HP 34401a - Drift in the 2W R mode / 100 Ohm range - Page 1
Forum section: electronics / repair

author: Zucca
author_rank: Unknown
timestamp: July 21, 2014, 12:43:45 am
content: Hello guys.I already (partially) fixed previously this unit, see the full story here:https://www.eevblog.com/forum/testgear/34401a-cal-error-707/but the cal lab is still reporting a drifting in the 2W R mode in the 100 Ohm range. Only in the 2W R mode not in the 4W!Since the unit was sent to me from ebay in a worst than terrible package (stupid seller and all those who thinks a package is not important), I think some joints on the board could have some issue (as already found in my previous repair..). Since the failure reported is only in the 2W I have a big hope to fix this problem.Now I will start the investigation and report my findings soon.Stay tuned,Z

author: Zucca
author_rank: Unknown
timestamp: July 21, 2014, 03:35:10 am
content: Since I have a good calibrated 34401a, I am going to compare the two side by side.First of all a sanity check with a 2W R and a 0 Ohm resistor (this onehttp://www.pomonaelectronics.com/pdf/d_MDP-S_100.pdf).(ignore the unit on the top)The good is connected with RS232, the bad one with GPIB (no ther devices on the bus).Settings:Auto Range: OnAuto Zero: OnMeasurement: Resistance (2W)NPLC: 10Range(Ohm): 100minumum sample interval, 10min testHere the graphs, left one the good one calibrated and right the bad one (not calibrated)Statistics of the good one (front side)Mean 0.002524814Standard Error 4.86997E-06Median 0.00252Mode 0.002609Standard Deviation 0.000196435Sample Variance 3.85869E-08Kurtosis -0.288419334Skewness 0.063261047Range 0.001202Minimum 0.001919Maximum 0.003121Sum 4.107873Count 1627Largest(1) 0.003121Smallest(1) 0.001919Confidence Level(95.0%) 9.55207E-06and bad one (front side):Mean 0.010605372Standard Error 6.77113E-06Median 0.010596Mode 0.010571Standard Deviation 0.000269573Sample Variance 7.26694E-08Kurtosis -0.036873015Skewness 0.054733768Range 0.001944Minimum 0.009568Maximum 0.011512Sum 16.809514Count 1585Largest(1) 0.011512Smallest(1) 0.009568Confidence Level(95.0%) 1.32813E-05Oh, the GPIB (158,5 sample/min) is slower and the RS232 (162,7 sample/min), let´s know investigate the rear side with the same sample numbers 1650 instead the same time 10min.Here the new settings:Settings:Auto Range: OnAuto Zero: OnMeasurement: Resistance (2W)NPLC: 10Range(Ohm): 100minumum sample interval, 1.65K Samplessame story, left one the good one calibrated and right the bad one (not calibrated):Statistics of the good one (rear side)Mean 0.00705325Standard Error 4.10731E-06Median 0.007048Mode 0.007124Standard Deviation 0.00016684Sample Variance 2.78355E-08Kurtosis 0.594448789Skewness 0.135870213Range 0.001535Minimum 0.006293Maximum 0.007828Sum 11.637863Count 1650Largest(1) 0.007828Smallest(1) 0.006293Confidence Level(95.0%) 8.05609E-06and bad one (rear side):Mean 0.016549085Standard Error 6.83344E-06Median 0.016528Mode 0.01654Standard Deviation 0.000277576Sample Variance 7.70483E-08Kurtosis 0.484874451Skewness 0.2889019Range 0.002157Minimum 0.015462Maximum 0.017619Sum 27.305991Count 1650Largest(1) 0.017619Smallest(1) 0.015462Confidence Level(95.0%) 1.34031E-05Conclusions:At 0 Ohm 2W the bad one is a little bit off of about 8m Ohm (not all the POMONA MDP-S are the same???). No significant drift present at 0 Ohm, although the Standard Deviationi is slightly bigger in the bad one.Soon the 100 R Range Test with a 90 R connected.Take care,

