Designing an Integrator circuit

[Qiaozhi]

When I joined this site to learn about detectors I had a problem with the circuit being called an integrator. For me integration had a time function, integrate velocity you get distance. Output continues to change if input isn't zero. DeBoo integrator looks like a true integrator to me. The ones we are using with our detectors look like low pass filters(they average). bbsailor calls it a lock in amplifier. Could someone explain why we call it an integrator.

Any dc offset at the input will cause the output of an ideal integrator to increase until eventually it hits the power rail and gets stuck. In a practical integrator (like the one's we use in our PI detectors) there is a resistor placed across the feedback capacitor to prevent integration of the dc input. This works because the impedance of the capacitor is extremely high at dc, and the feedback resistor is dominant. The reverse is true at high frequencies.

[green]

A test. Target, three layers 1x1inch aluminum foil swinging from a pendulum 10 inches above coil. Varied swing distance to see the effect speed had on signal strength. 200mm coil. Target is glued to center of a 200mm disk to cover photo cell(centered over coil about .4inches below disk) when the target is over the coil. Sweep speed, meters/sec=.2meters/cover time(sec). Target at edge, signal about half target centered.