# Find the 'Effective Voltage' with only the surface under and above the 't' axis

To find the 'Effective Voltage' and the 'Average Voltage' of a voltage over time we have the following functions:

$$V_{eff}=\sqrt{\frac{1}{T}\int_{0}^{T} f(t)^2 \text{d}t}$$ $$V_{av}=\frac{1}{T}\int_{0}^{T} f(t) \text{d}t$$

But in my case it is impossible to find a general function for my voltage so can I use the surfaces? And if I can how can I find the 'Effective Voltage' and the 'Average Voltage'?

• Why can't you find a general function? Aug 27, 2015 at 17:18
• What is f(t)? Because those formula apply to periodic function Aug 27, 2015 at 17:19
• It is a combination of 4 different functions, it is periodic Aug 27, 2015 at 17:19
• What functions? Aug 27, 2015 at 17:20
• Do them individually to find the RMS of each then add the RMS of each up as per $\sqrt{A^2+B^2 + ...}$ Aug 27, 2015 at 17:20

As you might know the definition of the definite integral $\int_{a}^{b} f(x)dx$ in layman's terms is area under the curve (and above the horizontal axis).
So, yes you could approximate the average value by just manualy calculating the area under the curve. But effective value contains $f(x)^2dx$, so you would first have to square the curve to get a new one and then calculate that area.