Author Topic: Live design flow of 'FX' 10V LTZ1000A-based reference  (Read 6843 times)

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Offline ManateeMafia

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #50 on: January 08, 2018, 02:10:33 am »
Any streaming video today of final assembly and testing?
 

Online TiN

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #51 on: January 08, 2018, 02:14:04 am »
No, maybe next weekend. I need figure out resistor situation and rearrange lab first.
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Online TiN

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #52 on: January 14, 2018, 03:44:00 am »
BTW, I'm streaming now assembly of 4th prototype with LTZ socket.

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Offline branadic

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #53 on: January 14, 2018, 04:12:39 am »
What does Edwin G. Pettis think about your resistor lead origami?

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Offline Edwin G. Pettis

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #54 on: January 14, 2018, 11:06:54 am »
For the first board about 55 minutes in, those bends are a bit tight, while they probably won't have any problems, a better way would be to use a needle nose next to the body and then bend the lead, more like TiN did at about 1:45:00 minutes on the second board I seen,  Sorry don't have time to watch it all right now.

The leads are 'anchored' into the bobbin and held in place by the epoxy sealant so mechanically it is normally not a problem, however, if soldering (or multiple soldering) takes too long it can damage the epoxy allowing the lead bend stress to migrate into the bobbin and in some instances, causing the weld to be broken by excess strain.  It doesn't happen very often but it can, even Bob Pease managed to mangle some resistors trying to remove them from a double-sided PCB.
« Last Edit: January 14, 2018, 01:05:51 pm by Edwin G. Pettis »
 
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Offline MisterDiodes

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #55 on: January 14, 2018, 12:12:28 pm »
Correct.  For "young players" not familiar with assembling precision analog circuits:  The -minimum- bend radius on component leads is typically 2X the lead diameter, and on PWW  / Foil resistors that's more like 3X - when you kink the leads that develops a cold-worked alloy concentrator zone that can eventually cause problems over time.  This can even show up on low value resistors as increased apparent TC.

Also keep the start of the bend at least some distance (2X diameter minimum) from the body to help prevent any mechanical strain making it into the wire weld area - this applies to any precision resistor, PWW or otherwise.

When bending leads, always support the leads so you're not "jacking" the lead against the body (i.e. pulling it out of the body).

The component should fit into the mounting holes before soldering with zero stress on the leads - for production we'll have a zero-stress bending jig system setup for the various parts. 

That "Origami" look is basically what you don't want. The circuit will still work, but might not pass a precision assembly inspection.

 
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Offline babysitter

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #56 on: January 14, 2018, 11:13:24 pm »
When bending leads, always support the leads so you're not "jacking" the lead against the body (i.e. pulling it out of the body).

A coworker (M.Sc. in physics, might play a role?) just arrived at that with a resistor from Edwin, i was barely able to believe it. I think I posted a photo on the E.L.T. I still don't know how he has done it, its his nasty secret.

Hendrik
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Offline Andreas

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Offline babysitter

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #58 on: January 15, 2018, 05:49:41 am »
Yes, that one, I thought it was in the Epic LTZ thread.
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Online TiN

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #59 on: January 17, 2018, 05:20:53 am »
Today's update:

Sorted LTZ chips by voltage output, using socket board. Now need to map-match Fluke networks for each chip.
LTZ resistor setup: Edwin's PWW 13K/1K, 120R, 2x70K.



 :box:


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Online TiN

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #60 on: January 24, 2018, 05:29:34 am »
Bit of progress of target device, why FX reference actually created... Conversion of 792A Power Pack into 10VDC battery-powered reference.
Main aluminum frame of 792A transfer box and power pack is actually exactly the same, only front face plate is different and guard inner shield does not have holes for shaft and terminals.
So off we go, drill missing holes for binding posts.

I need 4 posts, because FX output is 4-wire, force and sense wires are separate, so I can use it to drive resistive loads (to act as current source).



Looks somewhat decent, eh? I'll have to drill now holes in guard plate, and likely to lift PCB a bit further from shield, to avoid interference of binding posts and PCB.



Need to find out way to make white text marking on black background to add labels.



LEMO power supply output port still works as original design, providing regulated isolated +11/-11, in case I need connection to real 792A transfer unit.
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Offline Pipelie

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #61 on: January 24, 2018, 04:27:38 pm »
Maybe you can try the sublimation transfer, that's what I'm going to try out.
 

Online TiN

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Re: Live design flow of 'FX' 10V LTZ1000A-based reference
« Reply #62 on: May 02, 2018, 10:44:44 pm »
Since February I am using one of these modules in the modified Fluke 792A power pack, that provides battery power backup and triple shielding to the reference. Module that went into the box was trimmed to 10V +/-2ppm vs all my other current references and meters, and stays there since.

Here are some more details about this design, this time thermal image map, captured by Fluke Ti32:



Darker area : warmer temperature. You can see most of heat stay near the oven drive transistor, LDO and surprise - indicator LEDs  :-/O.



My layout efforts seem to pay off well, no uneven thermal gradients around output stage amp (ADA4522-2 in this case) or output pass transistors. I'll need to test this again during max loading test (40mA load to 10V output).



This reference is using 12.5K/1K VHD200 divider, 120R VHP202, 70K VHP and 71.5K RNC90 resistors. As can see on closeup on bottom image, thermal gradients around LT1013 and resistors are less than 0.5C in worst case.

Also small update on long awaited VHP resistors - so far ETA is ~July for all sets.  :-X
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