Is my new Fluke 289 multimeter faulty? - Page 1
Forum section: electronics / beginners

author: evava
author_rank: Regular Contributor
timestamp: May 05, 2017, 08:13:20 am
content: I acquired second hand Fluke 289 lately.Instrument is very clean, like new, display is in new condition, inside also clean, fuses seems OK.I was looking forward to 1uV resolution, I was wondering how it will be useful.But I am disappointed, on 50.000mV range there is often large offset which fluctuates a lot (IMHO).I recorded this fluctuation during 24hours.There is substantial fluctuation sometimes even during 10 seconds, during 30 seconds, during one minute, which makes it impossible to REL the offset reliably.Is it normal?Can someone tell me if my new meter is faulty?And YES, I shorted Volts and COM posts during recording, and YES I let the meter thermally stabilize for few hours before.

author: Kalvin
author_rank: Super Contributor
timestamp: May 05, 2017, 08:44:26 am
content: Your Fluke looks very good! From the Fluke 289 speces:http://www.fluke.com/fluke/r0en/digital-multimeters/advanced-multimeters/fluke-289.htm?pid=56061Accuracy in DC range is 0.025% and the measurement range is 50 000 counts, which gives accuracy of 12.5 counts. Looks your DMM is about within the given accuracy. The accuracy and resolution are not the same thing, though. In order to achieve 1 uV accuracy in 50 000 counts, the DMM needs to have 0.002% accuracy.

author: Wytnucls
author_rank: Super Contributor
timestamp: May 05, 2017, 09:02:15 am
content: Garanteed accuracy for a year after calibration on the 50mV scale is 0.05% of reading +20 counts, after zeroing.So the worst low voltage accuracy the meter must achieve is +/-20 uV. If your meter stays within that bracket, you're all good.

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 05, 2017, 09:36:18 am
content: I think the display auto-scaling makes the "problem" look much worse than it is. The approximately .015mV shown is a tiny, tiny reading.

author: evava
author_rank: Regular Contributor
timestamp: May 05, 2017, 10:49:25 am
content: Why I ask is, that I am used to my UT61e behaviour, which meter is absolutely stable 0.00mV on 220.00mV range all the time, just very occasionally reading jumps to 0.01mV but for very short time like 1s and then readings continues with 0.00mV.In the same order (tens microvolts) now seems me ut61e to be more stable than (or at least as good as) this top of the range Fluke - am I mistaken?I wonder if someone could try to record offset fluctuating on UT181a (I remember it is one of joeqsmith's favorite meters) in that range 60.000mV - that comparison would be of interest to me.

author: AndyC_772
author_rank: Super Contributor
timestamp: May 05, 2017, 11:29:53 am
content: I've tried the same experiment on my 289. This is the voltage on the 50mV range with inputs shorted, sampled every 20 seconds, for the couple of hours immediately after switch on.

author: Wytnucls
author_rank: Super Contributor
timestamp: May 05, 2017, 11:43:17 am
content: If you null the offset (about 10uV), your meter should fluctuates between +/- 5 uV.The 61E has an accuracy of 0.1%+5 or at best 50uV, with display fluctuations of 10uV.My Gossen 30M, after zeroing, shows fluctuations of 300nV, on the last digit.All very normal I would say.

author: awallin
author_rank: Frequent Contributor
timestamp: May 05, 2017, 02:24:41 pm
content: me too!https://goo.gl/photos/MWHjUjZ47sF4BkebAseems to warm up for about 30mins, then both offset and drift stays within 10uV. on 50mV range, inputs shorted. Meter in an office with stable temperature.

