Author Topic: Fluke 115 and Nanofarad Capacitance Readings  (Read 4862 times)

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Offline Barry A. WatersTopic starter

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Fluke 115 and Nanofarad Capacitance Readings
« on: April 15, 2023, 06:20:20 pm »
I just bought a Fluke 115 for general hobbyist & household use to augment an old Radio Shack 22-181 from the 1980's. The specs say it should be capable of reading in nanofarads (nF) to a resolution of 1 nF over a range of 1000 nF, where it jumps to uF scale. Accuracy for that range is  +/- ([% of Reading] + [Counts])  and is stated as 1.9% + 2.

When I attempt to measure a simple Ceramic Disc 104 capacitor (100000 pF) I expect to see somewhere around 100 nF depending on tolerance, quality, etc. and on my old Radio Shack meter I do. On the Fluke in both autoranging and manual nF settings it starts out around 370 nF and climbs to about 1.20 uF (1200 nF). I called Fluke support and they agreed that I should be seeing something closer to 100 nF and told me to take the meter back. I did and got a replacement and it does the same thing. I note that the meter appears to work in all other respects and is very accurate when testing electrolytic caps in the uF range (4.7, 10, 47, 100, 220, etc.).

Is there something I and the Fluke rep are not understanding here? Could anyone who has this meter check a 104 Ceramic Cap and let me know what they get? I'm baffled. If it's a calibration issue it may have been a batch because the serial numbers of the two units are only 42 apart.

Barry
« Last Edit: April 15, 2023, 06:39:10 pm by Barry A. Waters »
 

Offline bdunham7

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Re: Fluke 115 and Nanofarad Readings
« Reply #1 on: April 15, 2023, 06:27:11 pm »
Can you check that capacitor for resistance and leave it connected for some time?  If it is leaky--and yes ceramic discs can get leaky--then it might measure quite differently on meters that use different measuring methods.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline gamalot

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Re: Fluke 115 and Nanofarad Readings
« Reply #2 on: April 15, 2023, 06:54:16 pm »
Can you check that capacitor for resistance and leave it connected for some time?  If it is leaky--and yes ceramic discs can get leaky--then it might measure quite differently on meters that use different measuring methods.

I have a Fluke 117 and it measures 100nF ceramic disc capacitor without any problem. If I connect a 1 megohm resistor in parallel with the 100nF capacitor it will measure about 400nF.
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Offline Swainster

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #3 on: April 16, 2023, 11:29:14 am »
I've got a 115 in front of me, but I dont have an equivalent ceramic cap to test your scenario. Best I can do is a 47nF film cap, which reads 46.5nF on a cheap component tester, and 48nF on the fluke. The largest ceramics that I have on hand are 1000pF which, out of a random selection of 7 pieces before I got bored, all read 1nF, and 2 of them in parallel read 2nF, so looks like the fluke is operating well within it's datasheet spec.
 
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Offline Swainster

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #4 on: April 16, 2023, 12:26:20 pm »
(Decided not to add this as an edit as it is new data)

The plot thickens! By rooting around in a few more boxes I managed to find some unused 104 marked ceramic disks (of the budget aliexpress component kit variety). And these only read 50 to 60nF (e.g. 50nF on the cheap component tester and 60nF on the Fluke).. I was not able to measure any parallel resistance but I'm not really set up for that measurement at home - best I can do is the 100M range on an Aneng 8009. I also had a go at measuring the leakage current with a 1V bias and an old Keithley 480 picoammeter, but without setting up some shielding, all I can say is that the ceramic appears to have more leakage than a film cap (in the 10s of picoamp range), but not really quantify it. I also put a 3M resistor in series with the cap to stop/reduce oscillation.

Incidentally, the Aneng capacitance measurement agrees with the fluke and the component tester, but I believe that they all use the same measurement technique so that is not too surprising. Tomorrow I will try to remember to bring the suspicious caps to the office, and try them out on an LCR meter. To be honest, my current theory is dodgy cheap capacitors, but it is possible that the multimeter style measurement technique is causing this issue.
 
