Author Topic: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]  (Read 26816 times)

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Offline TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #25 on: November 11, 2016, 03:27:16 pm »
I'd surely enjoy reading thru 4808 teardown too :)

Didn't look much into AC side of the calibrator , that's to be corrected later.

Yea, I remember the snails stuff, let me check if I can make a video with them..
« Last Edit: November 11, 2016, 03:29:03 pm by TiN »
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Offline lukier

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #26 on: November 11, 2016, 03:39:59 pm »
Come to think of it it's quite sad TiN got all this gear (5700A, Time calibrator, 3245A, 4920M etc)  :P, now the KX project will grind to a halt as no longer needed  :-\. Bummer, having some open source / DIY / modern designs for AC, current or HV DC calibration points would be useful.

But on the other hand not everyday one can see what makes 5700A tick.
 

Offline doktor pyta

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #27 on: November 11, 2016, 04:27:21 pm »
#2000 Post... the atmosphere is like Tin has birthday :)
TiN, thanks for Your volt-nut activity, for Your very high quality posts with very informative content and for all Your efforts!
'Long live the TiN!'

Offline free_electron

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #28 on: November 11, 2016, 04:35:48 pm »
they sure love their 82c55's !
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Online Kleinstein

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #29 on: November 11, 2016, 05:11:43 pm »
...
And while we are at it: Does someone  know how the AC frequencies are generated?
More specific, reason why I ask: While performing AC calibration on DAQ cards we usually perform a sine fit and look at the residuals. At certain frequencies one can clearly see phase jumps in the residuals.  So the 5700 has some sort of accumulated phase error register, that results in added or skipped DAC values..  . In order to avoid that: Does  somebody know how one could pick output frequencies that avoid these jumps?   
Maybe something like : the 5700 has an internal clock frequency f_clk , use a M/N factor (both integer) add the internal x and/or divide by another y  and you get the 'clean' frequencies ?     ..  :)

Form the manual the internal oscillator is not using DDS to generate the AC signal, but classical old style phase shift RC oscillator with an PLL (actually more than one) for frequency control. So if everything is ok, there should be no sudden phase shifts. So no easy list of good and bad frequencies. It is more like a few frequencies (or ranges) that seem to show glitches on that special unit. The could be a general design weakness or tolerances on that special unit. I would consider 3 possible sources for this:
1) The PLL adjustment range somehow reaches limits as the internal control reaches limits. This might be fixable with some internal automatic readjustment of the frequency control. (coarse osc. settings).
2) Very small glitches might occur if the coarse setting is to good in some cases and the phase comparator is in a kind of dead zone. This should be really weak disturbances - don't know if one would see them on the scope.
3) The loop filters need to be adjusted with the frequency. There could be borderline cases where the loop filters are not really good, maybe too much direct feed through. So there could be frequency ranges that are not that good.

One could do a test with external reference frequency instead of the internal one, to check if the glitches come from the ref. frequency synthesizer or the main oscillator / PLL.
 
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Offline VintageNut

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #30 on: November 11, 2016, 05:19:41 pm »
TiN

Your teardowns and repairs are amazing. You have smarts, skills and you work incredibly hard. And now, you have one of the best toy collections of anybody.
working instruments :Keithley 260,261,2750,7708, 2000 (calibrated), 2015, 236, 237, 238, 147, 220,  Rigol DG1032  PAR Model 128 Lock-In amplifier, Fluke 332A, Gen Res 4107 KVD, 4107D KVD, Fluke 731B X2 (calibrated), Fluke 5450A (calibrated)
 

Offline TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #31 on: November 11, 2016, 06:20:58 pm »
Hah, far from it. I wouldn't bury DIY projects just yet. Actually A11 might be the good push towards DIY calibrator with it as base.
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Offline feedback.loop

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #32 on: November 11, 2016, 06:46:47 pm »
> Known instruments to implement SZA263/LTFLU-1AH as primary DC reference

Add Fluke 341A and 343A to the list.
 

Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #33 on: November 11, 2016, 08:09:47 pm »
@TiN: Can you please make a more detailed photo of the PWM-Filter, especially around U1 and tell us the name of Q4-Q7, which switch the PWM-MSB and LSB? I always thought that Q4-Q7 had to have charge injection cancellation and that the PWM-filter would be an active design like in the Datron 4911, but it seems that its just a normal 5-pole-RC-filter. So, im assuming one could replicate the design with good results.
 

Online Kleinstein

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #34 on: November 11, 2016, 09:15:57 pm »
The schematics shows a filter rather similar (slightly simpler) to the Datron 4811 - just using normal OPs instead of extra JFETs. This is a rather obvious change as better OPs are available.

A difference is the linearity circuit to compensate for the switch resistance.
However no obvious compensation for charge injection and no special gate drive.
 

Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #35 on: November 11, 2016, 09:31:30 pm »
My bad, i didnt see the full schematics at the service manual bottom and was still stuck at the DAC description.  :palm:
 

Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #36 on: November 12, 2016, 07:07:45 pm »
Im attempting to simulate the PWM-filter of the DAC-board in LTSpice, but im not getting the expected Vref/2 at 50:50 PWM-duty cycle. Since i dont know the filter topology and therefore cant see my error, maybe someone can point it out. Expected PWM-frequency is 200Hz.

The values in the filter are taken from page 422 of the service manual, the full schematic is on page 514/519. The LTC2057 is used as the DC driver OP, since an OPA527 wasnt included in LTSpice.

https://xdevs.com/doc/Fluke/5700a/Fluke_5700A_5720A_Multi-Function_Calibrator_Service_Manual.June_1996.pdf

« Last Edit: November 12, 2016, 07:09:47 pm by Echo88 »
 

Online Kleinstein

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #37 on: November 12, 2016, 08:47:38 pm »
In the simulation, the output amplifier part is quite different from the original, as it includes the inversion done in an extra amplifier in the original.
There seems to be trouble with the simulation of the switches. At least with my version of LTspice, current flow is strange / inconsistent (e.g. mA range at the 13 V source, but no current at the switch). Changing from switches to MOSFETs (so more like the original) it seems work - kind of.

