Multimeter accuracy comparison 34461A, 3456A, 7150+ and 8842A - Page 1
Forum section: electronics / testgear

author: rodpp
author_rank: Frequent Contributor
timestamp: February 28, 2020, 02:50:36 am
content: Hi,Today I did some tests trying to compare the accuracy of my 6 1/2 multimeters.The test setup was a Yokogawa 2560 DC calibrator set with all multimeter connected to it.That Yokogawa calibrator has a resolution of only 4 1/2 digits. To circunvent that limitation I used a 8 1/2 digits multimeter as reference, connected together with the other multimeters.Multimeters tested:- Agilent 34461A- HP 3456A- Solartron 7150 Plus- Fluke 8842A (5 1/2 digits)Reference multimeter:- Keithley 2002The collected data is the following:Code:YEW 2560K200234461A3456A7150+8842A0,0010000000,0010029910,0010025000,0009975000,0010120000,0010150000,0100000000,0100035210,0100030000,0099982000,0100140000,0100150000,0500000000,0500065640,0500048000,0499973000,0500230000,0500150000,1000000000,1000003320,1000011000,0999883000,1000270000,1000070001,0000000000,9999767200,9999780000,9999190001,0001310000,9999900005,0000000005,0006529005,0009400005,0008800005,0013700005,00060000010,00000000010,00027750010,00049000010,00046000010,00169000010,00020000050,00000000050,02208500050,02510000050,02150000050,03000000050,024000000100,000000000100,043592000100,049500000100,042600000100,058300000100,047000000500,000000000500,437140000500,545000000500,475000000500,518000000500,4600000001000,0000000001000,8620000001001,3250000001000,9990000001001,0230000001000,900000000Considering the Keithley 2002 as the reference, adjusting the data we have:Code:YEW 2560K200234461A3456A7150+8842A0,0009970090,0010000000,0009995090,0009945090,0010090090,0010120090,0099964790,0100000000,0099994790,0099946790,0100104790,0100114790,0499934360,0500000000,0499982360,0499907360,0500164360,0500084360,0999996680,1000000000,1000007680,0999879680,1000266680,1000066681,0000232801,0000000001,0000012800,9999422801,0001542801,0000132804,9993471005,0000000005,0002871005,0002271005,0007171004,9999471009,99972250010,00000000010,00021250010,00018250010,0014125009,99992250049,97791500050,00000000050,00301500049,99941500050,00791500050,00191500099,956408000100,000000000100,00590800099,999008000100,014708000100,003408000499,562860000500,000000000500,107860000500,037860000500,080860000500,022860000999,1380000001000,0000000001000,4630000001000,1370000001000,1610000001000,038000000And the percentual result:Code:ValueYEW 2560K200234461A3456A7150+8842A0,001-0,2991%0,0000%-0,0491%-0,5491%0,9009%1,2009%0,01-0,0352%0,0000%-0,0052%-0,0532%0,1048%0,1148%0,05-0,0131%0,0000%-0,0035%-0,0185%0,0329%0,0169%0,1-0,0003%0,0000%0,0008%-0,0120%0,0267%0,0067%10,0023%0,0000%0,0001%-0,0058%0,0154%0,0013%5-0,0131%0,0000%0,0057%0,0045%0,0143%-0,0011%10-0,0028%0,0000%0,0021%0,0018%0,0141%-0,0008%50-0,0442%0,0000%0,0060%-0,0012%0,0158%0,0038%100-0,0436%0,0000%0,0059%-0,0010%0,0147%0,0034%500-0,0874%0,0000%0,0216%0,0076%0,0162%0,0046%1000-0,0862%0,0000%0,0463%0,0137%0,0161%0,0038%The following graphic shows all data:The 1mV measurements (first bars) are much worse than the other measured values for all devices, except the 34461A that showed a very good performance at 1mV.Eliminating the 1mV measurements, we have a better picture:The substantial increase of the Yokogawa 2560 error from 5V to 1000V is because this set uses two devices to generate voltages above 10V. Bellow 10V only the 2553 DC Voltage Current Santandard is used and it shows better performance. Above 10V it is necessary to use the 2563 Voltage Unit too.With the calibrator data hidden, we have only the multimeters data:Here we see that in low voltages all multimeters had the worse performance, except the 34461A that performed better in the low ranges than in the high ranges. It is very clear that at 500V and 1000V the 34461A performance was not good compared to the others multimeters, even more when we note its very good performance in the other ranges.Now eliminating the extreme values, we have the data in the more common 0.1 to 100V:Here we see a very good performance of the Fluke 8842A, mainly considering that it is a 5 1/2 digits multimeter and all others are 6 1/2. Regarding the Solartron 7150 Plus, this graphic sugests that it needs some adjustments, showing a consistent bias compared to the Keithley 2002. If we discount that bias its performance is not bad.Critics and comments are very welcome.Thanks for reading!Regards,Rodrigo.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 28, 2020, 03:41:21 am
content: Interesting study, thanks for sharing.When was the last time each of these DMM and your voltage source get a traceable calibration? You got some very old equipment in the mix. without a fresh calibration, the comparison is somewhat meaningless to me.If your intention is to show what each meter is capable of, it may be far more interesting to send them all out for a traceable calibration, then compare what they can really do. But it can become a pretty pricy exercise if calibration is not something you do on a regular basis.

author: rodpp
author_rank: Frequent Contributor
timestamp: February 28, 2020, 02:51:13 pm
content: I have no recently calibrated instruments. The most recent calibrated is the 34461A in 29-05-2014. The Keithley 2002 was calibrated in 07-05-2012. So it´s not possible to talk about absolute accuracy here, unfortunately.At the moment I have no need to have absolut accuracy, and the cost to calibrate the Keithley 2002 is not irrelevant.These data maybe can show some "problems" with the instruments, for example:- that the calibrator performance degrades significantly above 10V;- that below 10mV only the 34461A has a good performance;- that above 100V the 34461A performance degrades;- that the 7150+ has a bias compared to all other multimeters.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 28, 2020, 03:29:32 pm
content: The tests with a bunch of old meters without a recent calibration does not tell very much abut the meter types in general. If at all it is about the specific units and there calibration.The large error at 1 and 10 mV could be effected by an offset at the input. Here the 3456 or 34461 and even the 8842 may actually be better than the K2002 or Solartron, if there is not current offset calibration is done. The K2002 and 7150 use a separate chopper amplifier at the input, that is not included in the normal Az mode. This does need separate zero calibration from time to time.The > 100 V ranges are effected by the self heating in the input divider. Here it is not guarantied the K2002 really has the best one. The 34461 looks like not that good in this respect, it is off from the others.

author: rodpp
author_rank: Frequent Contributor
timestamp: February 28, 2020, 07:31:30 pm
content: Regarding the 1 and 10mV errors, the K2002 and 34461A agrees very well. And the difference between the 3456 and the 8842 was the biggest, reaching an error of 1.75% at 1mV. It´s important to say that 1.75% of 1mV is only 17.5uV, so others factors like connections and cables ould interfere here. In both calibration certificates that I have (34461A and K2002) the lowest voltage tested after the 0V is 100mV (absolut value).The problem in the >100V measurents using the 34461A is strange, could be related with the change in the rated voltage of that instrument by Keysight from 1000V to 600V DC that occurred some time ago, that after was reverted to 1000V again (https://www.eevblog.com/forum/testgear/keysight-34460a34461a34465a34470a-maximum-allowable-voltage-change-notice/)?

author: Kleinstein
author_rank: Super Contributor
timestamp: February 28, 2020, 08:12:05 pm
content: For the 1 mV range a possible offset at the input is possibly a major error source. So the offset (reading with 0 V) would be interesting too - possibly more that the error at 1 mV. AFAIK the 34461 uses AZ switching right at the input and there should thus be little offset. 17 µV would be rather high, even for a 5.5. digit meter like the 8842.The difficulty with voltages higher than some 10/20 V is that they use a divider at the meters input. At higher voltage like > 100 V there can be an effect of self heating of that divider and thus a nonlinear error (part proportional to U³). There might also be a second offset error with the divider. I don't think the relatively large error with the 34461 is due to the voltage rating issue. AFAIK this issue is from voltage ratings of some relay(s), not the divider itself. The problem is more like a relatively high TC for the divider.