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Offline Performa01

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #5 on: April 16, 2023, 03:19:39 pm »
I have a Fluke 117 and it measures 100nF ceramic disc capacitor without any problem. If I connect a 1 megohm resistor in parallel with the 100nF capacitor it will measure about 400nF.
So this is a perfect demonstration of the fact, that a DMM is not the right tool to measure capacitance.

A proper LCR-meter would correctly indicate the 100 nF in parallel with 1 megohm (or the corresponding dissipation factor, according to the test frequency).
 

Offline bdunham7

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #6 on: April 16, 2023, 03:33:02 pm »
So this is a perfect demonstration of the fact, that a DMM is not the right tool to measure capacitance.

You can always make such declarations when given specific circumstances, but in other circumstances things change.  Think about the intended use of the DMM in question.  Now consider measuring a 35µF motor start capacitor that may or may not be charged to as much as 400V.  Now what is the right tool?  :)

Besides, measuring the DCR is within the grasp of the OP even if he had no other instruments.  Yes, these and most DMMs will interpret leakage as additional capacitance.  I suppose that's not in the manual (I haven't looked) but probably a lot of the intended users of the F11x products wouldn't understand anyway.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #7 on: April 16, 2023, 05:01:36 pm »
Ouch! With a sister meter (a 117) and another 115 both reading values nearer what would be expected it sounds like my experience is the odd man out so back the meter goes (for the second and final time!). I ordered another 115 from a totally different supplier in another state to insure I don't get one from the same batch as the two I've had. We'll see how that goes.

In the interim I tested both cheap ceramic Y5V 104Z KCK (several) and better blue plastic cube 1J63 1ND (several) with no joy while my Radio Shack 22-181 read all just fine at around 100 nF <OR> .1 uF. Damn...

Thanks to all who responded! I'll chime back in when my THIRD 115 is in hand...

Barry 
 

Offline BeBuLamar

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #8 on: April 16, 2023, 06:06:23 pm »
You know that Fluke doesn't repair the Fluke 11x series? If there is something wrong with it they simply destroy it.
 

Offline bdunham7

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #9 on: April 16, 2023, 06:37:49 pm »
Ouch! With a sister meter (a 117) and another 115 both reading values nearer what would be expected it sounds like my experience is the odd man out so back the meter goes (for the second and final time!).

How close were the other meters?  Can you try measuring the DC resistance of the capacitors with the meter in question?   Can you check what the meter reads in the capacitance range with an open circuit (no leads)? 

Whatever you have going on there is weird and the only explanation I can think of is some sort of leakage either inside or outside the meter.  Having two of them with the same problem seems extraordinarily unlikely unless there is a production issue and the problem managed to get by their QC and calibration.  The only F11x model I have is a 116 and it correctly reads capacitors down to single-digit nF with almost exact accuracy, +/- 1 count, so that would be my expectation for yours as well.

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #10 on: April 16, 2023, 07:43:38 pm »
You know that Fluke doesn't repair the Fluke 11x series? If there is something wrong with it they simply destroy it.

Yeah, I would imagine that the entire production, calibration and QC process is heavily automated for such a low end (for Fluke) series with little human intervention and not deemed worth repairing if any of them come back. Mass production = Mass disposal? Too bad....

Barry
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #11 on: April 16, 2023, 08:00:30 pm »
How close were the other meters?  Can you try measuring the DC resistance of the capacitors with the meter in question?   Can you check what the meter reads in the capacitance range with an open circuit (no leads)? 

The second 115 has been repackaged for return and is not accessible. The other meter (Radio Shack 22-181) was within the 20% tolerance for the ceramics 104s and the 5% tolerance for the blue cube 1J63s, which is what I would expect. If the third 115 shows up and has the same issue I will perform your tests. I assume testing the resistance would be the same as if I was testing a resistor. What would I be looking for result wise? For your 'open circuit' test are you asking for what the meter reads in the capacitance setting with no leads attached?

Barry
 

Offline bdunham7

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #12 on: April 16, 2023, 08:21:37 pm »
The other meter (Radio Shack 22-181) was within the 20% tolerance for the ceramics 104s and the 5% tolerance for the blue cube 1J63s, which is what I would expect. If the third 115 shows up and has the same issue I will perform your tests. I assume testing the resistance would be the same as if I was testing a resistor. What would I be looking for result wise? For your 'open circuit' test are you asking for what the meter reads in the capacitance setting with no leads attached?

You mentioned having and testing a 117 and another 115 as well.  What results did those give?  I would expect your plastic capacitors to read virtually the same on all meters, but of course the Y5V ceramics will vary wildly with measurement method and voltage. 

Testing a capacitor for DCR should eventually give an open circuit indication (>60M) although it can take a moment to get there.  Yest, the open circuit test can be just the meter with no leads set for capacitance.  It should read no more than 2 counts.  This is actually a calibration and performance test point.

I should have asked--how exactly are you connecting the meter to the capacitors?  Is it standard test leads with alligator clips and the tests are hands-off?  Or something else?
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #13 on: April 16, 2023, 09:38:44 pm »
You mentioned having and testing a 117 and another 115 as well...

Those were meters belonging to posters above that reported theirs working as I expect mine too.

Barry
 

Online Martin72

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #14 on: April 16, 2023, 09:40:49 pm »
. I called Fluke support and they agreed that I should be seeing something closer to 100 nF and told me to take the meter back. I did and got a replacement and it does the same thing. I note that the meter appears to work in all other respects and is very accurate when testing electrolytic caps in the uF range (4.7, 10, 47, 100, 220, etc.).

I guess the fluke use dc-signal for cap testing, therefore the lower the cap is, the worser it gets.

Quote
Is there something I and the Fluke rep are not understanding here? Could anyone who has this meter check a 104 Ceramic Cap and let me know what they get? I'm baffled.

We got several 117 here and 1 or 2 115, can check this tomorrow - Could be interesting because we never used them for cap testing.

Quote
If it's a calibration issue it may have been a batch because the serial numbers of the two units are only 42 apart.

There is a calibration "manual" avaible, the cap function won´t be calibrated.

https://dam-assets.fluke.com/s3fs-public/114_____cieng0200.pdf?c6lU5ClGysQYEd1McgX5RgPYq8k60kdP
 
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Offline bdunham7

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #15 on: April 16, 2023, 11:00:53 pm »
I guess the fluke use dc-signal for cap testing, therefore the lower the cap is, the worser it gets.

With a 0.22µF capacitor (an accurate and very good one) it does as shown in attached photo.  The connection of a 10X PP215 probe causes the reading to change from 220nF to 235nF.

A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #16 on: April 16, 2023, 11:45:37 pm »
We got several 117 here and 1 or 2 115, can check this tomorrow - Could be interesting because we never used them for cap testing.

That would be VERY much appreciated! Any ceramic or film cap in the nF range from 1 nF to 999 nF would be excellent!

Barry
 

Offline Swainster

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #17 on: April 17, 2023, 07:56:59 am »
For my particular case, the suspicious 100nF ceramic caps were tested on a hand held LCR meter and a nanoVNA - all confirm that the true capacitance really was arounf 50-60nF. I also found another budget kit of ceramic disc caps, and this was even worse! only 42nF capacitance for a 104 marked cap. In fact, in this particular kit, the 683 marked parts measured 50nF-ish vs 40nF-ish for the 104 :palm:. I guess that you really only get what you pay for (though the cheap SMD kits are usually quite OK).

So the verdict - my Fluke 115 is innocent, whereas cheap kits of ceramic disk caps, not so much. Plus I learned that the markings on cheap ceramics should not be relied upon.
 

