • Frequent Contributor
  • **
  • Posts: 936
  • Country: 00
  • can you tell me how to cal sesame street meter?
Re: MX Reference
« Reply #112 on: October 09, 2017, 03:45:01 am »
on the stuff everyone talked about regarding magnetic in this thread, a really funny coincidental discovery fell on me when i saw a stainless steel bowls and pans product page

https://img.alicdn.com/bao/uploaded/i4/2454910677/TB1I_c8kRcHL1JjSZFBXXaiGXXa_!!0-item_pic.jpg_430x430q90.jpg
https://img.alicdn.com/imgextra/i4/507489737/TB23bkcXNaK.eBjSZFBXXagMXXa_!!507489737.jpg
plate version appears to be under 0.5mm, bowl appears to be >0.5mm

since it would be terribly difficult hobby wise to obtain cheap and sphere formed mu-metal spherical shielding ...
by cupping 2 of these bowls together (20cents stainless steel), it is looks like a readily available magnetic shield


it seems my assumptions above  about stainless steel could be wrong. 304 is likely not enough of permeability to be effective.
again based on FEMM 4.2 simulations (finally understood some magnetic functions). thickness plays an important role (even for mu metal which is assume to work well at 0.1mm thickness, but it highly depends on the quality). in the below text, i am using (u) as relative permeability.

https://3.bp.blogspot.com/-fH6EU786D1A/Wdtgva3295I/AAAAAAAAC2Y/xUPfJ0_OIr0cCckbzB42khGHMRlx4KHAACEwYBhgL/s1600/B006.gif
a sphere with 0.1mm 83k(u) mu material. approx 0.001T fields still can leak into the sphere. (5mm hole is deliberate)

https://4.bp.blogspot.com/-sHgsVDaZuxE/WdtgwMiv3FI/AAAAAAAAC2c/S6gItopk-YQRiRL3UIKDevrml7iqIUxHgCEwYBhgL/s1600/B007.gif
same sphere with 3mm thick ferrite mix approx 100(u) material (at least 500x worse than than mu metal). this inferior material appears to block more. (5mm hole is deliberate)

https://1.bp.blogspot.com/-QltxZtqCENU/WdtguRKeHCI/AAAAAAAAC2U/2tJPa_a32psPO66ruqW2bpItPSFWEMgqwCEwYBhgL/s1600/B005.gif
ferrite mix, odd corners, thickness can be a detriment? i am unsure of this.

https://3.bp.blogspot.com/-jPJ1FgDRmIY/WdthFopeAII/AAAAAAAAC2g/MCf1iFBh1Bws_tqF_ps8aoDJGsRNASo4wCLcBGAs/s1600/B008.gif
symmetry seem to play a bigger role in diverting field completely than using the usual long boxes.

https://3.bp.blogspot.com/-eNBh0UvGEsw/WdtgsAYjBKI/AAAAAAAAC2E/Bu0uq8FPiGsI6d6Uz2EYbc4LHgEzrJkRwCEwYBhgL/s1600/B002.gif
the 83k(u) material needs at least 0.5mm thickness. all older equipments seem to it this way.

so it appears, for a ferrite mix (made into like a liquid PU dip mix?), it may likely have more advantage than mu metal sheeting (single layer vs single layer?)
(Mn Zn ferrite powder can be searched and found on ebay and alibaba. my last find shows about S$5 per kg, my guess is a liquid form will conform to all kinds of shapes and form a seemless layer esp around wire inlets)

https://2.bp.blogspot.com/-jtuhlepFSMg/Wdtgt60bpEI/AAAAAAAAC2Q/tzYSXa8Nug4LI_NTOhzpGZCyhBnbxW9pQCEwYBhgL/s1600/B004.gif
thin wall mu metal and long box, even worse than the sphere model? (2x mm size holes are deliberate)

additional simulation
using 0.1mm mu but in 3 layers.

1) seemless with 1mm hole (which is impossible to fabricate and re-anneal at DIY level)
https://3.bp.blogspot.com/-8R09rMSGDXc/Wdx9SQ5WhGI/AAAAAAAAC20/enB7nueVFKE4fYu-Zl5tmWXRMP4gTsgdgCLcBGAs/s1600/B009.gif

2) segmented, which results in heavy field lines at corners
https://4.bp.blogspot.com/-uwsGXNL6W10/Wdx9R14v0vI/AAAAAAAAC2w/BdJFh20dkjoTyVSbMqYAQ0KeCMpxwfP-wCLcBGAs/s1600/B010.gif

3) segmented but with overlaps, which is worse than seemless by 1 magnitude, but better than single layer by 1 magnitude
https://4.bp.blogspot.com/-X4G7X3vKvUk/Wdx9S-MwJQI/AAAAAAAAC24/ax7-SDW784o-Z3EfWUW05adLiJz-JbmwQCLcBGAs/s1600/B011.gif

4) 0.1mm mu sheet. 2 overlap seams 1mm hole. shielding down to as good as 1uT (original incoming field strength is around 1mT)
https://2.bp.blogspot.com/-E7VQTriQgeU/WdyCDEZmHrI/AAAAAAAAC3I/KjEz_2U9IVoDZvGExx_Lypuh6egQjYUMACLcBGAs/s1600/B012.gif

5) 3 overlap seams and 1mm hole. seams inside start to generate fields between each other
https://2.bp.blogspot.com/-QnEqqy1pUfg/WdyFy4eZ27I/AAAAAAAAC3U/LwYz3iPGFu0AvOYfdLL0whrNkMFes5PVgCLcBGAs/s1600/B013.gif
« Last Edit: October 10, 2017, 08:38:51 am by 3roomlab »
spheres of influence, example linustechtips. can you feel the brainwashing? showing off equipment, etc. were you swayed and baited? with immense popularity (and social "titles"), can you afford to disagree?
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf