Microamps and Millivolts Measurements on UT61E - Page 1
Forum section: electronics / testgear

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 07, 2022, 03:45:56 pm
content: I like my UT61E I just recently bought, but the Microamps reading mode -- 3rd from last on dial -- is way off compared to the same reading with Milliamps mode -- 2nd from last on dial. The same goes for the Volts vs Millivolts measurements -- 1st and 2nd on the dial respectively.Is this normal? The volts, milliamps and amps modes all seem fine and are within spec compared to my GDM-8251A.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 07, 2022, 04:11:19 pm
content: There should be no significant difference between the ranges. However the internal resistance is usually different and this can change the actual voltage / current measurend.So for the comparison one whould have the voltmeters in parallel and the amp-meters in series.

author: Fungus
author_rank: Super Contributor
timestamp: December 07, 2022, 05:50:55 pm
content: Quote from: JenniferG on December 07, 2022, 03:45:56 pmIt can be.Remember that what you're doing is inserting a small resistor in series with your circuit (the meter), and it's a different resistor on each range

author: rsjsouza
author_rank: Super Contributor
timestamp: December 07, 2022, 06:09:59 pm
content: What Fungus described above is what is called the "burden voltage", a voltage drop caused by the shunt resistor used to perform the current measurement.The UT61E has a somewhat high burden voltage when compared with many more advanced meters, but even expensive models suffer from that.This is well covered in the uCurrent project description page from Dave:https://www.eevblog.com/projects/ucurrent/

author: bdunham7
author_rank: Super Contributor
timestamp: December 07, 2022, 06:14:27 pm
content: Quote from: JenniferG on December 07, 2022, 03:45:56 pmCan you give specifics on how you measure this and what the numerical differences are?For current, you should have the GDM-8215A and UT61E in series so you can see how much the current actually changes when you shift ranges on the UT61E. Depending on your current source the current may change quite a bit due to the higher burden resistance of the microamp range.For voltage, both meters should be in parallel. I can't think of a good reason for the millivolt range to differ from volts, but we'd need to know your exact test setup and how much variation there is. Also, AC or DC?

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 07, 2022, 06:58:45 pm
content: Quote from: bdunham7 on December 07, 2022, 06:14:27 pmI just made a video and posted it up on youtube:I have the UT61E set to Milliamps to start and it's between the Pin 46 output of Arduino Mini Mega and a current limiting resistor to the LED side of a DIY vactrol -- so DC current. I wanted to see how much current is drawn with this particular resistor. At a PWM write setting of 128 (around 2.5v output), I am getting 294 microamps on the UT61E on Milliamps setting. I then connect the leads over to my GDM-8251A and it reads 299 microamps (there is a discrepency here and that's why I am looking forward to getting some resistance, amperage and voltage references to test my 8251A). Anywyas but the real problem is when I switch the UT61E to microamps mode it show only 250 microamps vs 294, or about 85% of the actual reading according to the mA reading on both my UT61E and GDM-8251A.

author: bdunham7
author_rank: Super Contributor
timestamp: December 07, 2022, 07:30:41 pm
content: Quote from: JenniferG on December 07, 2022, 06:58:45 pmThere's the problem--you need to have both meters connected at the same time, in series for current measurements and parallel for voltages. The meter is always part of the circuit--in this case it is a resistor. So you are putting three different resistors in your circuit and getting three different current readings, which is exactly what you should expect.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 07, 2022, 08:48:54 pm
content: Quote from: bdunham7 on December 07, 2022, 07:30:41 pmConfused. I have it wired in series. And within the same meter it's off by 85%. Forget the GDM-8251A.

author: coromonadalix
author_rank: Super Contributor
timestamp: December 07, 2022, 08:59:35 pm
content: loll I would not trust the Uni-T meter loll not the same resolution and precisionUp your game a little, with this kind of meter you get some very basic resolution, get an good 50k counts or 60k counts insteadIE: more specialized equipment if you play at low levels like this

