Handheld meter robustness testing

[Muttley Snickers]

There was also another series in the mix that frequently gets overlooked and that was the 863, 865 and 867b models, I'm not exactly sure on the time line for this series but I do believe that they may be the true predecessor to the 287/289 models, I have the 189 and 289 and do keep an eye out for a good 867b to complete the line up. I know member Wytnucls did have one and if anyone else here has one is there any chance of a manufacture date confirmation ?.

[joeqsmith]

IMO, the graphing on the 289 is just too slow to be useful.  I like the UT181A much more than the 289 from the UI standpoint.  I don't mind the menus on the 181A (very similar to the 289).  Some things are a little cleaner IMO.  Meter is complex enough, it needs some sort of menu system.   

189 just drives very nice.  IMO, it's well thought out with just the right features I was looking for when I thought about getting a new Fluke.   If they had this meter available, I may not have the Brymen today.  That's marketing for you.  I like a few things about the Brymen but would have been very happy with ether meter.   I did not trace out the front end on the 189 to compare it with the 87V.  If I could get a brand new one, I would run it.

There was also another series in the mix that frequently gets overlooked and that was the 863, 865 and 867b models, I'm not exactly sure on the time line for this series but I do believe that they may be the true predecessor to the 287/289 models, I have the 189 and 289 and do keep an eye out for a good 867b to complete the line up. I know member Wytnucls did have one and if anyone else here has one is there any chance of a manufacture date confirmation ?.

If you don't mind, please run that test for me on your 189 and let me know if you see the same thing.   This one shows revision 015.  I find it hard to believe this meter is not plagued with the same problem but this one sure seems to look good. 

[onlooker]

Sorry for stepping back a little here. I have just watched  the "lead testing" video. It reminds me about my long time concern and question about the aging of  the insulation material for   the leads I have.

Do we  have data to say which material is better and for how many years. What is the general consensus as to when to  throw away  the old leads (that have no visible damages)?

Were all the leads tested  in the video fairly new? It will be interesting to see some 10+  or 20+ years old leads get tested.

[alm]

Silicone leads are more chemical and heat resistant, so I would expect them to last longer than PVC leads under the same circumstances.

Fluke suggest a maximum resistance of 0.5 Ohm for two leads in series as the limit. Presumably to exceed that a significant number of strands would need to be broken.

[alm]

If you don't mind, please run that test for me on your 189 and let me know if you see the same thing.   This one shows revision 015.  I find it hard to believe this meter is not plagued with the same problem but this one sure seems to look good.

I conducted the tests at 50 Hz since that is my local mains frequency and the 189 is also set to that. I could redo the tests with the 189 set to 60 Hz if that would make any difference.

In the 500 mV AC range (the lowest ACV range), it reads 500 mV_RMS with 2.8 VDC offset (the maximum my function generator will do at this amplitude) without issue (within 0.1% from the value without offset, and that could easily be my function gen).

In the 50 mV DC range (manual ranging), a 45 mV DC signal with 50 Hz AC superimposed on it:

Generator mVRMS (50 Hz)	F189 reading (mV DC)
50	45.20
100	45.19
200	45.41
500	45.91
1000	46.76
2000	48.61 (last digit unstable)
3000	48.32 (last digit unstable)
4000	46.00 (last digit unstable)
5000	37.5 (last digits unstable)
6000	28.7 (last digits unstable)
7000	23.7 (last digits unstable)

If I upranged to 500 mV with 7 V_RMS AC, then it would show 51.7 mV, which could very well be correct. So I would say it seems to be performing worse than its NMRR spec of > 90 dB, which would have allowed only 0.2 mV DC change at 7 V_RMS AC. Changing the frequency to 49 Hz or 51 Hz did not change the reading at all, suggesting to me that the AC signal is not reaching the ADC (which should have a much worse NMRR at 49 Hz than at 50 Hz), but affecting the analog path. If you let it autorange, it would keep switching between 500 mV and 5000 mV above 2 V_RMS, so you do have to wrestle it to get it to display misleading values.

This is relying on the offset of the function gen to be correct at high amplitudes. It would probably be more accurate to AC couple the function generator and use a separate DC voltage source to add the offset. But that would have been more labor intensive.

[Fungus]

71pages and i dont think anybody mentioned the really important bit yet - the build quality of the supplied leads/probes

May 2016, Page 36, Post 897 starts the discussion if you want to read through it.    We are up almost 80 pages which does take us outside of the Dick and Jane reading level.    

It might be worth putting links to the principal topics in the first post.

[joeqsmith]

I had just put the signal generator in series with the power supply to DC couple the two.   This meter was set to 60Hz and I was testing at 60Hz.  Your 189 in the DCmV range seems more on par with what I would normally see.  I will attempt to replicate your data to give you some idea how this one behaves.  When I looked at it the first time, it seemed pretty good but maybe I screwed something up. 


Using 60Hz with roughly 45mVDC applied and the Fluke 189 set to mV and lowest manual range.  Again, I have the DC supply in series with the AC source. 