author: Zucca
author_rank: Unknown
timestamp: July 25, 2014, 04:49:32 am
content: Ok, it was a pretty nasty measure but I finally got it.Since the target is to test a drift on the R measured, I needed a way to check not only his value over time but also the current generated by the 34401A.Here my setup:I have the 34401A measuring a precision 90R in parallel with a 34461A to check the voltage across it (related to the current generated by the 34401A DUT).Basically the voltage measured by the 34461A divided by 90R will provide us the current sourced by the 34401A. The coax cables will minimize the noise pickup.Now I had the 34461A USB connected to the PC, and and the other 34401A connected as well using GPIB or RS232.I had two 34401A units (GOOD #1 and GOOD #2) fresh from calibration no problem to use as reference to compare with the, according to the calibration lab, bad one (BAD).Of course the units were properly warmed up and the measure time was over one hour period.Here the setting used for the R measures:Auto Range: OnAuto Zero: OnMeasurement: Resistance (2W)NPLC: 10Range(Ohm): 100and for the current ones on the 34461A:Auto Null Value: FALSEAuto Range: OnAuto Zero: OnInput Impedance: 10 MOhmMeasurement: DC VoltageNPLC: 10Null State: FALSENull Value(Vdc): 0Range(Vdc): 0.1Let´s dig into the results...GOOD #12W R measured:Statistic Mean 90.07426003Standard Error 3.79745E-06Median 90.074236Mode 90.074083Standard Deviation 0.000375295Sample Variance 1.40846E-07Kurtosis -0.493118701Skewness 0.283102244Range 0.002418Minimum 90.073072Maximum 90.07549Sum 879755.2978Count 9767Largest(1) 90.07549Smallest(1) 90.073072Confidence Level(95.0%) 7.44379E-06Current (90mV=1mA)Statistic [A*90]Mean 0.09014677Standard Error 2.22337E-09Median 0.090146746Mode 0.090146714Standard Deviation 2.22526E-07Sample Variance 4.95176E-14Kurtosis -0.075682427Skewness 0.473640809Range 1.4409E-06Minimum 0.090146106Maximum 0.090147547Sum 903.0001985Count 10017Largest(1) 0.090147547Smallest(1) 0.090146106Confidence Level(95.0%) 4.35824E-09GOOD #22W R measured:Statistic Mean 90.07989073Standard Error 3.09024E-06Median 90.079946Mode 90.079946Standard Deviation 0.000302496Sample Variance 9.15041E-08Kurtosis -0.177549751Skewness -0.477571608Range 0.0019Minimum 90.078848Maximum 90.080748Sum 863145.513Count 9582Largest(1) 90.080748Smallest(1) 90.078848Confidence Level(95.0%) 6.05752E-06Current (90mV=1mA)Statistic [A*90]Mean 0.088696667Standard Error 2.62486E-09Median 0.088696721Mode 0.088696711Standard Deviation 2.62263E-07Sample Variance 6.87817E-14Kurtosis -0.557971289Skewness -0.449007757Range 1.5119E-06Minimum 0.088695812Maximum 0.088697324Sum 885.4588291Count 9983Largest(1) 0.088697324Smallest(1) 0.088695812Confidence Level(95.0%) 5.14525E-09BAD2W R measured:Statistic Mean 90.02526044Standard Error 5.78764E-06Median 90.025232Mode 90.025119Standard Deviation 0.000564228Sample Variance 3.18353E-07Kurtosis -0.456379127Skewness 0.228340502Range 0.00326Minimum 90.02379Maximum 90.02705Sum 855600.0752Count 9504Largest(1) 90.02705Smallest(1) 90.02379Confidence Level(95.0%) 1.1345E-05Current (90mV=1mA)Statistic [A*90]Mean 0.089503874Standard Error 2.02854E-09Median 0.089503873Mode 0.089503842Standard Deviation 2.02641E-07Sample Variance 4.10633E-14Kurtosis -0.520592125Skewness -0.068937736Range 1.3154E-06Minimum 0.08950316Maximum 0.089504475Sum 893.159158Count 9979Largest(1) 0.089504475Smallest(1) 0.08950316Confidence Level(95.0%) 3.97634E-09CONCLUSIONSWe need a side to side comparison.2W R MeasurementsHere the yellow values are the only one concerning me. Still not a huge drift in my eyes. The BAD shows a negative drift decreasing the R value. The GOOD 1 also does that, but the gradient is less than the BAD one.Current MeasurementsPretty much here everything is acceptable, since the unit cal lab reported the drift only in the 2W R mode, I was not expecting a problem with the current:Maybe the current generated by the BAD one is suspiciously pretty nervous and irregular in the graph.Next steps0) Check/Understand the Spec. Tolerance (let´s do tomorrow. Is already 00:51 AM)1) Dig into the schematics and isolate the part of the circuit which can cause a drift only in 2W R mode2) Perform a 4W R 1 hour test as above to verify the drift is not there in 4W3) Check the 100 Ohm Range current generation, check if current is constant in 1K Range3) Open the unit and look the circuit for bad joints on the part of circuits founded in point 1 and 3I don´t know if I will fix this unit, it seems a nasty slightly out of spec. malfunction.On the side: EMI CRAP?I had the bad idea to work under the bench using my 12V impact drill during the 1 hour measurement and here what I got on a good one! (left current, right R measured)Even when I turned on my monitors from sleep, I noticed similar jumps. I decide to measure when I was not at the bench during night time (everything off, just the PC and the DMMs).

