Microamps and Millivolts Measurements on UT61E

[Gyro]

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.

[Veteran68]

I agree I am stupid; or more ignorant rather -- I actually have a genius IQ.

I don't think he was calling you stupid. 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.

[joeqsmith]

I agree I am stupid; or more ignorant rather -- I actually have a genius IQ.

I 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=829

I don't find a lot of people willing to do their own research. 

[JenniferG]

Just try not to come across like you don't believe them only because you don't understand it.

Well I am sorry I might of come across that way. I don't think that at all.

[JenniferG]

I agree I am stupid; or more ignorant rather -- I actually have a genius IQ.

I 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=829

I don't find a lot of people willing to do their own research.

Well 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 Electronics
1) Make: Electronics
2) Electroncis for Beginners
3) All New Electronics Self-Teaching Guide
4) ARRL Handbook
5) ARRL's Understanding Basic Electronics
6) Practical Electronics for Inventors
7) The Art of Electronics

What 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.

[bdunham7]

Once again at theses values  the uni-t meter will round them sometimes, IT IS not made for these low currents values

you are using cheap meters to do extensive work / measurements,  it kinda become stupid in a sense

I 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.

[Kleinstein]

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.

[JenniferG]

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.

[bdunham7]

What 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.

AoE 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.pdf

https://en.wikipedia.org/wiki/Th%C3%A9venin's_theorem

[mqsaharan]

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.

[bdunham7]

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.

The 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.

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.

Capacitor 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.

[JenniferG]

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.

[hugo]

Because a picture or an image is worth a thousand words:

[joeqsmith]

There are other common reasons why beginners are concerned about their brand new meters being defective.   

With the leads dangling in free space attached to nothing but the meter, the meter doesn't read zero AC or DC volts. 

A recent post about the Fluke 17B+ was someone bitching about the lack of TRMS.  I would say failure to read the manufacture's documentation BEFORE purchase is a BIG problem. 

AC+DC.

Autorange.

Beginners will contact me who just want to know they bought a good meter so they can feel good. 

Do I need a CAT IV 1000V meter to be safe when working on my toaster?