Older digital oscilloscope life of flash ram - Page 1
Forum section: electronics / general

author: quantumfall
author_rank: Regular Contributor
timestamp: October 16, 2010, 09:23:12 pm
content: I was going to buy an oscilloscope , an older Fluke / Phillips analog / digital from the ebay. I was a bit concerned that the seller said it had not been calibrated for a long time and I was worried that it was faulty.I did some googling and found out that the scope uses Flash Ram to store its calibration data, This got me thinking how long will this data stay in the flash memory ? I know with older flash chips some can only keep data reliably for 10 years or so without a refresh to the ram cells.Is this something to be concerned about with older scopes with calibration data stored in flash ? I would be interested in any knowledge on this subject.

author: dimlow
author_rank: Frequent Contributor
timestamp: October 17, 2010, 12:25:16 am
content: As it happens, my old Scope lost its memory last week. All calibration data had gone, but as is a HP54502A i was able to repair it today and self calibrate it. It had a 256K Battery Backed SRAM (DS1253Y-120). I managed to repair it by ordering Maxims Replacement the DS1230Y-120 as a sampleIt arrived in less than a week and now the Scope is calibrated an running again.I was told the scope was over ten years old when i bought it three years ago for £50, so the SRAM has out lasted its spec. Self calibration was easy but time consuming. If the scope can be self calibrated then i guess loosing the ram is not to bothersome. I cant speak for any others, this was just my experience of memory loss, for me it was not really a problem.

author: saturation
author_rank: Super Contributor
timestamp: October 17, 2010, 12:58:26 am
content: WOW, £50 is a steal. Those HP used a standard computer grade CRT and had interesting issues with burn-in and image retention, how is your screen?A lot of HP devices used battery backed up SRAM, and one notorious one is on the venerable 3458A, one of the best DMM still in existence, the early 1989 generation have lose their SRAM data, cannot be self calibrated and must go through formal calibration.Quote from: dimlow on October 17, 2010, 12:25:16 am

author: dimlow
author_rank: Frequent Contributor
timestamp: October 17, 2010, 07:06:32 am
content: The screen on this is ok, i do see some burn in, but there is not a lot, i only see it when i look for it. My thinks i was luck to have that scope then? I would have hated it if i would could not have calibrated it.PS. I liked the way this scope was built, if only it ad had a few less screws though, took me more time to remove all the screws than it did the to get the board out and replace the SRAM. But its quite modular, and that main board just slides out that back once you disconnect a few cables. I liked that.I guess if you have a 3458A, it would be an idea to take a backup of the Flash! you would be sorted then if you had problems. It may be worth doing that for others too.

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 17, 2010, 10:38:05 am
content: Quote from: dimlow on October 17, 2010, 07:06:32 amdont put several screws back in, toss it! then you'll have lesser screws to take care later on

author: saturation
author_rank: Super Contributor
timestamp: October 17, 2010, 11:46:44 am
content: For £50 or even $230, if its a good scope, I'll live with the screen, but sometimes it can be bad. It depends if it was taken from a production environment where its left on all day:Yes, there is a community of HP 3458A users discussing how to backup the SRAM, but the pain is the chip is soldered so its a lot of work removing it, then even if you retain the data, given how sensitive the DMM is, you still need to calibrate it. Since its probably one of, or the best DMM in the world right now, only Agilent itself can do a full 3458A performance verification & calibration, which is $1500+ to do!, but you can opt for a basic calibration is $600. Given those costs, the SRAM issue creates a major headache.For a DMM designed in 1988, it still commands a top price, used $5000, new $10,000, broken $1000-3000.Quote from: dimlow on October 17, 2010, 07:06:32 am

author: dimlow
author_rank: Frequent Contributor
timestamp: October 17, 2010, 01:07:21 pm
content: Here you go, since we are adding pictures. As you can seen no screen burn visible. Now for £50 id love to find a HP 3458A.