author: Zucca
author_rank: Unknown
timestamp: July 26, 2014, 04:02:28 am
content: I spent 3 hours on the service manual.The Ohm current source block is working since the 4WR is not failing.The Function Switch is working because the 4WR is not failing.The U101-5 sense (voltage measured on the High Post), DC amplifier and DAC is working because is not failing the Voltage Tests.Since the 1KOhm 2W Range is not failing also the 2W Voltage drop reading of a 1mA current source is also working.Here an interesting further measure 1 hour 100NPLC 2WR, 100 Ohm Range with 100Ohm R. I also did a null for the the cable resistance...I don´t like that exp transient...the device was already warmed up pretty good, it should not happen.mmmmm interesting.

author: Zucca
author_rank: Unknown
timestamp: July 26, 2014, 06:08:34 am
content: Another measure 1 hour 100NPLC4WR, 100 Ohm Range with 100 Ohm R attached. No drift or transient at all.

author: Zucca
author_rank: Unknown
timestamp: July 26, 2014, 01:17:03 pm
content: Damm it, 1 hour 100NPLC 2WR, 1 KOhm Range with 1 KOhm R attached. No drift herePS: The red box was probably because the R was cold and it took a little bit to settle with the temperature.

author: robrenz
author_rank: Super Contributor
timestamp: July 26, 2014, 01:51:57 pm
content: Quote from: zucca on July 26, 2014, 04:02:28 amJust some thoughts:Are you thermally shielding the resistor and leads during this test? The TCR of the copper test leads come into play in 2 wire mode. Also since there is no offset compensated ohms mode you are subject to errors caused by thermal EMFs. You have about a .004 Ohm span there which is only 4µV at the 1mA drive current of the 100 Ohm range so thermal EMFs will be significant.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 26, 2014, 02:04:36 pm
content: Quote from: zucca on July 26, 2014, 04:02:28 amI think, your logical conclusion is wrong!Function switch?Do you mean the Front/Rear switch, or the internal switching relays?Both are in series with the 2W resistor DUT, but they are both NOT compensated , but they are indeed in 4W Ohm!!Therefore, if one of the 2-3 components in this inner 2W circuitry (I listed them already, in the original thread) is faulty, and this obvious, then it will affect your 2W measurement, but NOT your 4W one.I still vote for the Front/Rear switch, which gets polluted by something and then has several ten milli Ohm change on its contacts if you actuate it.. Afterwards, it may also creep back to lower Ohm values, if you leave it alone, afterwards.Just redo the tracing function in 2W, 100Ohm, then switch front/rear and to front again, and measure the difference, also over time.I bet that will be not oK.A new or cleaned switch will have a few milli Ohm only, and this will not change that much after actuation.Frank

author: free_electron
author_rank: Super Contributor
timestamp: July 26, 2014, 02:43:48 pm
content: Notice that the machine reads 0.05 ohms lower than the others..That tells something.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 27, 2014, 09:45:49 am
content: Hi,here are my drift measurements.I have a massive short on the instrument, photo 1.fixed range 100Ohm, NPLC 10 (6digit, fast).In 2W and 4W mode, I first switch to rear and back to front, then I immediately start the measurement with benchview.You see, that in 2W mode, it takes sveral minutes that the zero reading is going down from 13mOhm to 6mOhm .At time of writing, the reading is down to 4mOhm, and it was initially 2mOhm, before I did the first actuation today.In 4W mode, the reading is directly below 100µOhm, and the negative reading lets you estimate the real internal offset voltages.You can repeat that as often as you like, but the switch, although cleaned, but not brought back to virgin condition, has some unsteady contact resistance.I think, that's due to the contact force getting weaker.I'd like to encourage you, to replicate my measurement.Frank

