Building a circuit to sum voltage per unit time?

I'm more or less a newb and was wondering if this was possible and/or practical. I would like to build a circuit that'll close after it reaches a sum of voltages per time interval equal to some larger voltage. Any ideas?

Google integrator. What you need may be as simple as a capacitor and a couple of resistors. You need to tell us what you are trying to do.

Mike.

I believe you want a boxcar integrator. It has a switch along with an integrator to integrate for a desired interval of time and then holds the value. A second switch resets the integrator for another measurement.

I'm trying to use the voltage output from a throttle position sensor in order to roughly determine how much fuel has passed through my fuel system. This is so that when I switch fuel supplies, I can have the appropriate lag between switching the line-in three-way valve and switching the line-out three-way valve in order to minimize fuel contamination. I'll definitely check out integrators, which look like they would fit my needs. Thanks!

How long do you need to do this integration? If it's more than a few seconds you may need to do it digitally. The general concept is to periodically add the measured value to an accumulated sum. The accumulated sum is the integtrated value. If you do this for a long period the values may need to be scaled to avoid overflow. A microcontroller such as a PIC could readily do all this.

If you have a feed and return line, then the fuel flow through those will probably be much larger than the fuel that is consumed.

It may be so large that the fuel used by the engine is insignificant.

Also the rate the fuel is used depends on the engine speed, not just throttle position.

I suggest that you just use a timer, and change the line-out valve a fixed time after the line-in valve.