author: evava
author_rank: Regular Contributor
timestamp: May 05, 2017, 02:46:45 pm
content: AndyC_772, awallin:Your both meters I like more than mine, because they go one way, then stabilize near to null (even if that stabilizing takes place after 1-2 hours.Can you please repeat that for 24hours, every 10 seconds (like I did), if yours drifts up and down during that time?I admit, that temperature was slightly changing in room during 24hours, between 18-22 degree celsius maybe (living room temperature). I started recording about 6:50 in the morning and stopped about that time next morning. I started recording immediatelly after switching meter on.My meter also was not calibrated lately (actually 9/2015) - which plays role of course.I do not like on mine that its reading goes up and down repeatedly, and too much IMHO.LSD digit on my meter should be called NSD (Not Significant Digitat all), because it changes itself round the clock...

author: AndyC_772
author_rank: Super Contributor
timestamp: May 05, 2017, 02:56:59 pm
content: What's happening to the temperature of your lab during those 24 hrs? Can you log that too and see if there's a correlation? You might just be seeing the perfectly normal effect of temperature on your unit.

author: Kalvin
author_rank: Super Contributor
timestamp: May 05, 2017, 03:11:22 pm
content: If you read the manualhttp://assets.fluke.com/manuals/287_289_umeng0200.pdfyou will see that your meter is within the specs. At the 50 mV DC Voltage range, the DMM accuracy is specified to be 0.05% when using the relative mode in order to compensate the offset. Like others have stated, the change of the room temperature may affect the reading - which is normal and expected. You may also want to check if your "short" is sensitive to temperature ie. will it create a tiny thermoelectric voltage (Seebeck effect,https://en.wikipedia.org/wiki/Thermocouple) due to temperature difference as you may have also successfully logged that voltage.

author: evava
author_rank: Regular Contributor
timestamp: May 05, 2017, 05:20:25 pm
content: Yes, thank you all!Now I am sure that my meter is OK, surely at least in spec.The only fear I have now is if I am not catching that disease, that contagious disease called VoltNutting, I think it starts with possessing meter with 1microvolt resolution, accuracy does not matter

author: joeqsmith
author_rank: Super Contributor
timestamp: May 05, 2017, 10:14:42 pm
content: Quote from: evava on May 05, 2017, 10:49:25 amI would guess my HF free meter would be very stable with it's 2000 count no mV range.If you still want the 181, I could run it. I would put it into my cardboard thermal test chamber along with my 61E. Drift of the 181 was much better than my other meters and the 61E was compensated for the temperature drift. The cardboard chamber does a fair job being temperature stable, good size fan. I would just run them 5 or so above room temp. I would also use the PC to log the data for the two.Let me know if you feel this would be helpful to you as it should be little effort to set it up. Just keep in mind that both meters are no longer stock and that these meters have not had an easy life. So your results may be different if you wanted to repeat the test.

author: evava
author_rank: Regular Contributor
timestamp: May 06, 2017, 06:59:05 am
content: Oh, Joe, it would be very kind of you, if you do it.I would be satisfied even with just recording for 24h in common room without temperature control, but I let it on you how you want to do that.Because: I have got another Fluke, 87V, and even that meter has got IMHO too much drift on 600mV range (at HiRes 20000count) - so its 0.00mV drifts and "offsets" much more than UT61e.So I sort of suppose/suspect Flukes drift and UNI-Ts do not drift (sorry Fluke)In another words: my experience with two Flukes (87V,289): their LSD digit fluctuates/drifts/offsets a lot and it bothers me.Your result would be very helpful for me.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 10:22:23 am
content: I assumed you were going to ask and started the test. I had not used my test box in a while and realized there is not enough room for both meters so I just ran the UT181A. I did not let the meter warm up at all. The room temperature was around 23 when I started. The box is set to 27 and I did not let it stabilize before starting the collection.I have not used the UT181A software in some time and forgot that you need to set the number of samples. So it's been running for about 7 hours and I lost more than half of that data.Would you like the raw data to do your own post processing or just a screen shot?

author: evava
author_rank: Regular Contributor
timestamp: May 06, 2017, 11:59:28 am
content: Screen shot is sufficient, of course. I am not into deep analyzing it, just want to see if ut181a is better in this respect.Thank you!Here on forum probably is not any other member possessing this meter, I wonder why, for low voltage it seems comfortable and handy.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 12:48:05 pm
content: There are several things I do not like about the UT181A. Lack of a spare battery and I am not aware of them offering one. LCD lens is easily scratched. No adaptors supplied with the AC charger. It has no EMC or safety certifications. The really bad thing is how such a low ESD event damaged it, which has been a common trait of UNI-T. Again it's not certified to survive such a test but that grill starter was a do nothing test.At $300 USD, I assume most hobbyist would rather have a decent used bench meter than a handheld. I never used a handheld for my own electronics hobby until I bought the Brymen. All of my cheap handhelds were just for low voltage electrical work where I really don't need much in performance. For me, I don't care about the size of these larger handhelds as I would be using them on the bench anyway. It does come with the serial cable and software where the Gossens I am looking at do not.That said, the UT181A does have some nice parts inside and after repairs and several mods to the PCB it actually performs quite well. If UNI-T ever makes a revision B, I would buy one.The test is moving along fine.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 01:53:56 pm
content: This is the temperature inside the meat packing container with the double foam box. I am using a RTD connected to the 34401A to determine the temperature. The heating is a fairly large heatsink with several power resistors mounted to it tied to my old HP programmable supply. And of course a fan. Its just a simple PI control using LabVIEW.The reason to run it in the box vs outside is if someone wanted to repeat the test, they could easily replicate the condition. It is still fairly cold outside and the furnace will cause a decent swing in temperature.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 05:09:50 pm
content: The meter is still running. I am not sure the significance of the 24 hours but as you can see there is very little drift in my UT181A. But again, I tested this meter over a very wide temperature range over the course of a several hours and saw very little drift. The UT61E was the second worst next to my CEM.You will notice the gap in the time between 3 and 6. This was the default 10K sample limit I mentioned. I just saved the second file and stitched the two together then reloaded. At one point the cat came in the office and started to scratch on the box. I think this disturbance caused the 0.004 shift.I had retuned the controller and this is showing after the third trim. It's well under +/- 0.01 degC. There was some effect when I started the test but hardly worth noting.

author: evava
author_rank: Regular Contributor
timestamp: May 06, 2017, 07:16:58 pm
content: Thank you very much!Seems to be very good, and about on par with what AndyC_772 and awallin had sent from theirs Flukes (after they stabilized).My extreme fluctuations wereprobablysurely caused by ambient temperature changing. In your rig would probably Fluke 289 behaved in a similar way.In this thread I realized that on 1microVolt level (instead of on 10microVolt level) there is real need for temperature stability during measurement.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 07:42:32 pm
content: My guess is this particular 181A is much more stable than the 289s shown over temp. I now have about 16 hours on the 181A and am planning to stop the test. Before I do, I will turn off the temperature control. You can see it starting to drop in the temperature graph. I'll let the meter continue to sample and open up a window to give you an idea on the drift.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 06, 2017, 09:02:25 pm
content: Opening the windows I was able to drop the temp from 27.0 to 18C. Ignore the large spikes. These are from me opening the box and then moving the meter towards the end. About 18 hours of runtime. I didn't see much point in continuing.I also took a picture of the battery condition after the test and the short I used.From 18 to 27, I would call it 5uVp-p. 4uVp-p if the temp is held somewhat constant. 14uVp-p if you plan to toss the meter around while making a measurement which I don't recommend.Hope you find this helpful.

