-1

I've created a full wave rectifier circuit and there is no DC offset in the AC power source. One thing that perplexes me is that the voltage shown by the Multimeter is different form the rms voltage in the Multisim probe. Aren't they supposed to be the same number? enter image description here

Cyrus
  • 3
  • 2
  • 2
    Comparing rike with like ... Vdc vs Vdc ... 5.25 vs 5.247 are pretty close. –  Feb 17 '20 at 21:00
  • What's the idea of updating this question and blanking the picture / deleting the relevant Vdc part of the probe? Would you like me to also manipulate the original picture in my answer? – Huisman Feb 17 '20 at 21:31
  • Because Vdc in the probe is irrelevant to my question and it wasn't hard for me to spot it. My question is very clear, Multimeters are supposed to show RMS value or true RMS value and i'm asking why is it different from the rms in the probe. – Cyrus Feb 17 '20 at 21:40
  • Why not post the right picture? You post a picture where the **Multimeter** shows the DC component... The higher quality your question is, the more useful quality the answer can be... – Huisman Feb 17 '20 at 21:52
  • 1
    for FW sine rect.... **Vavg=Vpk 2/π, Vrms=Vpk/√2** – Tony Stewart EE75 Feb 17 '20 at 22:03

1 Answers1

0

You selected the DC measurement in the Multimeter, so it will show the DC component.

I've created a full wave rectifier circuit and there is no DC offset in the AC power source.

The DC component is the average value of the rectified signal, which is 5.247 V shown by the Multimeter or rounded, V(dc): 5.25 V, shown by the probe.

enter image description here

UPDATE
When selecting the ~ you will get the root-mean-square (RMS) voltage (or current) of an the AC signal component.

Note that the RMS of a signal does not necessarily equal the RMS value of the AC component (only when the DC component is zero).

The RMS value of a signal is

$$V_{RMS}=\sqrt{V_{DC}^2+V_{RMS_{AC}}^2}$$ $$V_{RMS}=\sqrt{5.247V^2+2.925V^2}=6.01V $$

Huisman
  • 10,594
  • 2
  • 19
  • 40
  • I've done that and it shows 2.925 V which is not equal to 6.01 V V(rms) in the probe. – Cyrus Feb 17 '20 at 21:36
  • @Cyrus Please find the explanation of these different values in updated answer. – Huisman Feb 17 '20 at 22:15
  • What is Vdc? Vrms is supposed to be the equivalent of the DC voltage. How do you calculate Vdc and Vrms ac in this formula(2.925) ? – Cyrus Feb 18 '20 at 10:57
  • Vdc is the DC component of the signal, the average value. How to calculate it: check this question, esp the link only anwer https://electronics.stackexchange.com/a/328536/200815 – Huisman Feb 18 '20 at 12:35