One method to design a controller for a digital control system is to first design it in the s domain and then convert it. However, choosing a suitable sampling period is important.
In most problems I've faced up to this point I first find the smallest time constant c of my system. Then I choose the sampling period so that 0.1c< T <0.5c.
I just came across a problem in which the transfer function has two poles at the origin and I can't find a time constant. How should I choose my sampling period?