remove dc from signal
The DC level is from 0V to 3V. The frequency depends on the sampling rate and can be from minimum 100 Hz to 10 kHz. The sampling rate is however tuned for a specific application and can be fixed somethere in this interval. The system will be designed for a maximum sampling rate of about 10 kHz but if slower signals are sampled a much slower sample rate is good as it reduce the data.
A high pass filter will not work as the signal in it self have no DC. I understand now that I was very unclear in my description. The signal is small sampling spikes there the actual signal is fluctruations of the level of theese spikes. I need to take som sort of mean value of theese fluctruations and bring this down to 0V to be able to amplifiy them prior to feeding the signal into an AD converter. If the signal change very rapidly, this will of course result in that the signal temporary gets out of range but I am aware of that. There is often methods for forcing the signal fats back into range in such surcumstances.