0mVACrmsp-p   45.662mVDC
50                45.846
100              45.848
200              45.853
500              46.059
1000            46.455
2000            47.241
3000            48.595
4000            48.815
5000            49.091
6000            51.572
7000            51.647
8000            52.008
9000            52.284
10040          OL

Sadly I did not allow things to warm up but I went back and took the following after collecting the above, again with roughly 45mVDC applied:

ACrmsp-p         189
50 (30Hz)     45.865
50 (60Hz)     45.865
50 (120Hz)   45.865
50 (1KHz)     45.864
50 (2KHz)     45.865
50 (5KHz)     45.868
50 (10KHz)   45.868
50 (100KHz) 45.868
50 (500KHz) 45.869

With roughly 45mVACrms 60Hz applied,
DC offset       189
0                  45.311
1000             45.221
2000             45.214
3000             45.271
4000             45.338
5000             45.210
10000           45.214
20000           45.219   

It's strange the two 189s would behave so differently.  Again, my friend's is marked Rev 015. You would need to remove the PCB to check it.

corrected units.

[joeqsmith]

71pages and i dont think anybody mentioned the really important bit yet - the build quality of the supplied leads/probes

May 2016, Page 36, Post 897 starts the discussion if you want to read through it.    We are up almost 80 pages which does take us outside of the Dick and Jane reading level.    

It might be worth putting links to the principal topics in the first post.

If you want to take that on, you are more than welcome to do so.  I'm sure there are people who would greatly appreciate your efforts. 

[Fungus]

It might be worth putting links to the principal topics in the first post.

If you want to take that on, you are more than welcome to do so.  I'm sure there are people who would greatly appreciate your efforts.

I don't necessarily mean sitting down and doing it but things could be added every time one comes up.

[joeqsmith]

It might be worth putting links to the principal topics in the first post.

If you want to take that on, you are more than welcome to do so.  I'm sure there are people who would greatly appreciate your efforts.

I don't necessarily mean sitting down and doing it but things could be added every time one comes up.

That true.  If you or others decide to spend time to research the thread every time someone asks a redundant question, just post a note for the reference and I could keep a running TOC in the first post.  It's not a bad idea really.

[alm]

I had just put the signal generator in series with the power supply to DC couple the two.   This meter was set to 60Hz and I was testing at 60Hz.  Your 189 in the DCmV range seems more on par with what I would normally see.  I will attempt to replicate your data to give you some idea how this one behaves.  When I looked at it the first time, it seemed pretty good but maybe I screwed something up. 

I just redid the test with the following changes:
- Set the generator to 60 Hz
- Set the meter to 60 Hz (this causes DCV readings to be slightly less stable due it not rejecting mains interference anymore)
- Put a 10µF MKP capacitor in series to remove any DC offset (I measured about 5 mV DC offset with the generator set to 7V_RMS at 60 Hz)
- Used a resistive passive adding network to add the DC offset from a precision power supply (see attached schematic). This halves the effective AC voltage. I report the voltage as measured at the 189 terminals with a second DMM.

AC mVRMS (60 Hz)	F189 reading (mV DC)
off	44.98
50	44.99
100	44.99
200	45.64
500	45.00
1000	45.03
2000	48.78
3000	56.14 (OL on 50 mV range)
3500	60.30 (OL on 50 mV range)

Now a 45 mV_RMS 60 Hz signal with DC offset. I did not bother noting the last digit because it was often not very stable (meter set to 60 Hz means it is not rejecting 50 Hz interference).

DC offset (mV)	F189 reading (mV AC)
0	45.01
1000	45.02
2000	45.02
5000	45.02
10000	45.02
20000	45.02
30000	45.02
40000	45.02

The DC offset has no effect, even with much higher values (up to 40 V instead of up to 2.8 V). The AC offset has the same trend as your results (but starts deviating sooner). I put the earlier result down to the DC offset not being mV-level accurate at large output amplitudes. I would have to look into the specs of the generator (HP 33120A) if this is expected behavior.

[joeqsmith]

Your setup vs mine.   Same generator.   

The generator and supply were removed when measuring the zero points.   For the AC over range, the 50 ohm terminator was removed.

[alm]

How much DC offset do you measure from your function gen at high amplitudes? I measured 5 mV DC (with the 189) when DC coupled at 60 Hz / 7 V_RMS, and < 1 mV when AC coupled. I believe it went up with amplitude. Hence I chose to go for the AC-coupling and summing method, instead for the simpler series method.

[joeqsmith]

I can believe this.  If you look at some of the data we took, I would have considered even 20mV of error pretty good and typically I don't believe I was driving most of them this hard to get them have some major problems.   This 189 is one of the better ones I have looked at for this particular test.   

With the 50 ohm terminator, using my BM869 in the mV range and the HP344401A set to 10Vpp @ 60Hz, the Brymen shows about 6mVDC.  We are in the ballpark anyway.     