author: bdunham7
author_rank: Super Contributor
timestamp: December 07, 2022, 09:14:19 pm
content: Quote from: JenniferG on December 07, 2022, 08:48:54 pmYou can't forget the GDM-8251A. I meantboth metersin series, and of course the pair in series with your circuit. If you set it up that way, what you should see is both meters reading approximately the same current (within tolerances) and then the current changing onboth meterswhen you switch the UNI-T to the microamps range.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 07, 2022, 09:33:38 pm
content: Say I only had the UT61 -- I really wish I wouldn't of brought up the GDM-8251A now as it seems to be convoluting things.So you wire the UT61E in series to find out the current. You turn the dial between amps, ma, and ua. For any mode you still have it wired the same.. in series.What I'd really like to know is why I am getting 250ua for the microamps mode and 299ua for the milliamps mode.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 07, 2022, 09:57:18 pm
content: Attached are the measurements of the three ranges of the UT61E using a separate meter. You can tell how different their shunt resistance values are.On the circuit, the shunt resistor will be placed between the power supply and the circuit being tested. Depending on its value, a proportional voltage will be dropped by it (Ohm's law). Now, think the voltage that is powering your circuit is slightly lower as you progress from A --> mA --> µA ranges. That slight lower voltage will cause your circuit to draw a bit less current.shunt resistoron DMM|---------------------/\/\/\/---------------------|| |Vsupply Circuit| under load| ||-------------------------------------------------|

author: joeqsmith
author_rank: Super Contributor
timestamp: December 07, 2022, 10:03:51 pm
content: You're changing ranges, you're selecting 61E's different internal shunts. Different shunts have a different resistance that you now have in series with your circuit. Of course the current changes.I modified a UT61E to reduce the burden voltage in the uA range. The video goes over how this circuit works if interested.

author: colorado.rob
author_rank: Frequent Contributor
timestamp: December 07, 2022, 11:10:04 pm
content: Quote from: JenniferG on December 07, 2022, 09:33:38 pmBurden voltage. EEVBlog #2.https://youtu.be/u2yRR4G3yTA?t=202Look how young he is!

author: bdunham7
author_rank: Super Contributor
timestamp: December 07, 2022, 11:17:10 pm
content: Quote from: JenniferG on December 07, 2022, 09:33:38 pmIf you include the GDM-8251A in the circuit, then you will actually see the current change on its display even though you only changed the UT61E dial and you'll realize that the current is actually changing and it isn't a reading error. Try it!Lets say you take your original circuit and in addition to everything else, you put a 5 ohm resistor in series. You take a measurement, then you swap out the 5 ohm resistor for a 500 ohm. You'd expect less current, right? So when you turn that dial on your UT61E, that is exactly what you are doing--swapping out shunt resistors that are in series with your circuit.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 12:30:36 am
content: So this is normal? I shouldn't return it? I have 12 days to return it. The millivolts vs volts is off about the same as well.I'll have to study burden voltage and shunts and all that in multimeters.. I'm a newb. I just don't know if I got a lemon and only have aroudn 10 days to return it. Seems like Uni-T would of picked a better value for shunt resistor which is mroe accurate.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 08, 2022, 12:44:34 am
content: Yes, it's normal for the UT61E and others and basic circuits 101.QuoteLike anything, it's a tradeoff. If you want a constant burden, use an external shunt and measure the voltage across it.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 08, 2022, 01:16:15 am
content: As others have said and thereferences that were sent to youalso make it clear, it is not a lemon but a normal behaviour that does not indicate any problems with it. Any meter that measures currents with a shunt resistor will have this behaviour.

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2022, 01:16:41 am
content: Quote from: JenniferG on December 08, 2022, 12:30:36 amYes, the issue of shunts, resistance and the so called burden voltage (the voltage drop across the meter in the current ranges) is an issue with any meter and does not represent a defect. You should do what I suggest with your other meter in series just to make sure that the entire difference is actually due to this and there isn't some other problem. The readings will vary, but the two meters should agree (within tolerances) at all times if they are in series.The millivolts vs volts would concern me a lot more as there isn't a similar, readily apparent reason for it if the difference is significant. Can you elaborate on that?

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 01:39:15 am
content: Quote from: bdunham7 on December 08, 2022, 01:16:41 amDoing a PWM write of 7 (out of 255 values -- 8 bit) from pin 46 on Mini Mega 2560 to a resister/LED (same DIY vactrol as above for amperage test). The red terminal is connected to the resistor leg and the other terminal to ground. It reads 0.1418V -- as approximately predicted beforehand -- on volts setting and 67.2 mv on millivolts setting.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 08, 2022, 01:41:52 am
content: Quote from: rsjsouza on December 08, 2022, 01:16:15 amCertainly meters that are switching in different shunts would, which is most. It's been a while since I looked but it seems that Gossen Ultra I have uses a single shunt. Comes with a high price tag. It's so worth it!!

