Confusion over two Fluke Meter Reading? - Page 1
Forum section: electronics / beginners

author: IVLRNR
author_rank: Contributor
timestamp: February 21, 2021, 11:46:32 am
content: Hi Everyone,I just measured a powerboard with a Fluke 85v and a Fluke 83v. My methodology was to turn the meter to AC volts, put the probes in and then flick the power button for the board and turn it off before removing the leads. I think in Australia the Active is on the left, but I also tried to turn the leads around to see if I got a negative value sign? I am new to using both of these meters, and primarily wanted to check that I was using meters that could work at mains voltages. I do not expect to actually ever need to do this in life or work. I used a powerboard because the Sockets for the house are not wide enough to allow the probes entry. I do however want to be able to test to see if there is 240v (ish) actually coming into various devices to rule out that as an issue (for the electrician).So: I test the same socket one after the other, and I get incredibly different results, I know they are different meters, and one is TRMS, and one is Averaging, but I can't for the life of me figure out why they as so very different? I am also getting hold of the manuals for the Flukes for a bit more information than Youtube etc. Interestingly I seemed to pick up variances in the meters from having them near the power board really strange I think non trivial number movements. I am also just starting building the math skills to better understand electronics, and that was a bit of a push to try to do something practical (with the meters) to challenge me.Here are the readings? Does anyone have any idea why this might be, what it is? It seems very strange to me. Any advice or observations would be most welcome.

author: nightfire
author_rank: Frequent Contributor
timestamp: February 21, 2021, 12:03:55 pm
content: The Fluke 83 is measuring milliVolts- so it is probably switched to min/max or similiar, or something did not connect properly and in the AC setting, you measure only ambient noise via the test leads that serve as antenna...The pic is not big enough to determine the rest of the display...

author: srb1954
author_rank: Super Contributor
timestamp: February 21, 2021, 12:07:16 pm
content: Quote from: IVLRNR on February 21, 2021, 11:46:32 amThe two meters should read approximately the same in this situation regardless of the fact that one is true-RMS and the other is average responding. The average responding meter is calibrated to display the equivalent RMS voltage when measuring a sine wave, which the mains supply is (well at least to a close approximation).Due to the extremely wide variation in the readings you have to assume that the 83V is faulty or the leads were not making proper connection. Try swapping the leads between the two meters to see if that makes any difference. Turn the power off first!Other tests(1) Set the 83V to DCV and measure its input resistance using the 87V. You should get around 10Mif the 83V input stage is still intact.(2) Check the fuse integrity using the test procedure described in the manual

author: IVLRNR
author_rank: Contributor
timestamp: February 21, 2021, 12:25:29 pm
content: I will get some better pictures tomorrow when I try to work through some of the suggestions. I did you the min/max feature because I couldn't get a proper reading. But I will try again tomorrow with a better methodology and photos. I had terrible trouble with pictures too big for the posting function.

author: IVLRNR
author_rank: Contributor
timestamp: February 21, 2021, 12:26:40 pm
content: Also, that makes sense with the Antenna thing, it was all over the shop at different times. Is that induction that is causing that? I am only learning?

author: IVLRNR
author_rank: Contributor
timestamp: February 21, 2021, 12:30:06 pm
content: Thanks very much, I will do that tomorrow too. Switch leads, test fuses (although I have done this before, I will do it again), and I will try the DCV thingy, thank you for the insight.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 21, 2021, 12:57:51 pm
content: Also... until you have the meter connection problem sorted out, can you please measure something _other than_ your mains? Pick something low voltage that cannot possibly deliver a fatal shock to yourself or your meter(s).

author: tooki
author_rank: Super Contributor
timestamp: February 21, 2021, 06:06:56 pm
content: Quote from: IVLRNR on February 21, 2021, 11:46:32 amThe 83V is in min-max mode, which is totally different from AutoHold.I would say to just redo the same measurementwith the same settings on both, but the fact that you just I mentionedexpecting negative AC volts(which doesn’t exist) tells me that you are not knowledgeable enough to be going anywhere near mains electricity. No offense intended, just recognizing that you are an absolute beginner and do not want you to get injured.Maybe you can instead ask a knowledgeable friend or store employee to do a quick sanity check on the meters for you?I don’t think there’s any need to do the “other tests” srb1954 suggested, because they clearly didn’t notice the 83V being in min-max mode while the 87V was in AutoHold mode.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 21, 2021, 08:53:28 pm
content: tooki is correct, with an addendum: there is no need to check fuses, as the voltage ranges are not affected by them.One additional aspect: when I measure outlets, it is common for the meter to show something in the mV range until a good contact between the two leads and the metallic blades inside the outlet is made. Those mV readings are equivalent to "zero volts".Be extremely careful with the Null (the small triangle button) and the Min/Max, as they can hide the "real" reading and expose you to a shock.Also, when measuring these outlets, resist the temptation to hold one lead on each hand while inserting them into the outlet. Instead, tie one lead first and then tie the other, or practice holding both leads in between the fingers while connecting to the outlet - these methods only work if you also keep your other hand "in the pocket" (close to your body and not touching any other surface that may be grounded). This prevents you from having a discharge across your chest, which can cause cardiac arrest and potential fatality.One additional aspect: during this initial experimentation phase, make sure to put a tape over the A and mA/uA inputs, so you can prevent any accidents by distraction. (The current inputs are very low impedance and, if inserted in a high power outlet, will cause a reasonably big spark)

author: IVLRNR
author_rank: Contributor
timestamp: February 22, 2021, 02:34:30 am
content: Hi Everyone,1. Yes, I did expect a negative value to show up on AC if I had the leads the wrong way lol. Also, I do have very little experience testing AC and even less experience with fluke multimeters. I really just wanted to check it worked. It has worked on low voltage DC etc.2. The one hand rule for AC is great advice, I will follow it. The getting a good contact and being MilliVolts before a good contact is made is also great, thank you.3. I still think there might be issues with my meters, but I am not able to test further giving I thought I was particularly daring putting them into the mains sockets on the power board, it both stressed me, and made me very nervous a shock would have travelled straight from one arm to the other (the current), and I would have been dead on the floor when my wife came home; so it is DC volts and low for me from hereon in. I consider myself very lucky and won't test fate again.4. What does any one think of testing computer power supplies with meters? are they a safe enough voltage I think 5s, 10s of volts etc? although I won't be doing any more testing until I am a bit more switched on.At least the DC, Continuity, Ohms and other features work, and perhaps the AC too, although I don't know, and I am not in a position to risk further attempts.Thanks for all the help, especially the safety, I thought it through, but not correctly.Regards,IVLRNR

author: rsjsouza
author_rank: Super Contributor
timestamp: February 22, 2021, 03:45:55 am
content: Quote from: IVLRNR on February 22, 2021, 02:34:30 amIf you have a transformer or a small appliance that uses a transformer, you can test it the Vac scale of your multimeter at a much safer voltage.You can also download a 100Hz or a 1kHz waveform to your cellphone or computer, connect a plug to the headphone jack and connect your multimeter to the jack contacts and play the waveform. The meter will show a voltage reading in AC.Quote from: IVLRNR on February 22, 2021, 02:34:30 amIt is ok to test the power supplies at the point where they connect to the motherboard and peripherals - all voltages are safe there (you should have +5V, -5V, +3.3V, +12V on the connectors). Just be careful when probing around, as these power supplies are capable of providing significant current and a small short may also be followed by a loud bang, despite the voltages are relatively small.Inside the power supply there are much higher voltages and therefore I would wait to get a bit more experience before you get inside of it. By higher voltages I mean even higher than the oulet (300, 350V).Good luck with your experiments and don't feel defeated in case they do not work in the first place. We all learn bit by bit every day.

author: james_s
author_rank: Super Contributor
timestamp: February 22, 2021, 04:43:02 am
content: Quote from: IVLRNR on February 22, 2021, 02:34:30 amAC is alternating current. You have live and neutral, which is positive and which is negative changes changes 100 times per second (50 complete cycles) so it doesn't make sense to think in terms of positive and negative. Since the polarity of the voltage is constantly flipping it makes no difference which way around you connect the probes.Be careful! Those meters are both perfectly capable of measuring mains voltage but 240V can knock you dead in an instant if the circumstances are right. There's no second chance if you screw up, so make sure you know what you're doing before you try.