author: rodpp
author_rank: Frequent Contributor
timestamp: February 29, 2020, 01:03:25 am
content: Here is the measurements using the calibrator output = 0V:Code:K20020.002627mV34461A0.0026mV3456A-0.0024mV7150+0.013mV8842A0.011mVAnd now shorting all the probes together:Code:K20020.000658mV34461A0.0019mV3456A-0.0019mV7150+0.014mV8842A0.013mVFinally, removing the probes and using a short wire direct in the multimeters inputs:Code:K2002-0.000485mV34461A0.0023mV3456A-0.0018mV7150+0.014mV8842A0.001mV

author: Kleinstein
author_rank: Super Contributor
timestamp: February 29, 2020, 08:06:19 am
content: There is a surprising large difference between the 3 cases that should nominally give a zero reading. After connecting the wires it may take a few minutes for the temperature at the terminals to stabilize.Especially the 8842 shows a large difference - this could be from no to good terminals (or the cables/probes) and higher sensitivity to thermal effects.Some 13-14 µV of offset for the 7150 is likely a problem with the zero adjustment - it should not be so high.

author: rodpp
author_rank: Frequent Contributor
timestamp: February 29, 2020, 10:18:34 am
content: Thank you for sharing your knowledge and time giving me tips to understand the problems with my measurements and equipments, I appreciate that.In fact the cables/probes/connections I'm using are far from ideal. Only the K2002 and the 34461A are using proper multimeter probes, and the K2002 probe have no adaptors like alligators or similar. The others are using banana cables, and some of them have a loose tip. I will look for better cables/probes and I will make the measurements again.

author: Kleinstein
author_rank: Super Contributor
timestamp: February 29, 2020, 11:45:51 am
content: Many of the banana cables / plugs are relatively sensitive to thermal EMF. So if possible (good therminals), clamping a bare copper wire (like thin twisted pair like used for in house phone installation or the door bell) directly to the terminals is a simple and good solution.

author: beanflying
author_rank: Super Contributor
timestamp: February 29, 2020, 11:53:38 am
content: Depending on the Temperature stability of your Lab space even a few degrees of Temperature shift will make some difference.I have a 34461A and a 34401A side by side on the bench both were Calibrated last year by Keysight. On a DC source at 23-25C they are well inside spec and track each other very well over a large range/ranges BUT. The 34401A runs a Negative T/C while the 34461A runs positive this is circa PPM/C but with a 5C swing from the Temperature they were calibrated at the variation starts to become more important depending on what I am doing.If you have a Temperature Stable Lab then I am really jealous mine swings a lot and has no air con

author: maginnovision
author_rank: Super Contributor
timestamp: February 29, 2020, 03:44:42 pm
content: In his case he also has to worry about stability of the source. The 1 hours specs are not that great and since it's 4.5 digit there is going to be a lot of noise. Every meter has a different filter and if they aren't measuring the same exact period then it'll also throw the results off.

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: February 29, 2020, 04:16:20 pm
content: Looks like even if it was brand new, the Yokohama source was only 200 ppm accuracy in voltage, and 2200 ppm for current, with unknown drift characteristics. So I would agree that the source might not be stable enough for 6.5 digit meters for meaningful results.

