# Numerical intergration of a set of measured data points

1. Jun 23, 2012

### homim4

Hi,
I have faced the following question. In our lab we perform different measurements on Transistors. We program a scope and that controls the tests. For one of our tests we would like to calculate the total charge Q. Mathematically this is given by
Q=∫ dt i(t), where i(t) is given by i(t) = v(t)/R, i(t)= current, v(t)=voltage, R= resistivity ( constant value), for a time interval [t1, t2]
We cannot measure i(t) directly but we can measure v(t). This means
Q=∫dt v(t)/R.
We have noticed the following
1. if we define Q1 = ∫dt ( v(t)/R)
2. or if we define Q2= (∫dt v(t))/R
Mathematically these two integrals should produce the same result. But we see completely different results. I wonder if this depends on the numerical methods used in integration or has another reason.

2. Jun 23, 2012

### marcusl

If R is truly a constant, then the answer cannot depend on when you divide. You must be making a mistake in your calculations.

3. Jun 23, 2012

### Integral

Staff Emeritus
You have not told us how you are evaluating the intergrals. Without that bit of information there is no way we can hope to help you.

4. Jun 24, 2012