author: helius
author_rank: Super Contributor
timestamp: February 22, 2021, 05:32:47 am
content: The reply from rsjsouza is very instructive, but there is one other detail that I would emphasize.When you poke probes into an electric socket, the bare ends can easily touch one another, which while not dangerous to the meter, is a very stunning experience for the user and could lead to him touching the ends, with deadly results. Probing sockets is one of the first things most users do with a DMM, but it is really a dangerous exercise and should be minimized.The most basic test for whether or not a DMM is working is to set it on DC Volts, and check the reading with the probes touching (should be between -0.01 mV and +0.01 mV), and with the probes contacting the poles of a known-fresh 1.5 V battery. If you have any loose resistors on your bench, reading their resistance is also a good test.If you do probe the mains socket, a tip that can make your life much easier is to switch the DMM to a manual range. It makes reading the voltage faster and clearer, as you can see more or less instantly when the probes touch the contacts in the socket. Waiting for autorange can cause mistakes.

author: IVLRNR
author_rank: Contributor
timestamp: February 22, 2021, 10:59:42 am
content: Hi Team,In my defence; when I worked as an Electrical T/A, we got given rubber floor mats, rubber gloves, and leather (overs), and we tested the cable we pulled.The meter read 240v and that was proof the socket and the job was good. There was no explaination of why or how, I just did what I was told.It is only now, I am interested in Electronics, that I am starting to learn anything about electricity, lol. I was taught I suppose how not to kill myself, because we had protection. I don't know why I thought I didn't need the same mats, gloves x 2, as in the job? I think the more I learn now, the more I realise how people just get by, and live, when perhaps it is luck rather than skill or knowledge.I would very much like to thank everyone for their advice, I know I have learned something from this whole chain of events, now to get back to the hard mathematics which seems even harder to master, not to mention the physics involved with electricity and electronics? Good thing I am in for life!Thanks again.

author: D6123
author_rank: Contributor
timestamp: February 22, 2021, 03:10:07 pm
content: Probably, both of your Flukes are in fine working conditions, i am sure. You must make measuring 230-240volts on V -AC at your meters but not on V DC. Also be sure you are actually put meter probe's tips on contact lines of 230 AC volts.And switch off all extra pushed buttons like "hold",min-max" , range must be the similar(let it be 600v or simply "auto").Then you may check real voltage.Try to check on another socket with 240v ac.Did you use the same probes? If no, then use the same, may be one of its is broken or was bad pushed in a plug.Were you actually work electrician?

author: elekorsi
author_rank: Regular Contributor
timestamp: February 22, 2021, 09:58:21 pm
content: Oh come on guys, some of you are making it look like there is at least 50% mortality rate at people measuring the mains voltage with a multimeterI mean this is still low voltage, or did i miss something and he wanted to measure the high voltage distribution??You just scare the guy for no reason... He is using trustworthy instruments and as long as he has some common sense he is safe. There would be a problem if he would be using some cheap chinese multimeters, that is dangerous...If one is not able to do it safely, he should stay away from multimeters anyway and should not deal with anything electric....

author: helius
author_rank: Super Contributor
timestamp: February 22, 2021, 10:56:01 pm
content: Indeed. "Low voltage" means you aren't at risk of dying from arc flash, but there is some non-zero potential of heart arrhythmias which as we know can result in death. When people are aware of risks, they can take precautions and make informed decisions. I just worry when it's taught that the first thing a real newbie is supposed to do is probe their electric socket.

author: IVLRNR
author_rank: Contributor
timestamp: February 22, 2021, 11:41:57 pm
content: Quote from: D6123 on February 22, 2021, 03:10:07 pmThanks for the advice, I was on AC not on DC settings. I will try another socket, I did use both seperate and the same probes.Nope, I was never an Electrician, but I worked as a Trades Assistant to Electrician(s), and communications technician. Thanks very much for the advice, I think you are right, there probably is nothing wrong with the meters, it is me and my lack of experience with them and Electricty.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 23, 2021, 01:07:21 am
content: Quote from: helius on February 22, 2021, 05:32:47 amNot in a standard Australian socket, as the Live & Neutral normally have moulded plastic guides preventing this.QuoteAn even better tip is to turn the Mains off on the wall socket (GPO), insert the probes one at a time, ensure the DMM is on ACV, then turn the switch back on.Take note of the reading, turn off the Wall socket switch, then remove the probes from the socket.If a power board is used, it can be even safer.With the wall socket off, unplug the power board, so it has no electrical connection to the Mains, insert the probes, ensure the DMM is on ACV, plug the power board back in, turn the switch on the wall socket on, (& on the power board if there is one), take the reading, turn off the wall socket, unplug the power board, remove the probes.In countries which do not have a switched wall socket, the second procedure is the only really safe method.Obviously, in that case, you still have to unplug & plug in the power board with wall sockets that are still "hot".It is often hard to push DMM probes in deep enough to make proper contact with Australian power sockets.I think the OP ran into this problem , hence the silly reading.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 23, 2021, 01:27:01 am
content: Quote from: IVLRNR on February 22, 2021, 10:59:42 amNo, you don't need "mats, gloves x 2", etc.------ just a "Mk1" brain!Learning what to do, how to do it, & when to do it, is not really very taxing.You have perfectly capable DMMs, so with a little forethought, you should be able to safely test voltages of the order of 240v ac.There are always inherent dangers in testing any dangerous voltage, but using care, they are minimised to the point where people perform such tests every day.After all, if you were using a saw table, a bandsaw, or an oxy-acetylene welding set, you would takeappropriate precautions, butonly appropriate precautions, as others may be counter productive.The same thing applies here.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: February 23, 2021, 02:38:41 am
content: Quote from: elekorsi on February 22, 2021, 09:58:21 pmThank you. The self righteous safety crazies on here drive me nuts.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 23, 2021, 03:50:51 am
content: Quote from: Ground_Loop on February 23, 2021, 02:38:41 amI am not sure if this is directed at me. Given the way the first question was asked, the lack of experience with the equipment was palpable. So yes, in this case I will provide, to the best of my ability, all boundary conditions for the proper use of the instrument, including the shitstorm that may ensue in case of improper use. That is callededucation, not fearmongering.And no, I am not a safety crazy person that thinks anything less than an armored Fluke is good to probe a simple outlet. When experience is in the picture AND you are paying attention, pretty much anything goes in a CAT I or CAT II scenario.

author: IVLRNR
author_rank: Contributor
timestamp: February 24, 2021, 05:25:45 am
content: So. To close this topic off. There was nothing wrong with either meter. The salesman or vendor also wanted me to test on another socket.So, I put on my rubber gloves, and my leather rigging gloves over the top, and I tested both meters, they came up fine.Herein ends my journey through 240v, actually a little less according to the meters.Thanks everyone for the help, advice, and input; This has been a great learning experience for me.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 24, 2021, 07:50:23 am
content: Quote from: IVLRNR on February 24, 2021, 05:25:45 amWearing all that crap, I'm surprised you had enough manual dexterity to do so!Did you disinfect the meters & everything else, first, so as to not contract coronavirus?

author: srb1954
author_rank: Super Contributor
timestamp: February 24, 2021, 09:08:34 am
content: Quote from: rsjsouza on February 21, 2021, 08:53:28 pmChecking the fuses is a quick and easy test to that verifies the integrity of other parts of the input circuit as well as the fuse itself.Although voltage jack doesn't connect through the fuses the common path for voltage is also shared with the common path for current. If the fuse checks OK then you can be pretty sure that there is no other damage to any other part of the common circuitry.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 24, 2021, 02:37:06 pm
content: Quote from: srb1954 on February 24, 2021, 09:08:34 amThe description already mentioned the DC path was working fine, thus any common path was functional.

author: srb1954
author_rank: Super Contributor
timestamp: February 25, 2021, 10:08:15 am
content: Quote from: rsjsouza on February 24, 2021, 02:37:06 pmYes, but this information only came out in a later response from the OP. The original query that I responded to didn't make any mention of the DC functions being OK.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 25, 2021, 11:54:05 am
content: Quote from: srb1954 on February 25, 2021, 10:08:15 amYes, you are right. This information came later.However, to test the common path, testing fuses is nowhere near as convenient as simply moving the meter to ohms or continuity. But both are valid ways.