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2022, 04:21:36 am
content: Quote from: JenniferG on December 08, 2022, 01:39:15 amOK, so that doesn't mean it's broken either. What you have is not a steady voltage, but rather 5V about 2.7% of the time. In the voltage range the meter can accommodate and integrate the 5V peaks properly, but in the mV range, those peaks are clipped by the input circuitry and the meter's ADC gets reduced peaks to do the averaging with and gives you a lower number. That's not ideal behavior and it would be better if it simply displayed 'OL' or overload in that case, but it is a budget meter from Uni-T and in any case, all meters have their limitations. Short duty cycles and high crest factors are not easy to deal with and even good meters have their limitations in that regard.It's worth noting that for many purposes--such as figuring power dissipation--the integrated average DC current or voltage is actually not the reading you need. TRMS AC+DC is what is needed for that. IOW, 2 volts half the time is not always the same thing as 1 volt full time.

author: Fungus
author_rank: Super Contributor
timestamp: December 08, 2022, 11:35:27 am
content: Quote from: JenniferG on December 07, 2022, 09:33:38 pmBecause when you turn the dial you change the resistance of the meter.(and the meter is in series in your circuit)

author: coromonadalix
author_rank: Super Contributor
timestamp: December 08, 2022, 12:48:15 pm
content: Once again at theses values the uni-t meter will round them sometimes, IT IS not made for these low currents valuesYou are trying to do things with aproximatives equipment it seems ... seeing you make some arduino or mcu projects contradicts the knowledge you need to have for precises or low values measurementsSorry it seems harsh, but many members here gave you really solid explanations here and you need to understand them.The equipment capacities too, you are using cheap meters to do extensive work / measurements, it kinda become stupid in a sensethreads like this will go for ever loll

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 01:26:07 pm
content: Quote from: coromonadalix on December 08, 2022, 12:48:15 pmI agree I need to learn what has been said. I am very appreciative. I do plan on re-reading this thread to learn from it. A bit overwhelmed though as I am a newb to electronics. I've journaled the link to this post already. It's just one I have to come back to and re-read to try and understand it. So I guess I'll keep this meter, again I only have 10 days left in return widnow. That was my main concern right now. I understand about half of what's being said here.I agree I am stupid; or more ignorant rather -- I actually have a genius IQ.

author: Gyro
author_rank: Super Contributor
timestamp: December 08, 2022, 01:49:01 pm
content: Measuring current with a DMM is kind of a last resort. As has been explained in several of the posts above, introducing the shunt resistors causes a voltage drop and changes circuit conditions - particularly troublesome in low voltage situations (eg. 3.3V or 1.8V logic supplies). Anything that involves breaking into the circuit is less than ideal.With a bit of thought, you can often find one or more resistors in the circuit that you can measure the voltage across instead and derive the current by Ohm's law. A much more satisfactory solution all round.

author: Veteran68
author_rank: Frequent Contributor
timestamp: December 08, 2022, 02:27:37 pm
content: Quote from: JenniferG on December 08, 2022, 01:26:07 pmI don't think he was callingyoustupid. I'd like to think he was referring to the idea that a round-and-round discussion people get into when the question has been asked and answered but not agreed with or understood, so it keeps going like some debate when it's not a debate -- it's fact.We're all ignorant of something, no shame in that, genius IQ or not. While this topic seems elementary to me (I've been an electronics hobbyist for most of my life and have owned dozens of meters), there are still many aspects of the field that are way above my head. Nobody just *knows* from the womb, and must learn it. If you're just starting out, you're not expected to know it. Just try not to come across like you don't believe them only because you don't understand it.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 08, 2022, 02:51:29 pm
content: Quote from: JenniferG on December 08, 2022, 01:26:07 pmI am very ignorant on most topics and imagine my IQ is just high enough to be somewhat aware. Maryilyn Vos Savant had talked about her upbringing during an interview and tells of her mom's response to her childhood questions.https://youtu.be/U09O9DXWdHc?t=829I don't find a lot of people willing to do their own research.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 03:01:29 pm
content: Quote from: Veteran68 on December 08, 2022, 02:27:37 pmWell I am sorry I might of come across that way. I don't think that at all.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 03:10:28 pm
content: Quote from: joeqsmith on December 08, 2022, 02:51:29 pmWell like I've said, I've already journaled it and am going to get back to this thread. After I've gone through a few electronics books. Believe me I have the motivation to learn -- I just needed to know if I should return this meter or not.. if it acting normal (and I got that answer here). Regarding learning Electronics, I am just overwhelmed right now because there's so many books to choose from. I guess I am going to start with Make:Electronics then Getting Started in Electronics.The books I have seen recoommended to newbies:0) Getting Started in Electronics1) Make: Electronics2) Electroncis for Beginners3) All New Electronics Self-Teaching Guide4) ARRL Handbook5) ARRL's Understanding Basic Electronics6) Practical Electronics for Inventors7) The Art of ElectronicsWhat order should I read them? Which should I skip? I have the Art of Electronics and it's too overwhelming for a beginner I think.

