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ME 365
POSTLAB EXERCISE FOR LABORATORY 1
FALL 2011
1
To:
ME365 Student
From: Andy Dufresne,
Ellis
Corp.
Re:
Digital Multimeters
Date:
January 18, 2011
1. RMS value of a sine wave with DC offset
As we discussed briefly on the phone, we are having some difficulty understanding
readings from a DMM.
First, we couldn’t figure out how a DMM calculates RMS value of a sine
wave with DC offset.
When we applied an input of
, our DMM
displayed the RMS value of 3.674 V.
However, when we calculated the RMS value of the input
signal by summing the RMS value of the DC component (3 V) and the RMS value of the AC
component (3/
= 2.121 V), we obtained 5.121 V.
Is our DMM evaluating RMS value
accurately or am I making some calculation mistake?
To verify the results, we tried to calculate
the RMS value of the signal by using the following formula:
, where
and
T
is time period (
is the DC offset).
After expanding
as
, we couldn’t finish
integration due to the squared sine term.
Can you finish the derivation
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 Fall '07
 MERKLE

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