EEVblog #613 - Prema 6047 Multimeter Teardown - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: May 06, 2014, 11:19:49 pm
content: Teardown Tuesday.What's inside a 1980's vintage 8.5 digit multimeter, the 6047 from Prema. Or did Dave diddle himself?Hi Res photos:http://www.eevblog.com/2014/05/07/eevblog-613-prema-6047-multimeter-teardown/

author: quarks
author_rank: Frequent Contributor
timestamp: May 06, 2014, 11:46:08 pm
content: Nice score, but not 8.5 digitSee the real ones herehttps://www.eevblog.com/forum/testgear/8-5-digit-dmm/msg258880/#msg258880

author: FrankBuss
author_rank: Unknown
timestamp: May 07, 2014, 12:08:29 am
content: Reading the EPROM would be interesting. Sometimes there are hidden messages or easter eggs:http://www.lemon64.com/forum/viewtopic.php?t=49609

author: gaijin
author_rank: Contributor
timestamp: May 07, 2014, 01:11:00 am
content: The 100 milliohm shunt resistor was made by ISOTEK they have been around since 1989.http://www.isotekcorp.com/

author: senso
author_rank: Frequent Contributor
timestamp: May 07, 2014, 01:17:37 am
content: That thing looks like it was used in the shop floor so all the new assemblers could try and melt some FR4, that or it was repaired by someone else, but it really doesn't seem to have the spit and polish of a precision bit of kit, more like a 6 month special kit from elektor

author: Vgkid
author_rank: Super Contributor
timestamp: May 07, 2014, 01:37:50 am
content: That is a beautiful meter, and it arrived in good condition as well. Here is the manual W/ schematicshttp://www.ko4bb.com/manuals/index.php?dir=09)_Misc_Test_Equipment/Prema

author: david77
author_rank: Frequent Contributor
timestamp: May 07, 2014, 02:09:40 am
content: Nice score Dave!Love the SDS brand relays in there. That company used to be in my hometown, the factory is still there now owned by Matsushita/Panasonic. They're still making relays and industrial control gear there.Btw. Isabellenütte is rather older than 25 years...http://www.isabellenhuette.de/en/company/innovation-by-tradition/history/

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: May 07, 2014, 03:28:49 am
content: Did you say 6502?I wonder what the ROM looks like. Is there a ROM dump out there?

author: TiN
author_rank: Super Contributor
timestamp: May 07, 2014, 04:24:00 am
content: Lovely, volt-nuts will enjoy. Thanks for teardown.Moar precision DMM content, pleaseIs that ceramic resistor network Caddock 1737?

author: SeanB
author_rank: Super Contributor
timestamp: May 07, 2014, 05:20:24 am
content: Quote from: david77 on May 07, 2014, 02:09:40 amFunny enough I had a faulty thermal resistor from them, had to replace it with an Omron H3B timer. 11 pin timer block, 11 pin base, mount on DIN rail and wire it up, all to replace a single 2 wire part. The Isabellenhutte thermistor was taking too long to heat up, and the part number ( thanks to Google translate) is now obsolete 40 years.

author: Stonent
author_rank: Super Contributor
timestamp: May 07, 2014, 06:00:32 am
content: I was surprised he didn't point out the HP chips on there. I didn't catch what they were, though.

author: Huluvu
author_rank: Regular Contributor
timestamp: May 07, 2014, 06:20:04 am
content: Yeah - FRAKO Electrolytic Capacitor around 18:10

author: Mickle T.
author_rank: Frequent Contributor
timestamp: May 07, 2014, 06:27:13 am
content: Can't find a datasheet for HP R8200 optocoupler

author: Rasz
author_rank: Super Contributor
timestamp: May 07, 2014, 07:39:18 am
content: I bet the 6048 is just one bit flip in dallas ram6502 is trivial to reverse engineer

author: poorchava
author_rank: Super Contributor
timestamp: May 07, 2014, 08:05:37 am
content: Isabellenhütte produce shunt resistors and power resistors (up to several hundred watt) and roll their own resistive alloys. Great quality and stability too. I've seen some automotive qualification results (pretty stringent standards) and their standard range of products exceeded the pass criteria literally by orders of magnitude. Really good stuff

author: sportq
author_rank: Regular Contributor
timestamp: May 07, 2014, 08:27:23 am
content: Although it was labelled as serial number 1040-something, I bet they started at 1000. HP did this, nobody wants serial number 0001 (except eevblog uC fans)Pete

author: wiss
author_rank: Frequent Contributor
timestamp: May 07, 2014, 10:04:06 am
content: Quote from: Rasz on May 07, 2014, 07:39:18 amAlmost, substitute lm399 for ltz1000.But same input-amp.

