Dear Ladies and Gentlemen,
I set up a simulation, to calculate the inrush current of an equipment. The schematic is a bit complex but it contains the components at power input. The simulation is successful, it is similar to the measurements in the real world.
I also would like to calculate the I2t value through fuse F1. It is important to select the proper fuse. LTspice does it, using the
.meas I2T INTEG ( I(F1)^2) FROM 0 TO 400u
command. After 400 usec the current is practically 0, shouldn't affect the integral. By the above command, LTspice gave an irrealistic 2.34e-5 as a result. If I change the time of integration, the given value changes as well. These values have no relation to the real world.
However, if I export the simulation results and make another calculation in Excel, the result is realistic. First I calculate the 2nd power of every I. Then I multiply all these by the corresponding dt. At the end, I make a sum of all I2*dt values. Obviously, it doesn't matter if I make the Excel calculation only up to 400usec or do it until 1 sec (did it), zero current after 400usec doesn't affect the integral.
What am I doing wrong with the LTspice .meas command? What is the proper way to calculate the I2*t value?
