Thanks. My aplication is to measure the frequency from a Hydro generator PT signal (Potential transformer). I dont have to measure 0Hz, but as low as possible.
The voltage will be from 0 at startup and 220VAC at nominal speed. The frequency will be 50/60Hz at nominal (depending on the grid). 0 at startup and 120 at 100% overspeed. I need to measure the whole range. 0.1-220VAC and 5-120Hz.
Im using a microcontroller to calculate the frequency. I have control over that part, but I need help to design the voltage limiter and filter, as well as the signal isolator.
1. I need to isolate the PT signal with an isolation transformer. I like to integrate it into a PCB if possible?
2. The isolated signal must be cleaned for high frequencys. A 2 pole low pass filter is suggested. Any suggestion on how to design?
3. The voltage must be clamped so it not damage the microcontroller. The current must be low. I think less then 1mA. Clamp diodes are suggested. How is this done?
Thanks.