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2022, 03:11:00 pm
content: Quote from: coromonadalix on December 08, 2022, 12:48:15 pmI don't think the quality of the meter is all that relevant here and I don't think a 'better' meter is going to behave differently enough to matter much.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 08, 2022, 03:22:18 pm
content: The reistance is likely the smaller problem here. Mesuring the PWM signal causing likely internal clamping is likely the larger problem. Ideally a meter would catch that, but not many meters do that. With the larder rage there is enough headroom to accect the signal, but not with the smaller ranges. Even good meters will fail on this.For the books it is really hard to tell. The right book depends on the person to read it. To simple / low level makes it boring to read and likely missing out on parts. Too difficult / mathematical just causes frustration.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 03:26:45 pm
content: The PWM's duty cycle being an issue makes sense, especially at very low duty cycles like I did with the voltage reading I shared here. I can understand. I don't understand how the meter integrates or whatever.. but I do understand Integration with respect to calculus. It makes sense that the samples might not be small enough or whatever, to catch the duty cycle.If I wanted to measure the actual voltage, would it help to put an electrolytic cap in parallel to hold the PWM's average charge, or whatever.. I really am clueless lol.

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2022, 03:27:23 pm
content: Quote from: JenniferG on December 08, 2022, 03:10:28 pmAoE is way too advanced for where you are at. It might be interesting because it is full of practical working examples, but it assumes a certain level of theoretical knowledge.You can read Wayne Storr's free online basic tutorial (it goes quickly, but concentrate on a page per day or so--don't whiz through it). Also study Thevenin's theorem thoroughly, along with Norton's (linked in the Wikipedia page)http://www.energiazero.org/elettrotecnica/basic-electronics-tutorials.pdfhttps://en.wikipedia.org/wiki/Th%C3%A9venin's_theorem

author: mqsaharan
author_rank: Regular Contributor
timestamp: December 08, 2022, 03:30:06 pm
content: Hi JenniferG,You are right the difference shouldn't be this much in measurements within the different ranges of the same instrument but in your case it appears so. That is why bdunham7 has suggested to put both of your meters in series while measuring the current. When you'll change range on 61E from mA to uA, the other meter will verify if your 61E has any problem/fault or not. Also, please keep in mind that this meter is geared towards hobbyists not professionals so less attention has given in its design to keep things agreeable within the instrument.Sadly, manufacturers has stopped including detailed operating instructions in the manuals. I guess it makes their instruments appear less attractive.I am attaching here three pages from Fluke 8020A multimeter's user manual (https://dam-assets.fluke.com/s3fs-public/8020A___imeng0000.pdf) that'll hopefully explain you why you are getting such a big difference between mA and uA current ranges within the same instrument. Also, attached here is the schematic of UT61E. You can see that this meter uses 1k for the lowest range in uA position and 10 ohms in mA range. Please do watch Joeqsmith's video in reply #12 regarding burden voltage of this meter.If you want lowest error in current measurements you can get a meter that has lowest burden voltage. The cheapest meter I know that has lowest value shunts thus have lowest burden voltage is UT61D. It is using 50 ohms (uA range), *0.5 ohms (mA range) and 5 milliohms (A range) resistors as shunts.Edit: *0.5 ohms current shunt for mA range.

author: bdunham7
author_rank: Super Contributor
timestamp: December 08, 2022, 03:36:16 pm
content: Quote from: JenniferG on December 08, 2022, 03:26:45 pmThe actual problem is that the test signal needs to be amplified (or divided in other cases) so that it can be presented to the circuits that do the integration and analog-to-digital conversion. In that meter the ADC probably operates at a 0 - 2.2V level. So in the voltage range, the integration circuitry manages to average your pulses down into the ADC range, but in the millivolt range is used, the 5V peaks are clipped. If the millivolt range uses a 10X amplifier, then the 5V peaks would be 50V and the internal circuits of the meter just can't supply that.QuoteCapacitor across the meter is actually the appropriate solution for getting an average reading from peaky currents in many cases. Of course you now have a new element in your circuit and you have to consider how it will affect the rest of the circuit.

author: JenniferG
author_rank: Frequent Contributor
timestamp: December 08, 2022, 03:39:40 pm
content: Thank you everyone for the wonderful replies. Later after reading a few electronics books (beginners), I'll come back to this thread re-read the entire thing; I'll watch the video(s) and read the articles / schematics. It'll all probably make sense to me then. There is a lot of terminology I don't understand in this thread with my current experience in electronics.

author: hugo
author_rank: Regular Contributor
timestamp: December 09, 2022, 12:36:27 am
content: Because a picture or an image is worth a thousand words: