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Microamps and Millivolts Measurements on UT61E

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joeqsmith:

--- Quote from: rsjsouza on December 08, 2022, 01:16:15 am ---As others have said and the references that were sent to you also 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.

--- End quote ---

Certainly 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!!   :--  :-DD   

bdunham7:

--- Quote from: JenniferG on December 08, 2022, 01:39:15 am ---Doing 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.

--- End quote ---

OK, 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.

Fungus:

--- Quote from: JenniferG on December 07, 2022, 09:33:38 pm ---What I'd really like to know is why I am getting 250ua for the microamps mode and 299ua for the milliamps mode.

--- End quote ---

Because when you turn the dial you change the resistance of the meter.

(and the meter is in series in your circuit)

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

You 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 measurements

Sorry 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 sense

threads like this will go for ever  loll

JenniferG:

--- Quote from: coromonadalix on December 08, 2022, 12:48:15 pm ---Once again at theses values  the uni-t meter will round them sometimes, IT IS not made for these low currents values

You 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 measurements

Sorry 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 sense

threads like this will go for ever  loll

--- End quote ---

I 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.

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