[alm]

Just to double check, are you really reporting mV_RMS for the AC voltage, and not mV_p-p? Because most generators only go up to 20 V_p-p, or 7 V_RMS in a high-impedance load. That makes 10 V_p-p or 3.5 V_RMS with a 50 Ohm load (assuming a generator with 50 Ohm outputs). Your schematic lists a 50 Ohm load for the generator and shows voltages up to 10 V_RMS, which means it could output up to ~57 V_p-p in a high impedance load.

If your voltages are actually peak to peak, then that would mean they are 2*sqrt(2) high, which would bring out results much closer together.

I am wondering if this behavior is considered within specification. The signal is not high crest factor. It appears not to meet the normal mode rejection spec. Is there some other specification that covers this?

[joeqsmith]

    Yes p-p for the constant DC test but RMS for the constant AC test.  Good catch.   

Correct original post.

[alm]

I plotted your results and my second set of results for the constant DC voltage test (corrected both to RMS voltages). If you take into account that your generator may add a few mV DC offset that may account for some of the linear increase in your measurements, I would say our measurements are in agreement.

I also attached the raw data and R script I used for plotting in case anyone cares.

[joeqsmith]

Follow my videos and such you will find I make a fair number of mistakes.  Most are pretty basic. I catch most in editing and assume people will figure it out.   I could see this one causing confusion if I left it.

Have you looked at the other thread to see how this meter compares with some of the others?   If you have meters that no one ran, may be interesting to try them as well and see how they do.   I think this 189 may have been the second least effected meter of all the ones I looked at.   You would need to look at the percent and both modes.     

[alm]

Is this really still an open question? That other thread has not been updated for six months. and the original question of 'are there other meters that have this problem' has been answered with 'yes, several do, except for some high-end meters'. Not sure how testing more meters would contribute this is. Unless I am missing something?

To me it still seems like not meeting specifications, at least the DC mode with mains frequency AC offset. If NMRR is > 90 dB, then I expect a mains frequency signal that is ~37 dB above the DC level to have no significant influence on the readings of a 4.5 digit DMM. Changing the frequency in small steps did not seem to have any effect. But I do not see how testing more meters will answer this. You would probably need a response from the manufacturer (does Fluke still support the 189?) as to if they consider this meeting its NMRR spec.

The DC offset in ACV is not so clear, since I do not believe anyone specifies a DC rejection ratio in ACV mode. At best you could argue that it increases the crest factor beyond what is allowed. So I am not convinced that wrong ACV readings with a DC offset would be out-of-spec.

[joeqsmith]

I am not sure if there was an original question so much as OP seemed to be isolating Brymen for this problem (which was basically wrong readings without any indication of them being wrong).  Someone else attempted to replicate their test and eventually a few others started to look into its. 

For me looking at different meters continues to be an ongoing process.  I have answered my own original question that some meters are more robust than others and some very low cost meters are more robust than some high dollar ones.  The information I continue to collect may not add much to my original question, it seems I learn something from every meter I look at.  Sometimes I get complete surprises, like the Gossen Ultra with it's latching relays and high sensitivity to static.   

To what end?  I guess until I loose interest.   

I have not spent a lot of time looking at the 189 manual.  I've found most manuals pretty slim on specs.  I don't think I have ever seen NMRR spec'ed for the ones I have looked at.   

I have never attempted to contact Fluke about the 189.     

[joeqsmith]

After cleaning the 189 it was apparent how bad the lens was.  I looked to see if Fluke offered replacement parts. 

Shown are a before and after.  About a half hour of hand rubbing the lens with PlastX took out the majority of scratches.    Looks like it had some chemical overspray on it the etched the face and a few nicks and what almost looks like a hole punch got it.  Considering it has been in a pretty tough mechanical environment since new, it's weather well.     

[bitseeker]

Looks great, Joe. +1 for plastic polish. For really bad scratches, wet sanding does wonders prior to the polish.

[joeqsmith]

I had some paper (actually plastic, 1200 grit) but did not want to risk it.  I may try and get something a little finer then when I eventually clean up those old Fluke 97s give it a shot.  There's a lot more surface area on those.

What grit do you start and end with when you have wet sanded lenses?  Have you tried some different brands of meters?   I have though about trying to clean up my UNI-T but that plastic is very soft.   

I made an attempt to get better picture of the end result.  The dust has already collected on it.

[bitseeker]

It's been a while since I last did it. I believe I started with 1000 and worked up to 2000. Then, used clearcoat scratch remover polish with microfiber cloth. This was on a Greenlee DM820 (the old one, not 820A). Worked well for all but one really deep scratch. I didn't want to thin down the lens just for one scar.

[joeqsmith]

A few people have commented on how bad the UT181A's lens was looking.  It has some really deep scratches from working on it face down without really cleaning the mat well enough.  It seems to get scratched just taking it in and out of the case.  One of the weak points of this meter IMO. 

After a fair amount of rubbing most of the deeper scratches are gone now.   I may try and make up some protective covers for a few of these meters.