Products > Test Equipment
Fluke 115 and Nanofarad Capacitance Readings
bdunham7:
--- Quote from: Barry A. Waters on April 18, 2023, 07:30:46 pm ---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.
--- End quote ---
I tried my F116, which should yield the same results, using the TL175 leads and insulated alligator clips that came with the meter. I got exactly 220nF with my .22µF 'standard' and 7nF with a 6800pF mylar, so all within 1 count. Moving the leads around and even putting 1A @ 1kHz through a cable wrapped around one test lead 5X only resulted in a few counts of deviation. So either you have some industrial-grade interference at your location or something else is going on.
Are your leads twisted together or touching or something? I took no special precautions with mine. Did you try measuring DCR? Also, when you are turning the meter on, are you holding down any buttons, such as to defeat the power-off or backlight-off functions?
tautech:
--- Quote from: Barry A. Waters on April 18, 2023, 07:30:46 pm ---And I have discovered the problem. It's not the meter but its 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 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 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
--- End quote ---
;D
Welcome to the world where precise measurements are a science on their own !
However those of us with a few years under the belt will have seen many a twisted wire trimmer in a circuit used as some final trimming/tuning.
To the observant, long lead effects on measurements are just normal. ;)
Barry A. Waters:
--- Quote from: bdunham7 on April 18, 2023, 08:27:08 pm ---I tried my F116, which should yield the same results, using the TL175 leads and insulated alligator clips that came with the meter. I got exactly 220nF with my .22µF 'standard' and 7nF with a 6800pF mylar, so all within 1 count. Moving the leads around and even putting 1A @ 1kHz through a cable wrapped around one test lead 5X only resulted in a few counts of deviation. So either you have some industrial-grade interference at your location or something else is going on.
--- End quote ---
I can't speak to your success with the TL175 Test Leads as that is an upgrade from the Test Leads that currently come standard with a new Fluke 115. Perhaps you could repeat your test with the lesser quality Test Leads the 115 comes with?
Barry
bdunham7:
--- Quote from: Barry A. Waters on April 18, 2023, 10:58:50 pm ---I can't speak to your success with the TL175 Test Leads as that is an upgrade from the Test Leads that currently come standard with a new Fluke 115. Perhaps you could repeat your test with the lesser quality Test Leads the 115 comes with?
--- End quote ---
Which ones are they? The TL75 with plain red and black probes? And were you using the slip-on alligator clips or something else?
I'll try the TL75 before I finish this post....
...and I'm back, no change using TL75 and the older Fluke alligator slip-ons.
I keep begging you to measure DCR, and if you do also try measuring the DCR of the leads when shorted together. I had a strange problem recently with older but unused Fluke leads (TL71 IIRC) where there was a tarnish or something on the probe tips that had to be polished off--isopropyl didn't help--and I think it may have been outgassed stuff from the silicone leads. I was getting strange DCR readings up to 30R when shorting the leads, after polishing with "Barkeepers Friend" I now have 0.2R pretty reliably. I'm not saying that's your issue, but if using your own custom leads fixes the problem entirely I don't know how it could be anything else. It certainly isn't a natural characteristic of test leads, especially not in the 100nF region. 5-10pF, perhaps, but these meters and their measuring method doesn't get near those values.
Barry A. Waters:
--- Quote from: bdunham7 on April 18, 2023, 08:27:08 pm ---Are your leads twisted together or touching or something? ...
--- End quote ---
Yes... ME! And THAT was my issue. Thank you for not giving up on me bdunham7, even when I thought I had found my problem. As you and gamalot have pointed out, the Test Lead length of 55" is common and should not be the problem, and it wasn't (I have added a note to this effect in my post stating the leads were to blame above).
I was holding each lead of the capacitor in contact with its test lead with thumb and forefinger for lack of suitable alligator clips. I now assume I was measuring the capacitance of the capacitor AND the human tissue surrounding the contacts. The electrolytics measured OK because my fingers only threw things off +/- 1 uF, not really enough to notice. With nF stuff it was MORE than enough to notice, hence my dismay.
What a stupid problem to have :palm: Please feel free to tell me so! :-DD
Barry
(Who now has a fresh pair of mini-alligator clips)
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