author: rodpp
author_rank: Frequent Contributor
timestamp: February 29, 2020, 11:24:41 pm
content: Quote from: Kleinstein on February 29, 2020, 11:45:51 amOn the calibrator side it will be easy to connect the cables directly, but on the multimeter side it will be necessary to solder a banana plug. Now I removed all banana cables, replaced by a banana to coax adaptor connected to a coax aligator cable. See how it is connected now:If that setup does not perform well, I'll try the phone cable. The phone cable on the calibrator side will be easy to connect, but on the multimeters probably it will be necessary to solder a banana plug.Quote from: beanflying on February 29, 2020, 11:53:38 amUnfortunately my lab space has no ar con. These days at night the temperature is around 25ºC.And I do not have a stable DC reference suitable to teste the T/C of my multimeters.Quote from: maginnovision on February 29, 2020, 03:44:42 pmYes, the noise certainly is a problem. In the next measurements I'll use 50PLC in the K2002 (its maximum) and 100PLC on the 34461A and 3456A. The Fluke and Solartron seems to not have an explicity aperture configuration.Quote from: NoisyBoy on February 29, 2020, 04:16:20 pmI do not see the calibrator accuracy as a big problem, because I'm using the K2002 as reference. But the noise could be a problem, as maginnovision said. And the specifications of the 2553 says 200ppm of the range on all voltage and current ranges (plus 4uV on the 10mV range):Above 10V the 2563 is used too, and things get worse. The only specification that I have using the set is that the accuracy is 0.02% to 0.3% without details about each range. So considering the worst case we can consider 0.02% from 0 to 10V and 0.3% above 10V.

author: bdunham7
author_rank: Super Contributor
timestamp: March 01, 2020, 12:47:19 am
content: Quote from: rodpp on February 29, 2020, 01:03:25 amThe three lowest readings of the 8842a have the same absolute error of 15uV, which is almost entirely accounted for by the offset that you observe with any kinds of leads connected to it. I had an issue with mine that showed up as the resistance not zeroing, it turned out that the crimps on the wires ends that snap onto the banana jacks had a bit of resistance. I just fluxed and soldered them, cleaned the jacks with DeOxit and got it to zero nicely with a shorting plug. I'd suggest you have an issue with your leads, either thermal or surface corrosion or something else.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 01, 2020, 09:23:36 am
content: The banana to BNC adapters tend to be even worse than just banana plugs. It really looks like the meter don't support direct contract to bare wires. So it would be about getting known good or / testing banana plugs / cables. There should be some good ones around, but there are also rather bad ones with high thermal EMF and even poor contact. Sometimes the cheaper plugs perform quite well (a simple 1 piece construction can help), while some of the expensive ones may fail for low voltage (more suitable for high current).The DMM probes have a good chance to have quite some thermal EMF, as the thin pin part has to be relatively strong material - so more like brass and not pure copper.The noise of the calibrator can be a slight problem, but one would see this. So if the readings are reasonable stable the noise is not a big deal.

author: bdunham7
author_rank: Super Contributor
timestamp: March 01, 2020, 05:15:14 pm
content: One additional thing for the OP--are you using the 20mV range? There should be another decimal point...

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2020, 05:38:19 pm
content: That is definately not the optimal setup for tests. All those probes are bad for low voltage measurements, BNC likely worst. Alligator clips, adapters, all that stuff must be forgotten and never touched ever again for precision interconnects. Only direct post to wire and wire to post.Budget and easy solution - get some cheap round CAT6e RJ45 cable used for internet/network connections. Pick 1-1.5m length, cut the connectors out, clean insulation, leaving 2-3 cm of the bare wire. Keep wire pair twisted, bend the corners so it make something like a hook. You want to make exposed copper wire fluffy if it's multi-strand wire. Then shove the wire into K2002, and use Q-tip of proper size to push wire all the way in (one that fits banana jack in DMM tight, but not very tight to avoid plastic damage).Word of warning - K2002 banana jacks are not thru, so you don't need to worry about wire going inside of the meter and shorting anything. It may not be the case with other DMMs.This type of connection does not look special or fancy, but it does the job well with freshly cut and insulated wire. Getting "proper" copper banana test cables may cost more than most of those meters cost, so I'd say that is waste of money unless you calibrate banana-only instruments day and night.Every time you need to reuse cable - cut a piece of it to avoid using oxidized copper wire (copper oxide is worst enemy in connection quality).The second issue is instrument layout. K2002 makes quite a bit of heat, so your Solartron being cooked on top of the 2002. You want DMMs located on separate locations, so they don't interfere as much thermally.P.S. on a side note, can you share your K2002 calibration report? I'd like to see what's in it, as I always calibrate my 2002's myself and it's good to see what others doing.

author: rodpp
author_rank: Frequent Contributor
timestamp: March 01, 2020, 06:47:15 pm
content: Quote from: bdunham7 on March 01, 2020, 12:47:19 amAfter reading your comment I cleaned all connections with contact cleaner spray (N-hexane and butane/propane), hope it helps.Quote from: Kleinstein on March 01, 2020, 09:23:36 amIt seems everyone agrees that my connections are poor, and are getting worse...Quote from: bdunham7 on March 01, 2020, 05:15:14 pmI am using auto range, but not all these multimeters has a 20mV range.The lowest ranges are:K2002 - 200mV34461A - 100mV3456A - 100mV7150+ - 200mV8842A - 20mVI'll use the manual range instead, to avoid incorrect range selection by the multimeters.Quote from: TiN on March 01, 2020, 05:38:19 pmThanks for the tip about the cable. I have CAT5e cables and I'll try it.Regarding the calibration report, I already shared it after your ask in an older topic (https://www.eevblog.com/forum/metrology/taking-care-of-a-reference-multimeter/msg2455302/#msg2455302).

author: rodpp
author_rank: Frequent Contributor
timestamp: March 01, 2020, 07:36:18 pm
content: Here is the CAT6 setup:I did a first set of measurements of 1mV using the LAN/GPIB interface, measuring with all multimeters simultaneously 10 times and getting the mean value. Below is the graphic similar to the first one on the first post of this topic:Now I'll leave this setup running some hours and try to get all measurements at night.I can't forget and use these CAT6 cables to measure the 1KV...

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2020, 07:59:28 pm
content: Sorry, getting older, forgetting stuffYou may want that Q-tip trick.Q-tip keeps contact in place so it's less risk of wires loosing contact in banana jack.Also 2002 blasting hot air onto 34461A. Probably does not matter for 6.5 digit meter, but it definately does for 8.5d stuff, so just a good habit.

author: rodpp
author_rank: Frequent Contributor
timestamp: March 01, 2020, 08:29:44 pm
content: This Q-tip "connector" is great, much better now.

author: rodpp
author_rank: Frequent Contributor
timestamp: March 01, 2020, 11:58:12 pm
content: The performance is better now. I only tested until 10V because I'm using the CAT6 cables.All measurements using LAN/GPIB taking 3 measurements and calculating the mean:Removing the 1mV readings:Now from 100mV to 10V:And finally, the same graphic above without the Solartron 7150+ data:Now the calibrator performance is much better, showing results comparable to the 6 1/2 multimeters. Probably the poor performance of the calibrator in the previous measurements, in reality, was a poor performance of the K2002 measurements (because the probes).The cables change improved the performance for all meters, but the Solartron 7150+ performed much worse than the others. I'll try to adjust the 7150+ using the K2002, to discover if it is a matter of adjustment or if there is a problem with it.Thanks for all contributions.Regards,Rodrigo.

author: rodpp
author_rank: Frequent Contributor
timestamp: March 02, 2020, 01:13:06 am
content: Here are the complete data set, including the measurements >10V using probes/bananas:Removing the 1 and 10mV:Removing the calibrator that always increase the error above 10V:And removing the Solartron 7150+:The computer acquisition seems to have improved the 34461A performance on the high ranges. The probe and connections are the same. The only difference is that using the computer we have more control over the measurements, like simultaneous trigger and same integration time (on the K2002, 34461A and 3456A, because the other two meters doesn't have an exact PLC configuration).Surprisingly the Fluke 8842A 5 1/2 digits performed better than the 6 1/2 digit multimeters.

author: rodpp
author_rank: Frequent Contributor
timestamp: March 02, 2020, 03:11:11 am
content: At 1mV the calibrator/cables/multimeters noise seems to dominate. Here is the data from 100 consecutive measurements using the 5 multimeters, all the left plots are using the same scales:And only the K2002 measurements of the graph above:The elapsed time was about 40min, so the positive tendency can be temperature related. The noise is around 0.4uVpp, corresponding to 400ppm.The K2002 accuracy for 2 years at the 200mV range is specified as 23ppm reading + 10ppm range. So reading 1mV is (1mV +- 0.002023mV) with the error corresponding to 0.2%, or 2000ppm!So I think that it is better to forget using these regular multimeters to read such low voltages.