author: evava
author_rank: Regular Contributor
timestamp: May 07, 2017, 07:02:23 am
content: Thank you very much.I can only say (to paraphraze ...):It is stable,it is very stable- it isUNI-T!I sort of expected that.If I did not know you modded your meter, I would say it is caused by better input protection circuit in 289, but now I can not say that.289 is more electrician meter, its LSD has not much use.Interesting, that UNI-T has same "+-0.025%+20" accuracy tolerance stated in manual page 37http://www.batronix.com/pdf/uni-t/UT181A-Manual-English.pdfbut it "does not take advantage of it" like 289.Regarding batteries - both meters suck in that regard. IMHO the best solution to it would be pair of changeable 18650s, second pair to instant change when first pair is depleated, and common external charger.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 07, 2017, 03:06:56 pm
content: Most of the UNI-T and meters in general the ones I have looked at are just not able to read down low enough to detect any sort of drift. I doubt there are many electricians, home appliance repair techs and automotive techs that are going to care much about drift in the uV range. Grandma is sure not going to care when she uses her RadioShack meter with the battery check feature to test her 9V transistor batteries.The tempdata3 shows the bit of data I had collected from my last test just prior to coming up with a way to compensate the UT61E.I've shown pictures of the meat packing box before. I have attached a few pictures of the UT181A inside the inner box, with a USB extension cable. They really skimp on that USB cable length. This box works fairly well for what it is.I would rather have had the UT181A use standard size batteries that I could use NiMH and a standard charger with. They could save money not adding the circuitry, clip on charge adapter and AC power supply. When the UT181A dies, that's it. You have to use the meter to charge the internal pack. And when that battery starts to go bad in three or four years, what then?Hope you enjoy your Fluke 289. It's a nice meter and one of the few Flukes still available that will calculate AC+DC.The last round of temperature testing can be seen here:https://youtu.be/0ObW8AA42OY?t=515

author: evava
author_rank: Regular Contributor
timestamp: May 08, 2017, 08:00:49 am
content: Quote from: joeqsmith on May 07, 2017, 03:06:56 pmOf course I enjoy my F289, it is now my best meter at all. It is Fluke - reliable, trustworthy, safe, solid. And I know it. Very happy with this meter.Quote from: blueskull on May 07, 2017, 07:05:34 amYou said that.Quote from: blueskull on May 07, 2017, 07:05:34 amI am not so sure if in 1uV resolution and at reasonable accuracy is that possible, see:Quote from: usagi on April 24, 2017, 03:03:21 amhere:https://www.eevblog.com/forum/testgear/options-for-a-5-5-digit-bench-dmm/msg1192648/#msg1192648Finally, I found a solution to my problem, I have slightly modified my meterNow I am happy, that's how I like it: when there's zero voltage on input then there's zero on display!Again thank you all for your responses! For me, we can now finish this thread.P.S. looking forward to Dave's 121GW and it's supposed 1uV resolution...

author: joeqsmith
author_rank: Super Contributor
timestamp: May 09, 2017, 11:15:20 am
content: Nice fix. Maybe start at kickstart?The 34401 I have I purchased brand new when HP first released them. It's always sat on the self and was never abused. It's interesting that they mention their Agilent is unstable in the 10uV range.I could repeat the test with the jumper on this meter. It's a pretty decent general purpose meter for it's age.

author: evava
author_rank: Regular Contributor
timestamp: May 12, 2017, 08:53:54 am
content: Quote from: joeqsmith on May 09, 2017, 11:15:20 amFrom you that sounds strangeThe only one meter in your possession which never was abused? LOLMaybe you could start to "test" (your way) also benchtop meters, if they have enough endurance agains your grill starter?Somehttps://www.eevblog.com/forum/testgear/keysight-34460a34461a34465a34470a-maximum-allowable-voltage-change-notice/evidently not.

author: joeqsmith
author_rank: Super Contributor
timestamp: May 12, 2017, 05:56:29 pm
content: Quote from: evava on May 12, 2017, 08:53:54 amThe grill starter was a toy compared to the new gun. That think will put out a kick.I have a second HP bench meter that I also bought brand new many years ago that replaced my first Fluke. That meter has also never been abused and works great to this day. Of course, I did not think I ever abused my first Fluke but I did damage it twice where I had to replace a custom IC on it. Just a weak front end design. The two HPs have never been damaged and it's not like I gave up on my hobby.I am not normally expecting a precision bench meter to be as robust has a handheld meter. Electricians don't use them. Same with the scopes and such. I pretty much wear a strap most of the time. The scopes would be pretty sensitive to it. With the handhelds, I expect them to survive some basic levels.