author: Zucca
author_rank: Unknown
timestamp: July 27, 2014, 12:30:03 pm
content: Free_electron, robrenz and Dr. Frank are officially invited at my home in South Carolina.I will cook for you some Italian food and when afterwords some delicious wine we will finally see the reality in a proper way, we will move in my lab and discuss how to fix the 34401a.Thank you soo much!I am currently not in the lab, I will be back tonight.I agree with all of you, I need to do more investigation. BTW while I was driving those days thinking about your posts, I think I got a nice idea. For the details I will post soon something!Take care!

author: Zucca
author_rank: Unknown
timestamp: July 28, 2014, 04:17:40 am
content: Well... back in the lab, but it is 23:30 and it is time to sleep. Before that I want to respond to the you awesome guys who posted somethingQuote from: robrenz on July 26, 2014, 01:51:57 pmYou are correct, there is surely that error. Still I don´t know if it follows a exp(-t/T) decay over time...well may be because the temperature exchange between contact and the ambient will follow a exp(-t/T) to reach the equilibrium. If it is the case by inverting the high post with the low one on the DMM I should have a exp(-t/T) decay again but this time with R increasing. The EMF Thermal is always an offset in a defined direction, I mean it can´t be depended on the current direction. Tomorrow I´ll try.Quote from: free_electron on July 26, 2014, 02:43:48 pmI noticed that too immediately. Bad previous calibration? If the 2W R gain calibration value an old one? Still it must be investigated.Quote from: Dr. Frank on July 26, 2014, 02:04:36 pmHi Dr. Frank I missed you a lot the past days. I was talking about the internal relays not the front/rear switch, pag. 95 of the service manual, and you your are right I was not 100% right. I think only K101 is not compensated in the 2W, so it is definitely a candidate to be a bad guy. The others one don´t play a role, since they are not conducting the 1mA current and/or they don´t cause a voltage drop in the 2W measurement.Quote from: Dr. Frank on July 27, 2014, 09:45:49 amWow, also you are getting a exp(-t/T) decay! That warms my heart a little bit. Tomorrow I hope to have time to replicate your awesome tests and to go deeper in my theory/idea I got (i promise to explain it soon, not tonight.... have mercy on me). Anyway at the end of my theory/idea I agree with you: the front/rear switch needs to be cleaned and serviced.According on a previous post:https://www.eevblog.com/forum/testgear/hpagilentkeysight-34401a-2w-problem/15/I got following suggestion regarding products to use there:1) IPA bath, (obviously)2) Deoxit G100Lhttp://www.amazon.com/Deoxit-Gold-Solution-With-Brush/dp/B0032URX50/ref=sr_1_4?ie=UTF8&qid=1406520287&sr=8-4&keywords=Deoxit+G100L3) Meguiars NXT All Metal Polyshhttp://www.premiumboatcare.com/mg13005.html?productid=mg13005&channelid=FROOGI have some Stabilant available,http://www.amazon.com/Stabilant-5ml-Kit-Makes-30ml/dp/B001E50GQS/ref=sr_1_1?ie=UTF8&qid=1406520641&sr=8-1&keywords=stabilant+22but I am concern to mess up the switch property in such a precision measurement instrument.What I should buy? I mean, I have already the IPA and the Stabilant, do I need anything else?Good night and thanks again...Z

