Fluke multimeter calibration - Page 1
Forum section: electronics / testgear

author: bterrier
author_rank: Newbie
timestamp: July 26, 2018, 10:18:02 pm
content: Hello everyone,This is my first post here, just found this forum today. Looking into possibly purchasing a Fluke 8840a. The guy is selling it “as is.”It does power up but without any leads connected, it shows a voltage of about 2.5v. Are these easily calibrated by the user or does it need to be sent in to Fluke?I am hoping this is the only issue but I really have no way of knowing. I have some experience with electrical and electronics work, but I am still very much a beginner. Are these meters easily repairable?I apologize if these questions have been asked prior, but I could not locate anything specific to calibration etc.Sent from my iPad using Tapatalk

author: Fungus
author_rank: Super Contributor
timestamp: July 26, 2018, 11:15:14 pm
content: From back when manuals were real manuals:https://www.elso.sk/media/download/pdf/fluke/man/Fluke-8840A-umen.pdf

author: coromonadalix
author_rank: Super Contributor
timestamp: July 27, 2018, 02:32:48 am
content: Does it have the ac-08 optionIs the vfd display bright ?? If not don't bother to buy itAt the section 6 you have self tests procedures and calibration in section 6.6 , the dmm doesn't need to be openedTell the seller to do a self test, if its show errors move away from it ... sorry if you are "newbie" don't take the chance to have more problems, it may get costly ... hard to find parts or else ...BUT you have schematics in the manual and a there is knowledgeable people here.Normally you need a dc calibrator IE: fluke 5700 series ... or very stable/precision voltage sources and high precision resistorsSome ic's have normal part number, others have the fluke onesYou have a tear down here :https://www.eevblog.com/forum/testgear/fluke-8840a-bench-multimeter-teardown/

author: bterrier
author_rank: Newbie
timestamp: July 27, 2018, 03:24:19 am
content: Quote from: coromonadalix on July 27, 2018, 02:32:48 amI believe you are referring to “Option 09.” If that is the case, he says it has option 09. Can I tell by looking at the meter if this is true? or is it only internals that make a difference.I am not sure that it does need calibration. I only saw a photo with no leads connected and the voltage was reading at 2.5. Is this normal? My handheld meter stays pretty close to zero.....it drifts slightly but not 2.5 volts.Sent from my iPad using Tapatalk

author: Fsck
author_rank: Super Contributor
timestamp: July 27, 2018, 06:50:59 am
content: high impedance meters display a relatively high voltage when they're left open circuit

author: Fungus
author_rank: Super Contributor
timestamp: July 27, 2018, 09:14:34 am
content: Quote from: bterrier on July 27, 2018, 03:24:19 amIt might be.If you look at the manual I posted is says the input impedance is >10 GOhms on some ranges. In one of those ranges it will be perfectly normal to show numbers on screen when the leads aren't connected to anything.Look at the photos where you see 2.5V, if it's set to a high impedance range then worry about something else, eg. the display and whether or not it passes self-test.Quote from: bterrier on July 27, 2018, 03:24:19 amYour handheld probably only has 10MOhm impedance.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 27, 2018, 10:19:54 am
content: Well if the meter has an very high impedance over 20 megs in the giga ohms range below 20 volts, it can be normal, ask the seller to short the leads, if it gets to zero, it would be OkayHigh impedance can lead / or act like an antenna, even leaving a probe(s) plugged can give some parasitic values / resultsNormally for the 8040 it's the ac-08 optionFor the 8842 it would be the ac-09 option ??If you don't have it, you wont be able to measure Ac voltages ...And finally the other option is the gpid interface board IEEE-05 optionHaving those 2 board in it would be very useful to youIf you end buying it, check for bad solders on the transformer, Redo them all, I've seen lots of complaints of flickering display brightness.

author: threephase
author_rank: Regular Contributor
timestamp: July 28, 2018, 08:30:54 am
content: A 2.5V reading could well be due to a high input impedance of the meter. My 8846 when switched to high input impedance will read anywhere between 1.5V and 6.5V. It does tend to have higher readings when the leads are plugged in.As already stated, if the input is shorted, the reading should drop to zero.With regards to calibration, you can check the calibration yourself if you have access to a higher spec instrument, preferably with better than 10x the accuracy of the instrument you are checking, but it is acceptable to have an instrument 3x better accuracy. You then use that instrument to verify the voltage / current / resistance being applied to the instrument being checked. You will find however that measurement technique will also start to come into play, but it is a great way to learn about the instruments and their limitations.The high spec calibrators are really just for commercial calibration labs to get the instruments through the door and back out as efficiently as possible with recorded results. You can get just as good accuracy yourself with the right application and techniques used.If you have to adjust calibration, then that can be a different matter. You will need the specific values at the required accuracy to follow the manufacturer's procedure and you generally find that you need all of them as you have to go through the whole calibration procedure, otherwise it will be invalid. You will also need the correct stable ambient conditions.You can of course send it out to a cal lab, but be careful what you are getting. In my country, calibration means checking, if adjustments are required, then that is an extra charge. UKAS calibration (checks) of my 8846 costs circa £120, standard calibration checks are around £80. It has never needed adjustment, so do not know what that would cost.