author: dimlow
author_rank: Frequent Contributor
timestamp: October 17, 2010, 01:25:13 pm
content: Quote from: shafri on October 17, 2010, 10:38:05 amI don't see why i should do that, the scope does perform very well, only its a little big. I dont have anything on the bench to probe at the moment,so i cant show you. But you can see lots more detail with it than you can with the rigol. Also i trust the voltage and time readings from this more than the rigol.

author: saturation
author_rank: Super Contributor
timestamp: October 17, 2010, 01:38:39 pm
content: Nice photos! screen looks great. Even if big, its worth a 1000 words, far more detail that what we can type.The graticules do not appear with the HP off does it?Nevertheless, it looks in fine shape. it certainly is huge compared to the Rigol, 1052E which is roughly the size of a shoe box.I've given up on the 3458a as a home lab DMM because its high maintenance. Its precision is down to 1nVdc, so to calibrate it you need a source that is 0.1nV, which can only come from a reference laboratory, and thus much cost to check. We haven't begun to think about the Vac or the resistance ranges. You can avoid yearly calibration by running its self calibrations, but for best results it has to be done daily and the DMM is never powered down.I'll keep my eye out for options, but the good folks at volt-nuts so far can only get a home reference down to 1nVdc, I personally maintain10nVdc10uVdc, to check my 3456a at least to100nVdc100uVdc.Quote from: dimlow on October 17, 2010, 01:07:21 pm

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 17, 2010, 01:41:00 pm
content: Quote from: dimlow on October 17, 2010, 01:25:13 pmi'm not suggesting the scope functioning, i'm suggesting "if" you are annoyed with "too many screws". so if say you have 100 screws on it, then you can throw out 50 of it (the screws, not the scope!) (or them? not it? sorry maybe vocab mistake here), so you have just 50 screws to keep the scope intact and hence lesser for you to take care when you re-open the scope later. Cheersbtw, nice picture you got there

author: slburris
author_rank: Frequent Contributor
timestamp: October 18, 2010, 03:55:47 am
content: Quote from: saturation on October 17, 2010, 01:38:39 pmWhat are you using for a 10nVdc reference? I'm not playing in the realm of3458a, but even my lesser Fluke 8505a 6 1/2 digit meter can't be calibratedwith what I have. Although I suspect that my various Flukes don't driftvery much (or all drift exactly the same way), it still would be nice toprove it!I had asked on the time-nuts list (before volt-nuts got spun off) aboutsomehow bootstrapping a GPS locked frequency reference into a voltagestandard, and I got an answer back, but it involved using JosephsonJunctions -- not something a hobbyist like me is likely to dabble in.Scott

author: saturation
author_rank: Super Contributor
timestamp: October 18, 2010, 02:30:06 pm
content: I use Geller's SVR. JJ voltage references are based on frequency to voltage conversion; I don't know of a competing way to do the same at the nV level and hold it stable.My error, I don't maintain nanovolt DC, its microvolt, uV. I corrected my statement: I maintain 10uVdc to check my 3456a to a high of 100uVdc.I brought up a discussion at time/volt/HP nuts about the short term transfer stability of many cheap references are fairly stable if you control its environmental conditions tightly:temperaturebarometric pressurehumidityIn that order. There are many academic papers stating a common error in controlling variations in references is ignoring barometric pressure.To maintain a reference is mostly statistical work and not a ton of money involved, it will be far less than one professional annual calibration, and if successful, you'll be set for life!Even if you buy a new LTZ1000, it won't cost much to maintain a reference in good order:http://www.linear.com/pc/productPurchase.do?navId=H0,C1,C1154,C1002,C1223,P1204&partNumber=LTZ1000The procedure is to gather data on the daily variations of your reference, and after obtaining a curve of change, apply a correction factor for the environmental changes. You can buy a weather station USB dongle to track temperature, humidity and barometric pressure at your site, collect the exact voltage at the moment outputted by your reference, and derate the voltage relative to the ambient changes. In addition, to confirm the changes, you can have 4 references calibrated at peak of different seasons, to watch how they change and sync them when the ambient conditions are similar, usually when a season is transitioning from one, say winter, to spring. In lieu of multiple SVRs, I'm using multiple 3456a and collecting data when the 3456a are not in use. I also intend to buy several more Geller SVRs at different seasons to compare values.These data collection are tedious, so its good to have a computer interface to make the data collection automatic, so the HP buses help a lot. Its not much work once a computer is set up to collect the data continuously.A well aged reference hold its value tighter if you can get the exact ambient conditions the original voltage was made against the NIST traceable voltage standard or reference.A key is an aged reference, otherwise it will have its own internal drift independent of ambient conditions. At least 200 hours of aging, far older is better. There is no known time frame, but it seems to vary least after 200 hours.Enclosed are 2 sample graphs from members of volt-nuts, but only tracking room temperature changes. They were done on 2 different references, 2 different countries and completely different labs. The adjustment curve is pretty similar to my variation data, now going on 4 months. However, their charts cover variations covering only a few days, the cyclical changes itself is on the move, and varies with the existing climate, not only daily weather.I believe the MAX4053 curve is based on a long weekend, where the lab room temperature was left to drift, the abscissa is hours or minutes, not sure, and ordinate is variation from baseline.Both were reported measured using a 3458a.Quote from: slburris on October 18, 2010, 03:55:47 am

author: dimlow
author_rank: Frequent Contributor
timestamp: October 18, 2010, 03:16:06 pm
content: I can understand now why these things are so expensive to calibrate. I have been running through the service manual of the 54502 and see that i have to have a V meter of 0.05% Accuracy and a pulse generator with a rise time of <70ps to do a complete calibration of the unit. I got no chance of purchasing anything that can do this. My most accurate meter is 0.1% i got a long way to go before i get to 0.05% and the fastest rise time pulse i can make is only 2.7ns. So I am pretty stuffed if i want to fully calibrate the scope. Will just have put up with the self calibration. Anyway nothing i do will every really need to be super accurate.

author: saturation
author_rank: Super Contributor
timestamp: October 18, 2010, 05:04:07 pm
content: Strictly speaking, calibration is only checking the ranges of your device against a standard. It gets expensive when the limits of the range are very tiny, such as nV, over what I use the uV, because devices that maintain that level of accuracy are rarer.To calibrate my 3456a officially is about $100/year, for the 3458a, about $600-1000.Now to adjust the meter can be separate charge, and if the meter is particularly laborious to adjust, you can see the procedures usually on the calibration manual, then multiple the charge by 2x.Quote from: dimlow on October 18, 2010, 03:16:06 pm

author: quantumfall
author_rank: Regular Contributor
timestamp: October 18, 2010, 11:04:52 pm
content: Ok gents, we seem to have strayed a bit on this threadall good stuff as it is.I would still like to know if built in flash RAM is a death knell for modern scopes, can i risk buying an older model even just an analog one with a micro based design ?

author: qno
author_rank: Frequent Contributor
timestamp: October 19, 2010, 11:31:22 am
content: if it is a 338x or 339x series it has 2 AA cells in a battery compartiment on the back that can be replaced without opening the instrument.

author: saturation
author_rank: Super Contributor
timestamp: October 19, 2010, 11:38:12 am
content: I think that off tangent a bit, you read of how big a hassle it can be once battery backed up RAM loses its calibration data and it differs from device to device. If you specify exactly what model Fluke/Phillips that is, it might give you specific answer. Usually, the analog side of those old dual scopes are not affected.On a scope, calibration is often less of an issue, if you have the calibration instructions, scopes are usually less accurate than a good DMM, you can compare it against that and set the data. Since its a Fluke, chances the service manual is available from the Fluke site.Quote from: quantumfall on October 18, 2010, 11:04:52 pm