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 28, 2014, 06:36:08 am
content: Quote from: zucca on July 28, 2014, 04:17:40 amHello,before you clean the switch, you should test it, as described.As I said, there are about 3 components in the 2W loop, which may fail, the other one is the relays, and the third, I don't know any more. Also, their solder junctions may be suspect.But you can also test that by shorting temporarily these switches, and see what happens.Concerning the switch, I'd also be careful, myself I cleaned it with conservative stuff like alcohol and mechanically.Frank

author: robrenz
author_rank: Super Contributor
timestamp: July 28, 2014, 12:05:58 pm
content: Quote from: zucca on July 28, 2014, 04:17:40 amThermal EMF polarity is current direction dependent. That is why the current reversal technique works.Edit: That is not why the current reversal technique worksMy badFrom Keithley low level measurement handbook

author: Zucca
author_rank: Unknown
timestamp: July 28, 2014, 01:01:39 pm
content: ThanksRobrenz,Are you sure about that? (It could be I am totally wrong please don´t shoot at me)Other interesting links:www.keithley.com/data?asset=4658www.keithley.com/data?asset=10639http://zone.ni.com/reference/en-XX/help/375472A-01/switch/thermal_voltages/http://www.digikey.com/videos/en/v/Thermal-EMF-Error-in-Current-Sense-Resistors/1680490880001http://www.vishaypg.com/docs/49871/theremf.pdfhttp://en.wikipedia.org/wiki/Seebeck_coefficientThat´s why I love to repair stuff and post here, I am learning so much... O0

author: robrenz
author_rank: Super Contributor
timestamp: July 28, 2014, 02:04:44 pm
content: Fixed my erroneous post above

author: Zucca
author_rank: Unknown
timestamp: July 29, 2014, 03:19:14 am
content: Dr. Frank,this one is just for you, I want to replicate your tests and compare the results.I was searching in my lab for something with a really low resistance... I found this:but I was difficult to solder the banana jack on it:So I used 8 Pomona MDP S:Now here the result with 2W, exactly how you did:and 4W:mine 4W never goes negative in 4:25 min.Looking also to my previous results, this unit is out of cal (slightly or not I don´t care) so I would not trust the reading too much. Maybe the cal lab played too much on it.

author: Zucca
author_rank: Unknown
timestamp: July 29, 2014, 04:11:42 am
content: Let´s make it easy. The lab cal is telling us only the 2W 100 Ohm is failing, the rest is passing. If the 4W 100 Ohm test and all the others are ok, then the problem must beaR Highbetween the V Sense and the Hi post and/or aR Lowbetween the Lo post and ground, since R Low and R High are bypassed in the 4W measurement (as Dr. Frank also says).The idea is that (R High+R Low) is big enough to cause the 100Ohm test failure but small enough to pass the 2W 1KOhm.Back to the schematics:the first bad guy on the R High side is K101.Moreover (I draw the current just for the front posts)here we have another candidate for R High: S1-A. Finally the only bad guy for R Low is S1-G.Of course it could also be some tracks or whatever. Now it´s the time to open the unit and dig into it.The vibration stress theoryThis unit had survived a journey in a terrible package, the resistors in the red circle had cracked joints... Now by looking at the board shape, all the area around those resistors could have been seen the same deadly vibrations since (at least in mine) the only mechanical holding point is the screw on the bottom right and the big red plastic posts enclosure block have some freedom to move.Very interesting, all the suspected components are in that area.

author: robrenz
author_rank: Super Contributor
timestamp: July 29, 2014, 11:38:05 am
content: This postshows my low resistance short used for CC power supply testing. The jacks themselves are the weak point here. Very small resistance changes have quite an effect on what the minimum drive voltage is on CC mode.

author: Dr. Frank
author_rank: Super Contributor
timestamp: July 29, 2014, 04:27:35 pm
content: Hello Zucca,you marked correctly the relevant components for 2W, that are the input jacks themselves, the S1-A and S1-G switch (my favorite) and the K101 relays.And of course all of their solder junctions.During calibration, the lab has to short the front and rear jacks, then measure zero for all modes for front and rear.Therefore they have to actuate the front / rear switch.And they also put a mechanic force on the jacks, when they remove the shorts again.Both may give rise to that change in resistance over many minutes, which you also measured.The change can be as high 100mOhm, and may be as small as a few milli Ohm, after the switch has actuated several times.Then it's clear, that the 100Ohm calibration fails, as the zero Ohm value is not valid any more, after actuation.If you look closely at your 100Ohm , 2W calibration protocol, the difference between the measured, failed value is 99.9052, and the 'good' limit of 99.9806Ohm, this difference is about 80mOhm, or even 100mOhm compared to the nominal value, which can really happen by a bad switch, or bad solder junctions.You may test the switch resistance by directly shorting both 'front' position switches S1-A and S1-G and measuring the real change in resistance.The quality of the input jack may be measured by shorting High and Low first at the jacks and afterwards directly at switch S1-A and S1-G, so that you circumvent the jacks.Frank

