True-RMS Measurement Pt.1: AC vs. AC+DC

Roger demonstrates the difference between so called "True-RMS" (only AC) and "True-RMS AC+DC" multimeters and a simple AC-averaging multimeter.

Only "True-RMS AC+DC" multimeters give you a reliable measurement and the differences between the three tested multimeters are quite striking.
There remain some error-sources even with a good True-RMS AC+DC multimeter which will be investigated in Pt.2 of this video.

[trumanhw]

YOU ARE A GOOD TEACHER!! There are MANY youtubers TRYING to explain things ... BUT, they suck at remembering what it was like to not know things. Apparently -- people with Asperger's are more extreme versions of this phenomena, in which they lack a sufficient practical application of theory of mind ... to where they can imagine what it's like to not know something ...

You provided all of the information to appreciate your objectives ... and weren't just speaking out loud, audiblizing corresponding reactions to your own thoughts without explicitly helping us understand your thoughts... as (unfortunately) many (most) channels have done.
Keep up the great work: Subscribed!

[Ian.Gostling]

I finally understand RMS, You are the First utube video I've seen that properly explains the origin based on ohms law better, thanks!

[OZLQO]

Great series on a subject which many people find complicated. Very good points along the line, and even though I'm a professional myself, I still went straight to my bench to test and compare my three multimeters against the DSO :-) Thanks, I enjoy well-made videos on basics :-)

[yvesledanseurs]

Very interesting and very useful video for people who want to measure real power. Thank you

[techX]

Loved the explanation, thank you Raj.

[robra]

Thid really cleared some matters! Thanks a lot!

[Jnglfvr]

In the case of a sine wave with DC offset there is a workaround for a meter that is "true RMS" but not "true AC/DC RMS" such as the Uni-T in your demonstration. For sine waves only, the RMS value is the square root of the sum of the squares of the "symmetrical" sine wave and the DC offset. I.e., Vrms (DC offset) = sqrt(Vrms (no offset)^2 + DC offset ^2). Take for example a 4 V peak to peak sine wave with 1 V DC offset. The RMS value of this would be sqrt( (2/sqrt(2))^2 + 1^2)) = 1.73. If you use the Uni-T to measure this signal in AC mode you will get the non DC offset of 1.41. If you then switch it to DC mode it will correctly identify the DC offset as 1 V. SO with a little manual calculation taking the square root of the sum of the squares of both the AC and DC measurement you will get the true RMS value of the signal.

[robertingersoll]

First, for those criticizing - the German convention for voltage is U. Almost all great physicists who formed the basis of modern electronics used U. (That is why Travel is recommended for students.)
ROGER - you have a gift for teaching Electronics concepts. Quit this racket of selling gizmos and teach electronics at your local university.

[trumanhw]

I got lucky and guessed it was gonna be counterintuitive -- and actually assumed it'd be the sqrt of 2 ... :) What I DON'T know ... is when, why and how RMS is more useful except as a relative (comparative) value when you have "known good" hardware you're comparing against -- or, if a mfr gives their info in RMS -- requiring people purchase more expensive test equipment to audit the product.

[soffronitsky]

Please Roger, could you please explain me what you mean from 7:36 to 7:51? Thank you very much. Very clear and informative video!

[musarichesmabuyangwa]

very nice video...can you please help? i have just bought a trms digital multimeter..can you please help step by step on how do i connect my sginal gen and oscilloscope with the multimeters?

[engr.salaheldin]

Is this multimeter fluke 87v mesure (AC+DC)

[faustsmith]

Would you be doing a review of the "Victor 189" ac+dc multimeter?

[dimago]

great calculation abilities you got there... but where i live the square root of two squared equals TWO.

[davidprice]

Please you can't go around pronouncing V as a U.. Or writing it thus.. I understand your English is a second language.. Appreciate your effort though..