author: opablo
author_rank: Regular Contributor
timestamp: May 07, 2014, 12:33:33 pm
content: What's so special about Tellurium Copper ?I just read the wikipedia article on Tellurium and didn't got what's so special about it for electronic connectors...

author: robrenz
author_rank: Super Contributor
timestamp: May 07, 2014, 12:46:36 pm
content: IMO it is purely for the machinabilityONLY. It does nothing for electrical properties and is not as good as oxygen free copper electrically. If it was better electrically you would see it in spade lugs etc. but you don't. You will only see it used where the product is machined (turned milled etc.) not stamped like spade lugs. Telurium copper is readily available only in round stock further supporting my theory that it is purely for machinability.

author: Zbig
author_rank: Frequent Contributor
timestamp: May 07, 2014, 09:39:20 pm
content: Koax!

author: Dr. Frank
author_rank: Super Contributor
timestamp: May 07, 2014, 09:42:48 pm
content: Isabellenhütte produces very good low ohm shunt and power resistors.See here:http://www.isabellenhuette.de/en/home/I think the designation "Hütte" originates from the metallurgical "smelting" process. (I hope I have picked the correct English term.)Obviously that's the historical root of this company.In the famous oldRuhrgebiet, in Western Germany (Krupp, Thyssen, Mannesmann, etc.) they smelted the ordinary steel and iron alloys, but this company specialized in electrical alloys, obviously. Today, they still produce their own specialty alloys.The brand "Zeranin" is a special or selected Manganin alloy, T.C. being <3ppm/K, or even <1ppm/K, instead of >= 10ppm/K for the elder Manganin.High quality wire wound precision resistors are also made of Zeranin, and fully compete against the metal foil technology of Vishay.What I have noticed, all PCBs were labelled 6048, therefore, probably a different assembly and a different EPROM may turn this instrument into a real volt-nuts 8 1/2 digits one.Around the LM299, there's enough space for the LTZ1000 and its accompanying components.But anyhow, if calibrated properly, even this version is capable of ~1ppm stability, especially after 25 years of ageing.Therefore this instrument will definitely qualify Dave as a real volt-nuts.Frank(who initially created the term "voltnut")

author: guido
author_rank: Regular Contributor
timestamp: May 07, 2014, 10:53:54 pm
content: That blue philips cap is not original i think.I have a prema 5000 (5 euro), which has similar parts like the relays and reference. But more prema specific ic's, it is a lot more integrated and smaller. But 6.5 digit only. Those board to board connectors are horrible. Mine has only one towards the display pcb and it took some tinkering to get it reliable. But in the 5000 the other board to board connectors are flatcables with connectors pressed into regular ic socketsDid a full recap on mine, i use it a lot these days. Got it 'calibrated' at a real voltnutThe analog board:Interestingly the 6502 clock is derived from the analog side (adc) and transported to the dig side with an opto. In your meter it is "free running".Prema is very helpful if you mail them! They still support their meters. E.g. full calibration for your meter is 653 euro according to a pricelist i got last year. Calibration can probably be done via keys and gpib. They also still repair them, so i guess they have some of those prema chips available. They are also willing to answer technical questions via mail and send service manuals.My guess is that the battery is flat. In the 5000 are three 2114 rams. One is battery backupped and its a cmos version where the others are not (everyone that had an Acorn Atom in the past knows how power hungry the regular versions are)

author: rolycat
author_rank: Super Contributor
timestamp: May 07, 2014, 10:56:57 pm
content: Quote from: robrenz on May 07, 2014, 12:46:36 pmI'm not sure it's the only reason - tellurium copper combines low thermal EMF with better corrosion resistance than pure copper.

author: robrenz
author_rank: Super Contributor
timestamp: May 08, 2014, 01:49:17 am
content: Show me a couple of NON machined mass produced electrical components made of Tellurium copper and I might alter my opinion

author: Wytnucls
author_rank: Super Contributor
timestamp: May 08, 2014, 02:58:13 am
content: The Tellurium Copper machinist never runs out of elbow room

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 08, 2014, 07:34:15 pm
content: I don't think that it is a serial number on that resistor, 201189 looks too much like a date for me(24:45)

author: bronson
author_rank: Regular Contributor
timestamp: May 09, 2014, 09:22:37 am
content: http://www.onlinemetals.com/copperguide.cfm(search on tellurium)They agree with you Robrenz: tellurium doesn't improve electrical properties but it does improve machinability.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2014, 10:16:30 am
content: Then why do the connector manufacturers (like Pomona and others) promote them as such. And companies such as IETlabs, Agilent, Fluke that should know these things also claim it?:http://www.ietlabs.com/bp-1500-bindingposts.htmlhttp://www.home.agilent.com/en/pd-1000000309%3Aepsg%3Apro-pn-11058A/low-thermal-emf-banana-to-banana-jumper-set?&cc=AU&lc=enghttp://assets.fluke.com/manuals/54407002iseng0200.pdfhttp://www.lowthermal.com/cables-and-connectors.phpQuoteGear from the masters like Keithley also use "low EMF" tellurium copper input jacks I believe.It's not a tellurium on it's own, it's something to do with the interaction with the other platings. Perhaps tellurium allows direct gold plating whilst the others don't?

author: Mickle T.
author_rank: Frequent Contributor
timestamp: May 09, 2014, 10:24:10 am
content: Some information about the input terminals and my translation from chinese.

author: rolycat
author_rank: Super Contributor
timestamp: May 09, 2014, 10:33:23 am
content: Quote from: bronson on May 09, 2014, 09:22:37 amI wouldn't argue that tellurium copper has better electrical properties than pure copper. However, it is more resistant to oxidation, and copper oxide hasterribleelectrical properties. The Seebeck voltage of a copper-copper oxide junction is greater than 500 µV/°C, which is over a thousand times that of copper-copper or copper-gold.Robrenz is clearly an excellent machinist and I'm sure he knows a lot more than I do about metals, but I'm not sure his expertise on this matter is superior to that of professional metrologists.

author: quarks
author_rank: Frequent Contributor
timestamp: May 09, 2014, 11:57:50 am
content: For all I know so far, Tellurium is only/mainly used for better machinability.CuTe especially is for easier turning lathe use.AFAIK there are no CuTe sheets on the market. Therefore there are no spade lugs with CuTe.The Seebeck coefficient of Tellurium is suppose to be 500µV/K.So it is unlikely help in any way for low EMF.Copper-Oxide is suppose to have 1000µV/K.Copper Tellurium Alloy will improove corrosion resistance compared to pure copper.But to take better care of oxidation, gold plating is used.

author: robrenz
author_rank: Super Contributor
timestamp: May 09, 2014, 12:56:07 pm
content: Quote from: EEVblog on May 09, 2014, 10:16:30 amIts low EMF because its Copper instead of Brass not because its Tellurium Copper instead of pure Copper. If you scan the info from many suppliers below you will see the larger uses of Telurium copper are very mundane parts that could care less about thermal EMFs. BUT they all have one thing in common, they are machined items not stamped.@ rolycatIf the minimally better oxidation resistance was why it is superior why do many gold plate the Tellurium Copper?From Metal suppiers onlineApplications Welding and cutting torch tips, products requiring high conductivity and high machinability.From ANCHOR BRONZE AND METALSApplicationsForgings, screw machine products and parts requiring high conductivity, extensive machining, corrosion resistance, copper color, or a combination of these; electrical connectors, motor and switch parts, plumbing fittings, soldering coppers, welding torch tips, transistor bases and furnace brazed articles.From FARMERS COPPERFarmer’s Copper Ltd. inventories C14500 Tellurium copper round rod. C145 Tellurium is adapted for use in high-speed automatic screw machines. The copper telluride precipitations become finely dispersed throughout the matrix and assist in chip breakage into short pieces, thus enabling a much higher machining speed than with pure copper. Copper 145 Tellurium has a machinability rating scale of 85%, compared to pure copper of 20%, thus insuring longer tool life. The high conductivity of tellurium copper makes it a suitable material for electrical applications, and is an outstanding alloy for the production of hot forged products.Tellurium C145Typical applicationsElectrical Switches on power semiconductorsWelding Torch tipsTransformer & Circuit-breaker terminalsFastenersFrom LUVATA WOLVERHAMPTONPure copper is a very ductile metal. For many applications this is an advantage, but not when copper is to be machined. However, the cutting properties of copper can be significantly improved by alloying copper with half per cent of tellurium. The electrical and thermal conductivity and ductility of this free machining copper are only slightly altered.The effect of tellurium is based on copper telluride precipitations in the microstructure. These precipitates have the effect of cutting the chips into short pieces thus enabling a much higher machining speed than is possible with pure copper. On a machinability rating scale with 100 for free cutting brass and 20 for copper, tellurium copper is rated at 90. The tools last longer too.Tellurium copper is resistant to hydrogen embrittlement. Electrical conductivity is high, approx. 52 m/W mm2 (90% IACS).From ESPI METALSTellurium copper’s resistance to hydrogen embrittlement and high conductivity make it a good choice for electrical applications, especially those which require extensive machining. The addition of tellurium to copper results in short, clean chips and allows cutting speeds of five times those used with pure copper, with much less wear on tool life. Also, the electrical conductivity, thermal conductivity and ductility are only slightly altered from pure copper. Typical applications include welding tips, switch gears, bolts and studs, and relay parts.From Key to Metals websiteConducting springs, contacts and similar highly stressed members that also may have to be formed may use either chromium copper or beryllium copper. Parts are shaped soft and then strengthened by heat treatment. Parts that must be highly machined and highly conductive are made from the free-machining coppers. Widely used is tellurium copper, which has 90% minimum conductivity and a machinability rating of 80 to 90 (free-cutting brass = 100). Leaded copper (1% Pb) or sulfurized copper is also used because of the 80% machinability rating, with most other properties similar to copper. If tensile strengths of 440 to 525 MPa are required at 80% machinability, heat-treated and hard drawn forms of tellurium-nickel copper may be chosen, provided electrical conductivity of 50% is permissible.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2014, 02:08:27 pm
content: Quote from: quarks on May 09, 2014, 11:57:50 amYet almost every "low EMF" class low level and precision measurement product uses and promotes the use of tellurium copper on it's input jacks, and calls them "low EMF" input jacks in many cases. So there must besomethingin it. It can't just be for it's machine-ability. If it is then you have to be saying that Agilent, Fluke, Keithley, IET etc have all been mislead. I find that quite unlikely.

author: EEVblog
author_rank: Unknown
timestamp: May 09, 2014, 02:15:42 pm
content: Quote from: robrenz on May 09, 2014, 12:56:07 pmSure, but metal suppliers wouldn't know anything about low EMF measurement products.

author: rolycat
author_rank: Super Contributor
timestamp: May 09, 2014, 02:28:06 pm
content: Robrenz, an impressive list of references to be sure, but most of them mention the high conductivity and corrosion resistance of tellurium copper as well as its machinability.To reiterate my original point, you stated that theONLYreason for using tellurium copper was the machinability. From luvata.com, one of the sources you referenced: "On a machinability rating scale with 100 being for free cutting brass and 20 for copper, tellurium copper is rated at 90." So why not use brass contacts? They will certainly be cheaper.My contention is that the alloy provides a good balance between these three desirable properties. Better machinability and corrosion resistance than pure copper and better conductivity than brass.

author: robrenz
author_rank: Super Contributor
timestamp: May 09, 2014, 04:04:55 pm
content: Quote from: EEVblog on May 09, 2014, 02:15:42 pmThen explain why Pomona would use ETP copper on itsSpade lug patch cord for low thermal EMF measurementsand use a combination of ETP copper and Tellurium Copper on itsLow Thermal EMF spade lug to retractable banana plug patch cord.Notice the only part of this one that is Tellurium copper is the part that is machined and there is beryllium copper on the actual contact spring section.

author: quarks
author_rank: Frequent Contributor
timestamp: May 09, 2014, 05:53:42 pm
content: Quote from: EEVblog on May 09, 2014, 02:08:27 pmSo far my research showed that Tellurium has nothing to do with low EMF, only the copper is important.But pure copper is nasty with turnig lathe and would cause endurance problems with the cutting chisel.Therefore Tellurium is added.I would be very interseted to see/learn what I missed about the Tellurium "low EMF" part, so please let us know if you get details about it.

author: SeanB
author_rank: Super Contributor
timestamp: May 09, 2014, 06:44:03 pm
content: The basic requirement is to have all the parts made from the same metal. Thus copper wire, copper lugs and as close to pure copper terminals. That pure copper is not fun to machine, and that Tellurium is only needed in minute quantities which have little effect on the bulk properties is why it is used. the alternatives is to add tin or lead, to make brass or bronze, with both are easy to machine, but which have very different properties.You can quite easily have thermocouple wire being made in nickel, and a lot of high temperature wire for thermocouples is pure nickel, and the terminals and connections as well are the same metal. Works just as well as copper, but a lot better at high temperature. Higher resistance is not a problem, as you simply compensate by using a variable resistor to get to a predetermined value for the cold circuit. IIRC from doing EGT on helicopters the requirement was 8R +-0.1R for the circuit to the meter terminals, measured with an AVO8. I would get regular calls from the electrical guys to come fix "My wiring" when they had either broken the lug off, or had to remove a loom section with it in, or remove the engine. Always cleaned both sides, and then if I had to replace a lug I always got a pack of new lugs ( 100) and used 2 of them, leaving the rest for them to use wherever. the adjustment was a big wire wound resistor with a slider arm, complete with a locking screw to hold the setting fixed. Sat right behind the meter. Cal was adjust resistance, and then open circuit meter and see that the needle read room temperature, as a few degrees do not worry if you were looking at a 1200C reading to check that you are not melting the turbine back side off.

author: wiss
author_rank: Frequent Contributor
timestamp: May 09, 2014, 07:44:55 pm
content: So, soon I'll find out, I'm about to try a DIN5 on a Solartron 7075.

author: EEVblog
author_rank: Unknown
timestamp: May 10, 2014, 08:13:07 am
content: Quote from: Rasz on May 07, 2014, 07:39:18 amWouldn't surprise me. That would give the extra resolution.I searched the ROM and couldn't find an obvious string. So not as easy as an ASCII model number swap.

author: Dr. Frank
author_rank: Super Contributor
timestamp: May 10, 2014, 09:06:10 am
content: Quote from: EEVblog on May 10, 2014, 08:13:07 amHi Dave,more probably, there's a completely different firmware, as the EPROM in your unit is labelled "6047".If you go through the schematics, and compare with the photos, you'll find several differences between both models.Mostly, the 6048 contains additional components.There's an additional PREMA ASIC on the 6048 µP PCB, U18, seems to jitter the µP clock (for better averaging to 8 1/2 digits ??)As this circuitry interacts with the 6520 PIA, an EPROM update might not work without the additional circuitry.Also, an additional -5V is needed.On the analogue PCB, they mainly implemented the LTZ1000 instead of the LM399H (but that should not make a big deal).Here they run a certain OPAMP on -25V instead of -15V; so they have an additional -45V supply.Maybe Prema might help with a request how to update the instrument.Frank

author: Mickle T.
author_rank: Frequent Contributor
timestamp: May 10, 2014, 09:07:53 am
content: Quote from: EEVblog on May 10, 2014, 08:13:07 amIt is absolutely impossible to convert 6047 to 6048 because of incompatible hardware and firmware:1) voltage reference (LMx99-LTZ1000);2) Ohm mode current source (single mode - dual mode);3) floating power supply (6047 don't have -45 V channel);4) model 6048 have a dual PR BK7 ADC. The second ADC (U18 on the microprocessor PCB) is for temperature sensor.5) model 6048 have a firmware based temperature coefficients compensation.http://radiokot.ru/forum/viewtopic.php?p=1919201#p1919201

author: tszaboo
author_rank: Super Contributor
timestamp: May 10, 2014, 09:37:39 am
content: Quote from: EEVblog on May 10, 2014, 08:13:07 amCheck the instruction manual of the meter, page 5/3. Here you will see that the 6047 can do the same integration times as the 6048, but it stops at 7.5 digits. Also, in 4.8.1 it tells you that the calculations are made with 8.5 digit resolution. So I'm guessing you can force the meter to show 8 digits, by averaging 10-20 four second measurement with math functions. But OFC this will be only resolution, not accuracy, for that you need the LTZ1000, U18 and so on, but you already know that.

author: wiss
author_rank: Frequent Contributor
timestamp: May 10, 2014, 11:08:44 am
content: Are the schematics accurate?When I trace the input in the schematics I end up with an input impedance of 500 - 50k in series with a diode and no negative feedback for the input-amp...

author: Mickle T.
author_rank: Frequent Contributor
timestamp: May 10, 2014, 11:21:22 am
content: The 6048 schematics is accurate.The input amplifier is a voltage-to-current conveter and ADC have a current input.

author: quarks
author_rank: Frequent Contributor
timestamp: May 10, 2014, 11:43:29 am
content: Quote from: Mickle T. on May 10, 2014, 09:07:53 amI have seen that before, but I have to say it again, I am very impressed by your knowledge and building skills

author: wiss
author_rank: Frequent Contributor
timestamp: May 10, 2014, 12:20:31 pm
content: Quote from: Mickle T. on May 10, 2014, 11:21:22 amSo, the DUT isinsidethe feedback-loop?I assumed that the negative input terminal was floating-ground.Thanks

author: k2teknik
author_rank: Regular Contributor
timestamp: May 15, 2014, 07:07:58 am
content: Quote from: Mickle T. on May 10, 2014, 11:21:22 amWhat sw are you using for the drawing you had been showing here?

author: mwilson
author_rank: Contributor
timestamp: May 16, 2014, 02:08:47 am
content: Quote from: k2teknik on May 15, 2014, 07:07:58 amIt appears to be NI Multisim (http://www.ni.com/multisim/)