author: Zucca
author_rank: Unknown
timestamp: July 30, 2014, 03:39:31 am
content: Quick and dirty update.Between pin 20 and pin 2 of the switch, I measured 54 mOhm (4W with 34461a) the HO and LI Front were shorted by the Pomona MDP S.The 54 mOhm were so distributed:1) 07 mOhm between pin 20 S1 and pin 21 S1 (Front switch on)2) 26 mOhm between pin 21 S1 and LO3) 03 mOhm between LO and HI (across Pomona MDP S)4) 10 mOhm between HI and pin 1 S15) 08 mOhm between pin 1 S1 and pin 2 S1 (Front switch on)Just a roughly measure, tomorrow I will try to do something more accurate...

author: Zucca
author_rank: Unknown
timestamp: July 31, 2014, 05:20:19 am
content: Interesting evening...I open that bastard and took live measuresI activated the 2WR mode with a short bar between HI and LO. Then with my trusted 34461A I took some µV measures referred to AGND0 (Analog ground).Here the points I analyzed, let´s assign a letter for each one:The point A drifts pointing the sky.Here is my theory: if a constant current starts to flow through a R, the R temperature will rise for the Joule effect. Now if the temperature increase in a resistor and it has a positive temperature coefficient the resistor value will increase as well. Since the current is hold constant by the current source circuit, bingo, the voltage is linearly going to the sky until some other black magic happen in the R. I can be wrong.Anyway after playing around and measuring other points I don´t know why but the voltage jumped down to 200µV again. After that is start to going up slowly but it seems to reach equilibrium at about 211µV.Let´s measure all those points:The K101 Relay-Reed 2A 500 Vdc 5 Vdc-Coil is now under arrest, 105mOhm (even 110mOhm I got later on) is too much. I checked also the coil voltage, 5VDC spot on. Definitely a relay contact topic.Next step:1) Reflow the K101 joints (no hope step, but maybe?)2) High Contact Resistance RemediationThat´s cool!Quotefor more details:http://www.ni.com/white-paper/7200/en/I can´t wait to pump some current (YES 4A@1V?) in that little bastard... For the "buzz" method I have to desolder it and build something around it.3) Dremel and open it up for surgery...4) Replace itIt seems like it´s not so easy to buy a new one...https://www.eevblog.com/forum/chat/help-me-find-a-replacement-relay/So I need to buy a new kick ass 5VDC Relay and build a fixture for it...

author: Zucca
author_rank: Unknown
timestamp: August 01, 2014, 01:20:01 am
content: No.I checked other two calibrated 34401a and in both the R of a closed K101 is about 100/130 mOhm.I also compared the others points and nope nothing really different. The point A is also at about 211µV in the others.I have now to play the card of the sporadic failure (not reproducible under my eyes).Let´s reflow the 2W joints and pray.Take care, thank´s to all who posted here to help me.PS: Worst case I will try to calibrate the unit at home by comparing with the 34461a numbers.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: August 01, 2014, 02:57:14 am
content: Zucca,Did you check L101,L102, and L106 for cracked joints? They appear to be in the path too and not far from the other resistors you found with cracked joints.Also, Dr Frank mentioned jumping out the switch contacts, did you try that too? It should be easy to jump out across both contacts and watch the resistance change.This method has helped me track down the same issue with a couple of my meters, though not this particular model.

author: Zucca
author_rank: Unknown
timestamp: August 01, 2014, 03:29:01 am
content: HiManateeMafia,No I did not check those, but according to the theory L101,L102, and L106 will not cause just the 2W R Test to fail.I did also not performed the jumping out test, since the result would have been pretty obvious once you got all the ladder of voltages from point A to P.Anyway I reflow all the 2W joints, all the S1 switch pins and the tall capacitors since they are more sensible to vibrations. Now point A seems stable to 183µV in 2W R with a shortcut between HI and Lo.Maybe I´m lucky this time.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: August 01, 2014, 04:39:16 am
content: I re-read your readings and must have had my blinders on. Luckily your meter showed up better than a Fluke 510a I bought. The transformer broke free of its mounts and was rolling around inside the reference.Good luck with your repair.

