Post 2000!Fluke 5700A of course!
Offtopic introIf you may wonder, where did I disappear and why no posts last week, now you know why. I wanted to cook and publish this thread first to celebrate my 2000th (O-o) post here. But before that I'd like to have small retrospective. My first post here was
tear-down/repair of Tek CSA7404 thread bit over 3 years ago, and I really did not expected that to become so popular, as even broken these Windows-based old Tektronix scopes still often fetch pretty penny. Then
Keithley 2001 repair thread was started, covering about 7 years of my repair shenanigans, all stated with first bench-top DMM, bought on eBay for $200 USD. Rest of the story you may know, got infected with volt-nut virus and off we go down to the endless rabbit hole. Now there is a chance that I have more 8.5-digit DMMs than some of calibration labs might have
. And I'm still always information-starved.
But amount of old/broken/fixed accumulated equipment does not matter, if one can't get it used and calibrated. So to resolve this issue two things were started, one of which own design of DC voltage reference and DAC/ADC modules for experimenting and learning purposes. Second is calibration standards and equipment projects were kicked off to be able source stable DC, AC voltages and currents and resistance check points. Most obvious result of this are
my LTZ1000(A)-based voltage reference modules, some of which already got into EEVBlog members hands. I sent tens of blank PCBs to community too for their own tinkering, hopefully to see more weird and funny stuff posted. And recently in 2016 I was able to perform few cross-checks and DIY calibrate both K2002's to act as transfer standards for volt and ohm into my home-lab. I'm not very interested in RF stuff (mostly because I don't have deep understanding of it, I recon), but that might change in 2017, if I get
that 8753A VNA in functional condition.
Now before we dig deep into the teardown, I'd like to express my appreciation to daily lurkers of EEVBlog Metrology and T&M forums, especially
Dr.Frank, ManateeMafia, lowimpedance, Kleinsten, plesa, quarks, VintageNut, HighVoltage, chuckb, lymex, Andreas, Edwin, doktor pyta, Alex Nikitin, and many more. Wish only you guys post more often all that exciting and fun stuff
IntroFluke calibrators are often in the dreams of many volt-nuts. This class of instruments is mainly found only in calibration labs and scientific installations and less often in analog design houses. Old but still mighty units like 5440A/B sometimes manage into volt-nut hands, despite their 4U full rack-mount size weight and price over $1000 USD
But newer higher-spec 5500A/5700A series units are still even on used-marked in broken condition go for over $10K+ price tags. Even then their specs are barely reaching needs of average passionate volt-nut with DMM like 3458A to justify the cost. Of course having stable source of arbitrary voltages and currents is a great help in the lab, but that goal can be achieved by set of cheaper instruments. Over last decades Fluke multi-function calibrators become recognized and desired industry standards for many calibration and metrology labs all over the world, just like 8½-digit HP 3458A from DMM world. Started with Fluke 3xx series standards, today these instruments evolved into lab-in-the-box tools like
Fluke 5730A, some of the very best commercial calibrators money can buy.
I was given a chance to have access and play with mighty Fluke 5700A, including DIY-level service, so prepare yourself
.
Fluke 5700A is already discontinued model today, but that does not make it any worse. MFC such as covered here Fluke 5700A is a high precision instrument that can be used as stable source to calibrate electrical measurement instruments and sources. 5700A available functions and provided ranges allow to test, calibrate and adjust practically any handheld and bench multimeters with a reading resolution all the way up to 8½ digits. In corner cases with additional guard-banding Fluke 5700A can be used to test and calibrate metrology DMMs such as HP 3458A. This MFC in most of user cases allow to replace whole range of expensive and bulky calibration standards, and can be itself calibrated by only three reference standards - 1 ?, 10 K? and 10 VDC, similar to 3458A DMM. We will also dig a bit into design of the box, perform required service, repair damaged parts if any, and do some tests for it's performance. This also means we will not be doing expensive boards swap, unless absolutely unavoidable and necessary. If you think 3458A overhaul repair is expensive, you don't want to know pricing for 5700A...
