# Homework Help: Finding RMS value of strange column function

1. Dec 8, 2011

### Twinflower

1. The problem statement, all variables and given/known data
This is the given function:

2. Relevant equations
The RMS equation goes like this:
$$\sqrt(\frac{\int(f(t)^2 dt)}{b - a})$$

3. The attempt at a solution

The first part of the exercise was to find the mean value.
This is A/4.

The RMS value should be higher than the mean value, but I need the function to use the equation and I can't "see it" from the picture.

2. Dec 8, 2011

### Staff: Mentor

RMS == the square root of the average of ( the square of the signal).

You are given a graph of the signal. On the same axes you can plot the signal squared, then determine the average of this. Then ...

3. Dec 8, 2011

### Twinflower

Ah, thank you for putting it into perspective

RMS value = A/2

4. Dec 8, 2011

### Staff: Mentor

And it's not called a strange column function. It's called pulsed DC. Or 25% duty cycle switched DC.

5. Dec 8, 2011

### Twinflower

duly noted ^^

6. Dec 8, 2011

### Twinflower

And what happends if the "pulsed DC" varies between +1 and -1 V ? The signal squared = 1V anyhow (except for a few 0V periods)

Last edited: Dec 8, 2011
7. Dec 8, 2011

### Twinflower

Never mind. I got it :)

I made it too complicated at first

8. Dec 8, 2011

### Staff: Mentor

Then it's called a strange column function.

What you have sketched doesn't tally with your verbal description. For what you sketched, its RMS value will be equal to that of a 60% duty cycle switched DC, since a level of -1 contributes the same as does +1, in determining RMS value.

9. Dec 8, 2011

### Twinflower

the second picture is another problem which I had to determine the mean and RMS value.

the problem description does not mention any DC or functional description of the graph

10. Dec 9, 2011

### Staff: Mentor

You could call it a stepped waveform. Maybe a staircase.

11. Dec 9, 2011

### Twinflower

I'll keep that it mind, thanks :)