author: coldframe
author_rank: Regular Contributor
timestamp: September 21, 2014, 10:42:50 am
content: Hello Z,I’m looking forward to seeing your job.Good luck!.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 23, 2014, 07:52:17 am
content: Quote from: zucca on July 21, 2014, 03:35:10 amHello ZuccaMay I ask how you got these statistical data from BenchVue ?Thanks

author: Zucca
author_rank: Unknown
timestamp: September 24, 2014, 01:54:31 pm
content: Quote from: HighVoltage on September 23, 2014, 07:52:17 amExport in Excel, use the data analysis toolpackhttp://office.microsoft.com/en-us/excel-help/load-the-analysis-toolpak-HP001127724.aspxand run the descriptive statistic on the datahttp://www.excel-easy.com/examples/descriptive-statistics.html

author: HighVoltage
author_rank: Super Contributor
timestamp: September 27, 2014, 12:17:50 pm
content: Thank you, Zucca

author: Zucca
author_rank: Unknown
timestamp: October 07, 2014, 01:30:46 pm
content: Short update (don´t ask me the entire story please). It looks like the drift is gone (I think the reflow helped here) BUT the 100R 2W adjustment process does not work.Basically before and after the 100R 2W adjustment the meter is reading pretty much the same value out of tolerance.I allow myself to declare the issue is not an analog one (that´s why I was going in circle without huge steps forward) rather a digital one (bad cell memory on the 2W 100R value??, it won´t overwrite that value anymore???).Anyway I am close to put that unit on ebay as not working (just because I like to be honest), since 99% is working perfecty and only the 100R 2W is slightly out tolerance I think somebody of you guys can make a good deal.A friend of mine is an exorcist, but he told me he won´t deal with electronic devices as a 34401A

author: Gleb
author_rank: Newbie
timestamp: September 29, 2015, 10:47:06 pm
content: Hi there,Where did you find information that the Specifications of Agilent 34401A are given at 95% confidence interval?Because I have had a look through the whole User's Guide for 34401A and couldn't find that information anywhere.Gleb

author: Zucca
author_rank: Unknown
timestamp: September 30, 2015, 06:37:03 am
content: Quote from: Gleb on September 29, 2015, 10:47:06 pmThat value is not provided by Agilent, it is an empiric statistical number based on the data collected.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 30, 2015, 06:11:34 pm
content: Doing adjustments may need special codes or a hidden switch to be operated. So I would double check the instructions on how to do the adjustment. A memory fault is less likely than a user misunderstanding the instructions.Even with 100 Ohms in 2 wire mode is not perfectly working. It's still a good unit, if you know the limitations.

author: Zucca
author_rank: Unknown
timestamp: October 01, 2015, 08:24:07 am
content: Quote from: Kleinstein on September 30, 2015, 06:11:34 pmThe Cal Lab was not able to adjust the "100 Ohms in 2 Wire", all the other parameters were successful adjusted.Quote from: Kleinstein on September 30, 2015, 06:11:34 pmRight. It is a very good unit, even if 99,9% working.

author: Gleb
author_rank: Newbie
timestamp: October 01, 2015, 07:29:51 pm
content: So is it then safe to assume that all accuracy specifications of instruments are given at 95% confidence level unless otherwise specified??

author: Zucca
author_rank: Unknown
timestamp: October 02, 2015, 06:27:27 am
content: Quote from: Gleb on October 01, 2015, 07:29:51 pmNo, the 95% confidence level was calculated like this:https://www.eevblog.com/forum/repair/hp-34401a-drift-in-the-2w-r-mode-in-the-100-ohm-range/msg518734/#msg518734it can not be interpreted like a sort of specification value.The specification numbers are based on the device design, with statistical measures you can verify them not create new ones.This is what I believe but I´m open for corrections.

author: Gleb
author_rank: Newbie
timestamp: October 04, 2015, 11:49:19 pm
content: The uncertainties in accuracy specifications are all given at a certain confidence level, however some manufacturers don't specify the confidence level, I don't know why.i.e. if uncertainty is say 0.002% at 95% confidence, then you can calculate uncertainty at any confidence by dividing by coverage factor k, you can also find standard deviation by bringing uncertainty to 68% confidence.k=1 -> 68% confidence = standard deviation (sigma)k=2 -> 95% confidencek=2.58 -> 99% confidence