can someone please explain in laymans terms,root mean square. i know its to do with syne waves and ac current!

Question

is this easier with pictures??
still confused?

Answer 1

RMS (root mean square) involves some math that gives it its name. Basically what it means is if you take a sine wave and calculate the RMS value, you will get a number which is equivalent to a DC voltage or current of the same value. A 1 volt RMS sine wave will create as much heat in a resistor as 1 volt of DC. If you take the positive peak value of a sine wave and multiply it by .707, you'll get the RMS value.

Answer 2

This is awkward to explain without the benefit of a diagram but I'll try.

Alternating current, as you say, is delivered in the form of a sine wave. This means that AC voltage (or current) 'wobbles' up and down about a base line. Mathematically the average value must be zero since exactly as much of the curve falls below the base line as above it - the negative values cancelling out the positive values. To over come this effect
the values are squared, thus getting rid of the negatives. The mean value of the squares is then taken and the initial squaring is counteracted by obtaining the square root of this mean. Thus we get a 'root mean square' value instead of zero!

Answer 3

Break down the terms in Root Mean Square and it'll make more sense....

The RMS is the square root of the average of the squares of all the numbers in a set.

That is Sqrt((x1^2 + x2 ^2 + x3^2 ... + xn^2)/n)

That is, if you take all the numbers in a set, square them all, then take the average of those squares, then take the square root of that average, you'll have your RMS value.

Its used in waves and such which cross the X axis (0) all the time. If you were to take a true average of the points on a sine or cosine wave, your average would simply be 0 and that's not very useful

Answer 4

can be used with ac current , but has many other uses .
if you have something you wish to measure the average of and its oscillating about zero [positive and negative], if you take the average [mean] the answer is goingt o be about zero.
With AC current , as your example, this doesnt give a very useful answer.
The answer is to take all the data points and square all the numbers. [ ie multiply each number by itself]
If you square a negative number , you create a positive number , thus now all your data are a or above zero.
Then you take the average of all these new data [ called the mean as there are a few other methods of calculating an average- and the 'mean' is the term for this one].
Finally , you have a number , but is skewed because of squaring everything to start with , so you correct this by taking the square root of this average . [ the opposite of squaring you find what number multiplied by itself equals this average]
The answer is called the root mean square [ because this is what you've done ]

Answer 5

It is the Square root of the mean value of the amplitude of a sine wave that has been squared. It is the use able value of the wave. So in power systems a say a 250 volt supply would have a peak value off 353 volts Which is the amplitude the sine wave.. Another way to put it it is the d.c. equivalent.

Answer 6

The actual formula for computing RMS is a calculus integral.

- The waveform is Squared [example: sin^2(x) ]
- Then the arithmetic Mean is taken of that squared function over a particular time interval -- this is done by integration.
- Then that result is square Rooted.

So you have the Root of a Mean of a Square.

For certain waveforms, such as sine waves, the result is a simple multiplication of 0.7071... of the initial amplitude to get the RMS result.

For other repeating waveforms (square waves, triangle waves, etc), simple multiplications of the amplitude by constants (other than 0.7071..) are also the RMS result.

For complex waveforms you have to do the math.

.

Answer 7

everyone else has answered correctly, I'll try to make it simple (if its too simple just read their answers)

with sine waves you have a constantly changing figure, it would be inaccurate to say that any specific point is the "right figure" for the value of the sine wave.

but we need to have a defined value for how "big" the sine waves oscillation (movement up and down) is.

so we take a average value by "squaring" (multiplying by itself (eg 3 squared is 9) all of the component values.

then we find the "mean" (average (sum of all values divided by number of values)) value.

then finding the square root of the mean (the square root is the number that when multiplied by itself would be your value (eg the square root of 9 is 3)) gives us the RMS (root mean square).

so RMS is the (square)root of the mean (average) of the square (of all the values listed).

Answer 8

The RMS value of an alternative function is the equivalent continuous value associated to that function.
Plainly, they both do the same work.