I still get 6 V instead of 6.5 V.  This is due to hidden parallel resistance in C3/C4 !

The 100 p cap should be at the input side of the OP - not a big difference, but a little less spikes.
 

Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #38 on: November 13, 2016, 01:35:11 am »
Youre right, my bad. Forgot to delete the parasitic series resistance of the caps, sorry. Still dont really know where the spikes come from. Now i get 6.502565V @ 723µVpp ripple after 2s after the filter with 50:50 duty cycle, with an additonal simple 40kR/10µF-RC-low pass i get 1.4µVpp after 20s. In the simulation its perfectly linear, at least in the borders 10-90% duty cycle which i simulated. Of course one has to test it in reality.

But youre right, even with mosfets or with a simple voltage source spikes occure.

Updated working .asc attached.
 

Online Kleinstein

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #39 on: November 13, 2016, 09:22:16 am »
To get rid of the spikes, an additional RC (or LC) filter stage is enough, but I would have the as a first step. Soemthing like 10 K and 1 nF should be enough. So split the 40 K to 10 + 30 K and ad a small cap.
 

Offline SteveH

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #40 on: November 14, 2016, 05:43:29 am »
> Known instruments to implement SZA263/LTFLU-1AH as primary DC reference

Add Fluke 341A and 343A to the list.
Fluke 515 uses a pair.
 

Offline Mickle T.

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #41 on: November 14, 2016, 07:03:24 am »
Quote
> Known instruments to implement SZA263/LTFLU-1AH as primary DC reference
Philips PM2530 - 7.5-d DMM
 
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Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #42 on: November 14, 2016, 12:41:17 pm »
Im still trying to understand the series-linearity-control-schematic, maybe someone can tell me if im correct in my thoughts:

The series linearity control injects 650µA ((11k/14k * 13V) / 15.71k) = 650µA) at TP5, which cancels the assumed 650µA which flow though R12 to the filter, so it seems between TP2 and TP5 are 0R.
Since i do not fully understand the reference hybrid schematic, im assuming during the activated Q4/Q5 period the 13V reference produces a tiny bit more voltage because of the 650µA injected current, thus effectively compensating the voltage drop over Q5-RDSon.

Would have thought a voltage follower, with its output switched by Q4, could achieve the same function of compensating Q5-RDSon.
 

Offline TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #43 on: November 14, 2016, 02:02:27 pm »
Quote
> Known instruments to implement SZA263/LTFLU-1AH as primary DC reference
Philips PM2530 - 7.5-d DMM

Spasibo.

Not everyday I get to know 7.5d DMM which I did not heard about before.  ;D I'd love to see photos of it more in detail. eBay don't know these, to my relief.  :phew:
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Offline HighVoltage

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #44 on: November 14, 2016, 04:01:02 pm »
Spasibo.

Not everyday I get to know 7.5d DMM which I did not heard about before.  ;D I'd love to see photos of it more in detail. eBay don't know these, to my relief.  :phew:
Philips had the following meters, that I personally had, a long time ago:

- PM2525 (5 1/2 digit)
- PM2534 (6 1/2 digit)
- PM2530 (7 1/2 digit)
The PM2530 was only built for calibration labs and once I got lucky to obtain one.

But all three meters were ultra sensitive and I had constantly problems with them.
I sold them all like 15 years ago or so.
But that was before I opened instruments for fixing, so no pictures here

There are 3 kinds of people in this world, those who can count and those who can not.
 

Offline krivx

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #45 on: November 14, 2016, 04:09:33 pm »
Great post. I wonder if there are members here who don't understand what a 56k warning is.
 

Offline Mickle T.

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #46 on: November 14, 2016, 04:41:13 pm »
PM2530
 
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Offline TiN

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #47 on: February 02, 2017, 07:08:28 pm »
Since I want to have ability to generate voltages from ±22V to ±220V and perhaps AC voltages up to 220 V using discussed above DAC, I also bought broken Fluke 5700A's A16 board. This is power amplifier board, which takes DAC 11/22V signal and boosts to higher voltages. Let's take a look..



Nice channeled shield to direct air around heatsink and power components.





Similar to DAC board, most of routing done on inner layers.







Some preamp stage circuitry.



Magical glass hermetic Fluke resistor network thermally coupled to heater and chopper module to ensure stability.



LTC1052-based chopper opamp on ceramic substrate glued to heater hybrid. Resistor network tied on the back to keep all nice and thermally stable.



Magical glass hermetic Fluke 764399 resistor network Z1 (unheated)





« Last Edit: February 03, 2017, 02:23:29 am by TiN »
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Online Echo88

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Re: #2000 Post : Teardown and study of Fluke 5700A Calibrator [56K warning!]
« Reply #48 on: February 03, 2017, 04:44:11 pm »
Can you do me a favor and measure the HR6-Resistor Network between Pin 4 and 5 on the DAC-Board? From the schematic (the top left one in the Sense Hi Current Cancellation Circuit) im assuming its 4.4k, but im not sure.
 

Offline TiN

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

Here's call for parts in Buy/Sell section. If anyone has parts of 5700A/5720A/5790A, especially chassis/transformer - that would be great help.

I've already CCC'd 11 out of 22 boards from 5700A off ebay, some of which bad, some good. Hell, 50% done, some might say.  :-DD

Crowdbuilding calibrators - new word in electrical metrology 2017.  :scared:
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