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2010, 11:40:06 am
content: Quote from: qno on October 19, 2010, 11:31:22 amBut to keep the data in RAM, you'll need to do it whilst the power is on which might be risky or connect a 3V supply to the battery holder, whilst changing the cells.Some battery backed RAMs I've seen also use a little rechargeable battery or a supercapacitor so the data should be retained as long as power is applied once a year or so.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 19, 2010, 02:54:09 pm
content: What's more worrying is the trend for 'activated' features with license keys etc. held in battery-backed RAM. My Agilent MSO6034A has a large 2477 battery - I'm curious why they use something this big...

author: slburris
author_rank: Frequent Contributor
timestamp: October 19, 2010, 03:01:32 pm
content: Quote from: mikeselectricstuff on October 19, 2010, 02:54:09 pmOh, and it's soldered in too, bad Agilent! At least with my WaveTek 288, there'sa *socketed* coin cell battery, and the instructions are to just carefully change itwhile the instrument is powered up so as to not lose the NVRAM constants.That at least makes sense.None of this compares to the pacemaker batteries Tektronix used in their1240 logic analyzers! Yeah they provide power for years, but are impossibleto find like replacements, and when they fail, they spew acid all over the PCB.Scott

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 19, 2010, 03:16:47 pm
content: Man, you guys are making me pretty pleased with my Tek 475A.

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2010, 04:30:08 pm
content: I know CR2477 is normally lithium but are you sure it isn't rechargeable lithium ion or even NiMH in this case?If not, changing it would be a pain. I hope there's an on-board capacitor which will hold the charge for long enough to replace it but I wouldn't rely on it.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 19, 2010, 05:25:04 pm
content: Replacing something like this with unknown consequences of losing power, I'd either change it with power on (making sure soldering iron wasn't grounded!, or temporarily connect a backup power source while changing.

author: quantumfall
author_rank: Regular Contributor
timestamp: October 19, 2010, 11:00:37 pm
content: Quote from: saturation on October 19, 2010, 11:38:12 amI did not buy the Fluke, it was a FLUKE PM3380B looks a bit like a philips based design to me.I did download the service manual and the operator manual, it has a self check and a whole raft of tests to check proper operation in the service manual, but no way tore set it up if it looses its basic factory settings for the calibration base as far as I could see, I did not read it word for word. It said return for service to an official service center in this case, so no user can re set it correctly as far as I can see. This was a worry as I'm only a hobbyist with limited cash to spare and I know how expensive it could be. It did look a nice bit of gear.Not to worry I've taken the plunge on an analog Hameg HM1004 100 Mhz scope, its got a micro based control system. We will find out what its like in time.Hopefully I can get some good use out of it for a few years.

author: qno
author_rank: Frequent Contributor
timestamp: October 20, 2010, 07:40:06 am
content: Too bad you did not buy the the PM3380.The userinterface if much better than the Hameg I think.More options for post processing the signal and waveform measurements.Service manual is available on the web. O I can send you one.Calibration is done automaticaly.The scope has an internal voltage reference that consists of a bandgap reference and a calibration resistor.Timing is based on a chrystal based oscillator that can be verified with an external reference signal.Its either good or needs to be replaced.I have a PM3394 now for 15+ years. Never had any problems.

author: quantumfall
author_rank: Regular Contributor
timestamp: October 20, 2010, 12:25:34 pm
content: Quote from: qno on October 20, 2010, 07:40:06 amOh well that sounds like its a good scope, I had a bad feeling about the way the PM3380B was described as uncalibrated and as its an ebay one I'm very buyer beware.The Hameg has some measurments of the waveforms done by the computer and displayed I think, it also has an autoset feature and stored settings that can be called up.I'm sure it will have more than enough features for my level of use, I expect I will learn a lot more about measurements and foibles of the thing as I go along.Its a done deal now, as long as I get some value for the money I will be happy.The Fluke did look very modern, as I say I am wary of things that have flash memory that stores vital settings in any equipment that has an age to it, if it's a return to manufacturer for service only. That might not even get supported anymore. Still I'm only paying a fraction of the new cost.