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As usual, all photos are clickable with high-resolution version. Please note, that if you desire to use photo for your own reference/article/site, it's OK to do so only if you include link to this thread or originator of this content. It's NOT okay to steal photos for your eBay listings, sell threads or your pages without a reference. This simple rule is to ensure that our time not wasted, and community can benefit from the performed documenting work in equal and fair manner.Another note - if you get impression that buying used MFC (or even broken), like this Fluke beast for half of usual market price (which is often north of 20K$) and fixing it would be easy way to get high-end lab standard or nice profitable quick resale, consider
mountain of hidden costs and caveats ahead. Accredited calibration for top of the line MFC is not a trivial task and cost many thousands of USD, can usually be performed only by professional labs with 90-day calibration loops and characterized standards and even then you need to have multiple verified stable standards like Fluke 732B/742A and 3458A's with maintained calibration plans to ensure long-term calibrator operation and specs. So think clearly, when you entering this very conservative market, as it is just endless black hole for funds. But volt-nuts should already know that by now, having that JJA in garage
.
Calibrator purpose, typical use caseWhat scenario would justify paying high dollar for the instrument like calibrator? Often these are used for calibration and adjustment of other measuring and generating instruments, such as DMMs, power regulators, amplifiers of different kind, ADC/DAC testing, reference module evaluation and so on. Calibration commonly defined as determination of ratio relative from known signal to unknown signal. In case of measuring device - known signal is applied to the DUT meter, and DUT meter's reading is compared to expected signal value. In case of source - unknown output signal is measured and compared to known signal. To provide good confidence and meaningful results, reference known signal should be at least 2 times more stable than DUT unknown signal, better more.
Let's take a brief example with 5.5 digit DMM and calibrator as reference to perform a calibration and decide if adjustment is needed. To keep things simple test applied only on single function and single range of DMM, 10V, as idea is same for rest.
1. Verified and in-spec (8 ppm) calibrator is used to generate 10.0000 VDC reference signal.
2. Reference signal is connected to DUT DMM, which has specification 30 ppm for 10VDC range.
3. Expected value from calibrator is from 9.99992 to 10.00008 VDC.
4. DUT DMM measurement result is 10.0013 VDC
5. Calculated error is 10.0013 / 10.00000 is 130 ppm (0.013%) +/- 38ppm.
6. Even in best case (10.0010 (-30ppm) / 10.00008 (+8ppm) ) DUT DMM is out by +92 ppm
7. Adjustment/repair of DUT DMM is required to meet the spec.
Of course, this test and comparison can be done without calibrator, with only known tested 10V source. But even basic DMMs usually have many ranges, such as 100mV, 1V, 10V, 100V, 1000V, have multiple functions like DC voltage, AC voltage, DC current, AC current, resistance, capacitance and so on, with their own ranges. To have set of required sources for all these references signals to check each function and range will require huge investment and lab space if we talking about testing even mid-range 6.5 DMMs, leave alone high-performance 7.5+ digit devices. Having everything combined in single compact 4U unit makes multi-function calibrators perfect tool with added ease of use.
That's why calibrators, like Fluke 57xx series are often used as working standards in calibration labs, often just two steps behind national primary standards. In case of DC voltage first top level is primary standard, such as
Josephson-based Voltage Standard. Second level is bank of solid-state references, such as Fluke 734A/732B or "golden" stable metrology-level DMM like HP 3458A. Each underlying level is calibrated and compared to higher level, to determine error value, called measurement uncertainty. Then calibrator is tested to these higher standards and used as working standard for lower level comparison and instruments. Eventually every DMM , even those handheld have relation to the primary standard thru all middle levels, with added up uncertainties.
Another case of calibrator use is various precision and sensitive lab experiments in analog design. This is because high-end calibrators can provide much more stable signal, acting as reference source for voltage/current than most generators/supplies can provide. Common example of this need is ADC/DAC testing, opamps, voltage references, passive components characterization and so on. Today's even 5$ ADC can have 24-bit of resolution, which dictate difficult tasks for validation and testing such ICs to make sure they meet design specs.
Inspection and overviewAlright, enough theory, let's crack it open! We are dealing today with mighty Fluke 5700A Series I Calibrator today. Front panel plastic is yellow due to UV and age, but that's reversible and not a big deal breaker. No deep scratches or damages visible, that's good news.
It also has fairly recent calibration, dated August 2012. This is perhaps a good thing, if unit worked thru most of it's life and still was fine four years ago.
Both sides of calibrator are flooded with vent holes to get excess generated heat away. Given presence of active cooling in the unit, one should be ready to see plenty of dust inside. Label on bottom cover screw was removed before, so somebody had a peek inside, hmmm.
Rear side reveals installed rear terminals, which is an option and not always available. All connectors here are in good shape. Air filter is clean, so perhaps it was cleaned not so long time ago. This box was covered by Fluke's service plan warranty once, from 30 October 1992 till 29 December 1997, so it's likely that unit was manufactured and sold in 1992 but was not kept on continuous Fluke service plan since then. Still that some good 24 years till today, which is good and bad news. Good news - usually voltage references, resistors and parts are very well aged to get nice and stable performance. Bad news is that all electrolytic capacitors are likely at their end of life, and other parts perhaps got old enough to fail/reduce performance. That's if nothing drifts away/faulty like famous U180's in HP 3458A's.
Main
HI/LO on front saw some wear and tear, but rear ones are just like new, if not accounting yellowed plastic color. These banana posts are pure copper, to provide low-EMF connection to ensure good stable connections. Only downside is that pure copper oxidize easily, so connectors must be often cleaned to ensure best contact. Interesting note, these connectors look very much like
Lowthermal Model 2758 binding posts. I have bought some of these before, they are very nice, but cost about $23 USD, each.
Keyboard bit dirty, some of paint labels on rubber pads are gonsky, but all keys present and no major damage
. To clarify which series of calibrator we have, serial number can be used. Any serial number below
6565601 is first-generation Series I, while serial number from
6565601 are updated fancy Series II.
Manuals referencesFluke does provide
all main manuals, including service information right on their product page, without requirement of any pesky registrations or access requests, unlike Tektronix or Keysight. Thumbs up for Fluke, way to host the data on your product page. Few of key documents mirrored below, just in case they get moved.
Brochure: The 5700A/5720A MFC: Taking Accuracy to New LevelFluke 5700A/5720A Series II Operators Manual, May 1996, Rev.2Fluke 5700A/5720A Series II Service Manual, Nov 2007 w/o schematicsThe 5700A/5720A Series II High Performance Multifunction Calibrators - Extended Specifications, Rev. 04And of course, the most important document for repairs/maintenance - 570-page service manual. Credits for hosting it freely going to
KO4BB portal. We are lucky to also have schematics, list of parts, assembly drawings of the boards included in it!
Fluke 5700A/5720A Series II MFC Service Manual with schematics, Rev.1,3/02, June 19965700A Series I and 5700A/5720A Series II differenceAccording to a great
An evaluation of the 5700A Series II Artifact Calibration document, major change in Fluke 5700A/5720A Series II are related to Artifact Calibration. Artifact Calibration was improved on a number of ranges, to minimize biases. Also interpolation algorithms were changed for AC voltage, particularly at higher frequencies; corrections for the level dependent AC/DC differences at low frequencies (low frequency AC-sensor correction). A new interpolation algorithm is also used for lower ACI ranges. Digital processor board A20 and it's firmware was changed as a result. Model 5720/5700 Series II calibrator has a modification to the in-guard microprocessor circuitry to minimize noise in the low millivolt DC ranges. Also, because of the tighter specifications of the 5720A, there may be more selected components in the calibrator circuitry, than in the 5700A Series I and some other minor bug fixes and improvements.