I've got a 4 stage second-order-section filter. When I turn this filter on, it assumes it is starting from zero and takes forever to converge on the actual signal.
For example, let's say I have a position sensor that is reading 20mm. I would like to filter this sensor with a low-pass filter that has a low cut-off frequency of 0.001Hz.
Under typical, operating procedures this filter works great. However, it takes forever to reach the initial value of ~20mm. I'm curious how I would go about initialzing the filter output to 20mm instead of having to wait for it to go from 0mm to 20mm.
My current technique has been to simply write "20" into the filters memory, however, this seems to initialize the filter incorrectly such that it overshoots to a very very large number. Any thoughts?
Edit: Assume I'm using Direct Form II as shown in this wikipedia page on biquad filters - https://en.wikipedia.org/wiki/Digital_biquad_filter