Online Martin72

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #18 on: April 17, 2023, 05:31:17 pm »
Hi,

To my surprise we have at least 5 pcs Fluke115... ;)
I´ve test them all with the same result - No problems..
For the pic I got four from the five, bought between 2009 and 2020, on the desk, everyone measures the same type of cap (ceramic, 100nF).
After this I´ve connected a bnc cable to the scope - unfortunately I´ve forgot to make a pic from the 100nF measure... :palm:   ;)
Will repeat it tomorrow.

Martin
 
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Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #19 on: April 17, 2023, 10:11:26 pm »
Hi,

To my surprise we have at least 5 pcs Fluke115... ;)
I´ve test them all with the same result - No problems..

That's OUTSTANDING! Thank you Martin!

I tested several of the 100 nF and 220 nF caps I was using with the meters over the weekend in a charging circuit today on the DS1054Z and found them all to be close enough for my purposes (hobbyist). Even the wonky Ceramic Y5V 104Z KCKs came out OK (0.000066 s / 554 ohm = 119 nF) so I'm sure my problem is not faulty caps. Can't wait for the third meter to show up and see what's what!

Barry
« Last Edit: April 18, 2023, 01:28:40 pm by Barry A. Waters »
 

Online Martin72

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #20 on: April 17, 2023, 10:31:09 pm »
I find it remarkable that you already had such problems with two 115.
Not that it is a general error in the batch. :P

Offline BeBuLamar

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #21 on: April 18, 2023, 11:35:51 am »
I don't have problem with Fluke DMM but I do have problem with the Fluke IR3000FC unit. It uses the IR port on Fluke 189, 289, 187, 287 DMM to provide the Fluke Connect to connect to cell phone. I bought 2 units and one works but the other one doesn't. I keep exhanging about 3 of them and still not finding one that worked. So Fluke sent a rep to see me and the first thing he did was to upgrade the firmware and after that none of the units work. He gave up. And to this day I don't know how to buy a Fluke IR3000FC and make sure it would work. The serial number on the units that didn't work are all over the place. Not the same batch I don't think. Also the one that worked before he updated the the firmware has the lowest serial number.
So I mean it could happen to have a bunch of them not working right.
 

Offline Barry A. WatersTopic starter

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #22 on: April 18, 2023, 07:30:46 pm »
*** NOTE: The assertion below that the Test Leads were the issue is INCORRECT. The REAL issue was ME holding the capacitor leads in contact with the Test Leads with thumb and forefinger! See later posts for details ***

And I have discovered the problem. It's not the meter itself but the meter's test leads. It's like they are acting as additional storage capacity and making the the smaller caps look larger than they really are. If I dispense with the leads entirely and insert the cap leads directly into the meter's test lead sockets then everything reads as it should. The Radio Shack 22-181 I have has a dedicated Cap/Resistor test port so that's why it was reading OK - no lengthy test leads involved with it.

The test leads that came with the 115 are 55 Inches long so I guess that's a lot of insulated copper when you think about it. I cobbled together a 4 Inch long set and Voila, the meter reads nF caps as spec'ed. I am a happy camper once again!  :)

For those of you who were kind enough to test read some caps and reported success with your meters in the nF range, how long were the test leads you used? I'm thinking the shorter the better. I think I'm going to put something together with two banana plugs and a spare header connector so I can have a 'plugin test port' for these things with NO test lead length to worry about.

Thanks to everyone who assisted on this as it was driving me nuts! I just couldn't believe such a meter would have a problem like that. I feel bad about turning one in but at least I had my epiphany before I returned the second one. Now what to tell the wife about the third one that arrives tomorrow...  :-//
 
Barry
« Last Edit: April 19, 2023, 01:30:17 pm by Barry A. Waters »
 

Online Martin72

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #23 on: April 18, 2023, 08:10:01 pm »
Ah ! :D :-+

Offline gamalot

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Re: Fluke 115 and Nanofarad Capacitance Readings
« Reply #24 on: April 18, 2023, 08:17:12 pm »
55 inches of test leads should not cause any problem here, most of the test leads for multimeters in the world are similar to this length.

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